2-2014_geologi 2.06 12.02.15 15:20 Pagina 1
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 3-172 Bull. géol. appl. Boll. geol. appl Bull. Appl. Geol. Swiss Bulletin
für angewandte Geologie de géologie appliquée di geologia applicata for Applied Geology
Inhalt / Sommaire / Contenuto /Contents
D. Bollinger Editorial: Fracking – Segen oder Fluch? 3-4
K.M. Reinicke The Role of Hydraulic Fracturing for the Supply of Subsurface Energy 5-17
R. Jung Application and potential of hydraulic-fracturing for geothermal energy production 19-37
P. Reichetseder Clean Unconventional Gas Production: Myth or Reality? – The Role of Well 39-52 Integrity and Methane Emissions
S. Liermann Hydraulic Fracturing – Application of Best Practices in Germany 53-64
T. Engelder The Fracking Debate in Europe – An Assessment of the History behind 65-68 the European Bans on Hydraulic Fracturing
M. Stäuble Unconventionals in China – Shell’s Onshore Oil and Gas Operating Principles in Action 69-74
R. Wyss Die Erschliessung und Nutzung der Energiequellen des tiefen Untergrundes 75-93 der Schweiz – Risiken und Chancen
W. Leu, A. Gautschi The Shale Gas Potential of the Opalinus Clay and Posidonia Shale in Switzerland – 95-107 A First Assessment
D. Hartmann, B. Meylan Fracking in der Schweiz aus der Sicht des Grund- und Trinkwasserschutzes 109-113
E. Grosse Ruse Unkonventionelle Gasförderung im Klimaschutz: Teil der Lösung oder 115-122 Teil des Problems?
W. Wildi Voraussetzungen zur Nutzung von unkonventionellen Kohlenwasserstoffen 123-128 mit Hilfe von Fracking in der Schweiz
P. Burri The Global Impact of Unconventional Hydrocarbons (Hydraulic Fracturing on 129-139 the way to a clean and safe technology). AAPG Annual Convention Houston, April 2014 – Selected highlights
U. Seemann Energie aus dem Untergrund – who cares? 141-142
P. Burri Hydraulic Fracturing – Postscriptum. A geologist's attempt to summarize 143-150 what we know and where we go
R. Compagnoni High Pressure (HP) and Ultrahigh Pressure (UHP) metamorphism in continental 151-156 crust and oceanic lithosphere («subduction metamorphism»)
H.M. Bürgisser Bericht der 81. Jahresversammlung der SASEG vom 21. bis 23. Juni 2014 157-167 in Aosta (Italien)
P. Burri Heini Schwendener 1952-2014 169-170 2-2014_geologi 2.06 12.02.15 15:20 Pagina 2
Anleitung für Autoren und Autorinnen for any extra costs incurred by oversize tables and colour illustrations. Manuskripte müssen bis spätestens 1. März bzw. 1. September für das jeweils folgende Citations in the text and the List of Refer- Heft (Juni bzw. Dezember) als Word-Doku- ences are to be formatted according to the ment beim Redaktor vorliegen. Manuskripte standards of the Swiss Journal of Geosciences. können in Deutsch, Französisch, Italienisch The author is entitled to 25 reprints free of oder Englisch verfasst sein. Der Umfang charge. Additional copies may be ordered at sollte 20 Seiten nicht überschreiten. Die For- the time the pressproof of the manuscript is matierung der Texte ist möglichst einfach zu authorised. halten (einspaltig, kein Blocksatz, keine Further information is available on the automatische Silbentrennungen, kein homepage. manueller Seitenumbruch etc.). Tabellen können als Word- oder Excel-Doku- Instructions pour les auteurs mente abgegeben werden. Figuren müssen Les manuscrit – sous format Word – doivent als Hardcopy auf Papier eingereicht werden. être en possession du rédacteur au plus tard Für die digitale Form kommen nur PC- und le 1 mars ou le 1 septembre pour pouvoir Mac-taugliche Grafikformate wie pdf, tif, jpg être publiés dans le bulletin suivant, c’est à oder gif in Frage. Falttafeln und farbige dire celui du juin ou du décembre respective- Abbildungen oder Figuren sind mit Mehr- ment. Ils peuvent être rédigés en allemand, kosten verbunden, die durch den Autor zu français, italien ou anglais et ne doivent pas tragen sind. dépasser un total de 30 pages. Les textes Zitate im Text und das Literaturverzeichnis doivent être dans un format simple (pas de sind nach der Vorgabe des Swiss Journal of séparation de page, pas de césure automa- Geosciences zu formatieren. tique, pas de saut de page etc.). Der Autor hat Anrecht auf 25 Separata ohne Les figures et les tableaux doivent être Kostenfolge. Zusätzliche Exemplare können remises séparément et ne doivent pas être mit dem «Gut zum Druck» bestellt werden. inclus dans le texte! Les tableaux peuvent Weitere Informationen finden sich auf der être en format Word ou Excel. Une copie des Homepage. figures doit être envoyé en format papier. Pour les fichiers informatiques n’utiliser que Guidelines for authors les formats graphique Windows/DOS ou Macintosh compatibles tels que pdf, tif, jpg Manuscripts are to be at the disposal of the ou gif. Les illustrations devant être pliées ou editor no later than March 1st and Septem- reproduites en couleurs occasionnent un ber 1st for the June and December issues of surcoût qui sera facturé à l’auteur. the Bulletin, respectively. Manuscripts may be submitted in German, French, Italian or Les citations dans le texte aussi que la liste English but are accepted as Word documents bibliographique doivent suivre le modèle only. A total length of 20 pages should not be du Swiss Journal of Geosciences. exceeded. Text formats are to be kept simple, La publication est gratuite et comprend 25 i.e. single column, no line justification, no syl- tirés à part pour l’auteur. Il est possible de labication, no manual page break etc. commander des exemplaires supplémen- taires avec le «Bon à tirer». Tables may be submitted as Word or Exce l Des informations plus détaillées se trou- Figures documents. are to be submitted in vent sur le site internet. hardcopy format on paper. Supplementary digital submissions are accepted in graphic www.angewandte-geologie.ch formats suitable for PC or Macintosh, e.g. www.geologie-appliquee.ch pdf, tif, jpg or gif. The author is responsible www.geologia-applicata.ch
2 2-2014_geologi 2.06 12.02.15 15:20 Pagina 3
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 3-4
Editorial: Fracking – Segen oder Fluch?
Noch nicht lange ist es her, da wurde über mutlich Jahrzehnte, um alternative Energien die Peak Oil Frage debattiert, so auch im als tragenden Pfeiler der globalen Energie- Swiss Bulletin für angewandte Geologie. Nei- versorgung zu etablieren. gen sich die nutzbaren Reserven an fossilen In den USA hat die Fracking-Technologie im Kohlenwasserstoffen rasch dem Ende zu, Bereich unkonventioneller Kohlenwasser- wie das im Jahre 1972 der Club of Rome erst- stoffe einen wahren Boom ausgelöst, die Wirt- mals prognostizierte? − In den letzten Jahren schaft angekurbelt und die Abhängigkeit der ist indes eine andere Thematik zunehmend USA von Kohlenwasserstoffimporten funda- in die öffentliche Wahrnehmung geraten, die mental verringert, mit gewaltigen politischen Technologie des Hydraulic Fracturing Konsequenzen. Doch Hydraulic Fracturing (Fracking). Es vergeht kaum eine Woche, hat nicht nur Bedeutung bei der Förderung ohne dass in den Medien darüber berichtet von fossilen Kohlenwasserstoffen, sondern wird. Eine rasante Entwicklung im geologi- ist auch eine Schlüsseltechnologie in der Tie- schen Verständnis der Petroleumsysteme fengeothermie. Aber sie kann spürbare Erd- sowie der Bohr- und Fördertechnologie hat beben auslösen, wie die Projekte von Basel in den letzten zwei Jahrzehnten ganz neue (2006) oder Landau im Rheingraben (2013) Perspektiven eröffnet. Sie ermöglichen die zeigten. Eine Technologie des Teufels? Das Erschliessung von Kohlenwasserstoffen in könnte man meinen, wenn wegen der Beben Gesteinen, aus denen bislang keine rentable plötzlich zahlreiche Gebäude angeblich Förderung fossiler Ressourcen möglich war. frisch entstandene Risse aufweisen oder Sie verändert die Peak Oil Debatte funda- wenn man den brennenden Wasserhahn im mental, weil sich dadurch ganz neue Dimen- Film «Gasland» (2010) sieht. Obwohl Fachleu- sionen von Gas- und Ölquellen erschliessen te schon lange wissen, dass der brennende lassen. Die Versorgung der Welt mit fossilen Wasserhahn nichts mit Hydraulic Fracturing Kohlenwasserstoffen scheint plötzlich für zu tun hat, wirkt das für viele beängstigend. viele Jahrzehnte, beim Gas möglicherweise Es verunsichert und schürt Emotionen. Über- für Jahrhunderte gesichert. Der Peak wird all, wo Emotionen im Spiel sind, besteht auch nun zu einem solchen der Nachfrage, und die Gefahr der bewussten Desinformation. nicht mehr in erster Linie zu einem des geo- Leicht können − auch auf der Basis falscher logisch vorhandenen Angebots. Bilder − Ängste und Aversionen geschürt wer- Durch die enormen neuen Gas-Ressourcen, den, gerade bei einer für Laien kaum fassba- die eine schnelle Substitution von Kohle und ren, komplexen Technologie und in einem Öl in Stromerzeugung und Mobilität ermög- Land, das kaum eine Tradition in der Nutzung lichen, soll auch ein wirtschaftlich und des tiefen Untergrundes hat. Hydraulic Frac- gesellschaftlich verträglicher Übergang zu turing geschieht im Untergrund, in Tiefen von einer Versorgung durch erneuerbare Ener- mehreren Kilometern und ist scheinbar der gien sichergestellt werden. Nach anfäng- direkten Beobachtung entzogen. Eine ableh- licher Euphorie ist klar geworden: erneuer- nende Haltung solchen Technologien gegen- bare Energien sind trotz ihres grossen über ist daher verständlich. Ängste können Wachstums noch weit davon entfernt, auch indes abgebaut werden, wenn eine offene, nur den jährlichen Zuwachs des globalen objektive und sachliche Information und Aus- Energiebedarfs zu decken. Es braucht ver- einandersetzung stattfindet.
3 2-2014_geologi 2.06 12.02.15 15:20 Pagina 4
Wo Risiken sind, sind auch Chancen. Innova- Brauchen wir Fracking? Dieser Frage widmet tion und Entwicklung ohne Risiko ist unmög- sich E. Grosse Ruse (WWF Schweiz) in sei- lich. Wie gehen wir mit diesen Risiken um, nem Beitrag, mit speziellem energiepoliti- wie bewerten und nutzen wir die Chancen, schem Fokus auf das Zwei-Grad-Ziel. Ist die sich uns bieten? Fracking eine gesellschaftliche Notwendig- keit? W. Wildi (Prof. em. Uni Genève) geht In diesem Bulletin wollen wir ein breites dieser Frage nach und zeigt, wie wir mit ver- Spektrum von Aspekten des Frackings schiedenen Nutzungsansprüchen an den behandeln. Spezialisten mit ausgewiesener Untergrund umgehen sollten. langjähriger Erfahrung in ihrem Fachgebiet Das Thema Hydraulic Fracturing ist auch in äussern sich dazu: der globalen Erdöl- und Gaswirtschaft äus- Einleitend informiert K. M. Reinicke (Prof. serst prominent. P. Burri (Burri Consulting) TU Clausthal) über die technischen Aspekte resumiert dazu die Erkenntnisse der AAPG- des Frackings und dessen Bedeutung bei der Convention 2014 in Houston und schliesst Erschliessung von Kohlenwasserstoffen und die Fachartikel mit einer persönliche Ein- dem geothermischen Potenzial. R. Jung schätzung ab. (Jung Consultant) beleuchtet das Problem der Rissbildung und der induzierten Seismi- Die Auswahl der Beiträge soll dazu beitra- zität und zeigt Lösungsansätze auf. Die Bohr- gen, den Stand des Wissens und die Konse- lochintegrität und ihre Bedeutung für einen quenzen der Fracking-Technologie aufzuzei- zuverlässigen Schutz des Grundwassers gen und dadurch zu einer Versachlichung wird diskutiert von P. Reichetseder (Up- der oftmals emotionalen oder ideologischen stream – Energy Consulting und Prof. TU Diskussion beizutragen. Eine objektive Aus- Clausthal). S. Liermann (Wintershall) zeigt einandersetzung auf der Basis von Fakten ist auf, wie Fracking heute in Deutschland ver- die Voraussetzung für nachhaltige, rationale antwortungsvoll und erfolgreich eingesetzt Entscheide in unserer Energiepolitik. «Whet- wird. her or not shale gas development will turn Die Industrie hat zu den Anfangszeiten des out in the long term to have been a positive Fracking-Verfahrens Fehler gemacht. T. or negative influence on global well-being Engelder (Prof. Pennsylvania State Universi- will depend on how society understands ty) nennt die Versäumnisse und nimmt this technology and manages it.» (Council of Bezug zur Fracking-Debatte in Europa. M. Canadian Academies 2014: Environmental Stäuble (Shell China) zeigt die Schritte zu Impacts of Shale Gas Extraction in Canada. einer sicheren operationellen Erschliessung Ottawa, ON, 262 p). unkonventioneller Öl- und Gasvorkommen in China. Daniel Bollinger Als Einleitung zur Problematik in der Schweiz informiert R. Wyss (Roland Wyss GmbH) über die Randbedingungen, die Technologie des Frackings und deren Aus- wirkungen. W. Leu (Geoform Ltd.) und A. Gautschi (Nagra) evaluieren das Potenzial des Opalinustons und der Posidonien-Schie- fer als Schiefergasgesteine des schweizeri- schen Untergrundes. Anschliessend thema- tisieren D. Hartmann und B. Meylan die Pro- blematik des Grundwasserschutzes in der Schweiz.
4 2-2014_geologi 2.06 12.02.15 15:20 Pagina 5
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 5-17
The Role of Hydraulic Fracturing for the Supply of Subsurface Energy Kurt M. Reinicke1
Presented at the Symposium «Energie aus dem Untergrund − Who cares? (Chancen und Risiken von Hydraulic Fracturing)» der Eidgenössischen Geologischen Kommission, Gurten, Berne, October 7, 2014.
Key words: unconventional gas, deep geothermal energy, hydraulic fracturing, fracturing fluids, fracture growth, fracturing impacts, risk management, multi-frack, horizontal drilling, operational practices, laws and regulations
1 Introduction
Until a decade ago gas liquefaction plants the development of geothermal resources in were built in several regions of the world to the deep subsurface, the potential of which supply the U.S. market with liquefied natural is many times larger than the potential of the gas. The boom was sourced by the predic- unconventional oil and gas deposits, at least tion of an increasing gap between the theoretically. demand and the supply of natural gas, resulting from a predicted steady decline in domestic production. Things have changed. 2 Hydraulic Fracturing In 2015 the U.S.A. will start to export natural gas. An oversupply of natural gas has Hydraulic fracturing refers to the process of caused prices to fall, leading increasingly to the generation and propagation of fractures a re-industrialization of the country and can in a rock formation by pumping a liquid even be recognized in the CO2 emission of under high pressure into this formation. The the country, which has significantly high pressure liquid enters the formation decreased in the last years. through holes perforated into the cemented Key to this development is the technology of steel pipes, which protect and seal the well- hydraulic stimulation, also known as frack- bore, at the level of this formation. Pressure ing or hydraulic fracturing. The technology medium (frac-fluid) is in general water. is in use since the 40s of the last century. In Depending on the application, the water is the combination of horizontal drilling and mixed with proppants to keep the generated multi-fracking the technology has evolved fractures open, for example quartz sand, as into a tool allowing the development of even well as other substances as additives shale gas deposits, in rocks so tight, that the (Emmermann 2014, Reinicke 2012). concrete pavements of the highways look In conventional sandstone reservoirs, the like kitchen sieves. In the combination of treatment usually results in the formation of horizontal drilling and multiple fracking the a two-wing vertical fracture. The entity, technology is applicable in principle also for which looks much like a butterfly, has a half- length of less than 100 to approximately 300 m in modern applications (Reinicke 2012). As a result of the layering of the geo- 1 Clausthal University of Technology, Insitut für Erdöl- und Erdgastechnik, Agricolastrasse 10, 38678 Clausthal-Zel- logic subsurface, the fractures are typically lerfeld, Germany longer than higher, because individual sedi-
5 2-2014_geologi 2.06 12.02.15 15:20 Pagina 6
mentary layers, like for example clay layers, Pure water is not able to carry sand and act as «barrier formations», which impede transport it into the created fractures. To the growth of fissures in the vertical direc- achieve carrying capacity, the water is thick- tion (Fig. 1). ened or gelled by adding viscosifiers (Fig. 2). The growth of the fractures is influenced by To clean the created channels, the gels have the geo-mechanical and hydro-mechanical to be broken subsequent to the treatment, properties of the geologic layers, the stresses which is why breakers are added. Other acting in these layers, the injected fluid vol- additives serve to reduce frictional losses ume, the fluid properties and the pressure at when pumping the viscosified fluid, to avoid which the fluid is injected. Within these the introduction of biological substances dependencies the extension of the fractures into the subsurface, to prevent corrosion, is predictable, in particular their orienta- and to stabilize the target formation by, for tion, their geometry and their effect on well example, clay stabilizers, etc. productivity, if the properties of the subsur- In total, today all additives make up approx. face and the treatment parameters are 1% (0.2−3%) of the frac-fluid volume (Fig. 2). known (Economides & Martin 2007). The rest is water and proppants. Today’s The objective of a hydraulic treatment is the recipes result in mixtures, classified as generation of highly conductive flow paths weakly water contaminating, which means for the transport of fluids (liquids and/or they are in the same category as liquid gases) in an otherwise low permeable rock. manure. The classification according to the To have this effect, the generated fractures German Gefahrstoffverordnung (hazardous must remain open. To prevent them from substances ordinance) is not toxic and not closing and healing, when the pumps stop hazardous to the environment. Work is and the fractures start to close under the under way to further reduce the environ- influence of the acting rock stresses, prop- mental impact, for example by UV irradia- pants are introduced into the fractures, for tion instead of using biocides (Kassner example sand. 2014).
Fig. 1: Fracture propagation in a reservoir: left prognosis, right measurement. The prognosis of fracture propagation is made with recognized methods and commercially available simulators based on the know- ledge of the geo- and hydro-mechanical properties of the subsurface and its stress distribution. The meas- urement is made by monitoring the micro-seismicity associated with the fracture extension (right).
6 2-2014_geologi 2.06 12.02.15 15:20 Pagina 7
In unconventional (shale and coal bed) 3 Fracking Targets reservoirs and geothermal (hot dry rock) reservoirs the process of fracture genera- The targets of hydraulic treatments are at tion is usually more complex. The reservoir great depths, far below the geologic hori- rock often contains natural fissures and frac- zons, which are used or may be used for the tures. Often the rock is subject to shear withdrawal of drinking water. The water stresses like the basement rock in the Upper quality does generally not improve with Rhine valley for example. Both have an influ- depth. In Northern Germany it is brackish ence on the fracture system. already at depths below 50−400 m. The If the reservoir rock contains fissures and water contained in the rocks at large depths fractures, the fracture treatment does usual- is heavily loaded with salts and may in addi- ly not result in a two wing fracture system, tion – albeit at low concentrations – contain but in more complex tree-like structures, heavy metals and naturally occurring which follow the zones of weakness in the radioactive materials. In Northern Germany rock, i.e. the naturally occurring fissures. salt loading of the deep brines is mostly up Under these conditions the injected frac-fluid to saturation. With 200−300 g/l the salt con- is distributed over more fractures, which centration is far above that of our noodle reduces the dimensions of the fracture sys- water with 1 tea spoon/l or 8−10 g/l and it is tem. If shear stresses are present und if they almost a factor of 10 higher than the salt are sufficiently high, lateral displacements concentration of sea water (35 g/l) (Burri & along the rough fracture surfaces may Häring 2014). result. If the rock is sufficiently hard, flow For the only treated well in an unconventional channels remain after fracture closure even shale reservoir in Germany, treatment depths without the introduction of proppants, were lager than 1.200 m. The potable water because the fracture faces do no longer fit horizons at the location of the well reached perfectly into each other. These so-called down to approx. 40 m with thick barrier for- water fracs are the treatment of choice for mations from clay between the potable water petro-thermal energy recovery. The treat- horizons and the frac horizon. The depth ments cost less and they are of lower envi- range typically assumed for the exploitable ronmental impact, because the frac-fluids unconventional hydrocarbon deposits in Ger- require less additives or none at all. many starts at approx. 1.000 m. Shale gas developments shallower than 1.000 m are unlikely, because commercial rates require
Fig. 2: Frac-fluids.
7 2-2014_geologi 2.06 12.02.15 15:20 Pagina 8
high reservoir pressures which are not found The limits to vertical growth are supported at the shallower depths, which is also the by the mapping of real fracture growth data experience in the U.S.A. in thousands of fracturing treatments in the The targets in conventional reservoirs are typ- U.S.A. by monitoring the micro-seismicity ically found at depths greater than 3.000 m. associated with the propagation of fractures Geothermal targets are even deeper, because in shale gas deposits. Result is, that vertical the desired water temperature of 150 °C or growth of created fractures is in the order of more requires depths of approx. 4.000−5.000 m hundreds of meters at the most with more under average central European conditions. than 1.000 m of sediments separating the The fracking targets in these reservoirs are top of the fractures from the drinking water overlain not only by clay layers but usually horizons (Fisher & Warpinski 2012) (Fig. 3, also by several impermeable salt layers, which right). may reach thicknesses of several 100 m.
5 Methane Emissions 4 Fracture Height Growth Also, the often implied significant emissions According to the myth distributed by the of methane into the atmosphere by natural fracking opponents in the internet, the frac- gas wells and facilities do not represent real- tures reach from great depths up to the ity, at least not where best practice is drinking water horizons and create wide applied like in Europe. According to the Ger- flow paths for gas and frac-fluids (Fig. 3, left). man Umweltbundesamt (Federal Environ- For the above described depth ranges and mental Agency) and the Wirtschaftsverband the usual frac-fluid volumes this is physical- Erdgas und Erdölgewinnung (Oil and Gas Pro- ly impossible. The physical balance laws, ducers Association), 53% of the total according to which generated fracture vol- methane emission in 2012 originated from ume can at best be as large as the fluid vol- agricultural sources (UBA 2014a). Only ume used for its generation, are also valid in approx. 3% came from energy industry the geologic subsurface. In general, the vol- sources with a contribution of the natural ume will be even smaller, because fluid leaks gas production of less than 0.1% (WEG into the formation as it is fractured and is no 2012). If high standards are applied for the longer available for the creation of fracture construction and maintenance of natural gas volume. facilities – which can be assumed for the gas
Fig. 3: Fracture vertical growth: Myth and Reality.
8 2-2014_geologi 2.06 12.02.15 15:20 Pagina 9
operations in Western Europa – methane The influence of a hydraulic treatment on emissions are not an issue. Climate improve- the productivity of a well is significant. It is ments and avoidance of air pollutions like not unusual, that the initial production rate those for example in China require the sub- increases by a factor of 5−10 and more to stitution of e.g. coal by natural gas. stabilize after an initial strong decline at a significantly higher level than the original flow rate. In the example of a North German 6 Effect of Hydraulic Treatments gas well, the initial rate could be increased after two hydraulic treatments by a factor of Regardless of the type of fracture system, seven (Reinicke et al. 1983) (Fig. 4). which is generated in the course of a frac- The well shown is still producing today after ture treatment, it will change the flow pat- more than 35 years. The example illustrates tern in the rock. The reservoir content no not only the influence of hydraulic fracturing longer flows radially to the well bore, to treatments on the productivity of a well and squeeze into a bore of approx. 20 cm diame- its development, it documents also that ter, but more or less linear to the significant- hydraulic fracturing treatments are nothing ly larger fracture system, to then flow within new even in Central-Europe. The sample well this system to the wellbore. For a two-wing was fracked in 1977 and is part of a major system this system has an extension which campaign, during which a significant number is mostly a thousand times wider than the of gas wells were subjected to major fractur- wellbore. In a way, the effect resembles that ing treatments, so-called MHF treatment, of a highway across a city during the rush during the end of the 70s/beginning of the hour traffic. It attracts traffic and enables a 80s. To now suggest, that the technology is significantly faster influx and efflux to the something new is not correct. It is in use central business area(s). since the end of the forties and has in the
Fig. 4: Effect of a hydraulic fracturing treatment on flow pattern and well productivity (in 1.000 m3/h).
9 2-2014_geologi 2.06 12.02.15 15:20 Pagina 10
meantime been used worldwide approx. 3 Investments in the U.S.A. are rising. In the Million times. In Germany approx. 400 frac- chemical industry for example the addition- turing treatments have been carried out al investments up to 2014 are estimated to since the 60s without any measurable impair- amount to more than $ 100 Billion and this in ment of the environment ever reported. particular by companies headquartered out- side the U.S.A. The additional industry pro- duction expected from this investment is 7 Hydraulic Fracturing and Energy estimated to be more than $ 80 Billion, the Supply jobs created exceed 600.000. Because of the low gas prices, recent devel- The influence, which fracking can have on a opments focus increasingly on wet gas and national economy is represented using the light oil in the unconventional deposits with U.S.A. as an example. The U.S.A. has had its impacts for the oil production similar to peak natural gas production from conven- those for natural gas. The trend of decreas- tional deposits in the early 70s. The devel- ing oil production has been halted. Since opment of tight gas resources with the aid of 2007, domestic oil production in the U.S.A. is fracking, starting in the 70s, has reduced the increasing again and was 50% higher in 2013 decline of domestic natural gas production than in 2007. Production matches for the to reverse the trend in the 90s. With the first time for a long time again the oil development of the shale gas deposits since imports. In the first half of 2014, the U.S.A the second half of the last decade, the U.S.A. were even the largest oil producer world- have seen a rapid increase in production to wide. a level, which is today already higher than The effect of the American shale gas revolu- the peak production in the 70s. From a tion can also be recognized in the develop- dependent importer, the technology of ment of CO2 emissions of the country. Since hydraulic fracturing has enabled the U.S.A. 2005, CO2 emissions of the U.S.A. have to become an exporter of natural gas. Lique- decreased by approx. 600−700 million tons, fied natural gas originally developed for the mainly through substitution of coal in power U.S.A in the Middle East and West Africa is generation by gas. The decrease represents now shipped to the Far East and Europe. approx. 70% of the total CO2 emissions in The development in Germany is completely Germany, which are increasing again since different. Here domestic production has three years – also because of the use of coal decreased since 2003 from more than 20 Bil- – and it is 15 times the annual emissions of lion m3 (109 m3) to less than half in 2013. The Switzerland. It should be kept in mind, that trend will continue, if the government main- the emission of CO2 is only one part of the tains its «no» to the development of the Ger- environmental problems. Equally important man shale gas resources. The consequence are pollutants like sulphur, CO, and particu- is the increasing burning of coal. late matters. In North-America the natural gas surplus has led to a significant reduction in the price of natural gas. Prices have declined from 6 to 8 Is Fracking Needed? more than 10 $/Mscf (thousand standard cubic feet [gas]) to actually 3−4 $/Mscf or To meet the energy demand provides an approx. 0.9 Euro-cents/kWh. This is a third increasing challenge. During the last ten to a half of the price in Europe and a forth to years the demand of primary energy has a fifth of the price in the Far East. increased by 28%. Key drivers of this devel- The supply of secure and low-priced hydro- opment are the ever increasing world popu- carbons fuels an industrial job machine. lation, the increasing prosperity in particu-
10 2-2014_geologi 2.06 12.02.15 15:20 Pagina 11
lar in the developing countries, and econom- 9 Chances and Potential of Fracking ic growth (Reinicke et al. 2014). As long as there is no change in these drivers, energy The resources of the subsurface, which can demand will further increase. To meet it be developed through wells are crude oil requires a broad mix in energy. The further and natural gas in conventional and uncon- development of renewables should be ventional reservoirs as well as hydro-ther- encouraged and supported under all circum- mal and petro-thermal energy. stances. But even if this is continued suc- In this context the term conventional reser- cessfully, the world will remain dependent voir denotes a deposit in a storage rock. In on fossil energy sources for many decades, this rock the hydrocarbons are captured by possibly the whole century, in particular if buoyancy forces below an impermeable bar- nuclear energy is no longer an option. rier formation. For the capture, the barrier A closer look at the development of the con- formation must form a trap, for example a tribution of the individual energy sources bulge similar to a cheese dome. The trapped shows, that renewables have grown by more hydrocarbons have not been generated in than 300% (without hydraulic power) in the the storage rock, they have migrated to it last 10 years (BP 2014). This growth never- from a source rock. The permeabilities of theless covers only 7.5% of the total growth storage rocks are usually high enough to in energy demand during this period and allow a development and exploitation by use contributes today only 2.2% of the world- of classical drilling and production tech- wide primary energy consumption. Includ- niques. Under favorable conditions up to ing hydraulic power, the renewables con- 90% and more of the gas in place is recover- tribute almost 9% to the total consumption. able. If the permeabilities are low, as in the Approx. 86% of the primary energy con- case of Tight Gas reservoirs for example, sumption is still covered by fossil sources hydraulic fracturing may be used to improve with a strongly increasing share of coal. the productivity of the wells, which is done Despite the increase in the contribution since the middle of the last century. from renewable sources, the relative contri- Unconventional reservoirs are defined as bution of the fossil energies has remained deposits in source rock with oil and gas, almost constant compared to 10 years ago, which has not yet left the place where it was when fossil contribution was 87%. In generated. Pre-requisite for the existence of absolute volumes, the yearly consumption a deposit is solely a mature source rock, for of fossil energies is significantly higher example a shale, with a sufficiently high con- today than it was 10 years ago. tent of organic matter, which has been trans- The renewable energies should be encour- formed under the influence of pressure and aged, in particular geothermal energy, but temperature into oil and gas. Because of the despite the rapid growth of wind, solar ener- low permeabilities of source rocks, which gy, etc. the world is far from covering even are of similar magnitude as those of barrier the global growth in energy consumption, let formations, a significant amount of the alone to substitute fossil energies by renew- hydrocarbons stays behind in the source ables. If large quantities of fossil energies are rock. It was only in the last ten years, that needed also in the future, consideration geologists have discovered that this is often should be given to using the cleanest of the bigger portion of the generated oil and these energy forms. gas. To be able to economically utilize unconven- tional deposits in source rocks with pore throats in the order of nano-meters (1 nm = 1/1.000.000 mm) the use of elaborate hori-
11 2-2014_geologi 2.06 12.02.15 15:20 Pagina 12
zontal drilling and multi-frac technology is The world is neither at the end of the oil or an absolute necessity. By using these tech- the gas age – as predicted by the Club of nologies it is possible to recover gas vol- Rome – nor is there a steep decline of oil and umes in the one digit percentage range up to gas production imminent, as propagated by approx. 20% of the in-place volumes in the the Peak Oil organization. For both prog- subsurface. Despite this low fraction, the noses, previous knowledge of the past has incentive for a development of these been extrapolated. Over longer time spans, deposits is large, because other than the this has never been reliable. «discrete» accumulations of conventional The geologic subsurface does not only con- reservoirs, unconventional deposits occur tain hydrocarbons, it also contains geother- basin-wide with in-place volumes which are mal energy. To use it economically for the enormous. generation of electric power high tempera- According to estimates of the U.S. Energy tures (> 150 °C) and high volume production Administration Agency (EIA 2011) and the (several 10 to > 100 l/s) are required. High Bundesanstalt für Geowissenschaften und temperatures require great depths. In great Rohstoffe (BGR 2012) (Fig. 5), the economi- depths, however, rocks are highly compact- cally recoverable shale gas resources in ed and thus have low permeabilities. The Europe amount to 10.000−15.000 Billion m3. solution is to create permeabilities artificial- This is 40 times the current production and ly by hydraulic fracturing. 30 times the current consumption in Europe The theoretical supply potential of hydro- and not much less than that what is estimat- and petro-thermal energy is large and would ed for the U.S.A. (15.500 Billion m3). The be able to make a significant contribution to U.S.A. is no geologic exception. There are cover the demand, even then when only a significant unconventional resources world- fraction of it would be developed. According wide. to estimates published in Ganz et al. (2013),
Fig. 5: Potential for energy recovery through wells according to BGR (2012) and Ganz et al. (2013).
12 2-2014_geologi 2.06 12.02.15 15:20 Pagina 13
the geothermal supply potential for Ger- tal drilling technology coupled with the mul- many alone amounts to 1.700 EJ or ti-frac technology – already applied to devel- expressed in natural gas equivalents approx. op shale gas – to construct an Enhanced 44.000 Billion m3 (Fig. 5), in comparison to a Geothermal System (EGS) with many small shale gas potential for all of Western Europe heat exchangers in the hot dry rock (Fig. 6). of approx. 10.000−15.000 Billion m3. The With such a system, the seismic risk could be question is not, is this potential there? The greatly reduced, such that tremors of a mag- question is, how much of it can be realized nitude as observed in Basel could be avoid- technically and in particular economically? ed. It was one of the essential findings of the According to the quoted reference, the frac in Basel, that the magnitude of possible largest potential is that in crystalline rock, seismic events increases with the volume of which amounts to 1.150 EJ of so-called the injected fluid and hence with the size of petro-thermal energy, i.e. energy which is the fracture surface, which has been created. stored in the rock itself. To develop this The injected volume in Basel was 11.500 m3. potential in the «hot dry rocks» requires the In a system of several much smaller multi- use of the fracking technology. Aside from a fracs the injection volumes would be in the few conductive fault zones there is no order of 1.000 m3 per frac or less, which chance for an economic development with- would be injected without proppants and out this technology. The deep underground therefore also largely without chemical addi- is tight. Its conductivity must at first be gen- tives. erated. It is worthy of note that the noticeable seis- For the generation of this conductivity one micity observed so far in the context of can use high-volume fracs as in Basel, Soultz, hydraulic treatments was limited to injec- or Hannover, which is not without seismic tions of high volumes of fluids in deep hori- risks in tectonically stressed regions. One zons in or close to the basement, where they can also start with proven oil field technolo- led to the release of existing shear stresses gy and adapt it for use in geothermal appli- (in Basel for sure, likely also in St. Gallen and cations, for example the multilateral horizon- in Landau, also for the water disposal-
Fig. 6: Possible multi-frac heat exchanger system for the recovery of petro-ther- mal energy using a shale gas well with five horizon- tal laterals, fracked 10 times each.
13 2-2014_geologi 2.06 12.02.15 15:20 Pagina 14
induced tremors in Oklahoma). Contrary to the evident progress in best practice to man- this, no damaging tremors have so far been age risks and make the technology environ- reported for fracturing treatments in sedi- mentally compatible have hardly found their ments. Noticeable seismicity (up to a magni- way into the public debate until recently. tude of 2.5) induced by fracturing treat- With due respect for the concerns raised in ments in shale formations was recorded the context of the use of the fracking tech- near Blackpool (2012), which, however, nology, they are often based on images, not stayed significantly below damage levels representative for the real operations and (Emmermann 2014). they do not take into account the measures Granted, it is still a long way until a function- already implemented to manage risks. The ing multi-heat-exchanger system based on burning water tap in the movie Gasland has multi-fracturing technology can be imple- nothing to do with the production of natural mented on a large scale, let alone optimiza- gas and nothing at all with fracking. Also the tions thereof. The target horizons are deep- term «poison cocktail» regularly used to er and harder, the necessary wells are more denote frac-fluids, does not represent reality expensive, and the operation of heat (see also Fig. 2). exchanger systems is significantly more dif- The following definitions of the terms risk ficult than draining a hydrocarbon bearing and environment are the basis of the subse- reservoir. But the potential is large and quent elaborations regarding risks and offers a lot of incentives. measures to manage risks. Risk is defined as In summary, the potential for the recovery of the product of probability that an adverse geothermal energy is large and offers event occurs multiplied by the severity if the chances for implementing a secure and low event happens. Environment is defined as emission energy supply. However, it requires the totality of the resources humans-ani- the use of horizontal drilling and multi-frac- mals-plants, soil, (potable) water, landscape, turing technology. An economic implemen- climate, and cultural assets as well as all tation will likely be possible only when interactions. larger numbers of geothermal wells are Of largest concern is quite rightly the preser- drilled in a «factory style» process to feed vation of the potable water resources. It is sizeable geothermal power plants. As a first therefore in the focus of the subsequent step on the way to this, it is necessary to elaborations. Potential pathways for pollu- prove viable technical concepts for a petro- tants to potable water horizons are: sub- thermal recovery in pilot projects now. stance input from the surface, substance ascent along wells, substance ascent and dispersal through the overburden. Decisive 10 Fracking Risks and Possibilities for the severity of a possible event is the of Risk Management damage potential of the contaminants, in particular those contained in the frac-fluids Like everything in life also the fracking tech- (Fig. 7). nology is not free of risks. It is the subject of Against this background, there are the fol- very controversial discussions, which one lowing approaches to reduce the probability can read about almost daily. The discus- of an event from occurring and their severi- sions are dominated by gut feelings and gut ty if it occurs. The probability of a water reactions. This is true not only for Germany, damaging event can be reduced by (1) oper- this is the case internationally. In discus- ations sites and practices on these sites, sions facts are in most cases of only minor which prevent inputs from the surface, (2) or no importance. The results of reputable wells, proven to be tight, (3) a geologic sub- investigations, the efforts of industry, and surface, proven to contain barrier forma-
14 2-2014_geologi 2.06 12.02.15 15:20 Pagina 15
tions, and (4) a fracture propagation which many as well as the relevant specialist legal does not impair the effectiveness of the requirement like for example the Water overlaying barrier formation. To reduce the Resources Act. With these practices and severity of a possible damage it is necessary requirements there are clear rules in place (a) to reduce the damage potential of the for the execution of hydraulic fracturing substances used (not hazardous to water – treatments, which ensure, that existing risks no risk), (b) to be able to detect incidents are accounted for. and react immediately, and (c) to provide for The execution of a wellbore treatment, for unplanned events (Reinicke 2014). example, requires a mining authorization, which can be granted by the mining authori- For improved risk management the compa- ties only to organizations, which have the nies organized in the Wirtschaftsverband required technical qualification and the Erdöl- und Erdgasgewinnung (oil and gas pro- financial resources. The execution of activi- ducers association) in Hannover have iden- ties requires authorization within the frame- tified, analyzed, and evaluated the risks work of the Betriebsplanverfahren (mining associated with hydraulic fracturing and operations plan procedure). The admission jointly developed «best operational prac- of the operations plans requires evidence tices» (WEG 2014), and commissioned frac- that no damaging effects can be expected, in fluids of improved environmental compati- particular whether the requirements of the bility. The practices are a voluntary commit- Water Resources Act are fulfilled and ment of the industry in addition to the statu- whether relevant public interests like tory and official requirements, documented emmission prevention, soil protection, in Germany in the Bundes-Berggesetz (feder- regional planning, and nature conservation al mining law), the Tiefbohrverordnungen according to the relevant specialist legal (deep drilling ordinance) of the States of Ger- requirements have been accounted for.
Fig. 7: Potential pathways to potable water horizons and risk management.
15 2-2014_geologi 2.06 12.02.15 15:20 Pagina 16
Whether the existing rules and regulation The companies organized in the German require modification to even better account Wirtschaftsverband Erdöl- und Erdgasgewin- for the risks associated with hydraulic frac- nung (oil and gas producers association) in turing is currently being debated in Ger- Hannover have identified, analyzed, and many. In this context an environmental evaluated the risks associated with impact assessment for hydraulic treatments hydraulic fracturing and have defined addi- is under discussion, addressing in particular tional measures like frac-fluids that are envi- the subsurface risks of fracturing in a struc- ronmentally compatible. The agreed best tured and transparent evaluation process. operational practices represent the mini- An environmental impact assessment, mum standard of the German oil and gas which will break new grounds, will come. Its industry for carrying out hydraulic fractur- content, procedures, and evaluation criteria ing treatments. are currently being agreed with all stake- An environmentally compatible use of the holders. technology on the basis of these practices Even now there are no scientific reasons to and in compliance with existing laws and ban hydraulic fracturing as documented in regulations is already possible today. The German and Europe-wide expertises technology is therefore of no greater risk (Emmermann 2014, UBA 2014b, Neutraler than any other industrial activity. Expertenkreis 2012, NRW 2012, UBA 2012). The way forward should therefore be to cre- ate the preconditions for scientifically sup- ported demonstration projects executed under special requirements for the recovery of unconventional hydrocarbons and geo- thermal energy. Such projects would allow proving the technical and environmentally compatible viability of hydraulic fracturing in shale and hot dry rock, improving the technology, further developing standards, rules, and regulations, and earning trust by transparent information of the public. This applies both to the recovery of shale gas and to deep geothermal energy as well.
11 Summary
The development of unconventional natural gas and deep geothermal energy is only pos- sible by employing the technologies of hydraulic fracturing and horizontal drilling. Experience over many decades has shown that the risks associated with hydraulic frac- turing can be managed. For the thousands of frac-jobs carried out in Northwest Europe no environmental damages have been report- ed, in particular in Germany, The Nether- lands, the United Kingdom and Norway.
16 2-2014_geologi 2.06 12.02.15 15:20 Pagina 17
References Reinicke, K. M. 2012: Fracken in Deutschland. ERDÖL ERDGAS KOHLE 128. Jg. 2012, Heft 1. BGR 2012: Abschätzung des Erdgaspotenzials aus Reinicke, K. M. 2014: Hydraulische Bohrlochbe- dichten Tongesteinen (Schiefergas) in Deutsch- handlungen (Fracking) aus technologischer land. Mai 2012. http://www.bgr.bund.de/DE/The- Sicht. Niedersächsische Verwaltungsblätter, men/Energie/Downloads/BGR_Schiefer- 7/2014, 1. Juli 2014, 177−193. gaspotenzial_in_Deutschland_2012.pdf?_blob= Reinicke, K. M., Hueni, G., Liermann, N., Oppelt. J., publicationFile (retrieved 08.09.2014). Reichetseder, P. & Unverhaun, W. 2014: Ull- BP 2014: BP Statistical Review of World Energy. mann’s Encyclopedia of Industrial Chemistry, June 2014. http://www.bp.com/content/dam/ Oil and Gas, 1. Introduction. Wiley Online bp/pdf/Energy-economics/statistical-review- Library. http://onlinelibrary.wiley.com/doi/ 2014/BP-statistical-review-of-world-energy- 10.1002/14356007.a23_117.pub2/abstract 2014-full-report.pdf (retrieved 00.09.2014). (retrieved 09.09.2014). Burri, P., Leu, W. 2012: Unkonventionelles Gas – SPE 2010: Multilateral/Multifrac Aufschluss von Brückenenergie oder Umweltrisiko?. Aqua & Schiefergas in Texas. Programmheft Annual Gas, Vol. 9, 54−63. Technical Conference and Exhibition, SPE ACTE Burri, P. & Häring, M. 2014: Ressourcen Explo- 2010, Florenz, Italien. ration: Risiko oder Chance? – Das Spannungs- UBA 2012: Umweltauswirkungen von Fracking bei feld zwischen wissenschaftlichen Fakten und der Aufsuchung und Gewinnung von Erdgas aus öffentlicher Wahrnehmung. Swiss Bull. angew. unkonventionellen Lagerstätten. Dezember Geol., 19/1, 33−40. 2012. http://www.umweltbundesamt.de/pub- Economides, M. J. & Martin, T. 2007: Modern Frac- likationen/umweltauswirkungen-von-fracking- turing. ET Publishing, Houston, ISBN 978 1 bei-aufsuchung (retrieved 08.09.2014). 60461 688 0. UBA 2014a: Methanemissionen. http://www.umwelt- EIA 2011: World Shale Gas Resources: An Initial bundesamt.de/daten/klimawandel/treibhaus- Assessment of 14 Regions Outside the United gas-emissionen-in-deutschland/methan-emis- States. April 2011. http://www.eia.gov/analy- sionen (retrieved 08.09.2014). sis/studies/worldshalegas/ (retrieved 08.09. UBA 2014b: Umweltauswirkungen von Fracking bei 2014). der Aufsuchung und Gewinnung von Erdgas Emmermann, R. (Projektleitung) 2014: Bericht aus insbesondere aus Schiefergaslagerstätten. Juli dem Projekt «Hydraulic Fracturing – eine Tech- 2014. http://www.umweltbundesamt.de/sites/ nologie in der Diskussion». acatech – default/files/medien/378/publikationen/texte_ DEUTSCHE AKADEMIE DER TECHNIKWIS- 53_2014_umweltauswirkungen_von_frack- SENSCHAFTEN, Stand: 4. September 2014. ing.pdf (retrieved 08.09.2014). Fisher, K. & Warpinski, N. 2012: Hydraulic-Frac- WEG 2012: Stellungnahme Anhörung Umweltauss- ture-Height Growth: Real Data. SPE Production chuss Niedersachsen des Niedersächsischen & Operations. February 2012, 8−19. Landtages am 13. Januar 2012. http:// Ganz, B., Schellschmidt, R., Schulz, R.,Sanner, B. www.erdoel-erdgas.de/Der-WEG/ 2013: Geothermal Energy Use in Germany. Positionen/Stellungnahme-Anhoerung-Um- Proc. European Geothermal Congress 2013, weltausschuss-Niedersachsen (retrieved 08.09. Pisa, Italy, 3−7 June 2013. 2014). Kassner, H. 2014: Neue Frac-Fluide für Schiefer- WEG 2014: Praxis der hydraulischen Bohrlochbe- gas- und Sandstein (Bö Z11) Lagerstätten. handlung für konventionelle Speichergesteine. Drittes Statusseminar Fracking, Osnabrück. 1. Richtlinie Wirtschaftsverband Erdöl- und April 2014. http://newsroom.erdgassuche-in- Erdgasgewinnung e. V., Mai 2014. http:// deutschland.de/wp-content/uploads/Neue_ www.erdoel-erdgas.de/Themen/Technik-Stan- Additive_Dr_Kassner-ExxonMobil.pdf (retrie- dards/Hydraulic-Fracturing/WEG-Richtlinie- ved 08.09.2014) Hydraulische-Bohrlochbehandlung (retrieved Neutraler Expertenkreis 2012: Risikostudie Frack- 08.09.2014). ing. April 2012. http://dialog-erdgasundfrac.de /sites/dialog-erdgasundfrac.de/files/ Ex_risikostudiefracking_120518_webprint.pdf (retrieved 08.09.2014). NRW 2012: Fracking in unkonventionellen Erdgas- Lagerstätten in NRW; Langfassung, http:// www.umwelt.nrw.de/umwelt/wasser/trinkwas ser/erdgas_fracking/ (retrieved 08.09.2014). Reinicke, K. M., Brinkmann, F. W., Schwarz, H. & Hueni, G. 1983: Interpretation of Buildup Data Obtained from MHF Wells in Northern Ger- many. 1983 SPE/DOE Low Permeability Gas Reservoirs Symposium, Denver, March 14-16 1983 and JPT, 2173−2183, December 1985.
17 2-2014_geologi 2.06 12.02.15 15:20 Pagina 18
Ihr kompetenter Partner für integrale Tiefbohrtechnik
Exploration Tunnels Kohlenwasserstoffe Endlagerstätten Lagerstätten- erkundung Geothermie
Henauerstrasse 2 CH-9524 Zuzwil Tel.: +41 71 313 70 60 Fax: +41 71 313 70 66 www.foralith.ch
18 2-2014_geologi 2.06 12.02.15 15:20 Pagina 19
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 19-37
Application and potential of hydraulic-fracturing for geothermal energy production Reinhard Jung1
Key words: Hot-Dry-Rock (HDR), Enhanced-Geothermal-Systems (EGS), Hydraulic-Stimulation, Multi- frac-Systems, Waterfrac-Technique
Zusammenfassung Abstract Das grösste Hindernis für die breite Nutzung geo- The main obstacle for a wide application of geo- thermischer Energie ist die geringe Permeabilität thermal energy is the low permeability of the rock der Tiefengesteine. Dem Hydraulic-Fracturing at great depth. Hydraulic-fracturing is therefore kommt deshalb eine Schlüsselrolle bei der the key for exploiting this huge resource located Erschliessung des riesigen vor allem im kristalli- predominantly in the crystalline basement. A dozen nen Grundgebirge gelegenen Potenzials zu. projects have been performed since 1970. But still Obwohl seit 1970 ein Dutzend HDR- bzw. EGS-Pro- the technique, known as HDR- or EGS-technology jekte ausgeführt wurden, ist die Technik nicht aus- is not mature. In addition development is now hin- gereift. Ihre Weiterentwicklung wird derzeit durch dered by the risk of induced earthquakes. A review die Furcht der Bevölkerung vor induzierter Seismi- of the projects shows that the poor progress is zität behindert. Eine Analyse der Projektergebnisse mainly due to the exploitation concept applied since zeigt, dass die Hauptursache für den schleppenden the early 1980ties. Until then the leading concept Fortschritt das Erschliessungskonzept ist, das seit was to connect two inclined boreholes by a set of Mitte der 1980er Jahre angewandt wird. Das bis hydraulic fractures. This multi-fracture scheme dahin favorisierte Multiriss-Konzept sah vor, zwei was abandoned not the least for technical reasons geneigte Bohrungen mittels künstlicher Risse zu and replaced by the EGS-concept. This intends to verbinden. Dieses Konzept wurde nicht zuletzt enhance the permeability of the joint network by wegen technischer Schwierigkeiten durch das massive water injection. The results of the EGS- EGS-Konzept ersetzt. Dieses sieht vor, das natürli- projects however show that this is not happening che Kluftnetz durch hydraulische Stimulation auf- but that a single macro-fracture is created consist- zuweiten. Die Projektergebnisse zeigen jedoch, ing of natural and new tensile fracture elements. dass sich stattdessen grosse Einzelrisse ausbilden, Due to their enormous size and their specific prop- bestehend aus natürlichen und künstlichen Riss- erties they bear a seismic risk. Macro-fractures of elementen. Aufgrund ihrer Grösse und Eigenschaf- a smaller scale are less critical and their hydraulic ten bergen diese Makro-Risse ein seismisches properties are sufficient for multi-fracture sys- Risiko. Mit kleineren Abmessungen aber wären sie tems. These findings suggest a return to the origi- aufgrund ihrer hydraulischen Eigenschaften für nal HDR-concept. Multi-fracture concepts are Multiriss-Systeme gut geeignet. Eine Rückkehr applied with great success in shale-gas reservoirs zum Ausgangskonzept ist deshalb angeraten. Mul- and the techniques to establish these systems have tiriss-Konzepte werden in den Schiefergas-Projek- improved considerably. So it seems likely that geo- ten erfolgreich eingesetzt und die Technik hat in thermal multi-fracture systems can be realized in den letzten 20 Jahren grosse Fortschritte gemacht. the near future. Es ist daher wahrscheinlich, dass auch geothermi- sche Multiriss-Konzepte in naher Zukunft realisiert werden können.
1 JUNG-GEOTHERM UG, Gottfried-Buhr-Weg 19, 30916 Isernhagen, Germany
19 2-2014_geologi 2.06 12.02.15 15:20 Pagina 20
1 Introduction
Today, geothermal energy production for heats-up to rock temperature while circulat- direct use and/or power production is ing through the fracture system and is pro- restricted to hydro-thermal resources. duced in the second well. To prevent flash- These are intensely fractured, karstified or ing an overpressure is maintained in the highly porous rock-formations with extraor- geothermal loop. Steam for power genera- dinarily high permeabilty. Hydro-thermal tion is produced in a secondary loop gener- resources particularly those suitable for ally filled with an organic fluid (ORC- power production are rare especially in Process) or with an ammonia-water mixture countries with normal temperature gradi- (Kalina-Process) as working fluids. ents, where one has to drill deep to reach Industrial doublet-systems will have to be sufficiently high temperatures. The over- designed for an electrical power output of whelming part of the heat content of the 5−10 MWe and production flow rates in the upper crust accessible by drilling is stored range of 100 l/s. To ensure a service life of at in rock formations with extremely low per- least 25 years a separation distance of at 0.5 meability, particularly in the crystalline to 2 km between the two wells at depth and basement. The power potential of these a total fracture area of 5−10 km2 is required. petro-thermal resources is by far the biggest The volume of rock to be accessed by the energy resource of the upper crust exceed- fracture system has to be in the order of 0.1 ing the power potential of the hydro-thermal to 0.3 km3. The pumping-power to maintain and of all hydro-carbon resources by at least the geothermal loop can consume a signifi- two orders of magnitude. cant fraction of the produced power. For this First attempts to access this potential date reason the flow impedance of the fracture back to the early 1970s (Brown et al. 2012). system (difference between inlet- and outlet- The basic idea is to create large fracture sys- pressure divided by the flow rate) should tems in the crystalline rock mass in order to not exceed 0.1 MPa/(l/s). hydraulically connect boreholes over great Two concepts had been invented and tested distances. For power production cold water during 40 years of research. or natural brine injected in one of the wells The first regarded the crystalline basement
Fig. 1: Basic concepts.
20 2-2014_geologi 2.06 12.02.15 15:20 Pagina 21
as a competent unfractured rock mass and tem is completed by drilling a second bore- the idea was to connect two inclined bore- hole into the region of enhanced fracture- holes by a number of parallel tensile frac- permeability (Fig. 1), as indicated by the tures created by hydraulic-fracturing (Fig. spatial distribution of seismic events 1). The feasibility of this concept, known as induced during the stimulation process. Hot-Dry-Rock-concept (HDR), was proofed The change in the leading concept had by creating and investigating single fracture severe consequences: systems at several locations. Attempts to • Deviated or horizontal wells were no connect two inclined bore-holes by a multi- longer required and replaced by more or fracture system in the Los Alamos-project less vertical wells. however failed since the fractures did not • Development of high temperature packers propagate in the projected direction and was no longer important and was disre- due to technical problems with borehole garded. packers at high temperatures (Rowley et al. • Heat exchanging area as a measure for the 1983, Dreesen & Nichol-son 1985, Brown et service life of a HDR-system was replaced al. 2012). by the stimulated rock volume. Realizing that the crystalline basement con- • Geometrically simple fracture mechanical tained unsealed natural fractures even at models were replaced by geometrically great depth, and that these fractures started complex fracture networks lacking frac- to shear before the fluid-pressure reached ture mechanical mechanisms. the level for tensile fracture initiation, the All projects of the last 30 years followed this HDR-Concept was abandoned and replaced concept and fracture systems of enormous by the EGS-Concept (Enhanced Geothermal dimensions (several square-kilometres) had Systems). This concept aims to shear and been created during this period connecting dilate the natural fracture network by inject- boreholes over distances of up to 700 m. ing large quantities of water in long uncased Nevertheless, in several aspects the eco- borehole sections (Batchelor 1982). In order nomic targets defined above have not been to distinguish it from hydraulic-fracturing met. In particular the flow rates and the this mechanism was called «hydraulic stimu- power output are still far too low (Tab. 1). lation» (Murphy 1985). The circulation sys- The main reason is the high flow-impedance
Tab. 1: Key-parameters of the major EGS-projects.
21 2-2014_geologi 2.06 12.02.15 15:20 Pagina 22
in the fracture systems. It will be shown in future industrial systems (MIT 2006). All the next chapters that mainly the change of together more than a billion Euro have been concept is responsible for the poor progress spent in national and international projects. during the last three decades and that a About 20 deep wells with a total length of return to the multifracture-concept as envis- about 70 km had been drilled and numerous aged during the first decade of HDR- massive waterfrac-tests including pre- and research and practiced in the shale gas post-frac investigations had been performed industry is necessary. at the different locations. The following paragraphs are an attempt to describe and synthesize the main observations and 2 Test Performance results of these tests. Almost all stimulation tests of the EGS-proj- 2.1 Overview ects had been performed with water or brine as frac-fluid. Only in a few cases viscous-gels Nine research projects and three commer- and proppants had been used. All tests were cial HDR-projects have been performed done in open-hole sections with lengths since the beginning of Hot Dry Rock ranging from about 10 m up to about 700 m. research at around 1970 (Fig. 2). Some of the Generally these intervals particularly those early projects investigated fracture propaga- with greater lengths contained hundreds of tion and fracture properties at shallow joints, a number of fracture-zones and faults. depth in order to gain basic knowledge In addition they comprised long sections under well-defined but down-scaled condi- with axial or inclined drilling induced frac- tions, i. e. Le Mayet de Montagne (Cornet tures and sections with borehole break-outs. 1989), Falkenberg (Jung 1989), Higashihachi- Almost all open-hole sections except those in mantai (Hayashi & Abé 1989) and Fjällbacka the Fenton-Hill II and the Camborne System (Wallroth 1992). The majority of the projects were vertical or sub-vertical. The majority of however were carried out at greater depth the stimulation tests were performed with under conditions and on a scale similar to only moderate flow rates, ranging from less
Fig. 2: Locations of the major international EGS-projects.
22 2-2014_geologi 2.06 12.02.15 15:20 Pagina 23
than 10 l/s to about 50 l/s. Only a few tests declined continuously without a sign of frac- were done with flow rates above 100 l/s. ture closure. Basically two stimulation-schedules had The flow logs recorded during post-frac been applied: the step-rate and the con- injection tests showed an almost linear stant-rate injection schedule. decrease of the flow velocity with depth (Fig. 4). This is typical for axial fractures and 2.2 Example for a constant rate stimulation is commonly observed after stimulating oil test and gas wells in sedimentary rock for- mations. The logs indicate that the axial The basic idea behind the constant-rate stim- fracture extends over the entire length of the ulation schedule was to rise the pressure open-hole section accessible for logging. quickly to a high level so that fractures of var- The high flow velocity at the lower end of ious orientation could shear simultaneously. the flow logs and the seismic cloud indicate The test was performed in the open-hole sec- that it extents further down to the bottom of tion of borehole GPK4 in the Soultz II-system the well and another 500 m beyond of it. in the depth section between 4.500 m and The seismic cloud was almost planar and 5.000 m. The aim was to hydraulically con- was indicative for one through-going frac- nect the well to the fracture system stimulat- ture. Dip and strike were vertical and N-S ed earlier in wells GPK2 and GPK3. The dis- respectively. Stress conditions where tance to the next well GPK3 was about 700 m. transtensional with the maximum horizontal The test was started with about 600 m3 of stress oriented 170° E. The great number brine followed by 8.500 m3 of water. The well- and the character of the seismic signals, as head-pressure record shows the typical char- well as the slight deviation of the strike acteristics of a conventional hydraulic-frac- direction from the direction of the maximum turing test with a pressure maximum after horizontal stress indicate that fracture prop- start of injection (break-down pressure) and agation was not in a pure tensile mode but almost constant pressure until the end of contained a shear-mode component. injection (Fig. 3). During shut-in the pressure These observations proof that large single
Fig. 3: Flow rate and well- head-pressure record of a constant rate stimulation test in borehole GPK4 (Soultz II-system [Baria et al. 2005]). Dashed line in the pressure record: curve corrected for the density effect of brine injection.
23 2-2014_geologi 2.06 12.02.15 15:20 Pagina 24
Fig. 4: Left: front-view of the seismic cloud of the stimulation test in borehole GPK4 of the Soultz II-system (view to the east), middle: flow logs recorded during post-frac injection tests, right: scheme of the fracture trace along the borehole wall (right). Sources: seismic cloud (Dyer 2005), flow-log (Schindler et al. 2008).
artificial fractures can be created by order to isolate a permeable fault at about hydraulic stimulation in granite despite of 3.500 m depth the bottom part of the well the presence of hundreds of natural frac- had been filled with sand. Starting flow-rate tures. The presence of drilling induced axial was 0.15 l/s, the maximum flow rate at the fractures, the start of the stimulation at rela- end of the test was 36 l/s (Fig. 5). tively high flow rates and an appropriate ori- The pressure record did not show the typical entation of the borehole axis with respect to characteristics of conventional hydraulic- the stress field will favour the initiation of fracturing tests described in the previous artificial fractures. example. However the pressure reached a quite high level already during the first step 2.3 Example for a step-rate stimulation test and showed clear signs for a mechanical reac- tion from the beginning. The pressure The rational of the step-rate stimulation tests increase from step to step was less than pro- was to first activate the fractures most ready portional to the flow rate steps and pressure for shearing and then activate step by step remained almost constant for the final steps. fractures less favourably oriented for shear- This indicates that fractures had been jacked ing. The exemplary test was performed in open at this pressure level. As for the constant the open-hole section of borehole GPK1 rate test the pressure declined smoothly dur- extending from 2.850 m to 3.400 m. It was the ing the shut-in period before venting and first stimulation test in the Soultz I-system. In showed no indication for fracture closure.
24 2-2014_geologi 2.06 12.02.15 15:20 Pagina 25
The seismic cloud of this test was processed N-S striking fracture and some NNW-SSE- with the so called «collapsing method» striking and ENE-dipping faults. It appears (Jones & Steward 1997). This method that the fracture is crossing them with a cer- removes the random location error and tain offset. The vertical fracture is most like- leaves a more distinct image of the internal ly an artificial fracture created in the well structure of the cloud. The front-view of the section below the casing shoe that com- cloud (Fig. 6a) shows a quite complex inter- prised a group of en-echelon drilling- nal pattern with a central patch and lines or induced fractures (Fig. 7). This fracture con- stripes of intense seismicity, some of them sumed or produced 60% of the fluid at the radiating from the centre at different angles. end of stimulation and during post-frac In several directions the cloud has distinct injection and production tests. Three deep- almost straight boundaries. Views along the er outlets absorbing another 25% of the flow strike plane of the cloud as indicated in Fig. rate were identified by Evans et al. (2005) as 6c and d, show a through-going structure hydraulically linked to the main outlet below resembling a large wing-crack. The overall the casing shoe. This means that 85% of the strike direction of the vertical cloud is 155°. injected fluid were flowing into the main This is 15° off the direction of the maximum fracture. The remaining 15% were absorbed horizontal stress of 170°. by the permeable fault at 3.500 m depth after The step-like trace of intense seismicity in removing the sand and stimulating this low- the horizontal slice as shown in Fig. 6b indi- er part of the well. The pattern of the seis- cates that the lines of intense seismicity mic cloud at this depth indicates that even radiating from the centre are probably iden- this fault is connected to the main fracture. tical with the intersection lines of a vertical A more extensive analysis with a slightly dif-
Fig. 5: Flow rate and wellhead-pressure record for the step-rate stimulation test in borehole GPK1 of the Soultz I-system. Note the logarithmic scale of the flow rate axis. Source: Jung (1999).
25 2-2014_geologi 2.06 12.02.15 15:20 Pagina 26
Fig. 6: Processed (collapsed) seismic cloud obtained during the step-rate stimulation test in borehole GPK1 of the Soultz I-system. a] front view (view toward W), b] horizontal slice (3.000− 3.100 m) c] & d] views paral- lel to the plane of a] along indicated directions. Source: Niitsuma et al. (2004).
Fig. 7: a] Scheme of the central part of the macro-fracture created in borehole GPK1 of the Soultz I-system, derived from the flow logs and the seismic cloud (Fig. 6). b] flow-logs recorded during post-frac injection and production tests in borehole GPK1 at Soultz. Flow-log from Evans et al. (2005).
26 2-2014_geologi 2.06 12.02.15 15:21 Pagina 27
ferent interpretation of the seismic data was 6 l/s to 200 l/s. Furthermore some tests were made by Evans et al. (2005). performed according to the constant-rate In summary one can conclude that the step- schedule, others according to the step-rate rate stimulation test created a wing-crack- schedule. Well trajectories were predomi- like macro-fracture that despite of intersec- nantly vertical to sub-vertical but some tests tions with faults is mechanically and most (Los Alamos II and Camborne) were per- likely hydraulically a single large through- formed in inclined borehole sections. going entity. 3.1 Orientation of the stimulated fractures
3 General results and observations It is generally assumed that tensile fractures are oriented perpendicular to the direction Though the site- and test-conditions of the of the least compressive stress. Tensile frac- EGS-projects differed remarkably, an tures should therefore be vertical for normal attempt was made to derive results and and strike-slip stress conditions and hori- observations common to all EGS-systems. zontal for thrust-fault stress conditions. As The only constants were rock type (granite mentioned above all basic stress conditions and granodiorite) and frac-fluid (water or were covered by the major projects. Soultz brine with one exception) and the fact that had trans-tensional stress conditions which all tests were done in uncased borehole sec- is the transition between normal and strike- tions. All other test parameters and condi- slip stress conditions. tions were quite variable: Stress conditions Investigation of the dip of the seismic clouds ranged from normal- to thrust-faulting, of the major EGS-projects showed that the depth from 800 m to 5.000 m (Fig. 8), tem- seismic clouds were vertical to sub-vertical perature from 80 °C to 250 °C, length of frac- for strike-slip and trans-tensional stress con- interval from 3 m to 750 m, injected volume ditions, steeply inclined (60−70°) for normal from 20 m3 to 35.000 m3, and flow rates from stress-conditions and subhorizontal for
Correspondence of the dip of the seismic clouds with the stress conditions at the major EGS-sites. Scale on the left corresponds to the depth of the EGS-systems. (After Jung 2013).
27 2-2014_geologi 2.06 12.02.15 15:21 Pagina 28
thrust-faulting conditions (Jung 2013). This was taken as the measure for the size of the indicates that the dip of the stimulated frac- stimulated fracture systems similar to an tures is similar to but not identical with the earlier study of Murphy et al. (1983). The dip of tensile fractures. The biggest devia- area was grossly determined by drawing an tion is observed for normal stress condi- envelope around the projection of the seis- tions. In this case the dip of the fractures is mic clouds on a plane parallel to its main ori- optimal for shearing. For strike-slip condi- entation. tions the strike of the fractures may also be Despite of the big variation in test and test- optimal for shearing. But this was not site conditions a clear correlation was found proofed since there is often too high uncer- between seismic area and injected volume tainty in the direction of the principal hori- (Fig. 9). The whole set of data points except zontal stresses. In cases (e.g. Cooper Basin) that of a gel-frac in the Camborne-project it was suspected that the seismic cloud cor- can well be fitted by a power law with expo- responds to a pre-existing fault that had nent n = 2/3. This means that the area is 2/3 been sheared during the stimulation tests. increasing with VIN . The area did not cor- This argument cannot be disproofed but it relate with flow rate or length of the frac- seems unlikely that this is generally the interval (which could serve as a proxy for case. One can therefore conclude that the the number of natural fractures). These find- tectonic stresses are the main controlling ings and the high coefficient of correlation factor for the overall orientation of the stim- R2 of the data points with the fitting line ulated fractures. allow establishing the following hypotheses: • The stimulation process is mainly volume- 3.2 Size of the stimulated fractures controlled. Fluid losses have no significant impact. Fluid efficiency η (ratio of created Because of the 2-dimensional nature of the fracture volume and injected volume) is seismic clouds and the strong influence of high, at least in the order of 50%. the location error on their thickness not the • Friction pressure losses in the fractures volume but the area of the seismic clouds have no significant influence on the area to
Fig. 9: Area of the seismic clouds of all major EGS- projects vs. injected volume (after Jung 2013). Fitting line and coefficient of determination R2 is for the solid data points. Open cir- cle: Data point of a gel-frac test in well RH-15 of the Camborne system. Dashed line: Trend-Line for penny- shape fractures for E´ = 50 1/2 GPa and KIC = 1.5 MPa·m .
28 2-2014_geologi 2.06 12.02.15 15:21 Pagina 29
volume relationship. Static fracture mod- and post-stimulation injection or production els should therefore apply. tests (Jung 2013). In no case was the number of hydraulically significant fractures bigger One of the most popular static fracture mod- than five. Furthermore in most cases these el is the circular tensile fracture, the so fractures were close to each other and there called «penny-shape fracture». Though it is was always a hydraulically dominating frac- clear that this model is not applicable for ture among them. As demonstrated in the the stimulated fractures a comparison with example above (Fig. 7) it is likely that some this model is interesting. For the penny- of the fractures are only hydraulic links to shape fracture model, which neglects fluid- the main fracture since in most cases the losses and the vertical stress gradient, the main fracture stays close to the well over a 0.8 fracture-area is proportional to VIN and long well section. It may therefore be con- even more important it is by about one cluded that the number of hydraulically sig- order of magnitude higher than the area of nificant fractures after stimulation was in all the seismic clouds (Fig. 9). The major tech- cases close to one. nical consequence is that the fluid volume required for a certain fracture area is about 3.4 Fracture aperture ten times higher than the volume estimated with a penny-shape fracture model. Part of Fracture apertures were determined with this big discrepancy may be explained by three independent methods, first by calcu- fluid-losses. But as mentioned above fluid lating the ratio of injected volume during losses played not an important role. stimulation and area of the seismic clouds, secondly by the tracer break-through vol- 3.3 Number of stimulated fractures ume observed during inter-well circulation tests, and third by using the hydraulic Direct information on the number of con- impedance measured during interwell circu- ductive fractures was obtained from flow lation tests (Jung 2013). and temperature logging during stimulation The apertures determined by the ratio of
Fig. 10: Fracture apertures determined with different methods. Solid dots: ratio of the injected volume and seismic area, solid line: trend-line for the solid dots, open circles: aper- tures from tracer break- through volume, open tri- angles: apertures from hydraulic impedance, da- shed line: trend-line for penny-shape fractures 1/2 with KIC= 1.5 MPa·m and E´= 50 GPa, data from Jung (2013).
29 2-2014_geologi 2.06 12.02.15 15:21 Pagina 30
injected volume and area of the seismic 3.5 Hydraulic characteristics of 1/3 cloud increase proportional with VIN and the fractures reach values of some centimeters for the largest fractures (Fig. 10). It is not surprising Post-frac constant rate injection or produc- that the apertures determined this way are tion tests always showed a square-root or the highest since they are determined for fourth-root of time-behaviour. This means the propagating («inflated») fractures and since pressure in the test-well increases or decreas- fluid losses are included. It is however sur- es linearly with the square-root or fourth-root prising that most of the apertures deter- of time. In log-log-plots of the pressure and mined from the tracer break-through vol- the logarithmic pressure-derivative this umes are close to these values. Even more shows up as straight lines with slope ½ and ¼ striking is the fact that the apertures deter- respectively. Pressure-time curves of this mined from the inter-well flow-impedance type are characteristic for linear (parallel) are by about two orders of magnitude lower flow within a fracture of finite hydraulic con- than most of the values determined by the ductivity imbedded in an impermeable two other methods. This means that the matrix (square-root of time behaviour) or in a hydraulic conductivity of the fractures permeable matrix (fourth-root of time behav- (which is proportional to the cube of the iour). The square-root or fourth-root of time aperture) are by about 6 orders of magni- behaviour is commonly observed for tude lower than the hydraulic conductivity hydraulic fractures in stimulated oil- or gas- that one would expect for the apertures wells but the duration of these periods par- determined by the two other methods. This ticularly of the fracture linear flow-period is could easily be explained when not a single generally quite short. In the stimulated EGS- fracture but multiple fractures were wells however fracture-linear flow-periods of involved in the inter-well flow. But as the 10 hours or more are not uncommon (Fig. 11). flow-logs have shown this was not the case. For axial fractures extending over several hundred meters along the borehole wall these long fracture-linear or bilinear flow- periods are reasonable. But the same behav-
Fig. 11: Log-log-plot of the pressure (upper curve) and of the (logarithmic) pressure derivative vs. time of a post-frac con- stant-rate injection test at Soultz (Tischner 2013).
30 2-2014_geologi 2.06 12.02.15 15:21 Pagina 31
iour was also observed for fractures that 3.6 Thermal Draw-Down had a point-like intersection with the bore- hole. In these cases the most plausible expla- The decline of the production temperature nation is that the borehole is linked to a very during circulation is the ultimate criterion long and highly conductive flow channel for the success or the failure of an EGS-sys- within the fractures, which acts as the base- tem and is a very sensitive indicator for the line for the linear or bilinear fracture flow. applicability of the models established for Another or additional explanation is a strong the EGS-system. Unfortunately only a few anisotropy of the fracture-conductivity. thermal-drawn curves of EGS-systems are The hydraulic conductivity (transmissivity) available. In most cases the circulation tests of the fractures determined from the square- were too short to obtain a thermal-draw root or fourth-root of time-curves for single- down, or the test conditions were not well well tests are in good agreement with the constrained. hydraulic impedance measured during inter- The best examples concerning test condi- well circulation tests. Both values are most tions and test-duration are the thermal likely representative for the hydraulic con- draw-down curves of the Los Alamos I and of ductivity normal to the orientation of the the Camborne EGS-system (Fig. 12). channels or normal to the axis of the highest For both cases the temperature decline can fracture conductivity. well be fitted by single fracture models.
Fig. 12: Temperature de- cline during constant-rate circulation tests in Cam- borne II [a] and the Los Alamos I system [b]. Dots: data points, Solid lines: fit curves obtained with ana- lytical single fracture models, dashed line: tem- perature decline for a dou- blet in a permeable layer with thickness b = 10 m. Data from Brown et al. (2012) and Ledingham (1989). Tables: list of the parameter values used for fitting, a: inlet-outlet dis- tance, b: fracture aperture, Q: flow rate, T0: initial reservoir-temperature, TIN: injection temperature, A: fracture area.
31 2-2014_geologi 2.06 12.02.15 15:21 Pagina 32
For the Los Alamos I system a good fit was borne-system (Tab. 2). If one replaces the found for a model with parallel fluid-flow in a discrete fracture in this model by a perme- rectangular fracture accompanied by tran- able layer with a thickness of several meters sient conductive heat flow from the rock (a proxy for a volumetric system) the tem- toward the fracture plane. The area of the perature decline starts with a significant fracture of 10.000 m2 determined with this delay as demonstrated in Fig. 12. model agrees quite well with the value of In summary one can conclude that both 8.000 m2 obtained with a similar model by thermal draw-down curves can well be fitted the Los Alamos group (Brown et al. 2012) by a single discrete fracture model. There is and corresponds with the inlet-outlet dis- no indication for a volumetric or multi-frac- tance of about 80 m of this system. ture connection between the wells. For the Camborne-system a good fit was found by Ledingham (1989) by using a rec- 3.7 Induced Seismicity tangular fracture model similar to the one above but comprising two fractures with All tests except the gel-frac test in the Cam- flow-fractions of 79% and 21% respectively. A borne-project were accompanied by intense similar good fit (Fig. 12) is obtained with an seismicity. The rate of seismic events was analytical model that calculates the decline proportional to the flow rate but decreased of the production temperature for a bore- gradually with time for constant flow rate. hole-doublet in an infinite fracture with tran- The number of detectable seismic events sient conductive heat flow from the rock was generally in the order of one event per matrix toward the fracture plane. The inlet- cubic-meter of injected volume. The source outlet distance of 260 m determined by radius of the majority of events estimated using this model agrees quite well with the from the frequency-characteristic (corner- geometrical inlet-outlet distance of the Cam- frequency) was in the order of 5−10 m. A rel-
Fig. 13: Processed (col- lapsed) seismic cloud of the stimulation test in borehole BS-1 at Basel, view parallel to the central plane of the cloud (10° from vertical toward W). Processed Cloud from Baisch & Vörös (2007), stress-direction from Hä- ring et al. (2008).
32 2-2014_geologi 2.06 12.02.15 15:21 Pagina 33
atively small fraction of events had much nied by shearing and dilating of the natural bigger source radii and magnitudes and fractures is based mainly on the fuzzy appeared predominantly in the final part of appearance of the seismic clouds, the strong the stimulation tests and during pressure shear wave components of the seismic sig- depletion in the subsequent shut-in periods. nals, the great number of natural fractures In the Basel-system some strong events were encountered in granite even at great depth, observed several months after pressure and the onset of induced seismicity at a fluid depletion. pressure lower than the pressure required All seismic clouds of the major EGS-projects for the propagation of new tensile fractures. had a disk-like shape with a thickness of up Most of the results and observations to about 1 to 3 times the location error described above however do not support which was generally between 30 m and more this view. The small number of hydraulically than 100 m. Most of them had areas of significant fractures and the dominance of intense seismicity in the central part sur- one in post-stimulation flow-logs, the rapid rounded by a halo of low seismicity. The decline of the production temperature dur- transition between the two was abrupt and ing circulation and the shape of processed occurred in most cases along straight seismic clouds indicate that mainly one boundaries. The areas of intense seismicity trough-going macro-fracture is created dur- were often elongated in one direction and in ing the stimulation process. This macro-frac- the extreme case almost linear. Similarly ture is oriented almost but not perfectly per- there were elongated patches and lines with pendicular to the direction of the minimum no seismicity. Many of the regions in the principal stress. At least for a number of cas- inner part of the seismic clouds showed es the macro-fracture resembles a large repeated seismicity. Subsequent stimulation wing-crack. On this basis it is hypothesized tests in the same well produced almost no that the wing-crack mechanism plays a key seismicity until the injected volume role in the formation of these macro-frac- approached the injected volume of the ini- tures. tial test. The formation of wing-cracks is one of the The generally diffuse appearance of the seis- micro-mechanisms discussed in material mic clouds was to a main part due to the science to explain the inelastic behavior and location error. When this was removed or failure of brittle material under compres- reduced by applying appropriate processing sion. The basic observation is that fractures methods like the so called «collapsing of finite length failing in shear will not prop- method» (Jones 1997) more distinct images agate along their own plane but will form of the fracture systems were produced giv- tensile wing-fractures (Fig. 13). Referring to ing insight into their internal structure. A results of Coterell & Rice (1980), Lehner & number of these processed clouds showed Kachanow (1996) stated that the wings are the characteristics of a large wing-crack. The initiated near the fracture tips at an angle of most obvious example besides the one in 70° to the plane of the initial shear fracture Fig. 6 is the seismic cloud of the Basel-sys- and are then bending into the direction of tem (Fig. 13). the maximum principal stress. For natural fractures of the size of joints ini- tiation of the wings start at a fluid pressure 4 Discussion only a few bars above the pressure required for the onset of shearing. For natural frac- The present understanding of hydraulic tures of a larger scale (fracture zones or stimulation as a pressure diffusion process faults) the difference is even smaller. This in the natural fracture network accompa- means that natural fractures being sheared
33 2-2014_geologi 2.06 12.02.15 15:21 Pagina 34
during stimulation will inevitably develop their tips. The process will then continue as wings. These wings will probably connect to in the other case. For very high flow rates or neighboring fractures. The rising fluid-pres- viscous fluids the tensile fracture may cross sure within these fractures will cause them the natural fractures before the fluid pres- to shear and to develop wings at their tip. As sure had the time to migrate deeply into the a consequence a through-going fracture will natural fractures and to stimulate shearing. develop consisting of natural and new frac- This crossing however happens generally ture elements. It’s orientation will be slightly with a certain offset at the interception. So off the direction of the maximum principal also in this case the macro-fracture contains stress. When the pressure approaches the tensile fracture and natural fracture ele- minimum principal stress large wing-frac- ments but probably with a smaller propor- tures may develop at both ends of this series tion of the latter. so that the whole fracture appears as a large In any of these cases the orientation of the wing-crack. It seems that most of the stimu- macro-fracture is slightly off the direction of lated fractures at Soultz and the stimulated the maximum principal stress. As a conse- fracture of Basel are of this type. It is likely quence the maximum principal stress sup- that the development of the large-scale ports the propagation of the macro-fracture wings are the reason for the strong seismic and enables fracture propagation at a fluid- events in the final stages of these stimula- pressure below the minimum principal tion tests, since they enable large and simul- stress. taneous shear displacements of the whole For fluid flow in the macro-fracture the natu- series of natural and new fracture elements ral fracture elements act as resistors where- created earlier. as the tensile fracture elements play the role In long uncased borehole sections there are of capacitors. Accordingly the hydraulic basically two different starting conditions impedance of the macro-fracture is deter- for stimulation (Fig. 14). For step-rate stimu- mined by the natural fracture elements lation tests stimulation will most likely start whereas its aperture is determined by the with the shearing of a natural fracture and tensile fracture elements. In three dimen- the process will continue as described sions this pattern of natural and tensile frac- above. For constant rate stimulation tests ture elements will most likely cause a strong with moderate to high flow rates an axial anisotropy of the fracture conductivity with tensile fracture may be created. This tensile low conductivity parallel to the shear-direc- fracture will intersect natural fractures tion and high conductivity perpendicular to cause them to shear and to develop wings at it. Large wings at the tip of large natural frac-
Fig. 14: Scheme of the two basic starting conditions for the evolution of a macro-fracture during hydraulic stimulation in fractured granite. Left: start by shearing of a natu- ral fracture intersecting the well, right: start by creating an axial tensile fracture in the well.
34 2-2014_geologi 2.06 12.02.15 15:21 Pagina 35
tures or at the ends of a long series of natu- the flow rate and the length of the test inter- ral and tensile fractures may form long val or the number of natural fractures through-going channels after pressure exposed to the fluid-pressure. These macro- depletion. fractures were steeply dipping for normal During pressure depletion the tensile frac- stress conditions, sub-vertical for strike-slip ture elements will tend to close but at their and trans-tensional conditions, and sub-hor- roots they are hindered by the friction on izontal for thrust-faulting stress conditions. the natural fracture elements. Big quantities Their area to volume ratio was much smaller of elastic energy are therefore temporary or than that of tensile fractures. The macro- permanently blocked near the roots of the fractures did not close after pressure deple- tensile fractures, particularly of the large- tion but retained a hydraulic conductivity scale wings. This energy may be set free suitable for inter-well flow rates between explosively by sudden back-sliding of the some l/s and about 25 l/s over well distances natural fracture elements. This is a plausible of up to 700 m. During single well hydraulic explanation for the observation of strong tests the fractures showed long fracture-lin- events during the pressure depletion period ear or bilinear flow-periods indicating paral- and thereafter. lel flow within the fractures emerging from a In summary the wing-crack model delivers long highly conductive flow-channel. All plausible explanations for almost all obser- seismic events with magnitudes above the vations described in the previous chapters perceptible limit occurred in the final state in particular for: the onset of fracture propa- of stimulation but also during or after pres- gation at a fluid pressure lower than the min- sure depletion. It is suspected that most of imum principal stress, the high intensity and the macro-fractures created in the EGS-proj- mechanism of induced seismicity, the occur- ects are wing-cracks and that the wing-crack rence of lines of intense seismicity in the mechanism is also acting on a smaller scale seismic clouds, the long duration of the frac- by linking adjacent natural fractures via ture-linear or bilinear flow periods during fresh tensile fracture elements. post-stimulation well tests, the occurrence These findings suggest that the present EGS- of high magnitude events during and after concept will never lead to systems of indus- pressure depletion, the large fracture aper- trial size and performance. It has to be aban- tures. It also explains the striking discrepan- doned and be replaced by a multi-fracture cy between the only moderate fracture scheme as it was foreseen in the original transmissibility and the large apertures. It Hot-Dry-Rock concept with the main differ- seems therefore justified to use the wing- ence that the tensile fractures of this con- crack-model and the wing-crack-mechanism cept have to be replaced by a type of macro- as a base for further investigations. fractures consisting of natural and new ten- sile fracture elements. Fluid-flow in these macro-fractures is complex due to the pres- 5 Summary and way forward ence of flow-channels and anisotropy of frac- ture conductivity. This poses risks but also Observations and results of all major EGS- offers the opportunity to maximize the heat projects leave no doubt, that hydraulic stim- exchanging area by a proper positioning of ulation cannot be regarded as merely a pres- the second well. sure diffusion process accompanied by Industrial systems of this type require wells shearing and dilating network of natural being drilled parallel to the axis of the mini- fractures. The data rather suggest that gen- mum principal stress, i.e. horizontal wells erally only one macro-fracture was created for normal and strike-slip stress conditions during the stimulation tests regardless of and vertical wells for reverse faulting condi-
35 2-2014_geologi 2.06 12.02.15 15:21 Pagina 36
tions. An industrial system may consist of about 30 to 40 equidistant fractures con- necting two 1 km long parallel well sections with a well separation of about 500 m. Sys- tems of these dimensions would operate for at least 25 years at flow rates of 100 l/s, an electric power output of 5 to 10 MW and a pumping power of less than 1 MW. Direction- al drilling and high temperature-packer tech- nology have improved significantly during the last three decades (Shiozawa & McClure, 2014) and multi-fracture concepts are applied with great success in unconvention- al gas reservoirs. Though the conditions and requirements in geothermal applications are more demanding in various aspects it seems almost certain that geothermal multi-frac- ture systems of this type can be realized in the near future.
36 2-2014_geologi 2.06 12.02.15 15:21 Pagina 37
References Jung, R. 1999: Erschliessung permeabler Risszonen für die Gewinnung geothermischer Energie aus Baisch S. & Vörös, R. 2007: Personal Communica- heissen Tiefengesteinen. Schlussbericht BMBF- tion. Q-Con GmbH, Bad Bergzabern, Germany. Forschungsvorhaben 0326690A, Bundesanstalt Baria, R., Michelet, S., Baumgärtner, J., Dyer, B., für Geowissenschaften und Rohstoffe, Han- Nicholls, J., Hettkamp, T., Teza, D., Asanuma, H., nover, Archiv Nr. 118977, S. 38. Garnish, J., Megel, T., Kohl, T. & Kueperkoch, L. Jung, R. 2013: EGS – Goodbye or back to the future. 2005: A 5000 m deep reservoir development at In: Effective and Sustainable Hydraulic Fractur- the European HDR Site at Soultz. Proc. 30th ing, A. P. Bunger, J. McLennan & R. Jeffrey Workshop on Geothermal Reservoir Engineer- (eds.), 95−121, InTech, doi:10.5772/45724. ing, Stanford Univ., Stanford, Cal., Jan. 31 − Feb. Ledingham, P. 1989: Circulation results 1983−1986. 2. In R. H. Parker (ed.), Hot Dry rock geothermal Batchelor, A. S. 1982: The creation of Hot Dry Rock Energy, Phase 2B final report of the Camborne systems by combined explosive and hydraulic School of Mines Project, Vol. 1, Pergamon Press, fracturing. Proceedings of the International Oxford UK, 388−408. Conference on Geothermal Energy, May 1982. Lehner, F. & Kachanov, M. 1996: Modelling of Florence, Italy. BHRA Fluid Eng. Bedford, «winged» cracks forming under compression. 321−342. International Journal of Fracture 77, 1996, Brown, D. W., Duchane, D. V., Heiken, G., Hriscu, V. T. R69−R75. 2012: Mining the earth´s heat: Hot Dry Rock MIT 2006: The Future of Geothermal Energy – Impact geothermal energy. Springer-Verlag, Berlin Hei- of Enhanced Geothermal systems (EGS) on the delberg, ISBN 978-3-540-67316-3, DOI United States in the 21st Century. Idaho Nat. 10.1007/978-3-68910-2. Lab., Idaho US, http://geothermal.inel.gov. Cornet, F. H. 1989: Experimental investigations of Murphy, H. 1985: Hot Dry Rock phase II reservoir forced fluid flow through a granite rock mass. engineering. Los Alamos Nat. Lab. Rep. LA-UR- Proceedings of 4th Int. Seminar on the results of 85-3334. EC Geothermal Energy Demonstration, Flo- Murphy, H., Keppler, H. & Dash, Z. 1983: Does rence, Italy, April 27-30, 1989, 189−204. hydraulic fracturing theory work in jointed rock Cotterell, B. & Rice J. R. 1980: International Journal masses?. Geothermal Resources Council, of Fracture 16. 155−169. Transactions Vol. 7, Oct. 1983, 461−466. Dreesen, D. S. & Nicholson R. W. 1985: Well comple- Niitsuma, H., Asanuma, H. & Jones, R. 2004: person- tion and operations for the MHF of Fenton Hill al communication, Tohoku University, Sendai HDR Well EE-2. Proceedings Geothermal Japan & Camborne School of Mines, Redruth Resources Council, Kailua-Kona, Hawaii, Aug. Cornwall UK. 26−30, 1985. Rowley, J. C., Pettitt, R. A., Matsunaga, I., Dreesen, Dyer, B. C. 2005: Soultz GPK4 stimulation Septem- D. S., Nicholson, R. W. & Sinclair, A. R. 1983: ber 2004 to April 2005 – Seismic monitoring Hot-Dry-Rock Geothermal reservoir fracturing report. Seamore Seismic, Falmouth, Cornwall, initial field operations – 1982. Proceedings Geo- UK. thermal Resources Council 1983 Annual Meet- Evans, K. F., Moriya, H., Niitsuma, H., Jones, R. H., ing, Oct. 24-27, Portland, Oregon US. Phillips, W. S., Genter, A., Sausse, J., Jung, R. & Schindler, M, Nami, P., Schellschmidt, R., Teza, D. & Baria, R. 2005: Microseismicity and permeability Tischner, T. 2008: Summary of hydraulic stimu- enhancement of hydro-geologic structures dur- lation operations in the 5 km deep cystalline ing massive fluid injections into granite at 3 km HDR/EGS reservoir at Soultz-sous-Forêts. Proc. depth at the Soultz HDR site. Geophys. J. Int., 33rd Workshop on Geothermal Reservoir Engi- 2005, 160, 388−412. neering, Stanford Univ., Stanford, Cal., Jan. Häring, M. O., Schanz, U., Ladner, F. & Dyer B. C. 28−30, 2008. 2008: Characterization of the Basel1 Enhanced Shiozawa, S. & McClure, M. 2014: EGS Designs with Geothermal System. Geothermics, 2008. Horizontal Wells, Multiple Stages, and Proppant. doi:10.1016/j.geothermics.2008.06.002. Proc. 39th Workshop on Geothermal Reservoir Hayashi, K. & Abé, H. 1989: Evaluation of hydraulic Engineering, Stanford Univ., Stanford, Cal., Feb. properties of the artificial subsurface system in 24−26. Higashihachimantai geothermal model field. J. Tischner, T. 2013: personal communication, Bunde- Geothermal Research Soc. Japan, Vol. 11, No. 3, sanstalt für Geowissenschaften und Rohstoffe, 203−215. Hannover. Jones, R. H. & Stewart, R. C. 1997: A method for Wallroth, T. 1992: Hydromechanical breakdown of determining significant structures in a cloud of crystalline Rock. Publ. A 71, Diss., Chalmers earthquakes. J. geophys. Res. 102, 8245−8254. Tekniska Högskolar, OCH Göteborgs Universitet, Jung, R. 1989: Hydraulic In Situ Investigations of an Sweden. Artificial Fracture in the Falkenberg Granite. Int. J. Rock Mech. Sci. & Geomech. Abstr. Vol. 26, No. 3/4, 301−308.
37 2-2014_geologi 2.06 12.02.15 15:21 Pagina 38
38 2-2014_geologi 2.06 12.02.15 15:21 Pagina 39
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 39-52
Clean Unconventional Gas Production: Myth or Reality? – The Role of Well Integrity and Methane Emissions Peter Reichetseder1
«Das Antifragile steht Zufälligkeit und Ungewissheit positiv gegenüber, und das beinhaltet auch – was entscheidend ist – die Vorliebe für eine bestimmte Art von Irrtümern. Antifragilität hat die einzigartige Eigenschaft, uns in die Lage zu versetzen, mit dem Unbekannten umzugehen, etwas anzupacken – und zwar erfolgreich −, ohne es zu verstehen. Um es noch schärfer zu formulieren: Wir sind im Grossen und Ganzen besser, wenn wir handeln, als zu denken, und das verdanken wir der Antifragilität.» [aus: Nassim Nicholas Taleb, «Antifragiltät – Anleitung für eine Welt, die wir nicht verstehen», btb, Juli 2014].
Key words: Unconventional gas, methane emissions, well integrity, failure mechanism, barriers, best practice, casing design, well construction, cementing, stray gas
Abstract 1 Methane Emissions – This paper is focusing on Well Integrity, because it the «Achilles’ heel» of is an important subsurface element, which is the foundation for reliable and sustainable oil and gas Unconventionals? production. Shale gas production in the US, pre- dominantly from the Marcellus shale, has been Shale gas has been in the focus of discussion accused of methane emissions into the atmos- phere or contaminating drinking water under the in recent years and months because of many suspicion that this is caused by hydraulic fracturing economical and also technical concerns. in combination with compromised leaking wells. While this business has dramatically Several scientific studies seemed to prove this hypothesis mainly by geochemical and statistical changed and pushed both domestic gas and analysis over the last 4 years. oil production in North America, and in the A multiple line-of-evidence approach (isotope US alone 30.000 wells are drilled every year, analysis in combination with complex analysis of most of them multi-fracked, Europe is torn geology and broad inventory of gas and water well data) has helped to distinguish different possible between negative opinions (ban/moratori- sources and identify shallow gas formations («stray um in e.g. France, Germany) and early activ- gas») below the groundwater formations as main ities towards unlocking the potential for methane source, whereas the studies did not find any link between hydraulic fracturing and water unconventional gas production (Poland, contamination! Too slim well design and compro- UK). In the media mainly negative cases mised well integrity (cement, casing) are more like- from US are reported and dominate, while ly the enabler for possible gas migration behind casing. the huge benefits do not get much attention. This paper is attempting a critical review and re- Very slowly a more rational approach is interpretation of the wealth of available information growing. and opinions. If a best practice approach based on recent experience and standards is applied for One of the main concerns is the question, if proper well design, construction and operations, shale gas production can be considered as methane emissions into groundwater or atmos- favorable as conventional gas with respect phere can be avoided. The main barriers against any leakage are proper casing design and cement- to Greenhouse Gas (GHG) Emissions. ing. Baseline studies and monitoring of groundwa- Shale gas production in US has grown enor- ter quality need to be an integral part of shale gas mously and the Marcellus Shale in Pennsyl- developments. vania (Fig. 1) presently contributes 40% of US shale gas production (EIA 2014). However, the Marcellus region, because of special geological and historic reasons, has 1 Upstream – Energy Consulting; Lehrbeauftragter am Institut für Erdöl- und Erdgastechnik, TU Clausthal, also become a hotspot for problems with 45529 Hattingen, Tippelstrasse 100, Germany contaminated drinking water. McKay & Sali-
39 2-2014_geologi 2.06 12.02.15 15:21 Pagina 40
ta (2011) are referring to legal claims of 13 Groundwater contamination in water wells families in Lenox township having filed a from natural gas sources was not consid- lawsuit in Susquehanna County Court (in the ered. NE of Pennsylvania) in which «they allege that fracking contaminated their drinking Molofsky et al. (2011) published the results water supply and made them ill». Like the of a comprehensive investigation of more lawsuits, some media reports imply that than 1.700 water wells sampled and tested Marcellus Shale drilling and production prior to proposed gas drilling in the Susque- operations have caused widespread prob- hanna County, PA; this study concludes lems. methane to be ubiquitous in shallow ground- In a study from Duke University, Osborn et al water with a clear correlation of methane (2011) argue quite firmly «In aquifers overly- concentrations with surface topography. ing the Marcellus and Utica shale formations Specifically, water wells located in lowland of northeastern Pennsylvania and upstate valley areas seem to exhibit significantly New York, we document systematic evi- higher dissolved methane levels than water dence for methane contamination of drink- wells in upland areas, with no relation to ing water associated with shale gas extrac- proximity of existing gas wells. The correla- tion.» The authors are considering three tion of methane concentrations with eleva- possible mechanisms for fluid migration in tion would indicate that, on a regional level, the shallow drinking-water aquifers: elevated methane concentrations in ground- a. Displacement of gas-rich deep solutions water are a function of geologic features, from deep target formation. rather than shale gas development. b. Casing leaks from production wells, in Potential sources of this naturally occurring combination with lateral and vertical frac- methane include thermogenic gas-charged ture systems – which the authors consid- (from underlying Devonian layers) sand- er the most likely case. stones in the Catskill formation, which are c. Enhanced migration of gas via newly cre- tapped by most water wells in this region. ated fractures. These sandstones exhibit an extensive net-
Fig. 1: Marcellus Gas Production and Drilling per 8/2014 (EIA 2014).
40 2-2014_geologi 2.06 12.02.15 15:21 Pagina 41
work of fractures, joints and faults that nature of elevated methane concentrations serve as principle conduits of groundwater in water wells in Susquehanna County was flow and potential pathways for the move- consistent with an origin in deep shale gas ment of shallow-sourced dissolved methane deposits, such as the Marcellus and Utica (Fig. 2). formations. Biogenic methane, which is produced by the natural decomposition of organic material Molofsky et al (2011), however, show that within thick valley alluvium and glacial drift the isotope signatures of the Duke study’s deposits in the area, may also be found in thermogenic methane samples were more water wells that draw water from shallower consistent with those of shallower Upper sediment deposits. The source of this dis- and Middle Devonian deposits overlying the solved methane is important with regard to Marcellus shale. These findings indicate that understanding the potential effects of ongo- the methane could have originated entirely ing shale gas development and appropriate from shallower sources above the Marcellus measures for protection of water resources. that are not related to hydraulic fracturing Fig. 3 depicts a possible situation where activities. methane from different sources may be The apparent misinterpretation of the origin found in contaminated water wells. Foren- of the observed thermogenic methane sics using isotopes and noble gases give the underscores the need of the multiple lines- ability to unambiguously distinguish of-evidence approach for proper characteri- between biogenic and also different thermo- zation of methane gas sources, with careful genic gases (Sueker et al. 2014). integration of the relevant geologic, histori- This has important implications with cal, well construction, and isotopic data. regards to the findings of the recent study Duke University conducted a follow-up from Duke University (Osborn et al. 2011), study (Jackson et al. 2013) of their 2010/2011 which suggested that the thermogenic sig- study based on a more extensive dataset for
Fig. 2: Generalized Cross Section of Upper Devonian and Marcellus Formations (Molofsky et al. 2011).
41 2-2014_geologi 2.06 12.02.15 15:21 Pagina 42
natural gas in shallow water wells in NE The authors were immediately pointing Pennsylvania, comparing sources of thermo- towards well integrity problems (casing genic methane, biogenically derived leaks or imperfections of cement) also trig- methane, and methane found in natural gered by the fact that in 2010 PADEP (Penn- seeps. The team expanded the analysis by sylvania Department of Environmental Pro- investigating also ethane and propane con- tection) had already issued 90 violations for centrations to distinguish thermogenic from faulty casing and cementing on 64 Marcellus biogenic sources and using isotopic data for shale gas wells, 119 similar violations were methane, ethane and inorganic carbon, and issued in 2011. Are these only symptoms or helium analysis to reach better differentia- do they prove the cause? tion between different sources. Of course, the NE sector of Pennsylvania – Among the different parameters investigat- different to many other sedimentary basins ed: distance to gas wells, proximity to both where conventional and unconventional gas valley bottom streams (potential discharge is produced – is characterized by many shal- areas), and the Appalachian Structural Front low gas layers located between the deep (ASF; an index for the trend in increasing Marcellus (> 2.000 m) and the groundwater thermal maturity and degree of tectonic formations (< 300 m). Duke researchers, not deformation), distance to gas wells (Fig. 5) being very positive towards shale gas pro- was the dominant statistical factor for both duction in general, continued to follow this methane and ethane. The authors did not track with more research − and heavy statis- investigate naturally occurring contamina- tics. tions in water wells. Driven by strong suspicion that integrity of If hydraulic fracturing was not related to cement must be the weak link of the system methane contamination of drinking water the Duke researcher Ingraffea et al (2014) wells, what could be a plausible mechanism? published a paper in May 2014 based on the
Fig. 3: Stray Gas Forensics to distinguish methane in water well sample from multiple unrelated methane sources including thermogenic sources (Sueker et al. 2012).
42 2-2014_geologi 2.06 12.02.15 15:21 Pagina 43
hypothesis «Leaking oil and gas wells have wells across the state may be actually higher long been recognized as a potential mecha- than this, and upward 12% for unconven- nism of subsurface migration of thermo- tional wells drilled since January 2009. This genic and biogenic methane, as well as heav- wide range of estimates is influenced by the ier n-alkanes, to the surface». Quoting all significantly higher rates of impairment in potential failure cases of the casing/cement wells spudded in the NE counties of the state system known in literature it must be THE (average 12.5%, range 2.2−50%), with pre- main problem zone, if hydraulic fracturing dicted cumulative hazards exceeding 40%.» has to be ruled out. We have to differentiate between indicators «An analysis of 75.505 compliance reports (e.g. pressure) at the wellhead/annulus of a for 41.381 conventional and unconventional well and the immediate conclusion, that wells in Pennsylvania drilled from January 1, these indicators would already be a proof of 2000 – December 31, 2012, was performed loss of integrity or relevant impairment of a with the objective of determining complete well. These indicators are symptoms, but and accurate statistics of casing and cement not real causes themselves (see also Ener- impairment» (Ingraffea et al. 2014). It gyInDepth 2014), they are symptoms for remains to be demonstrated, how compli- potential weaknesses or a barrier defect. ance reports should be able to prove cement However, further tests and analysis are nec- impairment? essary to reveal their significance. Pennsylvania state inspection records – Another aspect is the supposed cumulative according to (Ingraffea et al. 2014) – show risk of unconventional wells in comparison «compromised» cement and/or casing with conventional wells. Unconventional integrity in 0.7−9.1% of the active oil and gas wells are generally characterized by good wells drilled since 2000, with a 1.6−2.7 fold initial production, followed by a strong higher risk in unconventional wells spudded decline of production and pressure after the since 2009 relative to conventional well first year. This does not increase the risk of types. Ingraffea et al. (2014) further con- leakages, rather the contrary. Because of clude: «Hazard modeling suggests that the that it is hard to believe that unconventional cumulative loss of structural integrity in wells should be more often «compromised»
Fig. 4: Comparison of Susquehanna County Methane Isotopic Signatures (Molofsky et al. 2011).
43 2-2014_geologi 2.06 12.02.15 15:21 Pagina 44
than conventional wells. Many wells in the Darrah et al (2014) feel quite confident initial phase of the shale gas boom were according to Snow (2014): «our data clearly drilled by smaller companies and a strong show that the contamination in these clus- need of low cost drilling with two casing ters stems from well-integrity problems strings only: surface casing and production such as poor casing and cementing». casing, but no intermediate casing. Conven- tional wells were the domain of the estab- Discussion lished players who had followed more con- a. This report clearly states that the servative designs. researchers (who initially related ground- The statistics at least correlate with the water impairment to hydraulic fracturing) higher number of methane problems in the did after further studies not find any link NE of the Marcellus region with a known between hydraulic fracturing and water strong presence of «stray gas» and in combi- contamination, which is a very strong nation with a slim well design this is not sur- result in itself. prising. b. Did the study find evidence of well integri- Recent investigations from Darrah et al. ty failure? Despite the strong conviction (2014) from Duke University on 113 drinking- of the researchers questions remain. The water wells in Pennsylvania and 20 samples sample in the Barnett area is challenged from the Barnett area in Texas, found by a study of the Texas Railroad Commis- methane contamination in ground water sion (RRC 2014), which did not find any table caused by impaired well construction, well in the Parker County with well however, «not fracking». integrity problems, which could be the According to their analysis gas geochem- cause for methane contamination in istry data would implicate leaks through ground water. annulus cement (4 cases), production cas- c. Are the statistics of «compromised» wells ings (3 cases), and underground well failure plausible at all? Information from EnergyIn- (1 case) rather than gas migration induced Depth (2014) raises concerns about the by hydraulic fracturing deep underground. plausibility of numbers in the studies of
Fig. 5: The ratio of ethane/ methane (C2/C1) and (inset) propane/methane (C3/C1) concentrations in drinking water wells as a function of distance to nat- ural gas wells (kilometers) (Jackson et al. 2013).
44 2-2014_geologi 2.06 12.02.15 15:21 Pagina 45
Duke University (Ingraffea et al. 2014) Norsok D-010 is a functional standard and which supposedly support very high fail- sets the minimum requirement for the equip- ure rates of wells. In 2011 the Ground Water ment/solutions to be used in a well, but it Protection Council looked at more than leaves it up to the operating companies to 34.000 wells drilled in Ohio from 1983 to choose the solutions that meet the require- 2007 and more than 187.000 wells drilled in ments. It also specifies that «there shall be Texas between 1993 and 2008. The GWPC two well barriers available during all well data reveal a well failure rate of 0.03% in activities and operations, including suspend- Ohio and only 0.01% in Texas (GWPC 2011). ed or abandoned wells, where a pressure dif- ferential exists that may cause uncontrolled We can draw several conclusions from these outflow from the borehole/well to the exter- investigations: nal environment». This sets the foundation Before embarking in heavy shale drilling for how to operate wells and keep the wells campaigns with many wells it is crucially safe in all phases of the development. important to understand the local/regional geology also above the targeted shale forma- UK: UK Oil & Gas has updated its «Well tions. If shallow gas (or «stray gas») is pres- Integrity Guideline» by July 2012 ent (something that has to be expected in (Oil&GasUK 2012) and developed a new large parts of Pennsylvania), extensive work comprehensive regulative framework which has to go into baseline studies to provide a is called «UK Onshore Shale Gas Well Guide- robust foundation for the design and execu- lines» (UKOOG 2013) and specifies in a simi- tion of wells. lar manner all relevant aspects of «good Well integrity has to be in the focus, espe- industry practice and reference to relevant cially in geological settings with stray gas legislation, industry standards and prac- concentrations. Well design, construction tices»: Well Design and Construction (Cas- and monitoring have to be performed with ing, Cementing, Barrier Planning), Manage- high degree of professionalism. This is the ment Supervision and Competence, as well purpose of «Well Integrity Management». as Well Examination during Design and Con- While ensuring that well integrity is a univer- struction (also «well examiners visiting the sal obligation for all oil and gas (production) well site to examine certain well integrity wells, the author selected to focus on issues and fracturing operations on site in real and solutions in the Marcellus area, because time» – to build trust) and Abandonment. it shows a hydrocarbon province with higher challenges than most other shale gas pro- US: The most comprehensive and also in the duction areas and also demonstrates indus- oil and gas industry widely used system of try’s best practice dealing with this issue. standards stems from the American Petrole- um Institute (API), which has developed standards for oil and natural gas operations 2 Well Integrity: Definition and since 1924. API’s formal consensus process Standards is accredited by the American National Stan- dards Institute (ANSI). API-standards are Norway: In the Norwegian system for stan- developed in an open process that requires dards for the petroleum sector Well Integrity regular review of its more than 600 stan- is defined in Norsok D-010 (2013) as «appli- dards (Emmert 2012). cation of technical, operational and organi- API has issued the following main guidelines zational solutions to reduce risk of uncon- and recommended practices (RP) for trolled release of formation fluids through- Hydraulic fracturing operations especially out the life cycle of a well». relevant to well integrity:
45 2-2014_geologi 2.06 12.02.15 15:21 Pagina 46
• API Guidance Document HF1: Hydraulic aquifers. Similar regulations are in effect in Fracturing Operations – Well Construction all countries and normally enforced rigidly.» and Integrity Guidelines (API 2009) The steel casing protects the zones from • API Standard 65-Part 2, Isolating Potential material inside the wellbore during subse- Flow Zones During Well Construction (API quent drilling operations and, in combina- 2010) tion with other steel casings (intermediate and production casing) and cement sheaths API states in the Guidance Document HF1 that are subsequently installed, protects the (API 2009) that «Maintaining well integrity is groundwater with multiple layers of protec- a key design principle and design feature of tion for the life of the well. all oil and gas production wells. Maintaining «The subsurface formation containing well integrity is essential for the two follow- hydrocarbons produces into the well, and ing reasons: that production is contained within the well 1. To isolate the internal conduit of the well all the way to the surface. This containment from the surface and subsurface environ- is what is meant by the term ‹well integrity›.» ment. This is critical in protecting the Design and execution are then followed by environment, including groundwater, and regular monitoring during drilling and pro- in enabling well drilling and production. duction operations, further periodically 2. To isolate and contain the well’s pro- testing to insure that integrity is maintained. duced fluid to a production conduit with- The standards are describing the main ele- in the well.» ments of the well design program, which are «Although there is some variability in the most relevant for hydraulic fracturing and details of well construction because of vary- establishing well integrity in Sec. 3 («Well ing geologic, operational settings, the basic design and Construction»). practices in constructing a reliable well are In 12/2010 API released Standard 65-2, a spe- similar. These practices are the result of cial standard dealing with practices for iso- operators gaining knowledge based on years lating potential flow zones (API 2010). This of experience and technology development standard refers not only to possible blowout and improvement.» situations threatening loss of well control, safety of personnel, the environment, and The general principles (Sec. 3) describe the drilling rigs themselves. They also point main steps as follows: towards the typical geological situations «Groundwater is protected from the con- described in chapter 1 in the Marcellus tents of the well during drilling, hydraulic region. A second objective is to help prevent fracturing, and production operations by a Sustained Casing Pressure (SCP), also con- combination of steel casing and cement sidered a serious industry problem. sheaths, and other mechanical isolation API 65-2 defines barrier elements as either devices installed as part of the well con- physical or operational. Physical barrier ele- struction process.» ments are classified as hydrostatic (fluid «The primary method used for protecting columns), mechanical (e.g. seals, packer, groundwater during drilling operations con- plugs), or solidified chemical materials (= sists of drilling the wellbore through the usually cement). Operational barriers are groundwater aquifers to a depth sufficient to practices that result in activation of a physi- protect the groundwater, immediately cal barrier (e.g flow detection devices). installing a steel pipe (= casing) and cement- While physical barriers dominate the ing this steel pipe in place. This surface cas- process, the total system reliability of a par- ing will be cemented normally from bottom ticular design is dependent on the existence to the top, completely isolating groundwater of both types of barriers.
46 2-2014_geologi 2.06 12.02.15 15:21 Pagina 47
It is worth mentioning that both the casing cementing are interdependent. The quality design and process of setting casings, and of the cement sheath depends very much on the process of cementing design and the design and running & cementing execu- tion operations of the casing strings and the associated equipment. However, both elements individually and in combination have to create sustainable bar- riers for the lifetime of the well to avoid any fluid leakage and migration outside of the well system.
3 Best Practice to Avoid Methane Leaks
For cementing not only accepted design best practices are relevant, but also accepted exe- cution best practices. The cementing prac- tices are specified in great detail in API 2010, outlining all activities to be considered to be important for good cementation, e.g.: Engi- neering Design, Wellbore Preparation and Conditioning, Cement Job Execution, Casing Shoe Testing, Post-cement Job Analysis and Evaluation. Prohaska & Thonhauser (2012) are dis- cussing the main failure scenarios (Fig. 6), if barriers against inflow and upward flow/migration are not intact after cement- ing: Leaking tubings and casings (connec- tion), poor cement allowing gas migration behind casing, (partly) missing cement allowing fluid inflow into annulus and upward migration to wellhead or between individual formations or into groundwater, etc. However, Prohaska & Thonhauser (2012) conclude: «If existing standards and current best practice are followed, groundwater contamination, resulting from well integrity failure, is very unlikely to happen.» Meanwhile several states in the US (Ohio 2014) have adapted their guidelines for Fig. 6: Schematic diagram of typical sources of flu- design and construction of shale gas wells in id that can leak (via failure mechanisms) through a order to improve well integrity (Pennsylva- hydrocarbon well. 1 - gas-rich formation such as coal, 2 - non-producing gas or oil formation, 3 - bio- nia «Chapter 78 Oil and Gas Wells» early genic or thermogenic gas in shallow aquifer, 4 - oil 2011, Texas «Well Integrity Rule» May 2013, or gas from oil/gas reservoir (Davies et al. 2014). Ohio early 2014).
47 2-2014_geologi 2.06 12.02.15 15:21 Pagina 48
Major changes have been introduced for intermediate casing is an integral part of cementing surface casing (casing setting well design to establish a second steel, depth, cementing to surface, minimum cement-sealed layer of well protection cement volume, use of centralizers, mini- extending well below the level of the aquifer, mum thickness of cement sheath, etc.) and which creates a barrier against a possible for casing design. New regulations are leakage path from the shale reservoir (or requiring an intermediate casing string. other lateral gas inflow) up to the aquifer. As mentioned above, previously shale gas The difference between the new and old wells in the Marcellus region did not have («inferior») design is shown in Fig. 8. intermediate casing strings, which was very Prohaska & Thonhauser (2012) are present- likely the reason for gas migration from ing a comprehensive list of typical Best Prac- stray gas accumulations. tices for establish effective cement barriers. Besides important general rules, the selec- The typical design of well integrity for tion of the right cementing process is unconventional onshore wells (Fig. 7) is depending on specific requirements for geol- shown by Cuadrilla Resources – the front ogy, purpose and design of the well and spe- runner of UK shale gas development. It cific experience. requires always at least three layers of steel One very relevant example of cement design casing at depths penetrating the aquifer. is given by McDaniel & Watters (2014) for The surface casing, the intermediate casing the Marcellus Shale. The cyclic hydraulic and the production casing are cement- fracturing process after cement has set and sealed and extend below the aquifer. The the challenge of stray gas migration are
Fig. 7: Wellbore Integrity Design for Cuadrilla Pree- se Hall#1 (Cuadrilla 2014).
48 2-2014_geologi 2.06 12.02.15 15:21 Pagina 49
important design criteria. There are proven under development with parameters such cement compositions available which can as tensile strength, inelastic strain, flexural cope with multi-fracturing applications strength, impact strength and mechanical (additives, such as polymers, bentonite, properties to determine the cement’s ability gypsum, foam). Instead of its traditional brit- to resist energy applications. tleness and high compressive strength, Evaluation techniques are also needed to cement should allow some (elastic) defor- investigate, if well integrity has been mation to withstand pressure fluctuations reached and is still maintained, focusing on during multi-fracturing operations. the main failure scenarios for any possible The paper shows that cement integrity of leakage. Which specific method or tool is the intermediate casing may be caused by effective in proving cement isolation of a mechanical damage to cement seal rather zone? Which method or tool should be than through unset cement. Compressive required on the surface casing cement or strength is therefore not a good indicator for other cement strings as a part of initial well seal durability, the latter can be reached by construction (or, if not required, when it different cement compositions. Cement may provide useful information)? API Stan- durability can be correlated to inelastic dard 65-2 (2010) gives guidance on different strain potential, mechanical properties and tools and their results. tensile strength of the cement system. Fur- King (2012) gives a very useful and pragmat- ther work will be directed towards as corre- ic summary on cement evaluation by point- lation between «Applied Energy vs. Energy ing out, that «The only cement test method Resistance». that can confirm zone-to-zone isolation is a For the given situation with combination of pressure test.» Pressure tests are mandatory cyclic stresses (short term) and resisting before drilling fresh formation after cement gas migration long term both aspects need has set. This formation integrity test is para- to be considered. Special cement testing is mount to prove that there is a seal.
Fig. 8: Well design with and without intermediate casing (Cuadrilla 2014).
49 2-2014_geologi 2.06 12.02.15 15:21 Pagina 50
Temperature logs are run usually to deter- sis, geology review, assessing casing & mine the top of cement within a time-win- cement: CBL, temperature & noise logging). dow. It is important to know, if the cement A combination of testing methods and analy- has been placed where it should be. sis can be used effectively to assess well Cement bond logs (CBL) have proven to be a integrity, but most testing methods do not widely used and accepted method. Cement offer an absolute and definitive answer bond logs can give a reasonable estimate of regarding well integrity. Regulatory agencies bonding and a semi-quantitative idea of tend to seek methods that provide a black & presence or absence of larger cement chan- white answer, but tend to recognize the com- nels, but will not certify pressure or fluid iso- plexities. lation of a zone. To provide an effective seal Physical remedial activities, such as perfo- and isolation of a zone, only part of the total rating the production casing and squeezing cement column must be channel free. cement or other products are challenging. Cement channels may be present in parts of Often, specialty products, such as micro-fine the cement, but as long as there are one or cement, resins, etc. may be required, and more significant, continuous sections of assuring perforations are sealed for purpos- channel-free cement, isolation of the zone es of production operation must also be con- along the wellbore will be adequate. sidered. Finally, we have to mention situations during the operations phase of a well, when pres- sure is emerging in the annuli of a well, 4 Conclusions which may eventually be considered Sus- tained Casing Pressure (SCP). Do these situ- In the early phase of shale gas production, ations mean that a vital barrier in the well is especially in the northeastern part of the broken or impaired? Marcellus region in Pennsylvania, US, While improved design has been updated in methane contamination of groundwater has regulations, there is strong activity at pres- been recognized and quickly attributed to ent in API but also in the industry and regu- hydraulic fracturing. latory bodies of states with emphasis on Investigations revealed that many water testing and, if deviations exist, re-establish- wells in the region were containing natural ing the integrity of wells which have critical gas contaminations from direct communica- pressure in the annulus. API has not yet pub- tion with the ubiquitous stray gas forma- lished Guidelines on SCP. Valuable guidance tions, even without the presence of any gas is given by Norsok (2013) and Oil&GasUK production well. A best practice approach (2012) under Sec. 9 «Annulus Management». clearly calls for comprehensive baseline Monitoring and analysis is important to studies and close monitoring during shale ensure a leak or breach of a well barrier is gas drilling and development. detected early and that corrective action Both for conventional and unconventional can be taken before the problem escalates oil and gas production, well integrity is a (Norsok 2013). prerequisite for safe long-term production. At the Stray Gas Incidence and Response While hydraulic fracturing could NOT be Forum 2012 in Cleveland, Ohio, Arthur et al proven to be the cause of methane contami- (2012) presented «holistic well evaluation» nation of groundwater formations, several methods with the focus on testing the annu- US-states (e.g. Ohio, Pennsylvania, Texas), lus situation of shale gas wells showing as a consequence of the lessons learned, annulus pressure: Pressure build-up testing, have been tightening the regulations for oil External Well Integrity testing (visual inspec- and gas wells, among others demanding an tion, venting rate testing, volumetric analy- intermediate casing string in combination
50 2-2014_geologi 2.06 12.02.15 15:21 Pagina 51
with strict rules for cementing the surface Literature casing string. Evaluation methods are avail- API 2009: API Guidance Document HF1: Hydraulic able to investigate the quality of these vital Fracturing Operations – Well Construction and barriers in oil and gas wells. If necessary, Integrity Guidelines. 1st edition, American repair methods have to be applied or as a Petroleum Institute, October 2009. API 2010: API Standard 65-Part 2, Isolating Poten- last resort the well to be abandoned. tial Flow Zones During Well Construction. 2nd With proper barriers in place groundwater edition, American Petroleum Institute, Decem- formations can be safely protected and leak- ber 2010. Arthur, J. D., Casey G., Kennedy, J. & Wilson, P. age of methane into the atmosphere avoid- 2012: Understanding and Assessing Well ed. European countries (e.g. UK, Norway, Integrity Relative to Wellbore Stray Gas Intru- Germany) have regulations in place which sion Issues. Stray Gas Incidence & Response already require best practice solutions to Forum, July 24−26, 2012, Cleveland, Ohio. Cuadrilla 2014: Well Integrity – Cuadrilla Land maintain well integrity for the lifetime of a Based Wells. Retrieved 29.09.2014: well. http://www.cuadrillaresources.com/wp-con- tent/uploads/2012/02/DrillingPage-Well- Integrity-Document.pdf Darrah, T. H., Vengosh, A., Jackson, R. B., Warner, N. R. & Poreda, R. J. 2014: Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales. Proceedings of the Nation- al Academy of Sciences, September 15, 2014, doi: 10.1073/pnas.1322107111. Davies, R. J., Almond, S., Ward, R. S., Jackson, R. B., Adams, Ch., Worrall, F., Herringshaw, L. G., Gluyas, J. G. & Whitehead, M. A. 2014: Oil and gas wells and their integrity: Implications for shale and unconventional resource exploita- tion. Marine and Petroleum Geology (2014). EIA 2014: Marcellus gas production and drilling. U.S. Energy Information Administration, retrieved 29.09.2014: http://www.eia.gov/todayinener- gy/detail.cfm?id=17411 Emmert, A. 2012: Oil & Natural Gas Industry Stan- dards for Hydraulic Fracturing & Unconven- tional Wells. IEA Golden Rules for Gas Work- shop, American Petroleum Institute, March 2012. EnergyInDepth 2014: Four Key facts on a New Well Integrity Study. Retrieved 29.09.2014: http://energyindepth.org/national/three-key- facts-on-a-new-well-integrity-study/ GWPC 2011: State Oil and Gas Agency Groundwater Investigations and Their Role in Advancing Reg- ulatory Reforms. Ground Water Protection Council, Ohio and Texas, Aug. 2011. Ingraffea, A. R., Wells, M. T., Santoro, R. L. & Shon- koff, S. B. C. 2014: Assessment and risk analy- sis of casing and cement impairment in oil and gas wells in Pennsylvania, 2000 – 2012. Pro- ceedings of the National Academy of Sciences, 111 (30), 10955−10960. Jackson, R. B., Vengosh, A., Darrah, T. H., Warner, N. R., Down, A., Poreda, R. J., Osborn, S. G., Zhao, K. & Karr, J. D. 2013: Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction. Proceed- ings of the National Academy of Sciences, 110 (28), 11250−11255.
51 2-2014_geologi 2.06 12.02.15 15:21 Pagina 52
King, G. E. 2012: Cement Evaluation Methods to UKOOG 2013: UK Onshore Shale Gas Well Guide- Prove Isolation of Barriers in Oil and Gas Wells: lines, Exploration and appraisal phase. Issue 1, Should a Cement Bond Log (CBL) Be Run or February 2013, UKOOG United Kingdom Required in Every Well? Retrieved 01.10.2014: Onshore Operators Group, retrieved http://gekengineering.com/id6.html 29.09.2014: http://www.ukoog.org.uk/images/ McDaniel, J. & Watters, L. 2014: Cement Sheath ukoog/pdfs/ShaleGasWellGuidelines.pdf Durability: Increasing Cement Sheath Integrity to Reduce Gas Migration in the Marcellus Shale Play. SPE 168650, SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, 4−6 February 2014. McKay, L. K. & Salita, L. A. 2011: Marcellus ground- water claims: A case for scientifically informed decisions. World Oil, 231/12. Molofsky, L. J., Connor, J. A., Farhat, S. K., Wylie, A. S. & Wager, T. 2011: Methane in Pennsylvania water wells unrelated to Marcellus shale frac- turing. Oil & Gas Journal, Dec. 5, 2011, 54−67. NORSOK 2013: Well Integrity in drilling and well operations. Norsok Standard D-010, Rev. 4, June 2013, retrieved 27.9.2014: http:// www.standard.no/en/webshop/Search/?search =Norsok+D-010+Rev.+4# Ohio 2014: Comparison of well construction stan- dards. Ohio Drilling Regulations, retrieved 30.09.2014: http://www.capitolintegrity.com/ documents/OhioDrillingRegulations.pdf Oil&GasUK 2012: Well Integrity Guidelines. Issue 1, July 2012. Oil and Gas UK 2012b, OP069, Avail- able for purchase online, retrieved 29.09.2014: http://www.oilandgasuk.co.uk/cmsfiles/mod- ules/publications/pdfs/OP069.pdf Osborn, S. G., Vengosh, A., Warner, N. R. & Jackson R. B. 2011: Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing. Proceedings of the National Academy of Sciences, 108/ 8,172−76. Prohaska, M. & Thonhauser, G. 2012: The Impor- tance of Wellbore Integrity for Groundwater Protection in Shale Gas Well Construction. June 22, 2012, retrieved 28.09.2014: http:// www.shale-gas-information-platform.org/nc/ categories/water-protection/knowledge- base/prohaska.html?sword_list[0]=well&swor d_list[1]=integrity RRC 2014: Water Well Complaint Investigation Report, Silverado on the Brazos Neighborhood, Parker County. Railroad Commission of Texas, May 23, 2014. Sueker, J. K., Clark, B. L. & Cramer, G. H. 2014: Iso- topic Forensic Techniques for Methane Source Discrimination. Stray Gas Incidence & Response Forum, Cleveland, Ohio, July 23−25, 2012. Snow, N. 2014: Study finds bad well construction, not fracing, fouled water wells. Oil & Gas Jour- nal 09/16/2014, retrieved 29.09.2014: http:// www.ogj.com/articles/2014/09/study-finds- bad-well-construction-not-fracing-fouled- water-wells.html
52 2-2014_geologi 2.06 12.02.15 15:21 Pagina 53
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 53-64
Hydraulic Fracturing – Application of Best Practices in Germany Steffen Liermann1
Key Words: Hydraulic fracturing, best practices, barrier, gas, tight gas, sweet water aquifer, Düste Z10, fracturing fluid, well design, well site, permit
Abstract 1 Introduction Today, many oil and gas fields would not be eco- nomically viable without hydraulic fracturing. For more than 50 years, the technology has been Since its first application in the 1940’s applied by the oil and gas industry in Germany (Montgomery & Smith 2010), oil and gas without any negative impact to the environment companies have been using hydraulic frac- (WEG 2013). However, due to an increasingly criti- cal public perception, the approval of recent oil and turing as the technology of choice for pro- gas projects requiring hydraulic fracturing has duction enhancement. Originally developed been adversely affected by a political de-facto to bypass drilling induced near-wellbore moratorium. Best practices have been developed for planning, permitting and execution of projects damage, it has been continuously refined to involving this technology including active stake- effectively increase the drainage area of a holder engagement. The Düste Z10 Tight Gas Proj- well. Hydraulic fracturing improves recov- ect, operated by Wintershall, is currently idle as the ery factors from conventional reservoirs, approval of required hydraulic fracturing opera- tions is outstanding. Best practices applied in the especially those in decline, and is the key project are described and discussed. technology enabling commercial production from unconventional reservoirs. To date, close to three million wells worldwide have Zusammenfassung been hydraulically fractured and the tech- Seit 1949 wird Hydraulic Fracturing in mehr als drei nology is applied to 60% of all newly drilled Millionen Bohrungen weltweit angewendet. Allein in Deutschland ist das Verfahren seit 1961 mehr als oil and gas wells (Montgomery & Smith 300-mal ohne negative Auswirkungen auf das 2010). About 35.000 new wells are drilled in nutzbare Grundwasser zum Einsatz gekommen. unconventional reservoirs in the USA per Die Technologie ist ausgereift und stellt bei Einhal- tung betrieblicher Best Practices kein Risiko für year alone (WEG 2014). In Germany, die Umwelt dar. Diese sind im Wesentlichen: 1. die hydraulic fracturing has been applied by oil sichere Prognose dichter Deckgebirge, 2. die Ver- and gas companies since the 1960’s with meidung des Eintrags von Schadstoffen von der Erdoberfläche in das Grundwasser, 3. die Gewähr- more than 300 operations carried out to leistung integrer Bohrungen, 4. die sichere Pro- date (WEG 2014). gnose und Steuerung der Ausbreitung hydraulisch induzierter Risse, 5. die Verwendung von Frac-Flu- id-Additiven mit maximal WGK 1-Einstufung und Offenlegung dieser, 6. die sichere Entsorgung von 2 Tight Gas Project Düste Z10 rückgeförderten Flüssigkeiten sowie 7. die Vermei- dung spürbarer, ausgelöster seismischer Erschüt- Wintershall Holding GmbH, a 100% oil and terungen. Anhand des aktuellen Tight-Gas Projek- tes Düste Z10 in Norddeutschland werden Beispie- gas subsidiary of BASF SE initiated the Düste le für die Anwendung dieser Best Practices aufge- Z10 Tight Gas Project in Northern Germany zeigt und diskutiert. in 2011. The gas well location is in Winters- hall’s 100% production license Ridderade- Ost in the State of Lower Saxony, about 50
1 Wintershall Holding GmbH, Friedrich-Ebert-Strasse 160, km south of the city of Bremen. The project 34119 Kassel, Germany is mainly comprised of the following stages:
53 2-2014_geologi 2.06 12.02.15 15:21 Pagina 54
• Drilling and completing a vertical well into different sands. Due to a variety of geologi- the tight Carboniferous sandstones; cal and technical reasons, production per- • Carrying out a comprehensive data acqui- formance was sub-optimal and the well had sition program; to be shut-in after a few years. • Hydraulically fracturing gas bearing sands The subsurface target of Düste Z10 was cho- within the Carboniferous; sen based on a structural high of the Car- • Carrying out a long term production test boniferous and the proximity to Düste Z9 to to determine the commercial production benefit from near offset geological data. The potential. project planning process incorporated les- sons learned from offset wells and the latest The target formation in Ridderade-Ost is developments in tight gas production tech- known to Wintershall from two previous nology including data acquisition along with wells. The well Düste Z7 was drilled in 1966 well and hydraulic fracturing designs. Düste and proved gas in the Carboniferous. How- Z10 was planned as a vertical well to deter- ever, only sub-commercial production rates mine the lowest gas bearing sand and gas- could be achieved from a vertical open-hole water contact and to provide the maximum test. The well was therefore plugged back. In flexibility for hydraulic fracture design. 1995 Wintershall started another attempt at The subsurface target coordinates deter- the Carboniferous. The well Düste Z9 mined the general area of the surface well explored the formation at a different loca- site location. The detailed selection of the tion of the reservoir. A total of five hydraulic well site took into account the legally fracture treatments were carried out across required minimum distances to communi-
Fig. 1: Düste Z10 well location in production license Ridderade-Ost.
54 2-2014_geologi 2.06 12.02.15 15:21 Pagina 55
ties, single houses, infrastructure and envi- In addition an Environmental Impact Assess- ronmental protection areas. The technical ment Study of the planned operations had to and economical reach to subsurface target be performed by a third-party. coordinates as well as the requirements for surface space for further wells (cluster The General Permit application, as opposed drilling) including a gas dehydration facility to a normal permit application («Sonderbe- also had to be balanced. triebsplanantrag») is distributed for endorsement to other relevant authorities, most importantly to the Water and Environ- 3 Permitting mental Protection Authority of the county. Therefore these authorities were formally Wintershall commenced the Düste Z10 proj- included into the permitting process. The ect in early 2011, when hydraulic fracture Düste Z10 General Permit was approved in treatments were still permitted and carried summer 2011. out in Germany. However, at that time, the As per the mining law, Wintershall also subject of hydraulic fracturing just started to applied for separate permits for each of the be viewed critically by the German public. different operational stages. These permit Therefore, Wintershall planned the execution applications included detailed technical of the project to be closely accompanied by a descriptions of the planned operations. The stakeholder engagement strategy, which applications for construction of the well site called for early and complete involvement of and drilling and completion operations were all relevant authorities, local politicians, the both submitted to the Mining Authority in public and immediate neighbors. Prior to any summer and fall 2011 respectively and sub- official permit applications the contents were sequently granted. The well site was con- presented to and discussed with relevant structed in fall 2011 and drilling and comple- authorities and local politicians. Multiple tion operations were carried out from Janu- public events with more than 1.000 visitors ary to beginning of May 2012. complemented the strategy in the communi- ty adjacent to the operation. Wintershall also The last hydraulic fracturing operations in created a special internet site for German Lower Saxony were permitted in summer operations, closely informing the public on 2011. Thereafter, the Mining Authority did not the progress at the Düste Z10 project. process any new permit applications. At the Due to the increased public perception of beginning of 2012 the authority issued a new hydraulic fracturing, the Mining Authority directive on structure and minimum content required application for a General Permit requirements for new hydraulic fracturing («Rahmenbetriebsplanantrag») for the entire permit applications, which was made a pre- project, which is possible under the existing requisite for the acceptance of new applica- mining law. In the past, General Permits were tions. Wintershall applied for the permit in only mandatory for large facilities but not for July 2012, with detailed descriptions of: single wells, even if hydraulically fractured. • Hydraulic fracturing operations; This General Permit required broad techni- • Composition of frac fluid and additives; cal descriptions of the different operational • Well site selection and construction; stages: • Well and completion design; 1. Site construction; • Well test operations; 2. Drilling and completion operations • Barrier formations above reservoir forma- including water usage; tion; 3. Hydraulic fracturing and well test opera- • Hydrogeological situation in the influence tions. area of well site;
55 2-2014_geologi 2.06 12.02.15 15:21 Pagina 56
• Environmental impact assessment of the 4 Technical Work operations. 4.1 Geophysical Analysis and Geological The Mining Authority accepted the Frac Per- Modeling mit application (incl. well test operations) as submitted by Wintershall. After additional During the planning stage of Düste Z10, data questions were answered to satisfaction, the from an existing 3D seismic survey from Mining and local Water Authorities techni- 1985 was reprocessed. The new data result- cally approved the Frac Permit early 2013. ed in a qualitative better characterization of However, the final approval was blocked at the reservoir and was used to build a new the political level in Lower Saxony (which static geological model. Three offset wells, had undergone a change of government in two from within the production license and 2013), arguing that more public participa- one from outside were used for calibration. tion is required in the approval process. Full The target coordinates for Düste Z10 were approval of the frac permit is therefore out- determined based on the structural high, standing. A new regulation, specifically gov- preferable reservoir characteristics and rel- erning hydraulic fracturing operations has ative proximity to the target coordinates of been drafted, but not been enacted yet. Düste Z9.
4.2 Well Design
The Düste Z10 well design has been opti- mized for hydraulic fracturing operations. Geophysical and geological data, offset
Fig. 2: Seismic X-Section with Düste Z9 and Z10.
56 2-2014_geologi 2.06 12.02.15 15:21 Pagina 57
drilling and production data, especially from The intermediate liner and casing sizes had Düste Z9 and other wells in the area served to be designed around these minimum as the main input with respect to general design requirements. Selected tubulars and casing design and corrosion aspects. Latest components have to withstand all major hydraulic fracturing parameters (mainly load cases that are possible throughout the pumping rates and pressures) as applied in life of the well. These are simulated with offset wells and comparable settings around standard well and completion design soft- the world defined minimum well design ware programs. Generally, the most severe parameters, which in practice were inner load cases throughout the life of the well diameters, pressure ratings and material include pressure tests, early life production strengths of production liner, production and shut-in scenarios, late life production tubing, completion components, tubing scenarios and fluid injection scenarios. head and X-mas tree. Hydraulic fracturing, for example, repre-
Fig. 3: Well design Düste Z10.
57 2-2014_geologi 2.06 12.02.15 15:21 Pagina 58
sents a fluid injection case. The simulator ids cannot get into contact with the produc- takes into account induced temperature and tion casing or any other parts of the well. pressure changes and simulates correspond- The production tubing can therefore be ing material forces and stresses, which have viewed as a «wear part», which could be to stay within 80% of the material specific replaced any time in case of an integrity maximum yield strengths. The well design issue. The Düste Z10 well design foresees process is iterative and ends when suitable five concentric tubulars across the depth size and material combinations are found for interval of the fresh water aquifer (0−50 m) the entire well. providing total protection from inner well A permanent down-hole pressure and tem- fluids (Fig. 4). perature gauge was selected for the produc- tion tubing close to reservoir depth to allow 4.3 Site Construction real-time pressure and temperature control during the hydraulic fracturing treatments In Germany, drilling sites are constructed and long-term reservoir monitoring. A per- according to guidelines as set out by the manent packer is required at the bottom of WEG (Wirtschaftsverband Erdöl- und Erd - the completion string. It creates an annulus gasgewinnung e. V.), which are some of the between production casing and production most stringent worldwide. All surface areas tubing (annulus #1, see Fig. 4). This annulus of the well site, which may get in contact is needed for well integrity monitoring and with fluids used during drilling, hydraulic pressure support, for example during stimulation and production tests, must be hydraulic fracturing operations. Anchoring built «leak tight» (WEG 2006). the tubing with a permanent production Prior to well site construction for Düste Z10, packer is part of the double barrier princi- the conductor pipe was driven to a depth of ple. more than 60 m, protecting the fresh water All fluids injected into or produced from the aquifer (0−50 m) from future drilling work reservoir are forced through the inner pro- (Figs. 3 and 4). Only afterwards construction duction tubing and production liner. The flu- of the roughly 10.000 m2 large site com-
Fig. 4: Düste Z10 design across fresh water aquifer; [*] permanently pressure and tempera- ture controlled.
58 2-2014_geologi 2.06 12.02.15 15:21 Pagina 59
menced, which was sealed against the con- it off (cased-hole logging). Most of the meas- ductor pipe. The inner area is equipped with urements run in the upper hole-sections a surrounding fluid barrier and an independ- were standard logs for stratigraphic descrip- ent drainage system to a double hulled tank. tion and determination of cement and casing The outer area is equipped likewise. quality. Standard mud logging was per- In order to take baseline analyses and per- formed during the entire drilling operations form long term monitoring of the fresh water at shortened intervals across the reservoir aquifer in the proximity of the well site, section. In the target formation, several three water wells were constructed. Data cores were taken to be able to carry out rou- taken from these wells was also used for the tine and special core analysis. This data was hydrogeological expertise, which was a used to calibrate the following well logging required input for the frac permit applica- measurements and provided geologists with tion. actual reservoir rock samples for improved geological modelling. 4.4 Drilling and Completion A specially tailored logging program was carried out in the reservoir section to allow The drilling rig was mobilized to the well site for thorough tight gas reservoir characteri- in December 2011. After drilling to the first zation and hydraulic fracturing design. Addi- casing section depth, the surface casing was tionally, a special VSP (Vertical Seismic Pro- run and cemented to surface. The cement file) log was run to be able to accurately tie quality was independently checked by wire Düste Z10 into the existing 3D seismic sur- logging methods and pressure tests before vey. Cased logging finally confirmed cement drilling of the next section commenced. quality and provided a baseline measure- Each following casing and later the liners ment for later planned log based frac-height were checked for cement quality and pres- determination. sure integrity in the same manner. Before running of the well completion, the Each well section was logged before (open- well was pressure tested to maximum antici- hole logging) and after casing and cementing pated annulus pressures during the
Fig. 5: Drilling rig on Düste Z10.
59 2-2014_geologi 2.06 12.02.15 15:21 Pagina 60
hydraulic fracturing process. Afterwards an detailed frac design was carried out as per inflow test confirmed pressure containment the actual stratigraphy in the reservoir. It from the reservoir. Afterwards the well com- specifically determined the number of pletion components including the down- required frac treatments, perforation hole pressure and temperature sensor and design, frac treatment sizes per gas bearing permanent packer were installed such to sand, fluid types and resulting formulations, ensure mechanical continuity to the produc- fluid volumes, proppant types and volumes, tion liner (mono-bore concept, Fig. 3). Fol- pump rates and pressures. lowing X-mas tree installation, pressure Wintershall carried out special regained tests confirmed pressure integrity and readi- conductivity tests to determine optimal frac- ness of the entire well construction for the turing fluid formulations using chosen prop- hydraulic fracturing operations. pants under in situ conditions (reservoir After demobilization of the drilling rig, the pressure and temperature). This involved wellhead was equipped with pressure and optimization of polymer-breaker and high- temperature sensors on the tubing head and temperature stabilization concentrations in on annulus #1(between production tubing the fluid. and production casing) and annulus #2 Generally, no single concentrated frac fluid (between production casing and intermedi- additive of the planned fluid formulation ate casing). These sensors together with the rates higher than water hazard class 1 (WHC permanent down-hole pressure and tempera- 1 = low hazard to water) according to the ture sensor on the production tubing were VwVwS (Verwaltungsvorschrift wasserge- connected to the distributed control system fährdende Stoffe). For example, the fluid providing a means for continuous pressure which forms on streets during winter, when integrity monitoring of the well (see Fig 4). sodium chloride is used as the de-icing This system will be used for real-time moni- agent, already is classified WHC 1. In the frac toring of well integrity during the frac opera- fluid the additives are highly diluted. In the tions and for long term monitoring of reser- Düste Z10 frac fluid formulation, water and voir and well performance. proppants (both not WHC rated) make up 99.2% and additives only 0.8% (max. WHC 1 4.5 Frac Design rated) of the frac fluid. Nevertheless, since the additives are rated WHC 1, the frac fluid The hydraulic fracturing design was carried mixture in total automatically rates WHC 1. out in different stages. Before Düste Z10 was drilled, a general design was drafted based 4.6 Frac Operations (Outstanding) on data from offset wells, namely Düste Z9. This data included stratigraphy, pore pres- The detailed frac design determined the sures, rock mechanics, local stress field and necessity of seven frac treatments for Düste job data from the five hydraulic fractures Z10. These were planned to be conducted pumped in 1995. The fracture orientation in over a two-month period, averaging about this area is well known from offset data from one frac treatment per week including mobi- several wells. Fractures in the Düste Reser- lization, all required auxiliary operations, voir at this depth develop vertically along well clean-up and demobilization. the maximum horizontal stress direction, There is no risk of fracturing fluid uninten- which is roughly North-Northwest – South- tionally leaking into the fresh water aquifer Southeast. during these operations. The following theo- As new data became available from Düste retical leak paths were examined and dis- Z10 (logging data, core measurements, actu- cussed: al well orientation, geometry and design), a • Surface leakage at the well site;
60 2-2014_geologi 2.06 12.02.15 15:21 Pagina 61
• Lateral leakage through the well; without control systems and operator per- • Vertical leakage up along the outside of sonnel taking notice of it. The 10 cm high flu- the wellbore; id barrier around the inner area has a fluid • Vertical leakage up through the formations containment capacity of 200 m3 with an inde- from the reservoir. pendent 100 m3 double hulled tank connect- ed to the drainage system. Therefore it is Surface leakage of fracturing fluid during impossible for the frac fluid mixture to leak operations are highly unlikely, since fractur- into the fresh water aquifer. Additionally, as ing fluid is not stored at the location, but confirmed by the findings of an independent only mixed «on-the-fly» immediately before hydrogeological specialist, the fresh water being pumped into the well. The entire frac- aquifer in the area of the well site is natural- turing equipment is located within the leak ly protected by 8−15 m thick natural clays. tight inner area of the well site. Only munici- This type of hydrogeological setting is e.g. a pal water is stored in tanks before the oper- prerequisite for the construction of munici- ation starts. A frac fluid additive truck trailer pal garbage disposal dumps in the state of contains all required liquid additives, which Lower Saxony in order to protect the fresh are stored according to the double barrier water aquifer. principle. It has to be noted that even the Lateral leakage of fracturing fluids through concentrated frac additives are within the the well is technically impossible. As WHC 1 rating. In the unlikely case of leaking described above, production tubing, annuli surface equipment downstream of the mix- #1 and #2 pressures are constantly moni- ing equipment, a maximum of about 2 m3 of tored. In case of a pressure integrity issue, frac fluid (incl. additives) could reach the hydraulic fracturing operations would not leak tight inner surface area of the well site be carried out. A pressure integrity issue
Fig. 6: Layout of fracturing equipment in inner area of Düste Z10 well site.
61 2-2014_geologi 2.06 12.02.15 15:21 Pagina 62
during fracturing operations would instanta- several hundred meters thick salt forma- neously lead to opening of a pressure relief tions are located above the reservoir. Spe- valve and to pump shut down. Since a total cial thick-walled casings had to be set across of five steel barriers exist, there is no direct these salt formations in order to keep the leak path of the fracturing fluid from the pro- salt from deforming the casings, as it is duction tubing to the fresh water aquifer mobile under the existing pressures and (Fig. 4). temperatures. Salt formations are therefore Vertical leakage from fractures created in «self-healing» and often provide the main the reservoir at more than 3.800 m depth up barrier above hydrocarbon reservoirs in along the outside of the well is impossible as Northern Germany. two (Zechstein- and Muschelkalksalinar) Vertical migration of fluids from the reser-
Fig. 7: Salt and clay barriers above Düste Carboniferous tight gas reservoir.
62 2-2014_geologi 2.06 12.02.15 15:21 Pagina 63
voir across more than 3.800 m of various models in the order of 10s of meters for impermeable barrier formations into the future frac operations. fresh water aquifer is impossible. Next to the The operations are not expected to induce salt formations, several thousand meters of any seismicity at the surface that can be felt impermeable clay formations exist. Addi- by humans or cause damage to buildings tionally, hydraulic fracs, designed for the (ML > 2.5). During several recent hydraulic Düste tight-gas reservoir, ideally will reach fracturing treatments of the same formation half lengths of up to 150 m and heights up to in a near offset well no induced seismicity at 100 m but normally less as they are con- the surface has been measured by the Ger- strained by shale barriers within the reser- man Regional Seismic Network (operated by voir. the Bundesanstalt für Geowissenschaften The larger the frac, the more reservoir rock is und Rohstoffe). exposed, into which frac fluid leaks off. There- A long-term production test was planned fol- fore there is a maximum frac size which can lowing the completion of hydraulic fractur- be reached, which is defined by the balance of ing operations. One of Wintershall’s own fluid leak-off and maximum fluid pump rate, well test equipment packages will be utilized which is constrained by maximum allowable for this test and installed within the inner pressures. Additionally there are rock area of the well site. The pipeline tie-in to an mechanical-, stress field-, lamination- and flu- existing raw gas production gathering sys- id-related effects impacting the maximum size tem was already constructed as part of the of hydraulic fracs just to name a few. well site preparation. Part of the hydraulic Conductive faults across the barrier forma- fracturing treatment fluids will be produced tions above the reservoir do not exist. If back with the gas and reservoir water. The they would exist and they would be conduc- fluids will be separated by the well test tive, the target gas reservoir would not exist. equipment and temporarily stored at the Moreover, frac fluids are heavier than hydro- well site in closed tanks. Safe fluid disposal carbons, i.e. if hydrocarbons do not migrate will either be organized by approved spe- up from the reservoir (in this case the target cialized companies or injected into reservoir would not exist) water will also approved disposal wells within depleted oil not migrate up against gravity. and gas reservoirs. During the frac-operations in the Düste Z10 well, which only last 1−2 hours per treat- ment, control systems and operations per- 5 Conclusions and Outlook sonnel monitor all relevant pressures and volumes constantly. If any abnormal pres- Hydraulic fracturing operations have been sures or volumes are observed, the pumps applied in Germany more than 300 times are immediately shut down. since 1961 without any harm to the environ- For Düste Z10 it was additionally planned to ment. The strict regulatory framework has carry out micro seismic monitoring of the ensured that operations are carried out con- created fracture geometries. The offset well sistently to high safety standards. Moreover, Düste Z9, which is only about 500 m away at in light of the critical perception of the tech- reservoir depth, was specifically prepared nology, the German oil and gas industry has for placing geophone receivers. Also, it was developed a catalogue of best practices that planned to use special proppants in some of is also publically accessible (WEG 2014). the treatments to be able to carry out frac- The Düste Z10 Tight Gas Project in Lower ture height logging at the wellbore. These Saxony has been planned, permitted and measurements were only intended to executed in accordance with these best improve the accuracy of the simulation practices, key elements of which are:
63 2-2014_geologi 2.06 12.02.15 15:21 Pagina 64
1. Evidence of effective geological barriers References above the reservoir; AAPG 2014: Data presented at the AAPG Unconven- 2. Prevention of surface spill risk by ade- tional Resources Technology Conference, quate well site construction; August 2014. 3. Prevention of subsurface spill risk by ade- Montgomery, C. T. & Smith, M. B. 2010: Hydraulic Fracturing – History of an Enduring Technology. quate well design; Journal of Petroleum Technology, NSI Tech- 4. Full understanding and control of created nologies. frac dimensions; Niedersächsisches Ministerium für Umwelt, Energie und Klimaschutz 2014: Erlassentwurf 5. Safe disposal of produced fluids after «Zulassung von Vorhaben zur Aufsuchung und hydraulic fracturing operations; Gewinnung von Erdgas aus konventionellen 6. Prevention of damaging induced seismici- Lagerstätten mittels hydraulischer Bohrloch- ty at the surface. behandlung zur Risserzeugung in einem Ver- fahren mit Umweltverträglichkeitsprüfung». UVP-Frac-Behandlung-Erlass, 03.03.2014, However, the hydraulic fracturing permit for http://www.umwelt.niedersachsen.de/down- Düste Z10, despite the fact of being techni- load/85118. WEG Kompakt 2013: Newsletter des Wirt- cally approved, was blocked at the political schaftsverbandes Erdöl- und Erdgasgewin- level in early 2013. The project is therefore nung, November 2013. on hold since that time. WEG Leitfaden 2006: Bohrplatzgestaltung. Wirtschaftsverband Erdöl- und Erdgasgewin- In 2014, the state of Lower Saxony drafted a nung e.V., 08/2006. new regulation concerning the approval WEG Richtlinie 2014: Praxis der hydraulischen process of hydraulic fracturing, which dis- Bohrlochbehandlung für konventionelle Spei - chergesteine. Wirtschaftsverband Erdöl- und tinguishes between operations in conven- Erdgasgewinnung e.V., 06/2014. tional reservoirs (including tight gas) and operations in unconventional reservoirs (Niedersächsisches Ministerium für Umwelt, Energie und Klimaschutz 2014). Generally, environmental impact assessments will become mandatory for all hydraulic fractur- ing operations and have to be made publi- cally available including permitting docu- mentation. The new regulation mainly aims at providing a solid legal foundation for more public involvement. However, this new regulation has not yet been enacted by Low- er Saxony. In parallel, Germany is working at the national level to adapt the existing legal framework to the new public perception. In the summer of 2014, the first hydraulic fracturing operation since three years has been approved and executed in Germany in the state of Mecklenburg-Western Pomera- nia. Assuming that the new regulation will be enacted in Lower Saxony by the end of 2014 and taking into account all statutory peri- ods, work on Düste Z10 realistically might only resume in early 2016.
64 2-2014_geologi 2.06 12.02.15 15:21 Pagina 65
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 65-68
The Fracking Debate in Europe – An Assessment of the History behind the European Bans on Hydraulic Fracturing Terry Engelder1
Reprinted from GEO ExPro Magazine, Vol. 11, no. 4, September 2014 (www.geoexpro.com) with minor mod- ifications. We highly appreciate permission for reproduction.
Introduction
During a recent four-week AAPG Distin- horizontal drilling in 2006. Yet a poll among guished Lecture Tour in Europe, my most Pennsylvanians would probably identify popular lecture was an analysis of the frack- driving as the safer activity! ing debate; «The Environmental Realities of The lecture started with a discussion of my Hydraulic Fracturing: Fact versus Fiction» – research on natural hydraulic fracturing in unsurprising considering the sensitivity to gas shale dating back to the 1970s, which was the prospect of shale gas exploration in concurrent with both the first horizontal much of Europe. My objective was to drilling of shale source rocks and the initial address the public fears that drove morato- use of massive hydraulic fracturing in the US. ria and bans on fracking in places as differ- Although both techniques date back 35 years ent as New York, the UK, and France. Central in the USA, none of this early work on fracking causes of public fear in America were a com- made much of an impression on the public. bination of early mistakes by industry and purposeful disinformation from activists, especially those seeking to profit from such Surprising Research anxieties. This fear has now spread beyond America to places with nothing more than a The process by which fracking entered the modest gas industry experience. general consciousness may have started My «environmental realities» lecture was a about 2007 with my calculation of the techni- clash between the recalcitrant notion that cally recoverable reserves in the Marcellus the worst will happen when the gas industry gas shale of the Appalachian Basin. In 2007 shows up and my American optimism that shale was not widely discussed as a source of gas can be produced at maximum benefit gas reserves and few people had any idea and minimum risk. Several people stated that what the extraction process involved. I slow- Europeans do not want fracking until they ly began to understand that gas shale pro- are sure it is safe. While everyone wants a duction would become a significant founda- safe industry, safety is never absolute. In tion for «new» gas reserves globally, pushing Pennsylvania, for example, where more than «Hubbert’s peak» for gas production well into 3.000 people are killed annually in automo- the future. My calculation was so much larger bile accidents, only a handful have died in than current estimates (25 times larger than fracking related accidents since the start of the USGS number) that several things came to mind. If people took me seriously and I was wrong, the industry and the economy could 1 Professor of Geosciences, The Pennsylvania State Uni- versity, Department of Geosciences, 334A Deike Buil- lose billions of dollars; however, if my esti- ding, University Park, PA 16802, USA mate was right, this new-found reserve would
65 2-2014_geologi 2.06 12.02.15 15:21 Pagina 66
slow the march towards a low carbon energy Risks and Rewards portfolio and reduced carbon footprint. Even if the estimate was accurate, speculators In late 2007 I went to the news media with were still going to lose money. Either way my results, receiving a great deal of public seemed like a net loss. However, all natural attention. At that time the term fracking was systems, including the human economy, grow not part of the English language; within a and thrive only in proportion to their access year it had become shorthand for gas to abundant energy, so it seemed to me that extraction by horizontal drilling and high- shale gas was that next source of relatively volume hydraulic fracturing, and most peo- inexpensive energy for us. Ideally it would ple now know what fracking is. backup those notoriously unreliable but car- In Europe, I was frequently asked, «How can bon-neutral renewables, wind and solar, until you be so certain [about fracking]?» My smart grids and long-term energy storage for American optimism must have been shining electrical generation were developed. through, because I point out in the lectures
Fig. 1: Terry Engelder is Professor of Geosciences at Pennsylvania State Uni- versity and a leading authority on the Marcellus gas shale play.
66 2-2014_geologi 2.06 12.02.15 15:21 Pagina 67
that shale gas comes with risk along with chemistry is measured after the arrival of reward. As Voltaire said: «doubt is not a industry, there is a belief that these chemi- pleasant condition, but certainty is absurd.» cals, particularly methane, result from Science is not capable of certainty beyond drilling. having a sense of when others are mistaken. Traditionally, the first oil wells in a region As the automobile fatalities example shows, were drilled where oil is leaking to the sur- people don’t do a very good job of normalizing face. Likewise, gas leaks are associated with risk. When asked for absolute numbers on risk, the great gas basins on the world, including all I can do is point to the millions of hydraulic the Appalachian Basin where there are sev- fracture treatments and stimulations under- eral towns named Burning Springs. Methane taken already, resulting in a modest number of was there all along but industry failed to examples of groundwater contamination from present these details to the public prior to subsurface sources, virtually all from methane drilling. Through the history of the O&G leaking along the cement-bedrock contact industry in the US, regions that leaked gas inside a borehole. Risks outside methane leak- exclusively were not nearly as interesting as age come from poor surface management of those that leaked both oil and gas. Pennsyl- fluids in the form of spills and leaks. vania, for example, had a long history of Air quality is at risk and ultimately, burning flaming faucets and bubbling stream beds, methane leaves a carbon footprint. These although the gas was not usually concen- are concerns. The leaks need be found and trated sufficiently in groundwater to mani- fixed – but replacing coal-fired power plants fest itself in drinking water. Intensified with natural gas led to a significant reduc- drilling in 2008 produced a heightened sen- tion in America’s carbon footprint over the sitivity to methane in groundwater, but with past five years, according to the EIA. This no baseline, it was impossible to know good news does not mean that mankind whether and how much methane resulted should discontinue its march toward a larg- from this drilling. Pennsylvania law held er renewable energy portfolio. operators responsible for the methane in groundwater within 1.000 ft of a gas well, regardless of whether it was their fault. A Number of Mistakes The second industry mistake involved the extent to which casing was cemented. Early Industry was responsible for six major «mis- on, surface and intermediate casing was takes» during the early days of high-volume completely cemented but as much as 5.500 horizontal hydraulic fracturing in the ft of open hole was left outside the produc- Appalachian Basin. I use the term mistake, tion casing, as traditionally done in sparsely because each might have been anticipated, populated parts of the country with few but only by someone with great clairvoy- water wells near gas ones. This is fine if the ance. None were a manifestation of single overburden section is not gas charged – but events like the engineering carelessness of in north-eastern Pennsylvania the overbur- the Macondo well blowout. However, they den contains Upper Devonian coals, full of did create a breeding ground for amplifying methane gas, which flowed into the open public fear of the unknown. holes and in some cases likely increased Arguably, the most serious one was the fail- groundwater concentration by leaking along ure to establish baseline water chemistry poorly cemented gas wells. Industry no before drilling campaigns. Many chemical longer leaves open-hole production casing, elements, (e.g. iron, magnesium, potassium) at least below the intermediate casing and compounds (e.g. methane) are dis- string. solved in drinking water, but when water
67 2-2014_geologi 2.06 12.02.15 15:21 Pagina 68
Secrecy and Earthquakes Purposeful Disinformation?
The use of air-drilling to penetrate the verti- Public anxiety arising from these very real cal legs of Marcellus gas wells was another mistakes was easily manipulated and magni- error. The pressure of air blowing into more fied by activists who either did not know permeable aquifers was sufficient to drive better or sought to profit by playing to this methane towards nearby water wells. It also fear. The most egregious case of purposeful increased the natural turbidity in groundwa- disinformation being used to manipulate the ter, which often worries people. public is found in the closing scene of the A fourth mistake was to lobby for elements in movie «Gasland», where a tap is lit. The own- the Energy Policy Act of 2005 that allowed er’s water well was drilled though a coal bed fracking companies to keep their additives giving off methane, and the film’s producer proprietary. The public feared that groundwa- admitted knowing that the methane had ter would become contaminated by unknown, nothing to do with fracking. possibly toxic, chemicals, and wanted to Public fear can also be manipulated by famous understand exactly what and how much was people. Movie star Matt Damon was quoted as being pumped into the ground. There was saying that «Everyone knows that fracking poi- also the (inaccurate) perception that this act sons the water and air», adding that fracking, exempted the industry from Clean Water and «[…] tears apart local communities and sub- Clean Air Acts. The industry elected to reveal verts democracies […]». Yoko Ono was quot- the details of additives on a website, «Frac ed in the media as stating categorically that Focus», and, while posting volume and chemi- «Fracking kills». Subsequently, signs declaring cal composition was voluntary, most opera- that fracking kills have shown up regularly at tors in the Appalachian Basin have joined in protest rallies in many places worldwide. an attempt to become more transparent. The most common prop at protest rallies The industry disposed of flowback in large has been the jug of rusty, brown water – eas- enough volumes to trigger minor earth- ily transported and, unlike the flaming quakes in Ohio and Texas, which naturally faucet, looking nasty enough to amplify fear played into the public fear. Water under of fracking. Rusty, brown water is a natural pressure flowing along faults reduces the product of the oxidation of dissolved iron. frictional strength sufficiently to cause slip; Tests suggest that nearly half the water triggering a large earthquake by injecting wells in parts of Pennsylvania have enough water was even the plot of a James Bond dissolved iron in the groundwater to make it movie. USGS studies confirmed that there is turbid when exposed to atmospheric oxy- a relationship between the injected volume gen, a process accelerated by pumping wells of water and earthquake size, but showed dry. In fact, the US EPA tested one water well that it was not possible to trigger a destruc- repeatedly and found the water safe to tive earthquake with the amount of water drink. Later, the owners admitted pumping used during fracking – incidentally proving their water well dry to supply turbid water the implausibility of the James Bond plot. when visitors came knocking. The sixth mistake involved management In summary, public pressure was largely issues associated with potentially leaking responsible for political decisions to place open pits, leading to the fear that groundwa- moratoria or bans on fracking. In a sense, ter could be contaminated if a lined pit was industry was directly responsible for these punctured or seals failed. Presently, only political decisions because of early mis- fresh water is stored in open pits. Any flow- takes, making it easy for activists using pur- back is contained in enclosed frack tanks poseful disinformation to further cement a where the chance of leaking is near zero. negative public position relative to fracking.
68 2-2014_geologi 2.06 12.02.15 15:21 Pagina 69
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 69-74
Unconventionals in China – Shell’s Onshore Oil and Gas Operating Principles in Action Martin Stäuble1
Key words: China, unconventional oil and gas, hydraulic fracturing, operating principles
Abstract Unconventionals in China Shell is operating four production sharing con- tracts (PSC’s) targeting a variety of unconventional onshore tight gas and shale plays in the provinces Unconventional gas is a key component of of Sichuan and Shaanxi, all in partnership with the energy reform of China – a country Petrochina. Three offshore PSC’s are also being whose energy demand will nearly double by executed in partnership with CNOOC targeting con- ventional gas in China. 2030. Initial production started in 2007 in the Changbei Related to energy, the Chinese government field, which, with 3.3 Bcm yearly gas production, recognizes three strategic drivers: 1] ensure today delivers ca. 40% of Beijing’s gas demand. The more recent acreage additions in Sichuan (Jinqiu, the economic prosperity of its 1.3 billion Fushun and Zitong) are in appraisal stage, with over people by supplying affordable energy, 2] 50 wells drilled since startup of operations in 2010. improve domestic energy production and Sichuan is home to a prolific conventional hydro- carbon system with multiple high quality source thereby reduce dependency on imported rocks and reservoir levels. Generally, reservoirs energy and 3] drive environmental improve- are very tight and hence Basin Centre Gas plays are ment by substituting coal with gas (Fig. 1). possible in addition to Shale Gas and Shale Oil While these strategic drivers are of great plays. Currently long term testing is progressing, aiming to prove that viable options exist to prof- importance to the Chinese people, their itably produce this resource. implication in particular on the environmen- Drilling and fraccing (hydraulic fracturing) in tal and climate agenda have global reach: densely populated areas requires a high degree of care and sensitivity. Shell has introduced five oper- substituting coal with gas as the primary ating principles that address safety and well energy supplier can reduce the CO2 foot- integrity of drilling and completions, water use and print by up to 50%. For these reasons, China disposal, safeguarding air quality, the footprint of our operations, and interaction with neighboring has set ambitious targets for unconventional communities. Experience shows that achieving the gas production. quality that the five operating principles demand is The China oil and gas scene is dominated by equal in importance to finding the right geology or being cost competitive. the three large national companies: CNPC (Petrochina), SINOPEC and CNOOC. Oil and gas infrastructure is installed and is being expanded at a relatively fast pace. China has excellent manufacturing capabilities and a long oilfield tradition, which means that drilling and fraccing equipment as well as oil field services are readily available. China has many prolific hydrocarbon basins (Fig. 2) in often fairly complex settings and a predomi- nance of lacustrine source rocks. The latter 1 Vice President and Managing Director Shell China Explo- are also the focus of the emerging unconven- ration and Production Company Limited, 51F China World Tower 3, Beijing 100004, P.R.China. tionals oil and gas activities. [[email protected]] Developing unconventional oil and gas as a
69 2-2014_geologi 2.06 12.02.15 15:21 Pagina 70
new resource has been a slow process with Onshore operating principles few foreign players acquiring acreage and only Shell being an active operator. The 2012, Shell published its Onshore Oil and main reason for this slow pace lies in uncer- Gas Operating Principles. The company is tainties as to the viability of the unconven- making all of Shell’s operated onshore proj- tional plays, immaturity of the regulatory ects where hydraulic fracturing is used to framework, lack of freely available data, the produce gas and oil from tight sandstone or high cost of the exploration and appraisal shale, consistent with these principles and phase and finally, limited access to bidding with local rules and regulations. The reason rounds. To date, approximately 200 wells for making these public was in response to have been purposely drilled into unconven- concern around the development of uncon- tional targets with even fewer long term ventional resources, especially with regard tests. This contrasts with over 10.000 wells to the practice of hydraulic fracturing. It cre- drilled on a yearly basis in North America. ates transparency as the public today Many of the ingredients to make unconven- demands and allows Shell to share «how we tional resources a success are present in do our business». It also demonstrates confi- China with good government support, a dence, which is based on 60 years of good supply chain and an active oil and gas onshore operational experience, including industry. However, it is an industry in its the use of hydraulic fracturing, and under- infancy, with few players and so far limited pins how the company works today and how experience. it aspires to improve. The operating princi-
Fig. 1: The strategic driv- ers for China policy mak- ers.
70 2-2014_geologi 2.06 12.02.15 15:21 Pagina 71
ples comprise five elements, each comple- The operating principles in action mented with detailed and auditable instruc- tions (not shown in this paper): In the following, two examples of applying • Principle #1: Shell designs, constructs and the Shell operating principles in China are operates wells and facilities in a safe and highlighted: Footprint reduction and com- responsible way. munity engagement. • Principle #2: Shell conducts its operations in a manner that protects groundwater Footprint reduction and reduces potable water use as reason- Sichuan has a population density of about ably practicable. 600 people per km2. The terrain in the oper- • Principle #3: Shell conducts its operations ating area is hilly with small villages, minor in a manner that protects air quality and roads and an abundance of small and medi- controls fugitive emissions as reasonably um rivers. As one of the most fertile regions practicable. of China, Sichuan hosts intense agriculture • Principle #4: Shell works to reduce its and is considered the bread basket of China. operational footprint. For drilling and fracturing operations, a well • Principle #5: Shell engages with local com- pad approximately the size of a football field munities regarding socio-economic (ca. 4.500−6.000 m2) needs to be construct- impacts that may arise from its opera- ed. This area provides room for the rig, crew tions. accommodation and fraccing equipment. Following successful testing, the well pad is converted into a production station, and
Fig. 2: Simplified tectonic map of China overlain with existing drilling locations and Shell’s operating loca- tions (modified from IHS data).
71 2-2014_geologi 2.06 12.02.15 15:21 Pagina 72
Fig. 3: The challenge of land acquisition in a densely populated provin- ce like Sichuan.
Fig. 4: Multiple horizontal wells from each location dramatically reduce the operational footprint.
72 2-2014_geologi 2.06 12.02.15 15:21 Pagina 73
excess land restored to vegetation. Finding to voice both concerns and needs. Thanks appropriate well locations can be a challeng- to the feedback from the community, the ing exercise in heavily populated areas, as impact of operation can more effectively be can be seen in Fig. 3. Many farm houses, ter- minimized. In addition, Shell aims at creating raced fields and steep sided hills dominate win-win situations where the community the picture. In addition to the well pad itself, gains long-term benefit from the company’s sufficient safety distance from the nearest presence in the area. This can take the form house must be maintained. of employment opportunities, social invest- As unconventional developments can typi- ment focused at improving people’s liveli- cally comprise hundreds, if not thousands of hood or the purchase from the community wells, minimizing the footprint not only is an of goods and services to support the opera- important operating principle but is a key tions. ingredient for success. The solution is to use the same well pad for multiple wells – up to Similar to the previously mentioned foot- 32, and use horizontal, far-reaching wells to print reduction, successfully working with drain a large subsurface area during devel- the community is understood by Shell as a opment as is show in Fig. 4. prerequisite for success. People will make their sentiment felt by opposing an activity Community engagement or blocking progress. Hence, regardless how Entering a new location requires diligent good the geology is, if the relationship work with the community ahead of any engi- between community and company is not neering activity. Community liaison officers sustainable, the company will not be able to are the first on the scene to engage the vil- operate efficiently. Fig. 5 shows how easily lage inhabitants, especially the village lead- operations are stopped when a community ership and anyone living near to the intend- disagrees with a certain activity – in this ed operational area. The officers’ task is to case what was considered excessive truck- generate an understanding of what a site ing activity passing through a small village construction and drilling operation entails, road. Likewise, when the relationship is thus giving the community the opportunity based on mutual respect and trust, it can be
Fig. 5: Peaceful communi- ty protest.
73 2-2014_geologi 2.06 12.02.15 15:21 Pagina 74
beneficial for both parties. The example in Having strong operating principles in place Fig. 6 shows the community close to the well has proven essential for progressing Shell’s site celebrating the completion of an irriga- operations in China. Adherence to these tion project that Shell put in place. principles minimizes impact of the compa- ny’s operations on environment and people and also serve as a foundation for a sustain- In summary able interaction with the community. In short, demonstrable adherence to the The exploration and production of uncon- Onshore Oil and Gas Operating Principles is ventional resources in China are in their considered to be of equal importance as for infancy, with relatively few wells drilled, an instance a good hydrocarbon system or a immature regulatory framework and a con- cost effective drilling operation. tractual regime designed for conventional oil and gas. However, several unconvention- al plays are producing first gas, government support is strong and an excellent supply chain is emerging.
Fig. 6: Celebrating the completion of an irrigation project that was executed for a local farming communi- ty by Shell and PetroChina.
74 2-2014_geologi 2.06 12.02.15 15:21 Pagina 75
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 75-93
Die Erschliessung und Nutzung der Energiequellen des tiefen Untergrundes der Schweiz – Risiken und Chancen Roland Wyss1
Stichworte: Geothermie, Erdgas, Potenzial, hydraulische Stimulation, Fracking, Grundwasser
Inhalt
Zusammenfassung ...... 75 Résumé, Summary ...... 76 1 Einleitung ...... 77 2 Umwelt, Grundwasser und der tiefe Untergrund...... 77 3 Kurze Einführung in die Tiefbohrtechnik ...... 79 4 Zur Hydrogeologie des tiefen Untergrundes ...... 81 5 Hydraulic Fracturing ...... 83 6 Risiken der Untergrunderschliessung und -nutzung ...... 87 7 Chancen der Untergrunderschliessung und -nutzung ...... 89 8 Schlussbemerkungen ...... 92 Literatur...... 93
Zusammenfassung Aufgrund der derzeit laufenden Energiediskussion eine sichere Anwendung von Fracking möglich ist. gilt es abzuklären, welche Anteile der grossen Für die hydraulische Stimulation in der Tiefengeo- Potenziale von Erdgas und Geothermie in der thermie wurden bis heute keine Additive verwen- Schweiz künftig nutzbar sein werden. Die Schweiz det, es ist jedoch wahrscheinlich, dass solche in hat ausreichende rechtliche Grundlagen zum Zukunft nötig werden. Schutz von Umwelt und Wasser (u. a. Grundwasser, Zwischen der Schiefergasnutzung oder der Nut- Trinkwasser), diese lassen sich aber nicht auf die zung von Tight Gas und der Tiefengeothermie gibt Nutzung des tiefen Untergrundes direkt anwenden, es grosse Ähnlichkeiten, aber auch deutliche da z. B. Tiefengrundwasser nicht Wasser im Sinne Unterschiede. Die operationelle Erfahrung in der der heutigen Gesetze ist. Bei Tiefengrundwasser Tiefengeothermie ist im Vergleich zur Schiefergas- handelt es sich meist um saline Wässer mit für die nutzung noch gering. Lebenswelt unerwünschten Inhaltsstoffen. Bei der Jede Erschliessung und Nutzung des tiefen Unter- Tiefenerkundung und -erschliessung muss in grundes stellt einen Eingriff in den Untergrund dar. erster Linie verhindert werden, dass durch Tiefen- Erfahrungen zeigen, dass es möglich ist, ohne grundwasser unsere Schutzgüter Wasser und Beeinträchtigung der Trinkwasserressourcen und Boden beeinträchtigt werden. Tiefbohrungen ohne Gefährdung von Mensch und Infrastruktur erfordern den Einsatz einer Spülung mit Additiven. den tiefen Untergrund zu nutzen. Es braucht klare Der Einsatz von Hydraulic Fracturing (Fracking) für Regeln ohne unnötige Hürden für die Branche und die Schiefergasgewinnung ist wegen der Verwen- eine transparente Information der Öffentlichkeit. dung von Zusatzstoffen (Additiven) in der Öffent- Es braucht aber auch innovative Projekte, sachli- lichkeit stark umstritten. Mit heutigen Additiven che Diskussionen und unternehmerischen Weit- kann eine Beeinträchtigung von Wasser und Boden blick, einheimische Ressourcen des tiefen Unter- aber ausgeschlossen werden. Studien zeigen, dass grunds vertieft zu Erkunden und zu Nutzen.
1 Dr. Roland Wyss GmbH, Zürcherstrasse 105, 8500 Frauenfeld, Schweiz
75 2-2014_geologi 2.06 12.02.15 15:21 Pagina 76
Résumé Summary Dans le cadre des discussions en cours en matière In light of current energy discussions clarification de politique énergétique, il s’agit de déterminer la is necessary on the question of which proportion of part des ressources géothermiques et de gaz natu- the high potential for natural gas and geothermal rel qui pourront être mises en valeur à l’avenir en energy in Switzerland can, in the future, be used. Suisse. La Suisse dispose d’une législation adé- Switzerland has adequate fundamental legal prin- quate en matière de protection des eaux (nappes ciples concerning the protection of the environment phréatiques, eau potable) et de l’environnement en and water (including groundwater and drinking général. Pourtant, cette législation ne s’applique water): These principles, however, cannot be pas directement aux eaux issues des profondeurs directly applied to the utilisation of low-lying sub- du sous-sol, car, par exemple, ces eaux ne sont pas strata since, for example, deep groundwater is not de l’eau au sens des lois en vigueur. Les eaux des «water» in terms of current legislation. Deep profondeurs sont le plus souvent salées et contien- groundwater, for example, is usually saline water nent des substances qui ne doivent pas entrer en which contains substances that are not compatible contact avec le monde vivant. Lors de forages pro- with the living environment. Primarily, when per- fonds, qu’ils soient exploratoires ou servent à l’ex- forming deep exploration and exploitation, it must ploitation d’une ressource, il faut surtout éviter que be prevented that commodities such as earth and nos biens protégés – l’eau et le sol – en subissent water are not compromised by the exploitation of l’impact. Les forages profonds nécessitent le deep groundwater. Deep boring requires the use of recours à des liquides de transport contenant des drilling fluids and additives. The use of Hydraulic additifs. La fracturation hydraulique (fracking) est Fracturing (Fracking) for the extraction of shale gas très contestée par le public à cause de l’utilisation is highly controversial in the general public de ces additifs. Toutefois, les additifs actuellement because of the use of additives. However, with utilisés permettent d’affirmer qu’aucun effet today’s additives, an influence on water and the néfaste pour l’eau ou le sol ne s’ensuivra. Des étu- ground can be ruled out. Studies show that the safe des montrent qu’il est possible de mettre en œuvre application of Fracking is possible. la fracturation hydraulique de manière sûre. Although no additives have been employed up to En géothermie profonde, aucun additif n’a été utili- now for hydraulic stimulation in deep geothermic sé à ce jour pour la stimulation hydraulique. Il est energy operations, it is probable, however, that in cependant probable qu’à l’avenir, il sera également the future additives will also become necessary for nécessaire de recourir à des additifs pour les fora- the development and use of deep geothermal ener- ges et l’exploitation de la géothermie profonde. gy resources. Il y a de grandes similitudes entre l’exploitation des There are great similarities between the use of gaz de schistes ou l’utilisation du «tight gas», d’une shale gas or the use of «Tight Gas» and deep geo- part, et la géothermie profonde, d’autre part. Mais thermal exploitation, but there are also important il y a aussi des différences importantes. En géo- differences. Operational experience in deep geo- thermie profonde, on ne dispose pas encore, et de thermics is still low in comparison with the loin, de la même expérience qu’en matière d’ex- exploitation of shale gas. ploitation des gaz de schistes. Every development and use of low-lying substrata Toute mise en valeur ou utilisation du sous-sol represents an intrusion in the underground. Expe- représente une atteinte à l’intégrité de celui-ci. Sur rience shows that it is possible to make use of the la base de l’expérience acquise, il est prouvé qu’il underground without having an influence on drink- est possible d’utiliser le sous-sol profond sans por- ing water resources and without endangering ter atteinte aux ressources en eau potable ni mett- human beings and the underground infrastructure. re en danger l’homme et les infrastructures. Des It is necessary to define clear rules for this sector règles claires qui ne créent pas d’obstacle inutile of business without any unnecessary hindrances pour la branche, ainsi qu’une information transpa- and to provide transparent information for the gen- rente du public sont nécessaires. Mais il faut aussi eral public. However, innovative projects and objec- des projets novateurs, des discussions objectives tive discussions are also needed, as well as entre- et une vision entrepreneuriale à long terme qui preneurial farsightedness in order to investigate permettent d’explorer le sous-sol profond et de le and benefit from local deep subsoil resources. mettre en valeur.
76 2-2014_geologi 2.06 12.02.15 15:21 Pagina 77
1 Einleitung Die nachfolgenden Ausführungen sollen einen Beitrag zur laufenden Diskussion lie- In der aktuellen in der Schweiz laufenden fern und beleuchten vorwiegend die geolo- Energiediskussion spielt die Energie aus dem gisch-technischen Aspekte der Untergrund- Untergrund eine zunehmende Rolle. In der erkundung und -nutzung. Energiestrategie des Bundes ist einerseits der Tiefengeothermie eine wesentliche Rolle zugedacht, andererseits sollen auch Gaskom- 2 Umwelt, Grundwasser und der bikraftwerke eine solche übernehmen. Aus tiefe Untergrund Geothermie werden heute in der Schweiz rund 2‘400 GWh Wärme gewonnen, jedoch 2.1 Rechtliche Grundlagen noch kein Strom produziert. Sämtliches in der Schweiz verbrauchtes Erdgas, rund Gemäss Bundesverfassung (Bundesverfas- 32‘000 GWh (etwa 13% des Gesamtenergie- sung 1999), Art. 74, Abs. 1, erlässt der Bund verbrauchs der Schweiz), wird importiert. Vorschriften über den Schutz des Menschen Neue Möglichkeiten der Untergrunder- und seiner natürlichen Umwelt vor schäd- schliessung durch abgelenkte Bohrungen lichen oder lästigen Einwirkungen. und hydraulische Stimulation/Fracking bie- In Art. 76, Abs. 1 wird ausgeführt, dass der ten sowohl für die Geothermie als auch für Bund im Rahmen seiner Zuständigkeiten für die Kohlenwasserstoffproduktion in der die haushälterische Nutzung und den Schutz Schweiz neue Perspektiven. der Wasservorkommen sowie für die Die Tiefengeothermie besitzt trotz bisher Abwehr schädigender Einwirkungen des ausbleibender kommerzieller Erfolge und Wassers sorgt. In Abs. 2 wird weiter darge- negativen Schlagzeilen wegen schwacher legt, dass der Bund Grundsätze über die Erdbeben in der öffentlichen Wahrnehmung Erhaltung und die Erschliessung der Wasser- eine grosse Zustimmung. Demgegenüber ist vorkommen, über die Nutzung der Gewässer bezüglich der Erdgasnutzung, insbesondere zur Energieerzeugung und für Kühlzwecke wegen des «Frackings», eine starke Ableh- sowie über andere Eingriffe in den Wasser- nung vorhanden. kreislauf festlegt. Die Erdgasversorgung in der Schweiz wird Zur Energiepolitik heisst es in Art. 89, Abs. 1: heute über Lieferverträge mit Firmen aus «Bund und Kantone setzen sich im Rahmen dem angrenzenden Ausland sichergestellt. ihrer Zuständigkeiten ein für eine ausrei- Rund drei Viertel des in der Schweiz ver- chende, breit gefächerte, sichere, wirt- brauchten Erdgases wird in Westeuropa schaftliche und umweltverträgliche Energie- gefördert, vorwiegend in Norwegen, versorgung sowie für einen sparsamen und Deutschland und Dänemark, 20% stammt rationellen Energieverbrauch.» Weiter steht aus Russland. in Abs. 2: «Der Bund legt Grundsätze fest Um mittel- und langfristig die schweizeri- über die Nutzung einheimischer und erneu- sche Energieversorgung auf eine solide erbarer Energien und über den sparsamen Basis zu stellen und die strategischen Optio- und rationellen Energieverbrauch.» nen zu kennen, ist es wichtig abzuklären, Artikel 1 des Umweltschutzgesetzes (Um- welche einheimischen Energieressourcen weltschutzgesetz 1983) definiert den Zweck aus dem Untergrund künftig einen Beitrag des Umweltschutzgesetzes: leisten können und wie gross dieser Beitrag Abs. 1: «Dieses Gesetz soll Menschen, Tiere sein kann. Dabei müssen sowohl Umwelt- und Pflanzen, ihre Lebensgemeinschaften aspekte als auch wirtschaftliche Faktoren und Lebensräume gegen schädliche oder berücksichtigt werden. Beide spielen über lästige Einwirkungen schützen sowie die unsere Landesgrenze hinaus eine Rolle. natürlichen Lebensgrundlagen, insbesonde-
77 2-2014_geologi 2.06 12.02.15 15:21 Pagina 78
re die biologische Vielfalt und die Fruchtbar- Luft usw.) und aller darin lebenden Organis- keit des Bodens, dauerhaft erhalten.» men sowie deren Wechselwirkungen in und Abs. 2: «Im Sinne der Vorsorge sind Einwir- mit dieser Umgebung. Mit Umwelt verstehen kungen, die schädlich oder lästig werden wir hier nicht nur alle auf die Natur wirken- könnten, frühzeitig zu begrenzen.» den Einflüsse, sondern auch die sozialen, Im Gewässerschutzgesetz (Gewässerschutz- kulturellen, ökonomischen und ökologi- gesetz 1991) werden in Art. 4, Bst. b., unter- schen Bedingungen und Einflüsse unter irdische Gewässer als «Grundwasser denen Menschen und Lebewesen leben.» (einschl. Quellwasser), Grundwasserleiter, Grundwasserstauer und Deckschicht» erläu- 2.3 Die Umwelt, das Grundwasser im tiefen tert. Untergrund? In der Wegleitung Grundwasserschutz (BUWAL 2004) wird Grundwasser wie folgt Die Begriffe Umwelt und Grundwasser definiert: «Das Grundwasser füllt die natür- haben im Gesetz eine andere Bedeutung, als lichen Hohlräume (Poren, Spalten, Klüfte) im naturwissenschaftlich-technischen Sinn. des Untergrundes zusammenhängend aus Bei dem in der Bundesverfassung und der und bewegt sich entsprechend der Schwer- Gesetzgebung verwendeten Begriff kraft. Grundwasserleiter können aus Locker- «Umwelt» handelt es sich um die Lebenswelt gesteinen (z. B. Kies, Sand) oder aus Festge- des Menschen. Die rechtliche Definition von steinen (z. B. Kalkstein, Granit) bestehen. Wasser bzw. Grundwasser hat die Nutzung Deren Durchlässigkeit ist ein entscheiden- des Wassers als Trinkwasser im Fokus. der Faktor für den unterirdischen Wasser- Naturwissenschaftlich gehört aber die fluss. gesamte Erde zur Umwelt. Im neuen, noch nicht in Kraft getretenen, Im tiefen Untergrund herrschen Bedingun- «Gesetz über die Nutzung des Untergrundes gen, die der Lebenswelt des Menschen (UNG)» des Kantons Thurgau wird in §7, jedoch sehr entgegengesetzt sind. Insbeson- Abs. 4 festgelegt: «Frackingverfahren […], dere das vorkommende Tiefengrundwasser welche die Umwelt, insbesondere ober- und (Kap. 4) hat einen Chemismus, der eine unterirdische Gewässer gefährden, sind ver- Gefährdung für unsere Schutzgüter Grund- boten. Der Regierungsrat bestimmt, welche wasser und Boden darstellt. Zwar kann das Chemikalien verwendet beziehungsweise genutzte Grundwasser mit den heutigen nicht verwendet werden dürfen.» (Kanton rechtlichen Grundlagen genügend geschützt Thurgau 2014). werden, jedoch können diese Grundlagen nicht auf das Tiefengrundwasser extrapo- 2.2 Der Begriff Umwelt liert werden, da dieses, obwohl grundsätz- lich zusammenhängend, sich stofflich meist Gemäss Duden steht der Begriff Umwelt für deutlich vom oberflächennahen Grundwas- 1) die auf ein Lebewesen einwirkende, seine ser (Trinkwasser) unterscheidet. Lebensbedingungen beeinflussende Umge- Für die Erschliessung und Nutzung des tie- bung und 2) Menschen in jemandes Umge- fen Untergrundes können die Begriffe bung (mit denen jemand Kontakt hat, in «Umwelt» und «Wasser», wie sie im bestehen- einer Wechselbeziehung steht). den Recht verwendet werden, nicht einfach Das Umweltlexikon (http://www.umweltlexi- auf den tiefen Untergrund ausgedehnt wer- kon-online.de) gibt folgende Definition: den. Die bestehenden Grundlagen gelten «Der Begriff der Umwelt ist geprägt durch jedoch für Einflüsse, welche sich durch die die anthropogene Sichtweise des Menschen. Tiefennutzung auf unsere Lebenswelt aus- Umwelt ist danach definiert, als einem Lebe- wirken können. wesen umgebende Medien (Wasser, Boden,
78 2-2014_geologi 2.06 12.02.15 15:21 Pagina 79
3 Kurze Einführung in die • Kontrolle des Druckes von Formationsflu- Tiefbohrtechnik iden (Wasser, Gas, Öl). • Bildung eines Filterkuchens zur Abdich- 3.1 Einleitung tung des Bohrlochs vor Zu- und Abflüs- sen. Zentrales Element der Erkundung, Erschlies- • Reinigung der Bohrlochsohle und Austrag sung und Nutzung des tiefen Untergrundes das Bohrkleins (cuttings). sind Tiefbohrungen. • Physikalische und chemische Stabilisie- Das Bohren in grössere Tiefen ist ein kom- rung des Bohrlochs. plexer Vorgang. Es handelt sich nicht ein- • Reibungsverminderung des Bohrgestän- fach um die mechanische Erstellung eines ges an der Bohrlochwand. Hohlraumes im Gestein, sondern um einen • Kühlung des Bohrmeissels. komplexen hydraulisch-mechanischen Vor- • Korrosionsschutz von Verrohrung und gang, bei welchem neben Gesteinsparame- Bohrgestänge. tern auch Gebirgseigenschaften (z. B. Span- nungen) und die im Gebirge enthaltenen Flu- Die Grundlage der Spülung bildet in der ide eine wichtige Rolle spielen. Regel Wasser. Ohne Zusätze wird Wasser als Tiefbohrungen werden in der Regel im Rota- Spülung meist bei untiefen Grundwasser- tionsspülverfahren abgeteuft. bohrungen verwendet (Klarwasserspülung). Die wesentlichen Elemente einer Tiefbohr- Mittels verschiedener Zusätze können die anlage sind: Der Bohrturm, die Antriebsag- chemischen und physikalischen Eigenschaf- gregate (Diesel oder elektrisch), das Hebe- ten des Wasser bzw. der Spülung beeinflusst werk, der Drehtisch (bzw. der Kraftdrehkopf werden. Als Spülungszusätze dienen: oder der Spülungsmotor), das Bohrgestän- • Bentonite: Bildung einer Gerüststruktur, ge, die Bohrwerkzeuge und das Spülungs- erhöht die Viskosität und das Austrage- system. Ein Blowout-Preventer verhindert vermögen der Spülung. Führt zur Bildung im Bedarfsfall den unkontrollierten Austritt eines Filterkuchens auf der Bohrloch- von Fluiden (Wasser, Öl, Gas) am Bohrloch- wand. kopf. Das Bohrgestänge beziehungsweise • Polymere und CMC (Cellulose): ergibt der Bohrmeissel (drill bit) wird bei der Rota- minimalen Filterkuchen mit erhöhter elas- tionsspülbohrung mittels Drehtisch (rotary tischer Abdichtung, table), Kraftdrehkopf (top drive) oder mit • Kreide, Baryt: Beschwerung der Spülung Spülungsmotor (mud motor) angetrieben. bei Gefahr von Fluid-Überdrücken. • Bakterizide: Verhinderung der Zersetzung 3.2 Spülungssystem von CMC. • Sägemehl, Zellophan, Muschelschrot, Ein zentrales Element einer Tiefbohrung ist etc.: Bekämpfung von Spülungsverlusten. die Spülung. Sie wird in der Regel durch Spü- lungspumpen über das Bohrgestänge in die Weitere Spülungszusätze (Additive) sind: Tiefe gepumpt. Via Bohrmeissel reinigt sie Leichtzusätze, rheologische Zusätze, Korro- die Bohrlochsohle und strömt über den Ring- sionsinhibitoren, anorganische Zusätze, Bio- raum nach oben. Dort gelangt sie über die zide, Entschäumer, Tonstabilisatoren. Bohrspülungsrückleitung (flow line) in die Als Bohrspülungen bei Tiefbohrungen wer- Spülungsaufbereitung (Schüttelsiebe, Ent- den thixotrope Flüssigkeiten verwendet. sander, Entsilter, Spülungsbecken). Die Spü- Eine Spülung wird entsprechend dünnflüssi- lung hat im Bohrloch vielfältige Aufgaben: ger, wenn man sie bewegt. Bei Stillstand ver- • Hydraulische Stabilisierung des Bohr- festigen sie sich wieder. Ihre Zusammenset- lochs. zung und ihre rheologischen Eigenschaften
79 2-2014_geologi 2.06 12.02.15 15:21 Pagina 80
werden ständig den Bohrumständen und • Technische Rohrtouren, Zwischenverroh- den geologischen Gebirgseigenschaften rung: Zementation bis in vorhergehende angepasst. Die thixotrope Eigenschaft der Rohrtour oder bis zu Tage. Bohrspülung verhindert dabei im Falle von • Endverrohrung, Produktionsrohrtour: Pumpenstillständen das Sedimentieren des Evtl. mit Filterstrecke versehene Rohr- im Ringraum befindlichen Bohrkleins, was zu tour, zementiert oder frei. einem Festwerden und schlimmstenfalls zum • Verlorene Rohrtour, Liner: Wird nicht bis Verlust des Bohrstranges führen könnte. zutage geführt sondern in die letzte Ver- Mit der Zugabe von Bentoniten können die rohrung eingehängt. chemischen und die physikalischen Eigen- • Förderrohrtour, Tubbing: wird in Produk- schaften der Spülung beeinflusst werden. tionsrohrtour eingebaut und dient zu Insbesondere bilden Bentonite eine Gerüst- deren Schutz. struktur, die zum Wachstum eines Filterku- chens auf der Bohrlochwand führt. Auch Die Zementation der Futterrohre (Ringraum- Zusätze von Polymeren und Zellulose erge- zementation) soll folgende Aufgaben erfül- ben Filterkuchen mit erhöhter elastischer len: Abdichtung der Bohrlochwand (Rota et al. • Verankerung der Rohre im Gebirge durch 2007). Haftung bzw. mechanische Verkeilung von Die Eigenschaften der Spülung werden wäh- Zement an Rohrtour und Gebirge. rend den Bohrarbeiten laufend überwacht, • Abdichtung des Ringraumes gegen ein- damit Veränderungen erkannt und die Spü- dringende Fluide (Wasser, Sole, Gas) und lung entsprechend aufbereitet werden kann. Verhinderung des Eindringens dieser Flui- Eine optimale Spülung trägt stark zur Ver- de in benachbarte Horizonte oder nach besserung des Bohrfortschritts bei. übertage. In besonderen Fällen können salzgesättigte • Mechanischer Schutz der Verrohrung bei Spülung, Ölspülung oder Schaumspülung drückendem Gebirge (Ton, Salz, Gebirgs- eingesetzt werden (z. B. Bohren in Salz). spannungen). • Chemischer Schutz der Verrohrung vor 3.3 Verrohrung Korrosion durch aggressive Wässer.
Um das Bohrloch über längere Strecken zu 3.4 Blow Out Preventer stabilisieren, wird es abschnittsweise und ent- sprechend den geologischen und hydrauli- Ist beim Bohren mit erhöhten Formations- schen Bedingungen der durchbohrten drücken zu rechnen (Wasser, Öl, Gas) muss Gesteinsformationen teleskopartig mit Futter- die Bohrung schnell geschlossen werden rohren (casing) ausgebaut. Das Verrohrungs- können, damit ein Eindringen von Fluiden in schema hat sich nach den Anforderungen der das Bohrloch (Kick) kontrolliert werden Bohrung zu richten (siehe auch Fig. 2). kann und es nicht zu einem unkontrollierten Üblicherweise werden die aufeinanderfolgen- Ausbruch (Blow out) von Fluiden kommt. den Rohrtouren folgendermassen bezeichnet: Dazu wird ein Blow Out Preventer (BOP) auf • Standrohr: Wenige Meter tief, zur Absi- der letzten, zementierten Verrohrung aufge- cherung der obersten Lockergesteinszo- baut. Dieser ermöglicht, eine Bohrung ne, Schutz der Fundamente vor Unterspü- hydraulisch zu kontrollieren. Er besteht aus lung, dient als Führung. folgenden Komponenten: • Ankerrohrtour: Einzementierte Rohrtour • Ringpreventer (annular blow out preven- zur Aufnahme der Sicherheitsarmaturen ter); (BOP), Führung zur Einhaltung der vorge- • Backenpreventer (blind ram, shear ram, gebenen Bohrrichtung. pipe ram);
80 2-2014_geologi 2.06 12.02.15 15:21 Pagina 81
• Anlage zur hydraulischen Preventersteue- 4 Zur Hydrogeologie des tiefen rung (accumulator system); Untergrundes • Ausbruchverhütungssystem (choke and kill manifold). 4.1 Begriffe
3.5 Bohrloch-Havarien Grundwasser wird nach DIN 4049 definiert als «unterirdisches Wasser, das die Hohlräu- Trotz fachgerechtem Einsatz von gutem me der Erdrinde zusammenhängend ausfüllt Material kann es bei einer Tiefbohrung zu und dessen Bewegung ausschliesslich oder Havarien kommen. Typische Havarien kön- nahezu ausschliesslich von der Schwerkraft nen sein: und den durch die Bewegung selbst ausgelö- • Festwerden des Bohrgestänges/des Meis- sten Reibungskräften bestimmt wird.» Diese sels; naturwissenschaftlich-technische Definition • Bruch des Bohrgestänges; umfasst somit alle im Untergrund vorkom- • Bruch oder Festwerden der Verrohrung; menden Wässer und unterscheidet sich vom • Probleme beim Zementieren; Begriff «Grundwasser» wie er in der schwei- •Fremdkörper im Bohrloch; zerischen Gesetzgebung verwendet wird • gerissene Seile/Kabel (z. B. bei Bohrloch- (Kap. 2). messungen). Felsgrundwasser und Lockergesteinsgrund- wasser bilden zusammen das Grundwasser Massnahmen zur Beseitigung von Havarien im naturwissenschaftlich-technischen Sin- sind zum Beispiel: ne. Der Begriff Bergwasser oder Grubenwas- • Bei Festwerden: Bestimmung der Lokation ser wird typischerweise im Untertagbau (Dehnungsmessung), Freischlagen, Freivi- bzw. im Bergbau verwendet. In einem Tunnel brieren, Freiziehen mit Verrohrungsein- abfliessendes Bergwasser wird auch Tunnel- richtung, Wechsel der Spülung, Überboh- wasser genannt. ren, notfalls Abschrauben oder Abspren- Formationswasser oder Tiefengrundwasser gen des Gestänges → Bohrung ablenken. können als synonyme Begriffe verwendet • Beim Bruch des Bohrgestänges: Fangarbei- werden. In den Berichten der Nagra wird für ten mittels geeigneter Fangwerkzeuge: die Nordschweiz in der Regel der Begriff Fangdorn (tap), Fangglocke (overshot) etc. «Tiefengrundwasser» verwendet (Schmass- • Bei Fremdkörper im Bohrloch: Einsatz mann 1990, Schmassmann et al. 1992). Bei von Sohlenreinigungswerkzeugen: Mag- Lagerstättenwasser handelt es sich um Was- netfänger, Fangspinne, Fangvorrichtung ser, das sich natürlicherweise in einer Lager- (junk basket) etc. stätte befindet und durch die Förderung von Erdöl oder Erdgas zutage gefördert wird. Wir Eine erfahrene Bohrunternehmung kennt verwenden im Weiteren den Begriff Tiefen- den Umgang mit Havarien. Entsprechende grundwasser für Wasser aus Festgesteinen Vorgehensweisen sind bekannt und erprobt, des schweizerischen Mittellandes. das notwendige Material ist auf dem Bohr- platz vorhanden. Die Ursachen von Bohr- 4.2 Tiefengrundwasser im schweizerischen lochhavarien sind vielfältig (geologisch, Molassebecken technisch, operationeIl) und können, trotz z. T. aufwendigen Gegenmassnahmen, zum In der Molasse sind die obersten paar 100 m Verlust des Bohrlochs führen, was eine durch Ca-Mg-HCO3- und Na-HCO3-Wässer Ablenkung der Bohrung (side track) oder ein geprägt, während darunter zunehmend Na- Neuansetzen der Bohrung zur Folge haben Cl-Wässer zu erwarten sind. kann. Grundsätzlich ist mit zunehmender Tiefe
81 2-2014_geologi 2.06 12.02.15 15:21 Pagina 82
eine Zunahme der Mineralisation zu erwar- wässer der Molasse liegt in der Grössenord- ten, welche mit einer längeren Verweildauer nung von wenigen 100 bis um 1’000 mg/l. Es des Wassers im Untergrund einhergeht. handelt sich somit um Süsswasser. Gemäss einer Studie der Nagra (Schmass- In den mesozoischen Schichtreihen findet im mann 1990) können für die Molasse der süddeutschen Raum mit dem Abtauchen ins Nordschweiz drei Hauptwassertypen unter- Molassebecken nach unten rasch ein Wech- schieden werden, deren Abgrenzungen sel von Ca-SO4-HCO3- zu Na-Cl-Wässern statt. diskordant zu den geologischen Schichtab- In Tiefbohrungen wurden nördlich des folgen verlaufen. Von oben nach unten Bodensees verbreitet Na-Cl-Konzentration sehen sie wie folgt aus (Fig. 1): von 10−80 g/l festgestellt. Es wird angenom- • Ca-Mg-HCO3-Wässer mit verhältnismäs- men, dass diese Solen im Tertiär infolge tek- sig kurzer Verweilzeit (< 35 Jahre) im tonischer Bewegungen eingeschlossen wur- Untergrund, welche oberflächennah den (Bertleff et al. 1988). Der Sulfatgehalt meist in weniger als 100 m Tiefe anzutref- nimmt in der Regel mit der Tiefe verhältnis- fen sind. mässig wenig zu. • Na-HCO3-Wässer, welche in erster Linie In Benken wurden im Malm 10 g/l gelöste auf kaltzeitliche, pleistozäne Infiltration Stoffe gemessen. Im Trigonodus-Dolomit des zurückzuführen sind und im Raum St. Gal- Oberen Muschelkalkes wurde in 813−826 m len vermutlich bis in mehrere 100 m Tiefe Tiefe Wasser vom Ca-Mg-SO4-(HCO3)-Typ charakteristisch sind. angetroffen mit einer totalen Mineralisation • Na-Cl-Wässer, bei welchen es sich um mit von rund 2.4 g/l (Nagra 2001). In seinen infiltrierten Wässern verdünnte Forma- Hauptkomponenten ist in Benken das tionswässer marinen oder brackischen beprobte Wasser typisch für den Muschel- Ursprungs handelt. Sie bilden die tiefen kalk-Aquifer und vergleichbar mit anderen Wässer, welche nicht oder kaum in Wech- Muschelkalkwässern aus der Nordschweiz. selwirkung mit jüngerem Wasser stehen. Im Permokarbon wurden in der Schweiz von In grösseren Tiefen bestimmen in Na-Cl- der Nagra hochsaline Wässer durchbohrt Wässern die Na-Cl-Gehalte weitgehend (36−120 g/l in rund 1‘100−1‘420 m Tiefe) die Gesamtmineralisation. (Nagra 1989). Im Kristallin ist mit heterogenen Wässern Die Gesamtmineralisation der Tiefengrund- ohne eine gesetzmässige Zunahme der Sali-
Fig. 1: Verbreitung der Wassertypen im schweizerischen Molassebecken (Schmassmann 1990).
82 2-2014_geologi 2.06 12.02.15 15:21 Pagina 83
nität mit der Tiefe zu rechnen. In den Boh- beständiger zur Bohrung fliessen und rungen der Nagra der Nordschweiz sind gewonnen werden» (Wikipedia: Hydraulic Anzeichen erkennbar, dass die Chemie je Fracturing, 2014). nach Durchlässigkeit des Gesteins ändert. Diese Definition hat offensichtlich den Einsatz Demnach sind in weniger durchlässigen in der Kohlenwasserstoff(KW)-Industrie im Bereichen tendenziell höher mineralisierte Fokus. Jedoch ist darin auch der Begriff der Wässer zu erwarten (Kanz 1987). In den bes- «hydraulischen Stimulation» enthalten, wie er ser durchlässigen Bereichen sind Mischwäs- in der Tiefengeothermie verwendet wird. ser aus den überliegenden Sedimenten und In der derzeit laufenden Diskussion, auch in aus tieferliegenden Bereichen des Kristallins Fachkreisen, wird der Begriff «Fracking» als wahrscheinlich. In der Nagra-Bohrung Wei- Begriff für die unkonventionelle Erschlies- ach wurden in rund 2‘200−2‘300 m Tiefe Na- sung von KW gesehen, und die «hydrauli- Cl-Gehalte von 6.4−8.0 g/l und in Schafisheim sche Stimulation» als Methode in der Tiefen- in 1‘500−1‘900 m Tiefe 7.9−8.0 g/l gemessen geothermie. Aus unserer Sicht mag diese (Pearson et al. 1989). Hochsaline Tiefenwäs- Unterscheidung heute noch gelten. Es stellt ser sind auch aus Tiefbohrungen im Kristal- sich aber die Frage, ob mit der Entwicklung lin in Deutschland bekannt. So wurden in der in der Tiefengeothermie nicht auch hier der Kontinentalen Tiefbohrung in der Oberpfalz Einsatz von Additiven notwendig sein wird, in rund 4 km Tiefe 63 g/l (Möller et al. 1997) um erfolgreich künstliche Wärmetauscher und in Soultz-sous-Forêts 97.6 g/l (145 °C) zu erzeugen und diese effizient betreiben zu Gesamtmineralisation gemessen (Aquilina können. et al. 2000). Von der Geothermiebohrung St.Gallen GT-1 5.2 Hydraulic Fracturing zur wurde für das aus dem Malm geförderte Kohlenwasserstoffförderung Wasser eine Gesamtmineralisation von ca. 20 g/l rapportiert. Diese Technologie wurde erstmals in den 1940er Jahren von der Kohlenwasser- stoff(KW)-Industrie zur Erhöhung der Aus- 5 Hydraulic Fracturing beute von Erdgas und Erdöl aus konventio- nellen Lagerstätten eingesetzt, d. h. aus KW- 5.1 Der Begriff Hydraulic Fracturing Vorkommen in porös-permeablen, von (Fracking) undurchlässigen Barriere-Formationen abge- dichteten Speichergesteinen. Hydraulic Frac- Im Wikipedia ist der Begriff «Fracking» wie turing hat sich seitdem zu einer Schlüssel- folgt definiert: «Hydraulic Fracturing oder technologie zur Erschliessung von Erdgas kurz Fracking (von englisch to fracture «auf- und Erdöl aus relativ dichten Sandsteinen brechen», «aufreissen»; auch «Hydrofrack - oder karbonatischen Speichergesteinen ing», «Fraccing», «Fracing» oder «Frac Jobs» (sogenanntes Tight Gas) sowie aus Schiefern genannt, deutsch auch hydraulische Fraktu- (shale gas) entwickelt. Weltweit sind inzwi- rierung, hydraulisches Aufbrechen, hydrau- schen rund drei Millionen Fracking-Massnah- lische Risserzeugung oder auch hydrauli- men in Bohrungen durchgeführt worden. In sche Stimulation) ist eine Methode zur Deutschland wird die Fracking-Technologie Erzeugung, Weitung und Stabilisierung von seit 1961 – ohne messbare Beeinträchtigun- Rissen im Gestein einer Lagerstätte im tiefen gen der Umwelt – zur Steigerung der Produk- Untergrund, mit dem Ziel, die Permeabilität tionsrate von weniger ergiebigen KW-Lager- (Durchlässigkeit) der Lagerstättengesteine stätten und insbesondere zur Gewinnung von zu erhöhen. Dadurch können darin befindli- Tight Gas eingesetzt (Deutsche Akademie der che Gase oder Flüssigkeiten leichter und Technikwissenschaften 2014).
83 2-2014_geologi 2.06 12.02.15 15:21 Pagina 84
5.3 Hydraulische Stimulation in der den, wird der Einsatz von sogenannten Tiefengeothermie Stützmitteln (Proppants) als Möglichkeit dargestellt (GtV - BV 2012). In derselben Publikation (Deutsche Akade- Bei den bis heute in Deutschland durchge- mie der Technikwissenschaften 2014) wird führten hydraulischen Stimulationen wur- die hydraulische Stimulation in der Tiefen- den Drücke von 100−400 bar (am Bohrloch- geothermie als «… vergleichsweise junges, kopf) angewandt. Es wird davon ausgegan- inzwischen aber weltweit etabliertes…» Ver- gen, dass mit hydraulischer Stimulation fahren für die Erschliessung von Erdwärme- horizontale Risse von mehreren hundert Reservoiren im tieferen Untergrund zur Metern Länge erzeugt werden können. Energiegewinnung (Tiefengeothermie) Bei der Geothermiebohrung Basel wurde bei bezeichnet. Es wird weiter ausgeführt, dass der hydraulischen Stimulation ein maxima- dazu in der Regel keine chemischen Additive ler Kopfdruck von 300 bar bei einer Fliessra- verwendet würden. te von rund 55 l/s während rund eines hal- Auf Additive kann verzichtet werden, da ben Tages angewandt. Insgesamt wurden davon ausgegangen wird, dass bei der Öff- während der gesamten hydraulischen Sti- nung bestehender Klüfte bzw. bei der Entste- mulation in 6 Tagen 11‘600 m3 Wasser ohne hung neuer Risse die auf Rissflächen wirken- Additive verpresst. Bei den derzeit in Pla- de Scherspannung zu einem Versatz entlang nung befindlichen EGS-Projekten der Geo- der Rissfläche führt, was bewirkt, dass sich energie Suisse AG wird davon ausgegangen, die raue Rissfläche nicht mehr schliesst dass bei der Erzeugung eines Wärmetau- («self-propping Effekt», GtV - BV 2012). Wenn schers eine Fläche von insgesamt ca. 4 km2 das Gestein nur geringe Scherspannungen erschlossen werden muss. Bei einer theore- aufweist oder nur Zugrisse parallel zur tischen Rissgrösse von 200 × 200 m ent- Hauptspannung erzeugt wurden, so dass spricht dies 100 Rissebenen. kein Versatz der Rissflächen zu erwarten ist, und die Risse sich wieder schliessen wür-
Fig. 2: Beispielhaftes Ver- rohrungsschema einer Horizontalbohrung (nicht massstäblich). TD: Länge der Bohrung gemessen vom Bohransatzpunkt (to- tal depth); TVD: Vertikaler Abstand des Bohrlochtief- sten zum Bohransatz- punkt (true vertical depth); Massangaben: 1 ft = 0.3048 m; 1 in. = 2.54 cm (aus Meiners et al., 2012, nach Rohwer et al. 2006).
84 2-2014_geologi 2.06 12.02.15 15:21 Pagina 85
5.4 Ablauf einer hydraulischen Stimulation / entsteht. Kreiselpumpen kommen zum Fracking-Massnahme Mischen und Befördern der Fracking-Fluide bei niedrigen Drucken zum Einsatz. Hoch- Nachdem eine Bohrung den entsprechenden druck-Verdrängerpumpen befördern das fer- Zielbereich erreicht hat, wird diese vollstän- tig gemischte Fluid (Suspension) in das dig verrohrt und zementiert (Fig. 2). Mit der Bohrloch. Verrohrung und der Zementation wird sichergestellt, dass aus der Bohrung keine Der Ablauf einer Frack-Massnahme gliedert Fluide in die Formationen gelangen können sich in folgende Phasen: (und umgekehrt) und dass ausserhalb der 1. Säure-Phase: Verdünnte Säure (HCl) dient Bohrung im Ringraum keine Fluidzirkulation der Säuberung des Bohrlochs von zwischen verschiedenen Formationen oder Zementrückständen im Bereich der perfo- nach Übertag möglich ist. Der Erfolg dieser rierten Verrohrung sowie dem Lösen von Massnahmen muss mit geeigneten Mitteln Karbonaten und der Erweiterung und geprüft werden (Drucktest, cased hole log- dem Aufbrechen bereits bestehender ging). Klüfte im Nahbereich der Bohrung. Der folgende Ablauf einer hydraulischen Sti- 2. Füll-Phase (pad stage): Frack-Fluid, u.a. mulation / Fracking-Massnahme ist nach mit reibungsmindernden Zusätzen, wird Meiners et al. 2012 beschrieben. ohne Stützmittel unter stufenweise erhöh- tem Druck und Verpressraten einge- Perforation: Ein erster Schritt für eine presst. Die Rissbildung wird dadurch ein- hydraulische Stimulation ist die abschnitts- geleitet. weise Perforation der Verrohrung im Zielbe- 3. Stütz-Phase (prop stage): In dieser Phase reich. Dabei kommt üblicherweise ein Hohl- wird nach eingeleiteter Rissbildung dem ladungsperforator zum Einsatz. Dieser ent- Fluid unter stufenweise erhöhter Konzen- hält Aussparungen, welche mit Sprengstoff tration Stützmittel in Suspension zugege- und Hohlladungen bestückt sind. Bei der ben. Aufgrund der Infiltration von Fluid in Zündung durchschlagen Projektile mit das Gestein erhöht sich die Konzentration hoher Geschwindigkeit die Rohrtour und der Suspension, während sie durch den den Zement und dringen in das Gestein ein. Riss strömt, da das Stützmittel in der Die Energie wird durch das konische Gehäu- Suspension verbleibt. se in einer Richtung konzentriert und durch 4. Ziel ist ein gleichmässiges Füllen des Ris- die resultierende Verformung entsteht ein ses mit dem Stützmittel. Die Suspension Projektil aus verflüssigtem Metall. Auf diese mit geringer Stützmittelkonzentration, Weise werden mehrere Perforationen gleich- mit welcher die Stütz-Phase eingeleitet zeitig pro Meter erzeugt. Um die Gesteins- wird, legt die längste Strecke im Riss bruchstücke und Überreste des Projektils zurück und verliert somit am meisten Flu- aus der Perforation zu entfernen, wird das id durch Infiltration in das Gestein. Zum Perforieren meist unter Spülungsdrücken Ende der Stützphase wird Suspension unterhalb des Porendrucks der Formation hoher Konzentration verpresst. durchgeführt. 5. Spül-Phase (flush stage): Diese Phase dient dazu, in der Bohrung verbliebenes Fracking: Grundsätzlich wird beim Fracken Stützmittel in den Riss zu spülen. Dazu abschnittsweise ein Fluid mit einer höheren wird Wasser verwendet. Rate in das Bohrloch gepumpt als durch Danach wird das Einpressen von Fluid been- Infiltration in das Gestein die Bohrung wie- det und die Bohrung für einige Zeit ver- der verlässt. Dadurch erhöht sich der Druck schlossen (shut-in). Durch die anhaltende bis zu dem Punkt, an dem ein Riss im Gestein Infiltration in das Gestein sinkt der Druck all-
85 2-2014_geologi 2.06 12.02.15 15:21 Pagina 86
mählich ab und der erzeugte Riss schliesst von maximal 588 m (Barnett Shale). Nur sehr sich, soweit es das Stützmittel zulässt. Der wenige hydraulische Risse können sich Zusatz und der Einsatz von Frack-Fluiden zufolge über mehr als 500 m ausbreiten, da erfolgen lagerstättenspezifisch und werden geschichtete Sedimentgesteine eine natürli- an den Frackverlauf angepasst. che Barriere bilden (Davies et al. 2012 zitiert Der beim Fracking maximal angewendete in Dannwolf et al. 2014). Fracs (Risse) aus Druck richtet sich nach den Spannungsver- mehr als 1‘000 m Tiefe bis an die Oberfläche hältnissen im Gebirge, die unter anderem sind daher nicht möglich. von der Tiefenlage abhängig sind. 5.6 Fracking-Fluide 5.5 Rissbildung Bei der Schiefergas-Gewinnung wird in die Entscheidend für die Orientierung der Riss - im Gebirge erzeugten Risse mit dem Frack- ausbreitung ist das im Reservoir vorherr- Fluid im Allgemeinen Stützmittel einge- schende Spannungsfeld. Die Rissausbrei- bracht (sog. Proppants, z. B. Quarzsand tung erfolgt bevorzugt senkrecht zur Rich- oder keramische Partikel). Diese halten die tung der geringsten Spannung. Risse gegen den Gebirgsdruck offen und sor- Gemäss einer amerikanische Studie von 44 gen dafür, dass die geschaffenen Wegsamkei- Regionen, in denen Horizontalbohrungen ten auch in der Förderphase erhalten und mit Fracking durchgeführt wurden, konnte damit dauerhaft bessere Fliessbedingungen eine Rissausbreitung im Untergrund von 12 für das Erdgas zur Förderbohrung hin beste- bis 295 m aufwärts und 10 bis 190 m abwärts hen bleiben. festgestellt werden (Maxwell 2011, zitiert in Weitere dem Frack-Fluid zugesetzte Additive Dannwolf et al. 2014). Eine weitere Studie haben u. a. den Zweck, den Transport des von 1‘170 Bohrungen in den USA zeigte eine Stützmittels in die Risse zu gewährleisten, hydraulische Rissausdehnung nach oben Ablagerungen, mikrobiologischen Bewuchs,
Fig. 3: Rissausdehung in «Barnett Shales», Texas (Fisher 2010). Mit mikroseismischen Messverfahren bestimmte Ausdehnung von Fracrissen in den Barnett Shales in the Fort Worth Basin in Texas (rund 2‘400 Fracs).
86 2-2014_geologi 2.06 12.02.15 15:21 Pagina 87
die Bildung von Schwefelwasserstoff und ein 6 Risiken der Untergrunderschlies- Quellen der Tonminerale im Frack-Horizont zu sung und -nutzung verhindern, Korrosion zu vermeiden und die Fluidreibung bei hoher Pumpleistung zu mini- Im Zusammenhang mit der derzeit intensi- mieren (Meiners, et al. 2012). Neben Stützmit- ven Diskussion zum Thema Fracking werden tel sind weitere Additive von Frack-Fluiden: die Risiken der Methode im Zusammenhang Ablagerungshemmer, Biozide, Gelbildner, mit der Schiefergasförderung in verschiede- Hochtemperaturstabilisatoren, Kettenbre- nen Studien und Berichten dargestellt und cher, Korrosionsinhibitoren, Lösungsmittel, erläutert. Im Folgenden wird insbesondere pH-Regulatoren, Quervernetzer, Reibungsver- auf die Risiken im Untergrund eingegangen. minderer, Säuren, Schwefelwasserstofffänger, Detaillierte Darstellungen der Umweltrisiken Tenside/Netzmittel, Tonstabilisatoren. Wie finden sich in umfassender Form in den bei- bei der Bohrspülung haben die Fracking-Flui- den Berichten des deutschen Umwelt- de vielfältige Eigenschaften aufzuweisen, bundesamtes, des Bundesministeriums für damit sichergestellt ist, dass die Fracking- Umwelt, Naturschutz und Reaktorsicherheit Massnahme sicher abläuft und die gewünsch- (Meiners et al. 2012 und insbesondere Dann- te Wirkung erzielt wird. wolf et al. 2014). Moderne Fracking-Fluide bestehen aus ca. Bezüglich der Risiken von Tiefbohrungen 70% Wasser und 29% Stützmittel. Die Additi- und Fracking werden verschiedene Wir- ve machen in Deutschland einen Anteil von kungspfade analysiert (Fig. 4): Schadstoff- ca. 1% aus. Als Additive stehen dabei etwa einträge von der Oberfäche (0), Schadstoff- 50 Inhaltsstoffe zur Verfügung, von denen aufstiege und -ausbreitung ausgehend von keiner die Wassergefährdungsklasse 1 (WGK der Bohrung (1), Wirkungspfade entlang von 1 = schwach wassergefährdend) übersteigt. geologischen Störungen (2) und flächenhaf- Für die Zubereitung eines Frack-Fluids wer- te, diffuse Aufstiege bzw. deren laterale Aus- den in der Regel 5 bis 15 dieser Stoffe ver- breitung durch geologische Schichten ohne wendet (Deutsche Akademie der Technik- bevorzugte Wegsamkeiten (3). wissenschaften 2014). Trotz rund drei Millionen Frac-Operationen Das eingesetzte Fluidvolumen pro Frackpha- weltweit gibt es keine Beispiele von Fracs in se richtet sich nach den lokalen Gegebenhei- Schiefergas-Fördergebieten oder in der Tie- ten. Pro Frackphase betragen die eingesetz- fengeothermie, bei denen künstliche Risse ten Volumen in der Grössenordnung von die Oberfläche oder Trinkwasserhorizonte 1‘000−1‘500 m3, pro Bohrung sind es Volu- erreicht hätten (Deutsche Akademie der men von 10‘000−20‘000 m3. Technikwissenschaften 2014). Verunreini- Die Stabilität von modernen Fracking-Flui- gungen von Oberflächen- oder Grundwasser den ist in mittleren Tiefen bei mittleren Tem- sind jedoch aufgetreten, wobei der Grund peraturen gewährleistet. Bei hohen Tempe- beim Transport, unsachgemässem Umgang raturen, wie sie in der Tiefengeothermie auf dem Bohrplatz oder bei defekten Boh- angestrebt werden, bestehen diesbezüglich rungen (Leckagen in der Verrohrung, Ring- noch keine Erfahrungen. Fracking-Fluide raumzementation) zu suchen ist, bezie- basierend auf Stickstoff (N2), Kohlenstoffdio- hungsweise im Zusammenhang mit der Ent- xid (CO2) oder Propan (C3H8) sind möglich, sorgung von Flowback steht (Transport, in Tight Reservoirs erprobt und bieten Handling). Die bei der Gewinnung von Erd- gegenüber wasserbasierten Fracking-Flui- gas aus konventionellen und unkonventio- den gewisse Vorteile, sind aber in der Schie- nellen Lagerstätten anfallenden Formations- fergasnutzung nicht im industriellen Einsatz. wässer und Flowback werden in Deutsch- land derzeit primär in sog. Versenkbohrun- gen/Disposalbohrungen entsorgt.
87 2-2014_geologi 2.06 12.02.15 15:21 Pagina 88
Die seismologische Gefährdung bei der • Bei der Tiefenerkundung und -erschlies- Gewinnung von Schiefergas ist gering. Dies sung muss verhindert werden, dass Tie- gilt insbesondere für die Betriebsphasen fengrundwässer aufsteigen und das nutz- Bohren, Fracken, Produktion und Rückbau. bare Grundwasser und den Boden verun- Bei der Betriebsphase Reinjektion von Flow- reinigen können. back/Produktionswasser, also bei Verpress- • Bei der Schiefergasnutzung ist das Thema bohrungen ist jedoch eine seismologische der induzierten Seismizität vorwiegend Gefährdung grundsätzlich nicht auszu- bei Injektionsbohrungen von Bedeutung. schliessen (Dannwolf et al. 2014). In Prague, • Bei der Tiefengeothermie, insbesondere bei Oklahoma, kam es in einem Gebiet mit zahl- EGS, ist die induzierte Seismizität während reichen Reinjektionsbohrungen zu einer der Erschliessung und der Nutzung des Zunahme der Erdbebenaktivitäten, wobei Reservoirs ein wichtiges Thema. auch Schadenbeben zu verzeichnen waren •Die bei einer Geothermie-Tiefbohrung ein- (USGS 2014). Schadenbeben, die dem eigent- gesetzten Fluide (Spülung) sind mit den- lichen Fracking zugeordnet werden können, jenigen in der KW-Industrie vergleichbar sind weltweit keine bekannt. bzw. identisch. • Sowohl beim Schiefergas wie auch bei der Für die Tiefengeothermie gelten grundsätz- Tiefengeothermie werden vom selben lich dieselben Ansätze wie bei der Kohlen- Standort aus mehrere, abgelenkte Bohrun- wasserstoffexploration und -produktion im gen (cluster) gemacht. Der Landverbrauch Allgemeinen bzw. bei der Schiefergasnut- pro Anlage für beide Technologien dürfte zung im Speziellen. Es gibt grosse Ähnlich- somit etwa in derselben Grössenordnung keiten bei beiden Gebieten, jedoch auch liegen. deutliche Unterschiede. Wegen der ver- • Auch der Wasserverbrauch für das Frack- gleichsweise geringen Erfahrung in der Tie- ing/die Stimulation dürfte sich bei der fengeothermie gibt es aber auch noch zahl- Schiefergas-Nutzung und der Tiefengeo- reiche offene Fragen. Wichtigste Aspekte thermie etwa in denselben Dimensionen sind: bewegen.
Fig. 4: Schematische Dar- stellung potenzieller Wir- kungspfade (Meiners, et al. 2012).
88 2-2014_geologi 2.06 12.02.15 15:21 Pagina 89
• Bei der Erschliessung und Nutzung von 7 Chancen der Untergrunderschlies- Tight Gas dürfte der Stimulationsaufwand sung und -nutzung und damit der Wasserverbrauch geringer sein als bei Schiefergas. 7.1 Potenziale • Die Tiefenlagen für die Tiefengeothermie, insbesondere für künftige EGS-Systeme, In der Kohlenwasserstoffindustrie sind dürften grösser sein als z. B. bei der Schie- Ressourcen nachgewiesene, aber derzeit fergasnutzung. technisch und/oder wirtschaftlich nicht • In der Tiefengeothermie (EGS) wurde bis gewinnbare sowie nicht nachgewiesene, heute für die hydraulische Stimulation aber geologisch mögliche, künftig gewinnba- praktisch ausschliesslich Wasser einge- re Energierohstoffmengen. Reserven sind setzt. nachgewiesene, zu heutigen Preisen und mit • Der künftige Einsatz von Additiven bei heutiger Technik wirtschaftlich gewinnbare hydraulischen Stimulationen in der Tiefen- Energierohstoffmengen. geothermie kann nicht ausgeschlossen Bei «possible reserves» besteht eine Gewinn- werden. wahrscheinlichkeit von mindestens 10%, bei • Bei der Nutzung der Tiefengeothermie «probable reserves» eine solche von minde- dürften Fragen wie Korrosionsschutz, Aus- stens 50%. Für «proved reserves» muss eine fällungen, Bakterienwachstum etc. die Wahrscheinlichkeit für deren Gewinnung Behandlung des zirkulierenden Fluids von 90% gegeben sein. Der Ausdruck «pro- erfordern. ved reserves» beinhaltet sowohl die bereits • Die notwendige Fläche eines geothermi- produzierten wie auch die noch nicht produ- schen Wärmetauschers ist erheblich und zierten Reserven. mit Drainageflächen in der Schiefergasnut- In der Geothermie ist das technische Poten- zung vergleichbar. zial jene Energiemenge, die mit bekannten • Wärmetauscher für EGS-Systeme der Tie- Methoden nutzbar ist. In Anbetracht der fengeothermie werden voraussichtlich noch jungen Technologie wurde entspre- vorwiegend im kristallinen Grundgebirge chend dieser Ausdruck in Anführungszei- erstellt werden (Schweiz). Dieses besitzt chen gesetzt. andere felsmechanische Eigenschaften als Formationen, die sich für die Produktion 7.2 Potenzial Erdgas von Schiefergas eignen. Die aktivste Phase der Erdöl- und Erdgasexplo- Die Energiedichte bei der Nutzung der Geo- ration in der Schweiz war in den Jahren 1960 thermie ist im Vergleich zur Energiedichte bis 1989. Verschiedenste Seismikkampagnen bei der Gasnutzung vergleichsweise gering. wurden durchgeführt und insgesamt 18 Tief- Entsprechend könnte der «ökologische foot- bohrungen nach Erdöl und Erdgas abgeteuft print» im Untergrund bei der Tiefengeother- (Lahusen & Wyss 1995). Mangelnde Erfolge in mie pro produzierter Kilowattstunde ver- dieser Zeit hatten zur Folge, dass die Kohlen- gleichsweise grösser sein als bei der Gaspro- wasserstoffexploration in der Schweiz im Ver- duktion. Demgegenüber ist der CO2-Ausstoss gleich zum Süddeutschen Raum vergleichs- pro kWh bei einem Tiefengeothermiekraft- weise wenig intensiv betrieben wurde. werk um ein Vielfaches kleiner als bei einem In zahlreichen Tiefbohrungen wurden Erdöl- Gaskraftwerk. und Erdgasindikationen festgestellt. Einzig aus der Bohrung Entlebuch-1 (1980) konnte in den Jahren 1985−1994 74.3 Mio. Kubikme- ter Gas gefördert und in die Transitgaspipe- line eingespeist werden.
89 2-2014_geologi 2.06 12.02.15 15:21 Pagina 90
Die Resultate dieser KW-Exploration in der porosity/low permeability» Reservoiren Schweiz lassen sich wie folgt zusammenfas- (Tight Gas) oder von tiefen Erdgaslagerstät- sen (Brink et al. 1992): ten im Bereich der alpinen Decken nicht wei- • Reife Muttergesteine sind vorhanden. ter bearbeitet (Lahusen & Wyss 1995). • Migration hat stattgefunden. Dank neuer Technologien in der KW-Explo- • Fallenstrukturen sind vorhanden (kom- ration und der nicht nachlassenden Nachfra- pressives Regime). ge nach Energie in der Schweiz im Kontext • Reservoirhorizonte sind vorhanden, der dynamischen Entwicklung auf dem Ener- jedoch ist die Reservoirqualität eher giesektor in Europa und der Welt ist das The- bescheiden. ma einheimischer Ressourcen nach wie vor Die Gas-Reserven (proved reserves?) wur- aktuell. Neuste Schätzungen zeigen, dass den auf ca. 0.1 Mrd. Kubikmeter Gas unter dem mittleren und dem südlichen geschätzt, etwas mehr, als in Entlebuch schweizerischen Mittelland ungefähr 50−150 gefördert worden war. Dass Erdgas im Mia. Kubikmeter förderbares Schiefergas schweizerischen Untergrund vorhanden ist, vorhanden sein könnten (Leu 2014). In Rela- lässt sich auch aufgrund der zahlreichen tion zum heutigen jährlichen Gaskonsum oberflächennahen Erdgasindikationen fest- der Schweiz von ca. 3.5 Mia. m3 ist dies eine stellen (Fig. 5). signifikante Ressource. Für Tight Gas liegt Auch der kurze Gas-Fördertest an der Geo- das Potenzial in der Grössenordnung von thermiebohrung St.Gallen GT-1 war mit über 150−300 Mia. m3, für Kohleflözgas liegen kei- 5‘000 m3 pro Stunde sehr eindrücklich. Die ne Zahlen vor (Leu, mündl. Mitt). Zum Ver- initiale Förderrate in Entlebuch (nach dem gleich: 1 Mia. m3 Erdgas entsprechen einer Produktionstest, im ersten Jahr der Produk- Energie von rund 10‘000 GWh, was ca. einem tion) lag bei ca. 3‘500 m3 pro Stunde. Drittel des heutigen jährlichen Gasver- brauchs in der Schweiz entspricht. Es ist Aufgrund tiefer Erdgaspreise kam die Erd- abzuklären, ob und in welchem Ausmass die- gasexploration Anfang der 90er Jahre prak- se Potenziale nutzbar sind. tisch zum Erliegen. Auch wurden «unkon- ventionelle» Projekte wie die Gasproduktion aus Kohleflözen, die Entwicklung von «Iow
Tab. 1: Potenziale von Kohlenwasserstoffen und geothermischer Energie.
90 2-2014_geologi 2.06 12.02.15 15:21 Pagina 91
7.3 Potenzial Tiefengeothermie gengrösse von 5 MWel, eine Dimension, wie dies für Basel oder St.Gallen angedacht war, Eine Studie des Paul Scherrer Instituts wären dies 27 Anlagen, wobei dazu jeweils (Hirschberg et al. 2005) schätzt für die 2−3 Bohrungen notwendig sind. Schweiz in 3−7 km Tiefe ein theoretisches Bis 2050 wird in der Energiestrategie von der Potenzial von 15‘900‘000 TWhth. Bei einem Geothermie eine Stromproduktion von 4‘400 Gewinnungsfaktor von 4% und, je nach Tie- GWh/a erwartet, was einer Leistung von 550 fenlage bzw. Temperaturniveau, einem elek- MW entspricht. Bei 5 MW-Anlagen wären trischen Wirkungsgrad von 10−14% lässt dies 110 Anlagen. Sollten mit zunehmender sich daraus ein «technisches» Potenzial von Reife der Technologie in Zukunft auch grös- 82‘500 TWhe abschätzen. Bei einem Strom- sere Anlagen möglich sein, würde sich die verbrauch in der Schweiz von rund 60 TWhe Anzahl der (Oberflächen-)Anlagen reduzie- pro Jahr ist dies eine bedeutende Ressource. ren, nicht jedoch die Anzahl der für diese Die in der Energiestrategie des Bundes vor- thermische Leistung notwendigen Bohrun- genommenen Schätzungen für die Geother- gen. mie beziehen sich nicht auf die effektiv vor- Es ist davon auszugehen, dass die an die handene Ressource, sondern auf einen mög- Geothermie gestellten Erwartungen nur lichen Zuwachs und somit auf das erfüllt werden können, wenn es gelingt, die Wachstum der Branche von ca. 10% pro Jahr. EGS-Technologie in einem entsprechenden Bis 2035 wird eine Stromproduktion von Ausmass zu entwickeln. Dazu müssen eben- 1‘100 GWh/a erwartet. Dies entspricht einer falls die Kosten erheblich gesenkt werden, installierten Leistung von ca. 135 MW (zum was nur durch das Abteufen von grossen Vergleich: im KKW Mühleberg ist eine Leis - Serien von Bohrungen möglich sein wird tung von 450 MW installiert). Bei einer Anla- (economies of scale).
Fig. 5: Erdöl- und Erdgasindikationen in der Schweiz. An der Oberfläche, in Tunnels, untiefen Bohrungen (‹ 400 m) und Tiefbohrungen gibt es zahlreiche Hinweise auf Erdöl und Erdgas in der Schweiz.
91 2-2014_geologi 2.06 12.02.15 15:21 Pagina 92
8 Schlussbemerkungen nicht erheblich und können geregelt werden. Die Entwicklung beider Technologien dürfte In der Energiestrategie 2050 des Bundes für beide wichtige Synergien bringen. spielen neben Energieeffizienz und neuen Für die Branche braucht es klare, verlässli- erneuerbaren Energien u. a. auch Gaskraft- che Regeln, die auf der Basis wissenschaft- werke eine Rolle. Weltweit nimmt die Nach- licher Erkenntnisse und Erfahrungen sach- frage nach Energie zu. Daher ist es für die lich fundiert sind. Unnötige Hürden und Schweiz wichtig, die Frage nach der künfti- Erschwernisse erhöhen die Kosten einer gen Energieversorgung, auch aus eigenen Technologie und vermindern somit deren Quellen, breit zu diskutieren. Durch neue Potenzial. Die Öffentlichkeit ist über die Methoden in der Untergrunderkundung Chancen und Risiken klar und transparent scheinen sich für die Schweiz Möglichkeiten zu informieren. zu eröffnen, eigene Energieressourcen zu Das Thema der Untergrunderkundung und erkunden und zu erschliessen. -nutzung muss über die weltanschaulichen In Anbetracht der sehr grossen vorhande- Grenzen hinweg diskutiert werden. Die nen Potenziale an Erdgas und Geothermie im Schweiz hat Geologinnen und Geologen mit Untergrund müssen diese untersucht wer- guten Kenntnissen über den tiefen Unter- den. Dazu braucht es neben Forschung an grund und über die Methoden, die Energie den Hochschulen insbesondere auch kon- aus der Tiefe zu gewinnen. Sie können zur krete Projekte: Seismische Untersuchungen Frage der Energiezukunft der Schweiz einen und Tiefbohrungen. Damit kann abgeklärt kompetenten und wichtigen Beitrag leisten. werden, welche Rolle diesen beiden Energie- rohstoffen in Zukunft zukommen kann. Dazu sind aber auch unternehmerischer Weitblick und Innovationsgeist notwendig. Durch die medial geführte Diskussion über das Fracking ist nicht nur die Ressource Erd- gas in Verruf geraten, sondern indirekt auch die Zukunft der Tiefengeothermie in Frage gestellt. Die Wortklaubereien über Fracking in der Schiefergasnutzung und hydraulische Stimulation in der Geothermie sind dazu wenig hilfreich. Spitzfindige Argumentatio- nen sind in der Öffentlichkeit kaum zielfüh- rend. Jede Erschliessung und Nutzung des tiefen Untergrundes stellt einen Eingriff in den Untergrund dar. Mannigfaltige Erfahrungen zeigen, dass es möglich ist, ohne den Schutz unserer Trinkwasserressourcen (Grundwas- ser, Quellen und Oberflächengewässer, Seen) zu beeinträchtigen und ohne Gefähr- dung für Menschen und Infrastruktur, sowohl Erdgas und als auch Geothermie zu erschliessen und zu nutzen. Allfällige Nut- zungskonflikte im Untergrund zwischen einer Gasexploration und -produktion und der Tiefengeothermie sind in der Schweiz
92 2-2014_geologi 2.06 12.02.15 15:21 Pagina 93
Literatur Kanz, W. 1987: Grundwasserfliesswege und Hydro- geochemie in tiefen Graniten und Gneisen. Aquilina, L., Genter, A., Elsass, P. & Pribnow, D. Geol. Rundschau , 76, 265−283. 2000: Evolution of fluid circulation in the Rhine Lahusen, P H. & Wyss, R. 1995: Erdöl- und Erdgas- Graben: Constraints from the chemistry of exploration in der Schweiz: Ein Rückblick. Bull. present fluids. Hydrogeology of crystalline schweiz. Ver. Petroleum-Geol. u. -lng. 62/141, Rocks. Kluwer Academic Publishers, Stras- 43−72. bourg, France. pp. 117−203. Leu, W. 2014: Erdöl-Erdgasexploration in der Bertleff, B., Joachim, H., Koziorowski, G., Leiber, J., Trendwende: Potenzial der unkonventionellen Ohmert, W., Prestel, R., Stober, I., Straygle, G., Ressourcen in der Schweiz und Europa – Villinger, E. & Werner, J. 1988: Ergebnisse der Anstrengungen und Kontroversen. Bull. angew. Hydrogeothermiebohrungen in Baden-Wür- Geol. 19/1, 29−32. temberg. Jh. Geol. Landesamt Baden-Würtem- Meiners, H. G., Denneborg, M., Müller, F., berg, 30, 27−116. Bergmann, A., Weber, F.-A., Dopp, E., Hansen, Brink, H. J., Burri, P., Lunde, A. & Winhard, H. 1992: C., Schuth, C., Buchholz, G., Gassner, H., Sass, Hydrocarbon habitat and potential of Swiss and I., Homuth, S. & Priebs, R. 2012: German Molasse Basin: A comparison. Eclogae Umweltauswirkungen von Fracking bei der geol. Helv , 85/3, 715−732. Aufsuchung und Gewinnung von Erdgas aus Bundesverfassung 1999: Bundesverfassung der unkonventionellen Lagerstatten – Risikobe - schweizerischen Eidgenossenschaft, 18. April wertung, Handlungsempfehlungen und 1999. Evaluierung bestehender rechtlicher Regelun- BUWAL 2004: Wegleitung Grundwasserschutz. gen und Verwaltungsstrukturen. Dessau: Bun- Voll zug Umwelt, Bundesamt für Umwelt, Wald desministerium für Umwelt, Naturschutz und und Landschaft, Bern. Reaktorsicherheit; Umweltbundesamt. Dannwolf, U., Heckelsmüller, A., Steiner, N., Rink, C., Möller, P., Weise, S. M., Althaus, E., Bach, W., Behr, Weichgrebe, D., Kayser, K., Zwafink, R., Rosen- H., Borchardt, R., Brauer, K., Drescher, J., winkel, K.-H., Fritsche, U. R., Fingerman, K., Erzinger, J., Faber, E., Hansen, B. T., Horn, E. Hunt, S., Rüter, H., Donat, A., Bauer, St., Runge, E., Huenges, E., Kämpf, H., Kessels, W., K. & Heinrich, S. 2014: Umweltauswirkungen von Kirsten, T., Landwehr, D., Lodemann, M., Fracking bei der Aufsuchung und Gewinnung von Machon, L., Pekdeger, A., Pielow, H. U., Reutel, Erdgas – insbesondere aus Schiefergaslager- C., Simon, K., Walther, J., Weinlich, F. H. & Zim- stätten. http://www.umweltbundesamt.de/pub- mer, M. 1997: Paleofluids and Recent fluids in likationen/umweltauswirkungen-von-fracking- the upper continental crust: Results from the bei-der-aufsuchung, Zugriff 5. Oktober 2014. German Continental Deep Drilling Program Deutsche Akademie der Technikwissenschaften (KTB). Journal of Geophysical Research , 102, 2014: Hydraulic Fracturing – eine Technologie in B8, 18233−18254. der Diskussion. http://www.acatech.de/filead- Nagra 2001: Sondierbohrung Benken, Unter- min/user_upload/Baumstruktur_nach_Web- suchungsbericht. Nagra NTB 00-01. site/Acatech/root/de/Projekte/Laufende_Pro- Nagra 1989: Sondierbohrung Weiach, Unter- jekte/Hydraulic_Fracturing/Hydraulic-Fractur- suchungsbericht. Nagra NTB 88-08. ing-Bericht-aus-dem-Projekt.pdf, Zugriff 8. Pearson, F. J., Locama, J. L. & Scholtis, A. 1989: Oktober 2014 von www.acatech.de. Chemistry of waters in the Böttstein, Weiach, Fisher, K. 2010: Data Confirm Safety Of Well Fractur- Riniken, Schafisheim, Kaisten and Leuggern ing. http://www.halliburton.com/public/pe/con- boreholes. Nagra NTB 86-19. tents/Papers_and_Articles/web/A_through_P/A Rota, A., Macek, A. & Wyss, R. 2007: Technik für OGR%20Article-%20Data%20Prove%20Safe- tiefe Bohrungen. (SIA, Hrsg.) Tec21, 133/11, ty%20of%20Frac.pdf, Zugriff 10. Oktober 2014. 23−29. Gewässerschutzgesetz 1991: Bundesgesetz über den Schmassmann, H. 1990: Hydrochemische Synthese Schutz der Gewässer (Stand am 1. Juni 2014). Nordschweiz: Tertiär- und Malm-Aquifere. GtV - BV (2012): Hintergrundpapier zur Stimulation Nagra NTB 88-07. geothermischer Reservoire. Von www.geother- Schmassmann, H., Kullin, M. & Schneemann, K. mie.de: http://www.geothermie.de/filead- 1992: Hydrochemische Synthese Nordschweiz: min/useruploads/Service/Publikationen/Hin- Buntsandsandstein-, Perm- und Kristallin- tergrundpapier_Stimulation_GtV-BV.pdf. Aquifere. Nagra NTB 91-30. Hirschberg, S., Bauer, C., Burgherr, P., Biollaz, S., Umweltschutzgesetz 1983: Bundesgesetz über den Durisch, W., Foskolos, K., Hardegger, P., Meier, Umweltschutz. 7. Oktober 1983. A., Schenler, W., Schulz, Th., Stucki, S. & Vogel, USGS 2014: Record Number of Oklahoma Tremors F. 2005: Neue erneuerbare Energien und neue Raises Possibility of Damaging Earthquakes. Nuklearanlagen: Potenziale und Kosten. PSI http://earthquake.usgs.gov/contactus/gold- Bericht Nr. 05-04. en/newsrelease_05022014.php, Zugriff 22. Kanton Thurgau 2014: Gesetz über die Nutzung des Oktober 2014. Untergrundes (UNG). http://www.tg.ch/docu- Wikipedia 2014: http://de.wikipedia.org/wiki/Frack- ments/UNG.pdf, Zugriff 5. Oktober 2014. ing, Zugriff 5. Oktober 2014.
93 2-2014_geologi 2.06 12.02.15 15:21 Pagina 94
94 2-2014_geologi 2.06 12.02.15 15:21 Pagina 95
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 95-107
The Shale Gas Potential of the Opalinus Clay and Posidonia Shale in Switzerland – A First Assessment Werner Leu1, Andreas Gautschi2
Keywords: Shale gas, Opalinus Clay, Posidonia Shale, Switzerland, Molasse Basin, organic richness, ther- mal maturity, recoverable gas resources
Abstract 1 Introduction There has been recent interest in the shale gas potential of the Opalinus Clay and Posidonia Shale (Middle and Lower Jurassic) below the Swiss Recently, the Opalinus Clay (Middle Juras- Molasse Basin in the light of the future role of sic, Aalenian) and the underlying Posidonia domestic gas production within the expected future Shale (Lower Jurassic, Toarcian) of the energy shift of Switzerland and possible conflicts in underground use. The Opalinus Clay of northern Swiss Molasse Basin have been mentioned Switzerland is a potential host rock for repositories in connection with the search for shale gas of both high-level and low-to-intermediate level (Chew 2010, Leu 2014a). Also the European radioactive waste and the exploitation of shale gas resources within or below this formation would Shale Gas Map (JPT 2012) shows two poten- represent a serious conflict of use. tial resource plays in Switzerland: Jurassic Well data from northern Switzerland shows that Shales (probably the Opalinus Clay and the these two formations are unsuitable for future Posidonia Shale) to the north of Lake Gene- shale gas recovery. They never reached the gas window during their burial history (maturity values va and Permian Shales in the eastern part of are ≤ 0.6% Ro) and as a consequence never gener- the Molasse Basin. ated significant quantities of thermogenic gas. The shale gas potential of these formations Geochemical data further shows that the average TOC values are in the range of 0.7%, i.e. clearly is currently being discussed in Switzerland below accepted values of more than 1.5% for because of two reasons: a] domestic natural prospective shales. gas resources, if present, could play an A review of available exploration data for the Opali- nus Clay and Posidonia Shale in the deeper and important role in the envisaged energy tran- western part of the Swiss Molasse Basin indicate sition and b] conflicting interests in the that their shale gas potential may be substantial. future use of the deep underground (natural The gross Posidonia Shale thickness increases from central Switzerland from less than 10 m to resources, storage, water, geothermal ener- over 100 m in the Yverdon-Geneva area and is char- gy etc.). acterised by numerous bituminous intervals. A In particular, the Opalinus Clay in northern simplified shale gas resource calculation results for a geologically likely scenario in a technically Switzerland is a potential host rock for recoverable gas volume of ~120 Mrd. m3. The cur- repositories for both high-level and low- to rent database for such estimates is small and as a intermediate-level radioactive waste (Nagra consequence, the uncertainties are large. However, these first encouraging results support a more 2008). The conceptual part of the Sectoral detailed exploration phase with specific geochemi- Plan for Deep Geological Repositories sets cal and petrophysical analysis of existing rock and out the procedure and criteria for selecting well log data. sites for repositories for all waste categories in Switzerland (SFOE 2008). One of the crite- ria to be evaluated (criterion 2.4) relates to conflicts of use. Within and beneath the host
1 Geoform Ltd., 1844 Villeneuve, Switzerland rock, there must be no natural resources 2 Nagra, 5430 Wettingen, Switzerland that would be worth exploiting in the fore-
95 2-2014_geologi 2.06 12.02.15 15:21 Pagina 96
seeable future with the potential for conflict group of extremely fine-grained sedimentary of use. Exploiting such resources within or rocks like clay- and mudstones composed of beneath the host rock formation of a radioac- particles like clay, quartz, feldspars, organic tive waste repository could compromise the matter and heavy minerals (Passey et al. long-term stability of the barrier system, 2010). The particle size is generally in the either by damaging the geological barrier or range of < 2 microns up to 62.5 microns (clay by drilling directly into disposal caverns. and silt fraction). The shale gas potential of the Opalinus Clay Part of the hydrocarbon gases that are gen- and the Posidonia Shale [corresponds to erated within the organic particles escapes Rietheim Member of the Staffelegg Forma- from the source rock rock (primary migra- tion (Reisdorf et al. 2011)], as one possible tion) and migrates into more porous, gener- conflicting natural resource, has been evalu- ally overlying reservoir layers that are ated as part of stage 2 of the Sectoral Plan sealed at the top with a tight barrier (classi- process (Leu 2014b, Leu & Gautschi 2012). cal or conventional gas plays). Shale gas is The objective of this paper is to provide a the gas component that remains trapped in first assessment of the shale gas potential of the tight, fine-grained rock and cannot nor- these Jurassic formations and its distribu- mally escape without artificial stimulation tion within the entire Swiss Molasse Basin. by fracturing technology and preferably The analysis differentiates between north- drilling of horizontal wells. These reservoir ern Switzerland (wider area surrounding the rocks have permeability's in the micro- to potential siting areas for radioactive waste nanodarcy range (BGR 2012). A gas shale is repositories) and the more southern parts of therefore a source rock, a reservoir and a the Molasse Basin (Central/Western Switzer- seal in one and the same formation (resource land). play). Today it is well known that often the greater part of generated gases remains trapped within the source rock (Burri et al. 2 Shale gas: origin, recovery 2011, Burri 2010). technology and rock parameters It has only been recognised in recent years that biogenetically generated methane can 2.1 Origin of shale gas form economically viable gas deposits in argillaceous rocks. Examples of this are the Besides coal bed methane and oil shales, gas New Albany Shale (Tab. 1; Devonian, Illinois shales are part of the group of unconven- Basin, USA) and the Antrim Shale (Devonian, tional resource plays (EIA 2011). Michigan Basin USA; Martini et al. 1996 and Shale gas consists principally of methane 1998). Two types of biogenic methane for- stored in micropores and in fractures within mation are distinguished: a) early diagenetic an organic rich shale formation (bituminous biogenic processes related to alteration and shale). Part of the gas is further adsorbed on decomposition of organic material that organic components and clay minerals with- begins shortly after deposition of the sedi- in fine-grained sediments (Passey et al. 2010, ment and b) relatively recent (last 1 to 2 mil- Jarvie et al. 2007, Curtis 2002, Canadian lion years) methanogenesis related to bacte- National Energy Board 2009). The gas is gen- rial activity associated with the infiltration erated by biogenic (early diagenetic and of meteoric waters into near-surface decom- recent; see below) and thermogenic paction and fracture zones. Theoretically it processes during geological burial and in is possible to distinguish between the two situ heating within the source rock. biogenic and the thermogenic gas fractions, The term shale gas originates from the com- using carbon and hydrogen isotopes of mon use of the term shale to describe the methane, ethane, propane and CO2. Com-
96 2-2014_geologi 2.06 12.02.15 15:21 Pagina 97
plex mixing processes, however, often make matter determine the microporosity, and the distinction not very straight forward hence the possible total storage volume of (Shurr & Ridgley 2002, Martini et al. 2003, free gases. The mineralogy also influences Curtis 2002 and 2010). the brittleness of the rock for hydraulic stimulation (Fig. 2). 2.2 Typical rock characteristics of proven • Thickness of the shale formation: Deter- shale gas resource plays mines the overall gas in place per unit area. Successful shale gas formations that have Examples of typical rock characteristics for been proven to be capable of producing gas historical shale gas formations with eco- at commercial rates can be characterised nomic production in the USA are sum- using typical values for specific rock para- marised in Table 1 (Curtis 2010, see also EIA meters. However, experience over the last 2011). ten years has also shown that economic Formation depth is only a relevant factor for recovery is often dependent on a combina- economic consideration because it influ- tion of these rock parameters that are very ences the necessary drilling costs to reach specific for one region. This clearly indicates the target formation. Prospective areas that there is no unique «recipe» for explo- should have shale resources in the depth ration of shale gas resources and each basin range of 1.000 m to 5.000 m (EIA-ARI 2013). and stratigraphic unit has its own learning Porosity, permeability and the density and curve. Several tens of specifically designed type of the natural fracture network are also exploration wells are normally necessary to important, but are secondary parameters assess the technical and economic poten- that determine the production rate and tial. As part of a broad based comparative recovery factor. Regions with intense and study, Gilman & Robinson (2011) showed deep reaching fault tectonics are normally that the minimum values that are generally avoided because of the increased risk of trig- published for typical rock parameters are gered earthquakes and possible inflow of often too pessimistic and that other factors formation waters from over or underlying such as stimulation technology, reservoir formations. temperature or natural fracture intensity The depositional environment determines also play an important role. the kerogen type (I-II-III) in sedimentary The following key rock parameters have to rock. Valid shale gas formations could have be investigated when exploring shale gas been deposited either in a marine, a lacus- plays: trine or a terrigenous (swamp) environment, • Organic richness (TOC, total organic car- as long as the organic richness is high (Fig. bon): Determines the amount of hydrocar- 2). Marine and lacustrine shales have a bons that can be formed by the transfor- greater potential to produce also oil before mation of kerogen. TOC has also a positive the gas. But marine shales tend to have a correlation with the total gas filled porosi- lower clay content with a higher proportion ty in shales (micro pores and adsorption of brittle minerals such as quartz, feldspar in organic particles, Passey et al. 2010). or carbonates (EIA-ARI 2013). • Thermal maturity: Measure for the degree The key rock parameters organic richness, of transformation of kerogen into hydro- thermal maturity, hardness and formation carbons (Fig. 1; early biogenic or thermo- thickness (discussed above) should general- genic formation during burial; oil window, ly lie at least within the ranges compiled in gas window). Table 2. • Rock mineralogy: The fractions of clay min- If reference wells are available in an explo- erals, quartz and carbonate and organic ration area, various parameters like TOC,
97 2-2014_geologi 2.06 12.02.15 15:21 Pagina 98
mineralogy or porosity can be estimated or 3 The shale gas potential of the calculated using geophysical measurements Opalinus Clay and the Posidonia from wireline logs (e.g. Passey et al. 2010). Shale in Northern Switzerland To optimise the hydraulic stimulation parameters, geomechanical properties and 3.1 Key shale rock properties (Northern local stress states are increasingly being Switzerland) determined from well data (borehole wall breakouts, analysis of dipole sonic and The Opalinus Clay, together with the directly image logs). underlying Posidonia Shale (Toarcian) has been considered in the context of the con- ventional hydrocarbon exploration as a potential source and cap rock (Brink et al.
Fig. 1: Thermal maturation scale (vitrinite reflectance) with typical values for oil shale, shale oil and shale gas rocks (modified after EIA-ARI 2013, BGR 2012).
98 2-2014_geologi 2.06 12.02.15 15:21 Pagina 99
1992, Greber et al. 1997, Schegg et al 1999). Jurassic unit has some similarities to known Boyer et al. 2011 include also the Swiss/Ger- historic shale gas formations (Tab. 1) but also man Molasse Basin in their global shale gas very distinct differences. review and Chew (2010) mentions explicitly A detailed compilation of key rock parame- the Jurassic shale formations in Switzerland ters of the Opalinus Clay for northern in connection with the shale gas exploration Switzerland based on ten Nagra exploration activities of the company Schuepbach Energy wells and further data from the Mont Terri LLC in Cantons Fribourg and Vaud. Although underground rock laboratory (Mazurek the Toarcian Posidonia Shale in northern 2011, Nagra 2002) have been summarized in Switzerland may reach up to 10 wt.% TOC Table 3. (Todorov et al. 1993, Bitterli 1960) its overall Very low organic richness values of ~0.7 wt.% thickness remains less than 10 m in the TOC indicate that the Opalinus Clay is a potential siting areas of Northern Switzerland rather lean source rock in this area and stays (Kiefer et al. 2014) and any assessment of the clearly below accepted minimum values of shale gas potential has to concentrate in this ~1.5 wt.%. Other formations that are also area on the Opalinus Clay. Related to its shaly being investigated by Nagra as potential host lithology with elevated organic contents rocks (e.g. «Brauner Dogger» and Effingen (grey to brownish/black colours) this Middle Member) have even lower values for TOC
Fig. 2: Characterization by compositional properties of shale reservoirs (modified from Ottmann & Bohacs 2014). The horizontal axis is a measure of the rock hardness, differentiating between soft and more brittle components. The vertical axis describes the organic richness (total organic content). Note that all units are in volume percent. Successful US shale reservoir rocks are indicated with green circles and potential shale gas reservoirs (Opalinus Clay and Posidonia Shale) of Western-Central Switzerland plot within the stippled outline.
99 2-2014_geologi 2.06 12.02.15 15:21 Pagina 100
Tab. 1: Examples of rock characteristics of historic shale gas plays exploited economically in the USA today (Curtis 2010, modified).
Tab. 2: Key shale rock properties and their minimal requirements for potentially economic shale gas plays (compiled after Jarvie et al. 2007, Gilman & Robinson 2011, Curtis 2010).
100 2-2014_geologi 2.06 12.02.15 15:21 Pagina 101
and maturity than the Opalinus Clay were several orders of magnitude higher and (Mazurek 2011). marked trip gas peaks were observed regu- The relatively low maturity values (imma- larly. ture to lower boundary for the oil window, In connection with stress measurements, Tab. 3, Fig. 1) of the Opalinus Clay in north- two multiphase hydro-fracturing tests with ern Switzerland is well documented with repeated cycles were carried out in the Opa- data from detailed analysis in wells Benken, linus Clay in the Benken borehole (Nagra Weiach, Herdern-1 and the Mont Terri rock 2001). Well stimulation of this type gener- laboratory (Fig. 3).These values are in good ates fractures with surfaces in the order of agreement with the regional coalification one to a few square meters. None of these trend of increasing maturity values of this tests indicated the presence of a free gas stratigraphic interval towards the Alpine phase. This is further confirmed by investi- front (Fig. 4). gations on numerous core samples, where combined porosity/water content and 3.2 Observed gas occurrences in the hydrochemical analysis resulted in 100% Opalinus Clay in northern Switzerland water saturation in the Opalinus Clay. It can be concluded that the mud gases observed In Nagra’s deep boreholes in northern during drilling are dissolved in pore water Switzerland, continuous gas measurements under in situ downhole conditions. were carried out as part of the drilling fluid Similar observations were made in the Mont monitoring programme (Hinze et al. 1989, Jäg- Terri underground rock laboratory: during gi & Steffen 1999). The measured gas concen- tunnel excavation gas measurements in the trations were always very low when drilling tunnel atmosphere showed only very low through the Opalinus Clay, with methane con- methane concentrations (i.e. below the centrations < 100 ppm (< 0.01 vol.%). No trip detection limit of 0.05 vol.%; written commu- gas peaks were observed, with the exception nication, Dr. Paul Bossart, swisstopo). of a small peak (< 100 ppm) in the lowermost Methane influx into sealed test boreholes clayey facies in the Riniken borehole. In com- monitored over longer times under high parison, the methane concentrations in the hydraulic gradients was also very low Muschelkalk and the Permo-Carboniferous (methane flux 1.7 × 10-5 mol/day/m2; written
Tab. 3: Average rock property values for the Opalinus Clay in Northern Switzerland (Mazurek 2011, Nagra 2002) compared to accepted minimum values (Tab. 2).
101 2-2014_geologi 2.06 12.02.15 15:21 Pagina 102
communication Dr. Agnès Vinsot, Andra). Essertines-1 and Treycovagnes-1 (see also Also gas migration experiments, including Schegg et al. 1999 and Todorov et al. 1993). numerous hydro-fracturing tests gave no The organic content in the overlying Opali- indication of a free gas phase (Bossart & nus Clay is expected to remain below 1.0 wt.%, Thury 2008). related to a lithological transition from shale The isotopic ratios of methane, ethane, dominated to more carbonate rich platform propane and carbon dioxide of the head- facies towards the west (Nagra 2008). space gases in boreholes in the Opalinus Despite these large uncertainties a compari- Clay at the Mont Terri further indicate that son with successful shale formations of the the formation of gases is complex. Thermo- US in a rock hardness/organic richness tri- genic gases generated at temperatures angular plot (Fig. 2) indicates that some of above 60 °C are subsequently altered by the characteristics could overlap. The avail- bacterial processes. In addition diffusive able data for the Molasse Basin (not includ- migration from underlying layers cannot be ing northern Switzerland) plot in a hardness ruled out (Eichinger et al. 2011). None of the range of 20−60% and an organic richness known economic shale gas plays indicate range of 2−12 vol.%. gas migration from underlying, more mature The maturity of the Opalinus Clay to Posido- source rocks. nia Shale interval (Fig. 4) is clearly increas- ing from oil window levels (0.6−0.9% Ro) into the gas window (> 0.9% Ro) towards the 4 The shale gas potential of the Alpine front. The iso-reflectance lines run Opalinus Clay and the Posidonia slightly oblique to the Molasse Basin axis Shale in Central and Western with generally higher maturities further Switzerland north and at shallower depth towards the western part of the basin. Hence, an inter- 4.1 Formation thickness, organic richness esting corridor for potential shale gas and thermal maturity resources (maturity range of 0.9 to 1.35% Ro, condensate/wet gas, Fig. 1) with a width of The question remains if the Opalinus Clay 15−30 km extends from Lake Constance over and the Posidonia Shale in the central and Lucerne-Berne towards Lausanne and western part of the Swiss Molasse Basin across Lake Geneva below the Molasse could have some relevant shale gas poten- Basin (see also Leu 2014b). The potential tial. Data remain scare with only a few deep clearly increases from central to western wells that indicate that the Liassic in general Switzerland related to more favourable rock is thickening towards the west with a basin characteristics (see above) and generally centre in the Besançon-Geneva area (e.g. shallower depth. The northern edge of the Röhl & Schmidt-Röhl 2005, Bitterli 1972, potential trends lies in depths of at least Büchi et al. 1965, Sommaruga 1996, Som- 2.000 to 2.500 m, whereas the southern limit maruga et al. 2012). In well Essertines-1 reaches ~5.000 m (economic floor) in the (Schegg et al. 1997) in the north-western east and 3.500−4.000 m in the west. The part of the Molasse Basin the Opalinus Clay depths are extrapolated from the available has a thickness of over 150 m and the Toar- deep well information and depth maps cian Shales 93 m, respectively. based on seismic data (e.g. Sommaruga et al. The organic richness (TOC) is likely to 2012). increase towards viable levels in the range of 1−4 (max. 10) wt.% in the Posidonia shale along the basin axis towards the southwest, as indicated by some data in wells
102 2-2014_geologi 2.06 12.02.15 15:21 Pagina 103
Fig. 3: Maturity profiles in Northern Switzerland based on cores and cuttings from wells Benken, Weiach and Herdern-1. For comparison also data of the Mont Terri underground rock laboratory are shown (Nagra 2002).
103 2-2014_geologi 2.06 12.02.15 15:21 Pagina 104
Fig. 4: Maturity map of the transition Base Opalinus Clay/Top Toarcian (Posidonia Shale) with approximate depths below ground level. Map constructed using borehole data and synthetic basin modelling points (after Greber et al. 1997, modified). The geological siting regions in northern Switzerland (Nagra 2008) are outlined in green and the depths were estimated from Sommaruga et al. (2012).
Tab. 4: Estimate of technically recoverable shale gas volume of the compound Opalinus Clay/Posidonia Shale interval in Central and Western Switzerland. Gas volumes are given for standard temperature and pressure conditions. See text for explanations for the three scenarios.
104 2-2014_geologi 2.06 12.02.15 15:21 Pagina 105
4.2 Estimate of technically recoverable gas In the likely scenario a technically recover- volumes able shale gas volume of 120 Mrd. m3 results (Tab. 4). In comparison, the current annual Keeping in mind the above discussed uncer- gas consumption of Switzerland is 3.5 Mrd. tainties, it is possible to estimate the techni- m3 and 100 Mrd. m3 for Germany. The wide cally recoverable shale gas potential for the range between the low scenario (7 Mrd. m3) Swiss Molasse Basin for the Opalinus Clay and the high scenario (3.000 Mrd. m3) and the underlying Posidonia Shale (Tab. 4). reflects the uncertainties at this early stage Detailed procedures for the calculation of of exploration in the Swiss Molasse Basin. recoverable shale gas reserves are described in BGR (2012) or EIA-ARI (2013). As no specif- ic data are currently available for several 5 Conclusions parameters used in the Molasse Basin we have chosen the following simplified The Opalinus of Clay and Posidonia Shale of approach: northern Switzerland are characterised by two parameters that are unsuitable in terms of future shale gas recovery: TOC and matu- rity. These formations did not reach the gas window during their burial history (maturity Three individual scenarios were calculated: values are ≤ 0.6% Ro) and as a consequence a] «Low» case, where all four parameters are significant thermogenic gas generation unfavorable, b] «Likely» case representing never occurred. median values (P50) and c] «High» case, Geochemical data for northern Switzerland where all four parameters would be very further show that the average TOC values favorable. are in the range of 0.7%, i.e. clearly below an For the GIP (gas in place per rock unit) norm accepted value (> 1.5%) for prospective values we took the assumptions for the Posi- shales. donia Shale as proposed by BGR (2012). A A review of available exploration data for likely value of 10 m3/m3 is conservative com- the Opalinus Clay and Posidonia Shale in the 3 3 pared to their range of 7 to 38 m /m (P05 to deeper and western part of the Swiss P95). Productive shale gas plays in the US Molasse Basin indicate that their shale gas have values in the range of 5 to 25 m3/m3 potential may be substantial. Especially, the (e.g. Curtis 2002). gross Posidonia Shale thickness increases For the net prospective shale thickness a from central Switzerland to over 100 m in the likely value of 40 m and for the likely Yverdon-Geneva area. prospective region an area of roughly 20 × A simplified calculation of the technically 150 km is assumed. Depending on the litho- recoverable shale gas indicates that for a logical characteristics of the shale formation geologically likely scenario a volume of and assuming today's state-of-the-art pro- around 120 Mrd. m3 is possible. The current duction technology (drilling and stimula- data base for such estimates is small and as tion) only a fraction of the GIP volume can a consequence the uncertainties large. How- be produced. In the US such recovery fac- ever, these first encouraging results support tors are in the range of 5 to 25% with some a more detailed exploration phase with spe- exceptionally high values of up to 60% in the cific geochemical and petrophysical analy- Antrim Shale of Michigan (Tab. 1, Curtis sis of existing rock and well log data. 2002, EIA-ARI 2013). For the Posidonia Shale assessment of Germany a likely value of 10% was assumed (BGR 2012).
105 2-2014_geologi 2.06 12.02.15 15:21 Pagina 106
Literature Gilman, J. & Robinson, Chr. 2011: Success and fail- ure in Shale Gas exploration and development: BGR 2012: Abschätzung des Erdgaspotenzials aus Attributes that make the difference. Search & dichten Tonsteinen (Schiefergas) in Deutsch- Discover article #80132, adapted from oral land. Bericht Bundesanstalt für Geowis- presentation at AAPG Int. Conference and Exhi- senschaften und Rohstoffe, Hannover, 57 p. bition, Calgary, Alberta, Sept. 12−15, 2011, 31 p. Bitterli, P. 1960: Bituminous Posidonienschiefer Greber, E., Leu, W. & Schegg, R. 1997: Hydrocarbon (Lias epsilon) of Mont Terri, Jura Mountains. Habitat and Potential of Switzerland: an evalua- Bull. Ver. Schweiz. Petrol.-Geol. u. Ing., 26/71, tion of oil and gas potential of Switzerland based 41−48. on public well data, seismic lines and basin Bitterli, P. 1972: Erdölgeologische Forschungen im modeling results. Unpubl. Internal Report Geo- Jura. Bull. Ver. Schweiz. Petrol.-Geol. u. Ing., form AG (revised version 2011), 107 p. 39/95, 13−28. Hinze, W., Jäggi, K. & Schenker, F. 1989: Sondier- Bossart, P. & Thury, M. (Eds.) 200): Mont Terri Rock bohrungen Böttstein, Weiach, Riniken, Laboratory. Project, Programme 1996 to 2007 Schafisheim, Kaisten, Leuggern: Gasmessun- and Results. Swisstopo Rep. 2008-01. Federal gen. Nagra Tech. Rep. NTB 86-11, Nagra Wet- Office of Topography, swisstopo, Bern. tingen, Switzerland. Boyer, Ch., Clark, B., Jochen, V. & Miller, R. L. 2011: Jäggi, K. & Steffen, P. 1999: Sondierbohrung Shale gas: A global resource. Oil Field Review, Benken: Geologisches Sampling, Bohrgasmes- Schlumberger, 23/3, 12 p. sungen, Sampler Logs 1:200. Unpubl. Nagra Brink, H.-J., Burri, P., Lunde, A. & Winhard, H. Internal. Rep., Nagra, Wettingen, Switzerland. 1992: Hydrocarbon habitat and potential of Jarvie, D. M., Hill, R. J., Ruble, T. E. & Pollastro & R. Swiss and German Molasse Basin: A compari- M. 2007: Unconventional shale-gas systems: son. Eclogae geo. Helv., 85/3, 715−732. The Mississippian Barnett Shale of north-cen- Büchi, U. P., Lemcke, K., Wiener, G. & Zimdars, J. tral Texas as one model for the thermogenic 1965: Geologische Ergebnisse der Erdölexplo- shale-gas assessment. AAPG Bulletin 91/4, ration auf das Mesozoikum im Untergrund des 475−499. schweizerischen Molassebeckens. Bull. Ver. JPT 2012: European Shal Gas Map. Journal of Schweiz. Petrol.-Geol. u. Ing., 32/82, 7−38. Petroleum Technology. Society of Petroleum Burri, P. 2010: A revolution in gas – The rise of the Engineers, Houston. unconventionals. Swiss Bull. angew. Geol. 15/2, Kiefer, L. M., Deplazes, G. & Bläsi, H. R. 2014: Se - 35−44. dimentologie und Stratigraphie der Staffelegg- Burri, P., Chew, K., Jung, R. & Neumann, V. 2011: Formation. Nagra Arb. Ber. NAB 14-95, Nagra, The potential of unconventional gas – energy Wettingen, Switzerland. bridge to the future (with a review of European Leu, W. & Gautschi, A. 2012: Das Shale Gas unconventional gas activities). Swiss Bull. (Schiefergas)-Potenzial des Opalinustons in angew. Geol., vol. 16/2, 3−55. der Nordschweiz. Nagra Arb. Ber. NAB 11-23, Canadian National Energy Board 2009: A Primer for Nagra, Wettingen, Switzerland. Understanding Canadian Shale Gas. Energy Leu, W. 2014a: Erdöl-Erdgasexploration in der Briefing Note, 27 p. Trendwende: Potenzial der unkonventionellen Chew, K. 2010: The shale frenzy comes to Europe. Ressourcen in der Schweiz und Europa – E&PMAG, March 1, 2010, 8 p. Anstrengungen und Kontroversen. Swiss. Bull. Curtis, J. B. 2002: Fractured shale-gas systems. angew. Geol., 19/1, 29−32. AAPG Bulletin, 86/11, 1921−1938. Leu, W. 2014b: Potenzial der Kohlenwasserstoff- Curtis, J. B. 2010: U.S. Shale Gas: From Resources Ressourcen in der Nordschweiz. Nagra Arb. and Reserves to Carbon Isotope Anomalies. Ber. NAB 14-70, Nagra, Wettingen, Switzer- Standford University, Energy Seminar, Jan. 20, land. 2010, presentation J. Curtis (http:// Martini, A. M., Walter, L. M., Budai, J. M., Ku, T. C. www.rpsea.org/attachments/contentman- W., Kaiser, C. J. & Schoell, M. 1998: Genetic and agers/429/Shale_Gas_Resources__Dr._ temporal relations between formation waters John_Curtis_Potentail_Gas_Agency.pdf), 38 p. and biogenic methane – Upper Devonian EIA 2011: Review of emerging resources: U.S. Shale Antrim Shale, Michigan basin. Geochimica et gas and shale oil plays. U.S. Energy Information Cosmochimica Acta, v. 62, no. 10, 1699−1720. Administration, 106 p. Martini, A. M., Walter, L. M., Ku, T. C. W., Budai, J. EIA-ARI 2013: Technically Recoverable Shale Oil M., McIntosh, J. C. & Schoell, M. 2003: Micro- and Shale Gas Resources: An Assessment of bial production and modification of gases in 137 Shale Formations in 41 Countries Outside sedimentary basins: A geochemical case study the United States. US Energy Information from a Devonian shale gas play, Michigan basin. Administration, 730 p. AAPG Bulletin, 87/8, 1355−1375. Eichinger, F., Eichinger, L. & Ertl, S. 2011: Genese Martini, A. M., Budai, J. M., Walter, L. M. & Schoell, der leichten Kohlenwasserstoffe im Opalinuston M. 1996: Microbial generation of economic des Felslabors Mont Terri. Nagra Arbeitsbericht accumulations of methane within a shallow NAB 11-33, Nagra, Wettingen, Switzerland. organic-rich shale. Nature 383, 155−158.
106 2-2014_geologi 2.06 12.02.15 15:21 Pagina 107
Mazurek, M. 2011: Aufbau und Auswertung der Sommaruga, A., Eichenberger, U. & Marillier, F. Gesteinsparameter-Datenbank für Opalinus- 2012: Seismic Atlas of the Swiss Molasse ton, den ‹Braunen Dogger›, Effinger Schichten Basin. Beitr. z. Geol. der Schweiz – Geophysik, und Mergel-Formationen des Helvetikums. 44, 90 p. Nagra Arb. Ber. NAB 11-20, Nagra, Wettingen, Todorov, I., Schegg, R. & Wildi, W. 1993: Thermal Switzerland. maturity and modelling of Mesozoic and Ceno- Nagra 2001: Sondierbohrung Benken – Unter- zoic sediments in the south of the Rhine Graben suchungsbericht. Nagra Technical Report NTB and the Eastern Jura (Switzerland). Eclogae 00-01, Nagra, Wettingen, Switzerland. geol. Helv. 86/3, 667−692. Nagra 2002: Projekt Opalinuston – Synthese der geowissenschaftlichen Untersuchungsergeb- nisse. Nagra Technical Report NTB 02-03, Nagra, Wettingen, Switzerland. Nagra 2008: Vorschlag geologischer Standortge - biete für das SMA- und das HAA-Lager. Dar- legung der Anforderungen, des Vorgehens und der Ergebnisse. Nagra Technical Report NTB 08-03, Nagra, Wettingen, Switzerland. Ottmann, J. & Bohacs, K. 2014: Conventional reser- voirs hold keys to «un's». AAPG Explorer, Feb- ruary 2014, 4 p. Passey, Q. R., Bohacs, K. M., Esch, W. L., Klimen- tidis, R. & Sinha, S. 2010: From oil-prone source rock to gas-producing shale reservoirs – Geological and petrophysical characterization of unconventional shale-gas reservoirs. Soc. Petrol. Eng. SPE, No. 131350, 29 p. Reisdorf, A. G., Wetzel, A., Schlatter, R. & Jordan, P. 2011: The Staffelegg Formation: a new strati- graphic scheme for the Early Jurassic of north- ern Switzerland. Swiss Journal of Geosciences 104/1, 97−146. Röhl, H. J. & Schmidt-Röhl, A. 2005: Lower Toar- cian (Upper Liassic) black shales of the central European epicontinental Basin: a sequence stratigraphic case study from the SW German Posidonia Shale. In: The deposition of organic- carbon-rich sediments: Models, mechanisms and consequences, SEPM Spec. Publ. No. 82, 165−189. Schegg, R., Leu, W. & Cornford, Chr. 1999: Migra- tion and accumulation of hydrocarbons in the Swiss Molasse Basin: implications of a 2D basin modeling study. Marine Petrol. Geol., 16, 511−531. Schegg, R., Leu, W., Cornford, C. & Allen, P. A. 1997: New coalification profiles in the Molasse Basin of Western Switzerland: Implications for the thermal and geodynamic evolution of the Alpine Foreland. Eclogae geol. Helv., 90/1, 79−96. Shurr, G. W. & Ridgley, J. L. 2002: Unconventional shallow biogenic gas systems. AAPG Bull. 86/11, 1939−1969, doi: 10.1306/61EEDDC8- 173E-11D7-8645000102C1865D. SFOE 2008: Sectoral Plan for Deep Geological Repositories; conceptual part. Swiss Federal Office of Energy, Bern, Switzerland. Sommaruga, A. 1996: Geology of the Central Jura and Molasse Basin: new insight into an evapor- ite-based foreland fold and thrust belt. Mém. Soc. Neuchâtel. Sci. Nat., XII, 178 p.
107 2-2014_geologi 2.06 12.02.15 15:21 Pagina 108
108 2-2014_geologi 2.06 12.02.15 15:21 Pagina 109
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 109-113
Fracking in der Schweiz aus der Sicht des Grund- und Trinkwasserschutzes Daniel Hartmann1, Benjamin Meylan2
1 Einleitung 2 Argumente der Stopp-Fracking- Initiative Die Autoren möchten mit diesem Artikel zur Versachlichung der Diskussion über Frack - Die Stopp-Fracking-Initiative wird im Wort- ing in Bezug auf den Grund- bzw. Trinkwas- laut folgendermassen begründet (http:// serschutz beitragen. Vor allem relativieren www.stopp-fracking.ch): sie die aus politischen Kreisen und den 1. Fracking vergiftet Boden und Wasser: Der Umweltorganisationen beschworene Gefahr beim Fracking verwendete Chemikalien- einer Grundwasserverunreinigung durch cocktail bedroht die Qualität der Grund- Fracking und weisen darauf hin, dass und Oberflächengewässer und damit des wesentlich akutere, aktuelle und flächende- Trinkwassers. ckende Probleme für die Wasserqualität, wie 2. Fracking untergräbt die Energiewende: Mit beispielsweise von den in der Landwirt- der Förderung von Schiefergas wird ein schaft verwendeten Pestiziden ausgehen. zusätzliches Potenzial an fossilen Medienberichten zur Folge kam es in den Ressourcen erschlossen. Die Abhängigkeit USA wegen Fracking mehrmals zu Umwelt- von fossilen Ressourcen wird verlängert – verschmutzungen. Am 20. Juni 2014 haben und der Umstieg auf erneuerbare Energien die Grünen Kanton Bern zusammen mit Pro damit torpediert. Das ist weder energiepoli- Natura Bern, Greenpeace Regionalgruppe tisch noch volkswirtschaftlich sinnvoll. Bern und der EVP (Evangelische Volkspar- 3. Fracking belastet das Klima: Schiefergas ist tei) die Stopp-Fracking-Initiative eingereicht. nicht nur deshalb klimaschädigend, weil Diese verlangt, dass die Förderung von Erd- bei der Verbrennung von Gas CO2 freige- gas und Erdöl aus sogenannt nicht-konven- setzt wird, sondern auch, weil die Förde- tionellen Lagerstätten im Kanton Bern ver- rung und der Abtransport überdurchschnitt- boten wird. Ähnliche Absichten, Moratorien lich viel Energie benötigen. Beim Fracking oder gar Verbote bestehen auch in anderen entweichen grössere Mengen an Methan in Kantonen. die Luft und ins Grundwasser; Methan ist 25 Mal klimaschädigender als CO2 und heizt das Klima an. Schliesslich: Die Schiefergas- förderung führt nicht zum Ersatz von Kohle und Erdöl, sondern zu einer Ausweitung des Verbrauchs fossiler Ressourcen. 4. Fracking führt zu Landverschleiss: Der für die Erschliessung der Bohrfelder erforderli- 1 Daniel Hartmann, Grundwasserschutz und Wasserver- che Landbedarf ist enorm (Strassen, Tanks, sorgung, Mühlerain 56, 3210 Kerzers, Schweiz; langjäh- riger Chef der Sektion Grundwasserschutz im Bundes- Abwasserbecken, Lagerplätze, Stellplätze amt für Umwelt usw.). Der Umstand, dass wegen der 2 Dr. Benjamin Meylan – Grundwasserschutz & Grundwas- raschen Erschöpfung der Lagerstätten sernutzung, Nelkenweg 7, 3006 Bern, Schweiz; langjäh- riger stellvertretender Chef der Sektion Grundwasser- immer neue Bohrlöcher erschlossen wer- schutz des Bundesamtes für Umwelt den, verschärft den Landverschleiss zusätz-
109 2-2014_geologi 2.06 12.02.15 15:21 Pagina 110
lich. Neben dem Landverbrauch erzeugt setz und die Vorschriften, welche den Natur- Fracking eine hohe Lärm- und Verkehrsbe- und Heimatschutz, den Landschaftsschutz, lastung, da das geförderte Gas in der Regel den Gewässerschutz, die Walderhaltung nicht per Pipeline, sondern per Lastwagen sowie die Jagd und die Fischerei betreffen. abtransportiert wird. Das Ergebnis der Prüfung bildet eine Grund- 5. Fracking produziert gefährliche Abfälle: lage für den Bewilligungsentscheid. Werden Das beim Fracking verwendete Wasser- nicht sämtliche Vorschriften eingehalten, Sand-Chemikaliengemisch muss speziell darf die Behörde keine Bewilligung erteilen. entsorgt werden. Ähnlich wie bei den radio- Sie hat zudem dafür zu sorgen, dass der aktiven Abfällen besteht keine Lösung für Bericht und der Entscheid öffentlich zugäng- die Entsorgung dieses Flowbacks. Bei Lecks lich sind. Somit können sich Interessierte am Bohrloch drohen unkontrollierte Vergif- informieren und allenfalls gegen das Vorha- tungen und Verschmutzungen durch die gif- ben Rekurs einlegen. In der Schweiz besteht tigen Flowbacks. zudem das Verbandsbeschwerderecht. Es 6. Fracking nützt nur ausländischen Grossfir- ist deshalb zu erwarten, dass insbesondere men: Im Gegensatz zu erneuerbaren Ener- Umweltverbände bei einem Fracking-Projekt gien profitieren vom Fracking-Boom allein von dieser Möglichkeit konsequent wenige multinationale Grosskonzerne – Gebrauch machen werden. und nicht die einheimische, regionale Wirt- schaft. Gewässerschutzrechtliche Bewilligung In der Schweiz benötigen Bohrungen in Ähnliche Befürchtungen finden sich in der besonders gefährdeten Bereichen, das Bevölkerung. Die Argumente der Initiative heisst in sämtlichen Gebieten mit nutzbaren möchten wir im Folgenden aus Sicht des Grundwasservorkommen, eine gewässer- Grund- und Trinkwasserschutzes kurz disku- schutzrechtliche Bewilligung nach Artikel 32 tieren, da die Rahmenbedingungen für der Gewässerschutzverordnung vom 28. Frack ing, insbesondere die gesetzlichen Oktober 1998 (GSchV, SR 814.201) und den Bestimmungen des Umweltrechts, in der kantonalen Bestimmungen. Um eine solche Schweiz wesentlich einschränkender und Bewilligung zu erhalten, müssen die Gesuch- präziser sind, als in den umliegenden Län- steller nachweisen, dass die Anforderungen dern und in den USA. zum Schutz der Gewässer erfüllt sind und die dafür notwendigen Unterlagen einrei- chen. Dafür sind gegebenenfalls auch hydro- 3 Gesetzesvollzug geologische Untersuchungen notwendig. Die zuständige Behörde darf die Bewilligung mit Umweltverträglichkeitsprüfung den entsprechenden Auflagen und Bedin- In der Schweiz benötigen Anlagen zur gungen nur dann erteilen, wenn sicherge- Gewinnung von Erdgas gemäss der Verord- stellt ist, dass ein ausreichender Schutz der nung über die Umweltverträglichkeitsprü- Gewässer gewährleistet werden kann (siehe fung vom 19. Oktober 1988 (Anhang 21.7 folgendes Kapitel). Die Behörde legt dabei UVPV, SR 814.011) eine kantonale Bewilli- auch die Anforderung an die Stilllegung der gung. Bei der Prüfung der Umweltverträg- Anlage fest (Art. 32 GSchV). lichkeit stellt die zuständige Behörde auf- grund des Umweltverträglichkeitsberichts Anforderungen zum Schutz der Gewässer des Gesuchstellers fest, ob das Projekt den nach Gewässerschutzrecht bundesrechtlichen und kantonalen Vor- Gemäss Artikel 3 des Gewässerschutzgeset- schriften über den Schutz der Umwelt ent- zes vom 24. Januar 1991 (GSchG, SR 814.20) spricht. Dazu gehören das Umweltschutzge- ist jedermann verpflichtet, alle nach den
110 2-2014_geologi 2.06 12.02.15 15:21 Pagina 111
Umständen gebotene Sorgfalt anzuwenden, (z. B. Tankstellen, Pipelines, Abwasseranla- um Verunreinigungen und andere Eingriffe, gen, Wärmenutzungsanlagen aus dem Unter- welche die Funktion des Grundwassers grund, Anlagen zur Lagerung nuklearer beeinträchtigen, zu vermeiden. Die Kosten Abfälle usw.) betroffen. Die Behörden haben, für die Sanierung einer allfälligen Beein- in Abwägung aller Anliegen, das Recht und trächtigung muss der Verursacher tragen die Pflicht, je nach Situation und Anlage ent- (Art. 3a GSchG). Insbesondere dürfen keine sprechende Auflagen zu verfügen. Mehrere Stoffe, die Wasser verunreinigen können, Kantone haben denn z. B. bezüglich Wärme- mittelbar oder unmittelbar ins Grundwasser nutzung bereits entsprechende Vorzugs- eingebracht werden. bzw. Ausschlussgebiete in ihren Gewässer- Bei der Prüfung eines Gesuchs wird die kan- schutzkarten festgelegt. tonale Behörde daher alle genannten Punkte prüfen. Die Gesuche müssen so dokumen- tiert sein, dass sie den zuständigen Behör- 4 Gegenargumente zur Stopp- den eine ordnungsgemässe Prüfung erlau- Fracking-Initiative ben. Nötigenfalls müssen diese ergänzende Untersuchungen verlangen (Art. 32 Abs. 3 Fracking vergiftet Boden und Wasser: In der GSchV), beispielsweise durch ausgewiesene Schweiz muss der Gesuchsteller der Behör- SpezialistInnen. Falls nötig, wird die Mei- de offenlegen, welche Stoffe zur Anwendung nung des Bundesamtes für Umwelt einge- gelangen. Chemikaliencocktails aus wasser- holt. Die Behörde wird eine Bewilligung für gefährdenden Stoffen sind klar verboten. ein Fracking-Projekt nur erteilen, wenn nach- Der Gesuchsteller muss nachweisen, dass er weislich ein ausreichender Schutz der ausschliesslich mit unbedenklichen Stoffen Gewässer gewährleistet ist. Die Anforderun- (in erster Linie mit Wasser und Sand) arbei- gen an inhaltlich umfassende und fachlich tet. Zur Sicherheit wird die Behörde entspre- einwandfrei fundierte Nachweise zur Erfül- chende Kontrollen durchführen und bei Ver- lung der genannten rechtlichen Vorschriften stössen die Anlage schliessen. Eine Sanie- sind entsprechend gross. rung allfällig verschmutzten Grundwassers würde zu Lasten des Gesuchstellers gehen. Das Gewässerschutzgesetz gilt für alle unter- Die pauschale Behauptung, dass Fracking und oberirdischen Gewässer (Art. 2 GSchG), Boden und Wasser vergiftet und dass der wobei es keine Tiefenbeschränkung für nutz- beim Fracking verwendete Chemikaliencock - bares Grundwasser gibt. Alle nicht bereichs- tail die Qualität der Grund- und Oberflächen- oder zonenspezifischen Bestimmungen gel- gewässer und damit des Trinkwassers ten flächendeckend und jederzeit, wie z. B. bedroht, ist unqualifiziert und bei Beach- die Sorgfaltspflicht nach Art. 3 GSchG, das tung der geltenden rechtlichen Bestimmun- Verursacherprinzip nach Art. 3a GSchG oder gen falsch. Das Grundwassergefährdungspo- die Behandlungspflicht für verschmutztes tenzial der schweizweit nach wie vor im Abwasser (inkl. jenes von Bohrstellen) nach unmittelbaren Umfeld von Trinkwasserfas- Art. 7 GSchG. Grundwasser, das nicht sungen eingesetzten Pestizide ist nachweis- genutzt werden kann, ist im Sinne von insbe- lich wesentlich problematischer. sondere Art. 2 und Art. 3 GSchG geschützt. Fracking produziert gefährliche Abfälle: Für Auch ausserhalb der besonders gefährdeten die Entsorgung von belasteten Materialien Bereiche, welche in der Schweiz ungefähr gelten die bestehenden Regeln des Umwelt- 30% der Landesfläche umfassen, gelten rechts sowie allfällige präzisierende Vorga- grundsätzlich die Anforderungen des ben aus der Bohrbewilligung. Gefährliche, Gewässerschutzschutzgesetzes. Davon sind nicht behandelbare Abfälle dürfen beim alle potenziell wassergefährdenden Anlagen Fracking schon darum nicht entstehen, weil
111 2-2014_geologi 2.06 12.02.15 15:21 Pagina 112
sonst das Gesuch abgelehnt werden müsste. gen der ursprüngliche Zustand wieder her- Der Gesuchsteller muss deshalb in seinem gestellt wird, wie dies in der Regel auch bei Umweltverträglichkeitsbericht auch nach- allen anderen Bohrungen, beispielsweise weisen, dass er sein Abfallproblem umwelt- zwecks Energiegewinnung, verlangt wird. verträglich lösen kann. Das benutzte Wasser • Dass Fracking nur ausländischen Grossfir- sollte im Kreislauf verwendet und kontinu- men nützen würde, ist nicht nachvollzieh- ierlich gereinigt werden. Beispielsweise mit bar. Schliesslich bietet die Erschliessung der Umkehrosmose kann das verwendete einer einheimischen Ressource die Chan- Wasser wieder Trinkwasserqualität errei- ce, die Abhängigkeit vom Ausland zu ver- chen. Der Vergleich der Abfallproblematik ringern. beim Fracking-Verfahren mit derjenigen von radioaktiven Abfällen dient daher primär der Angstmacherei. Eine Verschmutzung 5 Allgemeine Betrachtungen zum von Boden und Grundwasser kann bei fach- Fracking gerechter Ausführung weitestgehend ausge- schlossen werden. Selbstverständlich kann Wie oben aufgezeigt, muss jeder Gesuchstel- ein Hydraulikschlauch platzen, aber dies ler in der Schweiz nachweisen, dass er sämt- kann auf jeder Baustelle passieren. liche umweltrechtlichen Bestimmungen ein- hält. Der vertikale Abstand zwischen den Zu den andern Argumenten der Stopp-Frack- Gesteinen, die gefrackt werden sollen und ing Initiative: den Grundwasservorkommen muss genü- • Wie manch andere Treibhausgase generie- gend gross sein, um zu gewährleisten, dass renden Tätigkeiten des Menschen kann die künstlich erzeugten Risse nicht bis in Fracking das Klima belasten. In der nutzbare Grundwasservorkommen hinauf- Schweiz mittels Fracking gewonnenes Erd- reichen können. In einem Gebiet, dessen tie- gas dürfte jedoch eine mit durch die Ver- fer Untergrund geologisch wenig bekannt brennung von Kohle produziertem Import- ist, wird die Behörde daher den Nachweis strom oder unter zweifelhaften Rahmen- verlangen, dass durch das Fracking keine bedingungen gewonnenem, über Meere nutzbaren Grundwasservorkommen betrof- und Flüsse verschifftem Erdöl durchaus fen werden. konkurrenzfähige Umweltbilanz aufweisen Ein generelles Verbot von Fracking in der (Anm.: die Schweiz importiert aktuell rund Schweiz ist daher aus der Sicht des Grund- 80% ihrer Energie. Der Anteil fossiler und Trinkwasserschutzes wenig sinnvoll. Brennstoffe beträgt 66%, der Anteil des Ein solches Verbot würde zudem auch die mehrheitlich importierten Erdgases am geothermische Nutzung des Untergrundes Endenergieverbrauch 13%). in Frage stellen. Viel problematischer für das • Tatsächlich würde mit der Förderung von Grundwasser sind ohnehin die zahllosen Schiefergas ein zusätzliches Potenzial an Erdwärmesonden, die momentan – unter fossilen (einheimischen) Ressourcen Kostendruck und in teilweise krasser erschlossen. Dass dies, wie in der Stopp- Unkenntnis der lokalen Gegebenheiten im Fracking-Initiative behauptet wird, «weder Untergrund – erstellt werden. Bei unsachge- energiepolitisch noch volkswirtschaftlich mässer Hinterfüllung des Bohrlochs entste- sinnvoll» ist, kann bezweifelt werden. hen präferenzielle Fliesswege, durch welche • In der Schweiz würde Fracking kaum zu Schadstoffe ungehindert von der Oberfläche einem wesentlichen Landverschleiss führen. in den Untergrund gelangen können und ver- Der grösste Teil der Anlagen ist temporär schiedene Grundwasserstockwerke in und die Behörden würden vom Gesuchstel- unkontrollierter Weise miteinander verbun- ler verlangen, dass nach Abbruch der Anla- den werden. Da eine korrekte Hinterfüllung
112 2-2014_geologi 2.06 12.02.15 15:21 Pagina 113
des Bohrlochs Zeit beansprucht, wirkt sich Pestizide bis 10 Meter neben einer Trinkwas- der Kostendruck verheerend auf die Qualität serfassung ausbringen. Dass diese dabei ins dieser Erdwärmesonden aus, wodurch für Trinkwasser gelangen, ist nicht weiter ver- das Grundwasser die Gefahr einer Verunrei- wunderlich. nigung entsteht. Aus Sicht des Grundwasser- Eigentlich müsste der Öffentlichkeit – im schutzes wäre es daher wünschenswert, Hinblick auf die Gesundheit der Schweizer wenn zur Gewinnung der Erdwärme aus- Bevölkerung – ein Pestizid freies Trinkwas- schliesslich grosse Anlagen gebaut würden, ser so viel Wert sein, dass auf eine intensive die eine grössere Anzahl Haushalte mit Wär- Landwirtschaft im unmittelbaren Vorfeld me versorgen. Solche Anlagen werden pro- von Trinkwasserfassungen verzichtet wür- fessioneller erbaut, betrieben und gewartet. de. Biolandwirtschaft oder besser noch Vor allem sinkt die Anzahl der für die Erd- Graswirtschaft wären ja weiterhin möglich. wärmenutzung notwendigen Bohrungen und Im Einzugsgebiet von Trinkwasserfassungen somit die Anzahl Perforationen des Unter- würde der Landwirt damit auch zum Trink- grundes, durch welche Schadstoffe ins wasserproduzenten. Grundwasser gelangen können. Mit dem Vergleich zur Landwirtschaft möch- Das grösste Problem beim Fracking sehen ten wir bewusst auf die effektive Tragweite wir in den Erdbeben, die dabei ausgelöst verschiedener Gefährdungspotenziale für werden können. Ob in Anbetracht der Sied- das Grund- und Trinkwasser hinweisen, da lungsdichte der Schweiz ohne schwere Man- wir in den letzten Jahren die zunehmende gellage in Bezug auf Erdgas, solche Beben Fokussierung auf «trendige», sprich «medien- von der Bevölkerung in Kauf genommen trächtige Nebenschauplätze» wie den Nach- würden, erachten wir als eher unwahr- weis von Assugrin in Gewässern, brennende scheinlich. Trotzdem sollte jedoch die Wasserhähne, Dünger auf Skipisten, Wasser- Erkundung des tiefen Untergrunds in der knappheit und andere «Schauerlichkeiten» Schweiz vorangetrieben werden. Damit sol- feststellen mussten, bei gleichzeitig völliger len vor allem Erkenntnisse zur Errichtung Gleichgültigkeit gegenüber realen und pro- von petrothermalen Geothermieanlagen blemlos vermeidbaren Beeinträchtigungen gewonnen, aber auch das Potenzial an nutz- (z. B. Landwirtschaft oder Eingriffe in Ober- barem Schiefergas abgeklärt werden. Es ist flächengewässer im unmittelbaren Vorfeld bedauerlich für ein Land, das lange in der von Trinkwasserfassungen). Geologie führend war, dass die Kenntnisse über den eigenen Untergrund und den Umfang allenfalls vorhandener natürlicher 7 Fazit Ressourcen so gering sind. Ohne die Unter- suchungen der NAGRA und der Erdölindu- Fracking in der Schweiz ist, wenn die gelten- strie wäre die Kenntnis des geologischen den Vorschriften und der Stand der Technik Untergrunds der Schweiz noch dürftiger. strikte eingehalten werden, im Hinblick auf die Sicherstellung der Qualität des Grund- und Trinkwassers eine verantwortbare 6 Defizite des Grundwasserschutzes Technologie. Der Schutz von Mensch und in der Schweiz Umwelt kann gewährleistet werden, wenn die geltenden Vorschriften und die Tech- Die Grundwasservorkommen in der Schweiz nikstandards eingehalten und konsequente, sind quantitativ gut geschützt. Mit der Qua- regelmässige Kontrollen durchgeführt wer- lität des Grundwassers gibt es indes Proble- den. Gravierend ist indes das Problem der me, insbesondere wegen der Landwirt- Pestizide im Grund- und Trinkwasser als Fol- schaft. In der Schweiz dürfen Landwirte ge intensiver landwirtschaftlicher Nutzung.
113 2-2014_geologi 2.06 12.02.15 15:21 Pagina 114
114 2-2014_geologi 2.06 12.02.15 15:21 Pagina 115
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 115-122
Unkonventionelle Gasförderung im Klimaschutz: Teil der Lösung oder Teil des Problems? Elmar Grosse Ruse1
Stickworte: CCS, Energiewende, Erdgas, Fracking, Geothermie, Klimapolitik, Kohlenstoffbudget, Methan, Schweiz, USA
Zusammenfassung Abstract Der vorliegende Artikel bewertet die Hydraulic In this article the hydraulic fracturing technology Fracturing Technologie (Fracking) aus der Per- (fracking) is assessed from the perspective of glob- spektive der globalen Klimapolitik. Die genannten al climate change mitigation policy. The presented Argumente zeigen, dass aus dieser Sichtweise arguments show that from this perspective frack- Fracking in den allermeisten Fällen nicht Teil der ing is in most cases part of the problem and not Lösung, sondern Teil des Problems ist. Allein die part of the solution. Simply the fact that two thirds Tatsache, dass zwei Drittel aller heute schon of all known fossil fuel reserves must remain in the bekannten fossilen Energiereserven im Untergrund ground in order to comply with the two-degree-lim- verbleiben müssen, damit die Zwei-Grad-Grenze it bans the investment of political, technological eingehalten werden kann, verbietet es, politische, and financial resources in projects to exploit the technologische und finanzielle Ressourcen in known and future reserves of natural gas. This is Praktiken zur Erschliessung der bekannten und all the more true as the invested capital de facto künftigen Erdgas-Reserven zu investieren. Dies gilt competes with increased investments in renewable umso mehr, als die investierten Ressourcen meist energies and energy efficiency. In addition, capital- de facto in Konkurrenz zu einem verstärkten Enga- intensive infrastructure for fracking leads to a car- gement für Energieeffizienz und erneuerbare bon-lock-in: in order to prevent decaying hulks of Energien stehen. Und kapitalintensive Fracking- abandoned projects, natural gas would have to be Infrastruktur führt in ein Kohlenstoff-Lock-in: Um exploited and used energetically to a great magni- Investitionsruinen zu vermeiden, müsste in gros- tude over a long period of time. This in turns fosters sem Ausmass und über ausreichende Zeit unkon- climate change und minimizes the scope for cli- ventionell gefördertes Erdgas energetisch genutzt mate change mitigation. This is all the more true, in werden. Das wiederum heizt den Klimawandel an case the growing evidence is confirmed that frack- bzw. schränkt den Spielraum für Klimaschutz- ing goes with much higher methane emissions massnahmen weiter ein. Diese Argumentation gilt than previously thought resp. than conventional umso mehr, wenn sich die wachsende Evidenz exploitation of natural gas does. As a political con- bestätigt, dass Fracking deutlich höhere Methan- sequence of these findings a general ban of the emissionen mit sich bringt als bislang vermutet exploitation of all hydrocarbons in Switzerland is bzw. als aus der konventionellen Erdgasförderung recommended. bekannt. Als politische Konsequenz dieser Erkenntnisse wird ein generelles Verbot für die Förderung jeglicher Kohlenwasserstoffe in der Schweiz empfohlen.
1 WWF Schweiz, Hohlstrasse 110, 8010 Zürich, Schweiz
115 2-2014_geologi 2.06 12.02.15 15:21 Pagina 116
1 Einführung über einen spezifischen Zeitraum maximal zu emittierendes Treibhausgas-Kontingent Die massive Förderung von unkonventionel- abgeleitet. Dieser Ansatz – das sogenannte len Erdgasvorkommen mithilfe der Hydrau- Kohlenstoffbudget – ermöglicht deutlich lic Fracturing Technologie (im Folgenden präzisere Aussagen zu politischen und tech- vereinfacht «Fracking» oder «Schiefergasför- nologischen Optionen für zwei-Grad-kompa- derung») in den USA und entsprechende Vor- tible globale Entwicklungspfade als blosse haben in Europa haben umfassende Diskus- Reduktionsvorgaben mit Bezug auf ein Aus- sionen in Medien und Zivilgesellschaft aus- gangs- und Zieljahr (wie beispielsweise «80% gelöst. Gegenstand dieser Auseinanderset- weniger Treibhausgasemissionen bis 2050 zungen sind meist die Auswirkungen von gegenüber dem Jahr 1990»). Denn letztge- Fracking für gesellschaftliche Anliegen wie nannte Vorgaben lassen letztlich offen, wie Boden- und Gewässerschutz, Luftreinhal- viele Tonnen Treibhausgase in der betreffen- tung, Erdbebenschutz, Landschaftsschutz, den Zeitspanne noch emittiert werden. Lärmschutz und Verkehrsvermeidung. Da Dabei ist die Menge der in die Atmosphäre Fracking lokal bzw. regional vor allem auf die emittierten Treibhausgase die entscheiden- genannten Schutzgüter einwirkt, ist diese de Einflussgrösse für das zu erwartende Schwerpunktsetzung aus Sicht der vor Ort durchschnittliche globale Temperaturni- (potenziell) Betroffenen nachvollziehbar. veau (IPCC 2013). Aus einer globalen Perspektive ist jedoch Das für eine gegebene Zeitspanne verfügba- ein anderes von Fracking betroffenes re, zwei-Grad-kompatible Kohlenstoffbudget Schutzgut mindestens ebenbürtig: die Ein- bietet also wertvolle Informationen: Es lässt dämmung der globalen Klimaerwärmung. Im sich beispielsweise dem Kohlenstoffgehalt Folgenden wird daher die Förderung unkon- der zu einem bestimmten Zeitpunkt bekann- ventioneller Gasvorkommen mittels Frack - ten, wirtschaftlich förderbaren Reserven ing aus der Perspektive der nationalen und fossiler Energierohstoffe gegenüberstellen. internationalen Klimapolitik bewertet. Aus Daraus wird ersichtlich, welcher Anteil die- der Analyse werden Empfehlungen für die ser Reserven im betreffenden Zeitraum politische Steuerung der Schiefergasförde- maximal gefördert und energetisch verwer- rung abgeleitet. Diese beziehen sich auf das tet werden darf. Diese Gegenüberstellung politische System der Schweiz, sind aber haben bereits Meinshausen et al. (2009) verallgemeinert auch auf andere Staaten durchgeführt. Ihr Ergebnis – vor dem Höhe- übertragbar. punkt des Fracking-Booms in den USA: Weni- ger als die Hälfte der in den damals bekann- ten, wirtschaftlich und technisch förderba- 2 Die klimapolitischen ren fossilen Energierohstoff-Reserven ent- Auswirkungen von Fracking haltenen Treibhausgase dürfen bis zur Mitte des Jahrhunderts emittiert werden, wenn 2.1 Das Kohlenstoffbudget als zentrale die Zwei-Grad-Grenze einzuhalten ist. Grenze für die Energierohstoffförderung Neuere Studien haben diese Erkenntnis aktu- alisiert und präzisiert. Dabei ist zu beachten, Meinshausen et al. (2009) haben mithilfe dass keine objektiven Aussagen über ein probabilistischer Modelle aus dem politisch definitives Kohlenstoffbudget für einen gesetzten Ziel einer Begrenzung der durch- bestimmten Zeitraum möglich sind. Einfluss- schnittlichen Erderwärmung auf maximal variablen auf die Grösse des Budgets sind u. zwei Grad Celsius gegenüber dem vorindus- a. der vorgegebene maximale globale Tem- triellen Temperaturniveau – die sogenannte peraturanstieg, die Wahrscheinlichkeit, mit Zwei-Grad-Grenze – ein dementsprechendes der dieser einzuhalten ist, der Einbezug von
116 2-2014_geologi 2.06 12.02.15 15:21 Pagina 117
nicht-energetischen Treibhausgasquellen rund 200 Billionen Kubikmeter (tcm) Erdgas und von nicht CO2-Treibhausgasen (inkl. als technisch und wirtschaftlich förderbare deren Umrechnung in CO2) sowie Annahmen Reserven – ein Grossteil davon vermutlich über Klimaschutzbeiträge der nicht-energe- konventionelles Erdgas (IEA 2014). Geför- tischen Treibhausgasquellen (Carbon Trak- dert und verbrannt entspräche dies rund ker Initiative 2014). Neuere Schätzungen 400 Gt CO2, die in den 2‘860 Gt der IEA beziffern das globale Kohlenstoffbudget – (2012a) enthalten sind. Die technisch förder- unter der Vorgabe, dass die globale Durch- baren Erdgas-Ressourcen sind jedoch deut- schnittstemperatur mit 80-prozentiger lich grösser: 752 tcm – entsprechend rund Wahrscheinlichkeit um nicht mehr als zwei 1‘500 Gt CO2 – wovon 331 tcm (rund 660 Gt Grad ansteigt – auf 900 Milliarden Tonnen CO2) unkonventionelle Erdgas-Ressourcen Kohlenstoffdioxid (Gt CO2) für den Zeitraum sind (IEA 2012b). Es verbleiben also rund von 2013 bis 2049 und lediglich weitere 75 Gt 1‘100 Gt CO2 in technisch förderbaren Erd- CO2 für den Zeitraum von 2050 bis 2100 (Car- gas-Ressourcen, von denen vermutlich mehr bon Tracker Initiative 2013). als die Hälfte unkonventionelle Ressourcen Demgegenüber stehen 2‘860 Gt CO2, die sind. Die Überführung von weiteren Erdgas- emittiert würden, wenn die gesamten im Ressourcen in die Gesamtheit der Reserven Jahr 2012 bekannten fossilen Energieroh- und ihre Förderung durch Fracking würde stoffreserven gefördert und energetisch das oben skizzierte Problem also massiv ver- genutzt würden (IEA 2012a). Die damals schärfen. Schliesslich werden alle Energie- bekannten – aber noch äusserst geringen − Konzerne versuchen, einen möglichst gros- unkonventionellen Öl- und Gas-Reserven sind sen Teil bereits getätigter Explorationsinve- dabei berücksichtigt, die viel grösseren stitionen durch Förderung der entsprechen- unkonventionellen Ressourcen dagegen den Reserven zu amortisieren. nicht (IEA 2104). Die fossilen Energierohstoffe Erdöl, Stein- Die Schlussfolgerung aus diesen beiden kohle, Braunkohle und Erdgas unterschei- Daten – Kohlenstoffbudget und bekannte, den sich teilweise deutlich in ihrem jeweils förderbare Kohlenstoffreserven im Unter- spezifischen CO2-Gehalt (siehe z. B. BAFU grund – liegt auf der Hand und wird auch 2014; inwiefern diese Werte auch für unkon- von der Internationalen Energie Agentur ventionell gefördertes Erdgas gültig sind, expliziert: Zwei Drittel der bekannten Reser- wird unten diskutiert). Es liessen sich also ven fossiler Energierohstoffe dürfen nicht klimaverträglich mehr Energierohstoffe gefördert und verbrannt werden, wenn ein extrahieren, wenn es sich dabei um verhält- gefährlicher Klimawandel jenseits der Zwei- nismässig CO2-armes Erdgas handelt, als Grad-Grenze vermieden werden soll (IEA wenn beispielsweise CO2-intensive Braun- 2012a) – und zwar selbst über einen länger- kohle gefördert wird. Aufgrund längst getä- fristigen Horizont bis Ende des Jahrhun- tigter Investitionen in brennstoffspezifische derts. Damit ist klar: Für eine verantwor- Energie-Infrastrukturen (Kohlekraftwerke, tungsvolle Klimapolitik ist die weitgehende Erdöl-Pipelines, Gasnetze, heizöl- oder erd- Förderung und Verbrennung der bekannten gasbetriebene Wärmeerzeuger, Mineralöl- Öl-, Gas- und Kohlereserven tabu. Tankstellen etc.) sind dem theoretisch denk- In den oben genannten 2‘860 Gt CO2 sind baren Optimieren des noch zu fördernden Energierohstoff-Ressourcen noch gar nicht Energieträgermix in der Praxis allerdings berücksichtigt. Im Fall von Erdgas bedeutet kurzfristig deutliche Grenzen gesetzt. In dies: Den übereinstimmenden Statistiken Bezug auf das Kohlenstoffbudget bedeutet der US-amerikanischen Energy Information dies: Die weitgehende Begrenzung des kli- Administration (EIA 2014) und des World maverträglich noch förderbaren Kontin- Energy Council (2013) zufolge gelten derzeit gents gilt für alle Energierohstoffe: Erdgas,
117 2-2014_geologi 2.06 12.02.15 15:21 Pagina 118
Erdöl, Kohle – sei es konventionell oder 2.2 Ausweg Carbon Capture and Storage? unkonventionell gefördert. Oder politisch ausgedrückt: Ohne eine global gültige, wirk- Die Carbon Capture and Storage Technologie same CO2-Obergrenze bedeutet mehr (CCS), mit der bei der Verbrennung fossiler (unkonventionelle) Gasförderung zwangs- Energierohstoffe entstehendes CO2 abgeschie- läufig global steigende CO2-Emissionen (Bro- den und durch unterirdische Ablagerung von derick & Anderson 2012). der Atmosphäre ferngehalten werden soll, Ganz abgesehen davon stellt sich die Frage wird das oben genannte Dilemma nicht ent- der fairen internationalen Verteilung eines scheidend mildern. Selbst in dem bezüglich gegebenen Kohlenstoffbudgets entlang des CCS äusserst optimistischen Szenario der IEA in UN-Verträgen anerkannten Prinzips von (2012a) würde ein umfassendes Roll-Out der «equity» (United Nations 1992, p. 9). Derarti- Technologie das klimaverträglich förderbare ge Überlegungen dürften dazu führen, dass Kohlenstoffbudget bis 2050 nur um 125 Gt CO2 wohlhabenden Industriestaaten wie der vergrössern. IEA (2013) zufolge würde CCS die Schweiz ein deutlich kleinerer Anteil des klimaverträgliche Förderung von sogar nur verbleibenden Kohlenstoffbudgets zusteht, maximal drei Prozent mehr Reserven – vor als dies nach ihrem aktuellen Bevölkerungs- allem Kohle – erlauben. Die genannten Grös- anteil zu erwarten wäre. Dies hätte entspre- senverhältnisse – höchstens ein Drittel der chende zusätzliche Restriktionen für die kli- Energiereserven dürfen gefördert werden, maverträglich förderbaren fossilen Energie- zwei Drittel müssen im Boden bleiben – wer- rohstoffe in diesen Ländern zur Folge. den dadurch kaum berührt.
Fig. 1: Schematische Darstellung der Ressourcen und Reserven fossiler Energierohstoffe im Verhältnis zum klimaverträglichen Kohlenstoffbudget bis zur Mitte des Jahrhunderts (Datenquellen: IEA 2012a, IEA 2012b, IEA 2014, Carbon Tracker Initiative 2014).
118 2-2014_geologi 2.06 12.02.15 15:21 Pagina 119
Hinzu kommt, dass CCS aufgrund der hohen tet sich für wohlhabende Staaten wie die erforderlichen Investitionen zumindest auf Schweiz erst recht jede Investition in neue absehbare Zeit eher für emissionsintensive Infrastrukturen zur Gasförderung, egal ob Energieträger wie Braun- oder Steinkohle konventionell oder unkonventionell. Denn wirtschaftlich darstellbar scheint (ZEP eine für die Amortisation der Investition aus- 2011). Mit CCS ausgestattete Kraftwerke auf reichende Nutzung der Infrastruktur verbie- Basis des in dem vorliegenden Artikel im tet sich aus klimapolitischen Gründen (siehe Fokus stehenden Energieträgers Erdgas hät- zur Lock-in-Gefahr in Bezug auf den Frack - ten ein deutlich ungünstigeres Kosten-Nut- ing-Boom in den USA auch Spencer et al. zen-Verhältnis als beispielsweise Kohlekraft- 2014). werke, sodass CCS für die konventionelle und unkonventionelle Erdgasförderung 2.4 Die Rolle von Fracking in der sicher keine «Rettung» aus den Begrenzun- (internationalen) Energiewende gen des Kohlenstoffbudgets bietet. Fracking wird von seinen Befürwortern häu- 2.3 Lock-in durch Investitionen in fossile fig eine wichtige Rolle im Übergang des heu- Energie-Infrastrukturen tigen Energieversorgungssystems in eine kli- maverträgliche Zukunft zugeschrieben. Der- Potenzielle CO2-Emissionen sind nicht nur in artige Thesen beruhen teilweise auf Beob- den bekannten Reserven fossiler Energie- achtungen der Entwicklungen in den USA rohstoffe gespeichert, sondern implizit auch und sollen im Folgenden einzeln kurz in der existierenden energierelevanten Infra- betrachtet werden. Davon unberührt blei- struktur (IEA 2012a). Damit setzen auch ben die zuvor genannten prinzipiellen Argu- wirtschaftliche und infrastrukturpolitische mente gegen eine umfassende Förderung Überlegungen klare Grenzen für die weitere der fossilen Energierohstoffe. Förderung von Energierohstoffen. So hat Die erste These lautet kurz: «Shale Gas sogar die – nicht als ideologische Umwelt- ersetzt Kohle». Demzufolge hat der Fracking- schutzorganisation bekannte – Internationa- Boom in den USA dazu geführt, dass unkon- le Energie Agentur gefordert, dass aufgrund ventionell gefördertes Erdgas die – ver- klimapolitischer Überlegungen nicht weiter meintlich noch klimaschädlichere – Kohle in wie bisher in fossile Energieversorgungsin- der Stromerzeugung verdrängt und somit frastrukturen investiert werden darf (IEA einen positiven Netto-Effekt auf die globalen 2012a). Andernfalls wäre bereits im Jahr Treibhausgasemissionen hat. Während der – 2017 durch die bis dahin geschaffene Ener- womöglich nur vorübergehende – Rückgang gie-Infrastruktur und ihre über die Lebens- des Kohleverbrauchs in den USA zweifelsfrei dauer zu erwartende Nutzung der gesamte festgestellt werden kann, ist der Netto-Effekt CO2-Ausstoss festgelegt («locked-in», IEA beim Blick über die amerikanischen Landes- 2012a, p. 25), der bis 2050 noch klimaver- grenzen weniger positiv. So zeigen Broderick träglich emittiert werden darf. Investitionen & Anderson (2012), dass vermutlich mehr in die (unkonventionelle) Förderung, Trans- als die Hälfte der in den USA durch reduzier- port und Verbrennung von Erdgas ziehen ten Kohleverbrauch gesunkenen CO2-Emis- zwingend hohe Fördermengen und/oder lan- sionen durch steigenden Kohle-Export (vor ge Nutzungsdauern der Infrastrukturen nach allem nach Europa) kompensiert wurden. sich, um sich zu rentieren. Schwellenländer Eine häufig vorgebrachte These attribuiert wie Indien oder China werden bei realisti- die in den vergangenen Jahren gesunkenen scher Betrachtung nicht von heute auf mor- CO2-Emissionen der USA auf den Fracking- gen sämtliche Investitionen in fossile Ener- Boom: «Shale Gas senkt die CO2-Emissionen gieversorgung stoppen. Umso mehr verbie- der USA». Afsah & Salcito (2012) belegen
119 2-2014_geologi 2.06 12.02.15 15:21 Pagina 120
jedoch, dass dieser Effekt offenbar nur mar- steigen die globalen Durchschnittstempera- ginal war. Die preisgetriebene Verdrängung turen zum Beispiel um 3.5 °C über vorindu- von Kohle durch Shale Gas ist danach strielle Werte – deutlich jenseits der Zwei- zumindest in den ersten Jahren des Frack - Grad-Grenze und damit auf dem Pfad zu ing-Booms 2006 bis 2011 nur für 10% der US- einem gefährlichen Klimawandel. Dem neue- amerikanischen CO2-Reduktionen verant- sten Bericht des Intergovernmental Panel on wortlich. Fast 90% des Emissionsrückgangs Climate Change (IPCC) zufolge passt eine sind zurückzuführen auf den gesunkenen vorübergehend steigende Erdgasnutzung Mineralölverbrauch im Verkehrssektor und nur unter sehr restriktiven Bedingungen die Verdrängung von Kohle durch andere (geringer Methanschlupf, Nutzungsrück- Faktoren wie erneuerbare Energien, behörd- gang bis unter das heutige Niveau bereits liche Vorgaben und Kampagnen von Umwelt- vor 2050, etc.) zu Zwei-Grad-kompatiblen organisationen. Spencer et al. (2014) kom- Szenarien (IPCC 2014). men zu ähnlichen Resultaten. Aufbauend auf den beiden voran genannten 2.5 Methan-Emissionen der – zumindest teilweise widerlegten – Thesen unkonventionellen Gasförderung wird von einigen Fracking-Befürwortern postuliert: «Shale Gas ist eine notwendige Im vorangehenden Satz ist eine wesentliche Brücke zwischen Kohle und erneuerbaren Bedingung für die klimapolitische Diskus- Energien». In der Bildsprache bleibend könn- sion von Fracking erwähnt, die bislang te man darauf antworten: Die Gas-Brücke ist ausser Acht gelassen wurde: Das Ausmass womöglich kurz und führt vor allem zu noch der Methan-Emissionen und damit die Kli- mehr Erdgas. Denn die durch Fracking mabilanz von unkonventionell gefördertem bedingten vorübergehend günstigen Gas- Erdgas im Vergleich zu konventionell geför- preise in den USA haben zunächst vor allem dertem Erdgas und/oder Kohle. Verschiede- zu einem deutlichen Anstieg des Gasver- nen Autoren zufolge kommt dieser Variable brauchs geführt. Gleichzeitig wurden jedoch eine entscheidende Bedeutung zu, die die Investitionen in Energieeffizienz und erneu- klimaverträgliche Nutzung von unkonventio- erbare Energien teilweise deutlich gesenkt nellem Erdgas zusätzlich limitieren könnte (Martin 2013). Ausserdem wurden zeitgleich (IPCC 2014, Wigley 2011, Broderick & Ander- mit dem Fracking-Boom in einigen US-Staa- son 2012). ten die regulatorischen Rahmenbedingun- Eine kürzlich erschienene empirische Analy- gen für erneuerbare Energien verschlechtert se der Methan-Emissionen in den USA legt (Martin 2013). Offenbar sinkt durch die – nahe, dass der Methanschlupf bei der Gas- vermeintlich – günstige und unerschöpfliche förderung deutlich höher ist als bislang ange- Energiequelle Shale Gas die Bereitschaft von nommen (Miller et al. 2013). Danach entwei- Politik und Wirtschaft für förderliche Rah- chen circa drei Prozent des geförderten menbedingungen und Investitionen zugun- Methans direkt in die Atmosphäre (Romm sten von Effizienz und erneuerbaren Ener- 2013). Brandt et al. (2014) schätzen die gien. Auch Spencer et al. (2014) gehen davon Methan-Emissionen von unkonventioneller aus, dass der Fracking-Boom nicht zu einer Gasförderung noch höher ein – bis zu sieben nachhaltigen Decarbonisierung der amerika- Prozent des geförderten Gases. Das genaue nischen Energieversorgung führen wird. Aus Ausmass der Methan-Emissionen ist offenbar globaler Perspektive scheint ein umfassen- umstritten und hängt u. a. stark von den ein- der Ausbau der Gasförderung nur begrenzt gesetzten Technologien und dem Bohr- kompatibel mit der Einhaltung der Zwei- standort ab. Unstrittig ist jedoch, dass der Grad-Grenze (Levi 2013, Wigley 2011). Im Methanschlupf deutlich höher ist, als häufig Golden Age of Gas-Scenario der IEA (2011) in öffentlichen Statistiken oder Angaben von
120 2-2014_geologi 2.06 12.02.15 15:21 Pagina 121
Bohrloch-Betreibern beziffert (Miller et al jede Förderung von Kohlenwasserstoffen 2013, Brandt et al 2014). Entscheidend ist, ab eingeschränkt wird. Für die Schweiz – der- welcher Schwelle die energetische Nutzung zeit ohne Anlagen zur kommerziellen Förde- von unkonventionell gefördertem Gas eine rung von Kohle, Erdöl oder Erdgas – bedeu- schlechtere oder nur unwesentlich bessere tet dies sinnvollerweise ein umfassendes Klimabilanz als die von Kohle hat. Wigley Verbot jeglicher Förderung von Kohlenwas- (2011) zufolge ist dies bereits bei zwei Pro- serstoffen. Entsprechende Vorgaben können zent Methanschlupf der Fall. Das bedeutet: die Kantone problemlos in ihren jeweiligen Im ungünstigen Fall heizt unkonventionell Landesgesetzen verankern. gefördertes Erdgas den Klimawandel sogar Auf der Basis einer solchen konsequenten noch mehr an als Steinkohle. Position lässt sich auch einfacher eine diffe- renzierte positive Bewertung der tiefen Geo- thermie begründen. Denn Projekte zur 3 Schlussfolgerungen Gewinnung von Erdwärme unterscheiden sich von Fracking aus klimapolitischer Per- Die genannten Argumente zeigen, dass aus spektive grundsätzlich durch das Förderziel klimapolitischer Perspektive Fracking in den und die Treibhausgasemissionen – auch allermeisten Fällen nicht Teil der Lösung, dort, wo sich die eingesetzten Verfahren sondern Teil des Problems ist. Allein die Tat- ähneln: Hier soll weitgehend erneuerbare sache, dass zwei Drittel aller heute schon Wärme aus dem Erdinnern gewonnen wer- bekannten fossilen Energiereserven im den, um nahezu CO2-frei Strom und Wärme Untergrund verbleiben müssen, verbietet es, zu erzeugen und ausserdem womöglich fos- politische, technologische und finanzielle sil betriebene Heizungen zu ersetzen. Eine Ressourcen in Praktiken zur Erschliessung konsistente Energie- und Klimapolitik in der der bekannten und künftigen Reserven zu Schweiz würde demnach die Nutzung der investieren. Dies gilt umso mehr, als die tiefen Geothermie – unter Beachtung der investierten Mittel meist de facto in Konkur- spezifischen lokalen Chancen und Risiken – renz zu einem verstärkten Engagement für fördern und zugleich die konventionelle wie Energieeffizienz und erneuerbare Energien unkonventionelle Erdgasförderung aus- stehen. Und kapitalintensive Fracking-Infra- schliessen. struktur führt in ein Kohlenstoff-Lock-in: Um Investitionsruinen zu vermeiden, müsste in grossem Ausmass und über ausreichende Zeit unkonventionell gefördertes Erdgas energetisch genutzt werden. Das wiederum heizt den Klimawandel an bzw. schränkt den Spielraum für Klimaschutzmassnahmen wei- ter ein. Diese Argumentation gilt umso mehr, wenn sich die wachsende Evidenz bestätigt, dass Fracking deutlich höhere Methanemis- sionen mit sich bringt als bislang vermutet bzw. als aus der konventionellen Erdgasför- derung bekannt. Ausser dem letztgenannten Aspekt sprechen alle in diesem Artikel genannten Argumente auch gegen die konventionelle Erdgasförde- rung. Aus diesem Grund ist es aus klimapoli- tischer Perspektive nur konsequent, wenn
121 2-2014_geologi 2.06 12.02.15 15:21 Pagina 122
Literatur IPCC, 2014: Climate Change 2014: Mitigation of Cli- mate Change. Contribution of Working Group III Afsah, S. & Salcito, K. 2012: Shale Gas and the Fairy to the Fifth Assessment Report of the Intergov- Tale of its CO2 Reductions. Zugriff: 02.10.2014: ernmental Panel on Climate Change [Eden- http://co2scorecard.org/home/researchitem/24. hofer, O., Pichs-Madruga, R., Sokona, Y., Fara- BAFU (Bundesamt für Umwelt) 2014: Faktenblatt hani, E., Kadner, S., Seyboth, K., Adler, A., CO2-Emissionsfaktoren des Treibhausgasin- Baum, I., Brunner, S., Eickemeier, P., Krie- ventars der Schweiz. Ittingen. mann, B., Savolainen, J., Schlömer,S., von Ste- Brandt, A. R., Heath, G. A., Kort, E. A., O’Sullivan, F., chow, C., Zwickel, T. & Minx, J. C. (eds.)]. Cam- Petron, G., Jordaan, S. M., Tans, P., Wilcox, J., bridge University Press, Cambridge, United Gopstein, A. M., Arent, D., Wofsy, S., Brown, N. Kingdom and New York, NY, USA. J., Bradley, R., Stucky, G. D., Eardley, D., Har- Levi, L. 2013: Climate consequences of natural gas riss, R. 2014: Methane Leaks from North Amer- as a bridge fuel. Climatic Change, 118 (3−4), ican Natural Gas Systems, Science, 343(6172), 609−623. 733−735. Martin, C. 2013: U.S. States Turn Against Renew- Broderick, J. & Anderson, K. 2012: Has US Shale able Energy as Gas Plunges. Zugriff: Gas Reduced CO2 Emissions? Examining recent 02.10.2014: http://www.bloomberg.com/news/ changes in emissions from the US power sector 2013-04-23/u-s-states-turn-against-renew- and traded fossil fuels. Tyndall Manchester. able-energy-as-gas-plunges.html. Machester. Meinshausen, M., Meinshausen, N., Hare, W., Rap- Carbon Tracker Initiative 2013: Unburnable Carbon er, S. C. B., Frieler, K., Knutti, R., Frame, D. J. & 2013: Wasted capital and stranded assets. Allen, M. R. 2009: Greenhouse-gas emission http://www.carbontracker.org/report/wasted- targets for limiting global warming to 2 °C. capital-and-stranded-assets/ Nature 458 (7242): 1158. Carbon Tracker Initiative 2014: Resources. Zugriff: Miller, S. M., Wofsy, S. C., Michalak, A. M., Kort, E. 30. September 2014: http://www.carbontrack- A., Andrews, A. E., Biraud, S., Dlugokencky, E., er.org/resources/. Eluszkiewicz, J., Fischer, M. L., Janssens- EIA (Energy Information Administration) 2014: Maenhout, G., Miller, B. R., Miller, J. B., Montz- International Energy Statistics. Zugriff: ka, S., Nehrkorn, T. & Sweeney, C. 2013: 06.10.2014: http://www.eia.gov/cfapps/ipdb- Anthropogenic emissions of methane in the project/IEDIndex3.cfm?tid=3&pid=3&aid=6. United States. Proceedings of the National IEA (International Energy Agency) 2011: World Academy of Sciences, 110 (50), 20018−20022. Energy Outlook 2011. Special Report. Are we Romm, J. 2013: Bridge Out: Bombshell Study Finds entering a golden age of gas? OECD/IEA, Paris. Methane Emissions From Natural Gas Produc- 131 S. tion Far Higher Than EPA Estimates. Zugriff: IEA (International Energy Agency) 2012a: World 02.10.2014: http://thinkprogress.org/climate/ Energy Outlook 2012. OECD/IEA, Paris. 690 S. 2013/11/25/2988801/study-methane-emis- IEA (International Energy Agency) 2012b: Golden sions-natural-gas-production/. Rules for a Golden Age of Gas. World Energy Spencer, T., Sartor, O. & Matthieu M. 2014: Uncon- Outlook Special Report on Unconventional Gas. ventional wisdom: an economic analysis of US OECD/IEA, Paris. 150 S. shale gas and implications for the EU. Institut IEA (International Energy Agency) 2013: Redrawing du développement durable et des relations the energy-climate map. World Energy Outlook internationals (IDDRI). Paris. Special Report. OECD/IEA, Paris. 134 S. United Nations 1992: United Nations Framework IEA (International Energy Agency) 2014: Mitteilung Convention on Climate Change. New York. 33 S. per E-Mail an den Verfasser, 07.10.2104. Wigley, T. 2011: Coal to gas: the influence of IPCC 2013: Climate Change 2013: The Physical Sci- methane leakage. Climatic Change, 108 (3), ence Basis. Contribution of Working Group I to 601−608. the Fifth Assessment Report of the Intergov- World Energy Council 2013: World Energy ernmental Panel on Climate Change [Stocker, Resources: 2013 Survey. London. 468 S. T. F., Qin, D., Plattner, G.-K., Tignor, M., Allen, S. ZEP (Zero Emissions Platform) 2011: The Costs of K., Boschung, J., Nauels, A., Xia, Y., Bex, V. & CO2 Capture, Transport and Storage. Post- Midgley, P. M. (eds.)]. Cambridge University demonstration CCS in the EU. Press, Cambridge, United Kingdom and New York, NY, USA.
122 2-2014_geologi 2.06 12.02.15 15:21 Pagina 123
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 123-128
Voraussetzungen zur Nutzung von unkonventionellen Kohlenwasserstoffen mit Hilfe von Fracking in der Schweiz Walter Wildi1
Angepasste Version des Vortrags vom 7.10.2014 am Symposium «Energie aus dem Untergrund – Who cares?» unter dem Titel: «Schiefergas und Fracking, braucht die Schweiz ein Moratorium?»
Stichworte: Unkonventionelle Kohlenwasserstoffe, Schiefergas, Fracking, Schweiz, Bergregal
Abstract Résumé Five conditions must be met in order to consider Cinq conditions de base devraient être remplies non conventional hydrocarbon production in pour envisager l’exploitation d’hydrocarbures non Switzerland using fracking: 1. Clear and specific conventionnels à l’aide du fracking en Suisse: 1. legal regime, 2. Sufficient scientific and technolog- Une législation spécifique et claire, 2. Des connais- ical expertise, 3. Effective and competent supervi- sances scientifiques adéquates et la maîtrise de la sion and control, 4. Sustainability, 5. Limited poten- technologie, 3. Une surveillance et un contrôle tial for conflicts and risks; political and social effectifs et efficaces, 4. La durabilité du projet, 5. acceptance. Potentiel de conflits et risques limités; acceptance The analysis comes to the conclusion that the con- politique et sociale. L’analyse arrive à la conclusion ditions for unconventional hydrocarbon production que les conditions pour l’exploitation d’hydrocarbu- and the massive use of fracking are not given so far res non conventionnels à l’aide du fracking ne sont in Switzerland, and suggests possible improve- de loin pas remplies en Suisse. Elle propose enfin ments in the case the project should continue. des pistes pour des actions à engager si le projet devait être poursuivi.
Zusammenfassung Fünf Bedingungen müssten erfüllt sein, um die Einführung Produktion unkonventioneller Kohlenwasserstoffe mit Hilfe von Fracking in der Schweiz zu erwägen: 1. Klare und spezifische rechtliche Regelung, 2. Seit einigen Jahren entwickeln sich die Pro- Hinreichende wissenschaftliche und technologi- spektion und Förderung von unkonventio- sche Beherrschung, 3. Effektive und kompetente Überwachung und Kontrolle, 4. Nachhaltigkeit, 5. nellen Kohlenwasserstoffen in rasanter Begrenztes Konfliktpotential und Risiko; politische Weise. Aufgrund dieser Entwicklung werden und soziale Akzeptanz. Die Analyse kommt zur selbst die Vereinigten Staaten von Amerika, Schlussfolgerung, dass die Bedingungen für die Produktion unkonventioneller Kohlenwasserstoffe bis jetzt ein grosses Importland, zu einem mit Hilfe von Fracking in der Schweiz bei Weitem Exportland. Das Ganze gleicht einem neuen nicht gegeben sind und schlägt mögliche Pisten «Goldrausch», diesmal für Schwarzes Gold. vor, wie weiter vorgegangen werden könnte, falls Europa zieht bei dieser Entwicklung nicht das Projekt weiter verfolgt werden sollte. voll mit. Starke Widerstände haben sich namentlich in Frankreich, in etwas geringe- rem Masse auch in andern Ländern entwi- ckelt. Dabei stehen sowohl die generelle Ablehnung eines neuen Gas- und Petrol- booms, die Frage des nachhaltigen Grund- und Trinkwasserschutzes und des Schutzes der Atmosphäre vor Gaslecks (v.a. Methan), 1 Institut F. A. Forel and Institut des sciences de l’environ- nement, University of Geneva, route de Suisse 10, sowie die in Europa höheren Förderpreise 1290 Versoix, Suisse [[email protected]] als in den USA im Vordergrund (siehe z.B.
123 2-2014_geologi 2.06 12.02.15 15:21 Pagina 124
Schnyder 2013, Titz 2013 und andere Presse- 1 Klare und spezifische rechtliche berichte). Kritisiert wird oft auch die zur Regelung Förderung verwendete Technik des Frack- ings in abgelenkten Bohrungen, bei welcher Heitzmann (2007) gibt einen Überblick über Erdbeben auftreten. die rechtlichen Grundlagen der Nutzung mineralischer Rohstoffe in der Schweiz. Die Schweiz verfügt, aus geologischer Sicht, Gemäss Bundesverfassung und Zivilgesetz- über ein reelles, wenngleich nicht ausge- buch haben die Kantone bezüglich der Nut- sprochen attraktives Potential für unkon- zung von Bodenschätzen über ihre Bergrega- ventionelle, und in geringerem Mass auch le weitgehend freie Hand. Gewisse Ein- für konventionelle Kohlenwasserstoffvor- schränkungen und begleitende Massnahmen kommen (Brink et al. 1992, Burri et al. 2011, erwachsen aus anderen Gesetzgebungen, Leu 2008, 2014). Deshalb laufen Anstrengun- wie etwa dem Umweltschutz, dem Gewässer- gen verschiedener Akteure, um Konzessio- schutz und dem Kernenergiegesetz. Dement- nen zur Prospektion zu erlangen. Allerdings sprechend gelten bezüglich Prospektion und kam es bisher zu keinen neuen Prospek- «Schürfung» mineralischer Rohstoffe, inklusi- tions- oder Förderbohrungen. Es bleibt also ve fossiler Kohlenwasserstoffe, ebenso viele ein gewisser Raum, um darüber nachzuden- unterschiedliche Bergregale wie die Schweiz ken, ob die Rahmenbedingungen für die Pro- Kantone zählt. Einige Kantone vereinigten spektion und eventuelle Ausbeutung unkon- sich im Hinblick auf die Erdölprospektion in ventioneller Kohlenwasserstoffe unter Ver- einem Konkordat, was aber aufgrund der wendung von Fracking überhaupt gegeben schwachen Tätigkeit in diesem Sektor in den sind. vergangenen Jahren zu keiner weiteren Ent- wicklung führte. Generell kann festgehalten werden, dass die Grundvoraussetzungen zur Prospektion Schweiz und ihre Kantone über keine klaren und Förderung von unkonventionellen gesetzlichen Regelungen zur Erteilung von Kohlenwasserstoffen in der Schweiz Konzessionen für die Prospektion und Aus- beutung von unkonventionellen Kohlenwas- Folgende Grundvoraussetzungen müssten serstoffen und für die Überwachung und heute zur Bewilligung der Prospektion und Kontrolle verfügen. Angesichts der Erwar- eventuellen Förderung von unkonventionel- tungen der Öffentlichkeit an die Sicherheit len Kohlenwasserstoffen mit Hilfe von Frack- und Nachhaltigkeit der Nutzung derartiger ing erfüllt sein: Bodenschätze, müsste das Bergrecht ent- 1. Klare und spezifische rechtliche Rege- sprechend ergänzt und interkantonal und lung. national koordiniert werden. Dabei wären 2. Hinreichende wissenschaftliche und tech- namentlich folgende wichtigen Themen zu nologische Beherrschung. berücksichtigen: 3. Effektive und kompetente Überwachung • Vollständigkeit der Gesuchsunterlagen und Kontrolle. und ihr öffentlicher Charakter. 4. Nachhaltigkeit, im Sinne der Umweltver- • Rahmenbedingungen und Grundregeln träglichkeit, sowie der sozialen und wirt- beim Einsatz von Fracking, wie z.B. Regeln schaftlichen Verträglichkeit. zur Verwendung von chemischen Substan- 5. Begrenztes Konfliktpotential und Risiko, zen zur Mobilisierung der Kohlenwasser- politische und soziale Akzeptanz. stoffe. • National geregelte Umweltverträglich- keitsprüfung, von der Prospektion bis hin zum Verschluss der Bohrungen. Nachweis
124 2-2014_geologi 2.06 12.02.15 15:21 Pagina 125
der Nachhaltigkeit des Vorhabens. Der Nutzung der Kernenergie. Sie kontrastiert Umfang der Prüfung ist heute gemäss Ver- mit der Geschichte der Maschinen-, der ordnung über die Umweltverträglichkeits- Uhren- und der chemischen Industrie, wel- prüfung (UVPV) den Kantonen überlassen. che seit weit mehr als einem Jahrhundert • Risikoanalysen, inklusive langfristige mit robustem Hintergrund in Forschung, Trinkwassersicherheit, Seismizität, Boden- Entwicklung und Ausbildung prosperieren. senkung, etc. Eine derartige Entwicklung im Bereich der • Überwachung und Kontrolle durch die fossilen Energieträger würde entsprechende Behörden. mittel- und langfristige, öffentliche und pri- vate Anstrengungen verlangen, sowohl in Übergeordnete Anliegen müssten auf natio- der Nachwuchsförderung, als auch in der naler Ebene geregelt werden. Dazu zählen Forschung und Entwicklung, etwa so, wie insbesondere landesplanerische Aspekte dies heute auf dem Gebiet der Geothermie der Nutzung des Untergrundes und die Defi- geschieht. nition von Prioritäten zwischen unterschied- lichen Nutzungen. 3 Effektive und kompetente Überwachung und Kontrolle 2 Hinreichende wissenschaftliche und technologische Beherrschung In den meisten gesellschaftlich relevanten Bereichen erlassen in der Schweiz Parla- Die nachhaltige Entwicklung eines neuen ment und Regierung auf nationaler Ebene technologischen und industriellen Wirt- Gesetze und Verordnungen, deren Umset- schaftszweigs, behaftet mit Schwierigkeiten zung den Kantonen obliegt. Die Landesregie- und Risiken für Mensch und Umwelt, ver- rung bzw. die Zentralverwaltung überwa- langt eine wissenschaftliche und technologi- chen die Umsetzung. Dagegen ist der Bund sche Beherrschung auf hohem Niveau. z.B. in den Bereichen des Eisenbahnwesens, In der Schweiz wird zurzeit unseres Wissens der Sicherheit der Gas- und Ölpipelines und keine Grundlagenforschung zu Themen der nuklearen Sicherheit gleichzeitig als betrieben, welche das Fracking und andere regulierende, ausführende und kontrollie- Fragen der Kohlenwasserstoffprospektion rende Instanz tätig. Bei der Umsetzung der oder -förderung direkt betreffen. Damit wer- Minenregale sind die Kantone alleinige Mei- den auch auf dem Hochschulniveau keine ster an Bord, solange keine anderen, dem Fachleute auf diesem Gebiet ausgebildet Bund unterstellte Bereiche betroffen sind. (etwa auf dem Niveau Master oder Dokto- Zu Fragen der Kohlenwasserstoffprospek- rat). Die Thematik wird allenfalls in Vorle- tion und der Produktion verfügen die Kanto- sungen und Masterkursen gestreift. Expo- ne allerdings in der Regel weder über qualifi- nenten, welche in Fachzeitschriften und Vor- ziertes, kompetentes Personal, noch über trägen zur Diskussion beitragen, tun dies entsprechende technische und wissen- meist auf Grund von Erfahrungen aus einem schaftliche Ausrüstung. Auch wenn sie industriellen Kontext in Weltregionen mit gewisse Überwachungs- und Kontrolltätig- geringerer Bevölkerungsdichte und weniger keiten an externe öffentliche oder private entwickelten Infrastrukturen, d. h. mit klei- Institutionen delegieren würden, wären sie neren Risiken für Mensch und Umwelt. weder imstande, die Pflichtenhefte zu redi- Eine ähnliche Entwicklung einer neuen Indu- gieren, noch die Resultate zu prüfen. strie, ohne nachhaltige wissenschaftliche Damit ist die Frage der Überwachung und und industrielle Verankerung, erlebte die Kontrolle offen. Lösungen könnten entweder Schweiz im Bereich der zu Ende gehenden durch eine Zusammenarbeit zwischen den
125 2-2014_geologi 2.06 12.02.15 15:21 Pagina 126
Kantonen, oder durch die Schaffung einer 5 Begrenztes Konfliktpotential und nationalen Fachstelle gefunden werden. Risiko, politische und soziale Akzeptanz
4 Nachhaltigkeit, im Sinne der Fracking zur Gewinnung von fossilen Koh- Umweltverträglichkeit, sowie der lenwasserstoffen beinhaltet verschiedene sozialen und wirtschaftlichen Risiken. Diese können sich während der Pro- Verträglichkeit spektion, der Produktion, oder gar nach dem Verschluss der Bohrungen realisieren: Akzeptiert man den Begriff der Nachhaltigen − Erhöhte Seismizität: Kleinere Erdbeben Entwicklung in seiner ursprünglichen Defini- können sich während dem Bohrvorgang tion (United Nations 1987), so bedeutet er bzw. dem Frackingprozess, aber auch namentlich Gerechtigkeit zwischen den heu- während der Nutzung einer Ressource te und den zukünftig lebenden Menschen, ereignen. Wichtigere Ereignisse können und dass auch künftige Generationen knap- vermutlich einzig in eigentlichen Erdbe- pe Ressourcen nutzen können. bengebieten ausgelöst werden. So betrachtet, kann die Nutzung einer − Bodensetzung: Mit Subsidenz ist während beschränkten Kohlenwasserstoffressource, und bis einige Jahre oder Jahrzehnte nach welche durch die heutige Generation ausge- der Ausbeutung einer Lagerstätte zu rech- beutet und nachher verlassen würde, nicht nen. Sie kann Bauten und Infrastrukturen als nachhaltig betrachtet werden. Allenfalls beschädigen. Subsidenz ist in Bergbauge- könnte die Ressource z.B. als Notreserve bieten und Gasfeldern eine übliche bereitgestellt und im Falle einer Krisensitua- Erscheinung (Ketelaar 2009). tion zu einer teilweisen Nutzung freigegeben − Gasaustritte in die Atmosphäre: Diese kön- werde. nen bei Undichtigkeit direkt aus der Boh- Weitere wichtige Aspekte, welche die Nach- rung austreten und damit das Klima haltigkeit der Nutzung einschränken kön- beeinflussen. Das Risiko ist etwa mit nen, betreffen eventuelle Ressourcenkonflik- jenem von Lecks an Gasleitungen zu ver- te, namentlich mit der Nutzung von Geother- gleichen. Es verschwindet mit dem saube- mie, der Nutzung als Wirtsgestein oder als ren Verschluss der Bohrung. Caprock für die Untertagelagerung (radioak- − Grundwasserverschmutzung: Grundwasser tive Abfälle, Kohlendioxyd, flüssige Kohlen- kann durch die chemischen Zusatzmittel wasserstoffe und Gas), oder für die Anlage zur Mobilisierung der Kohlenwasserstof- von Transportinfrastrukturen. fe, aber auch durch die Kohlenwasserstof- Die Ausbeutung von fossilen Kohlenwasser- fe selbst erfolgen. Meist ist oberflächen- stoffen im geologischen Untergrund steht nahes Grundwasser betroffen, da es sich damit bezüglich der Nachhaltigkeit in kras- vor allem um Verschmutzungen verur- sem Gegensatz zur Nutzung der erneuerba- sacht durch unvorsichtigen Umgang mit ren Geothermie und der Nutzung von Tiefen- Bohrflüssigkeit und Wasser aus der För- grundwasser im Allgemeinen. Bei einer derung handelt. Grundwasserverschmut- Abwägung zwischen den verschiedenen zung kann aber, beispielsweise etwa bei möglichen Nutzungen des Untergrundes mangelhaftem Bohrlochverschluss, noch schneidet die Ausbeutung dieser fossilen weit über die Nutzungsperiode hinaus ein Energieträger schlecht ab. Thema sein. − Veränderung der tiefen Wasserzirkulation: Fracking lockert die betroffene Gesteins- formation auf. Diese kann dadurch ihre Eigenschaft als Aquitard verlieren. Damit
126 2-2014_geologi 2.06 12.02.15 15:21 Pagina 127
kann die Tiefenzirkulation stark verän- förderung und fehlender Grundlagenfor- dert werden. A priori geht die Verände- schung, ungenügende Überwachung und rung in Richtung einer verstärkten Was- Kontrolle, ungenügende Nachhaltigkeit der serzirkulation. Dies kann bei Tiefenlager- Projekte und mangelhaftes Risikomanage- projekten, Geothermieprojekten, bei der ment können nicht mit Aussagen wie den Gewinnung von tiefer gelegenem Trink- Folgenden aus dem Wege geräumt werden wasser oder bei Projekten für Transport - (Burri & Häring 2014): «Wissenschaftliche infrastrukturen zu Beeinträchtigungen Fakten sind zunehmend mit unzureichender und Konflikten führen (siehe Punkt 4, Information von Bevölkerung und Behörden oben). konfrontiert. Der leichte Zugang zu Informa- tionen über Internet führt zu einem starken Eine teilweise weitergehende Analyse der Anstieg des Pseudo-Wissens. […] Die Kritik Risikofrage, inklusive ökonomischen und basiert mehr auf Glauben, denn auf Fakten sozialen Risiken, wurde durch IRGC (2013) und es ist deshalb schwierig, ihr mit rationa- für die Entwicklung unkonventioneller Gas- len Argumenten zu begegnen.» ressourcen präsentiert. Sollen die Projekte zur Prospektion und Pro- duktion von konventionellen Kohlenwasser- In der öffentlichen Diskussion überwiegen in stoffen in der Schweiz mit Aussicht auf Europa die Themen der erhöhten Seismizität Erfolg weiter verfolgt werden, so müssen und der Grundwasserverschmutzung. Dabei diese Mängel sicher korrigiert werden. vertreten die Befürworter der Projekte zur Dabei ist der wichtigste Punkt jener, dass Prospektion und Produktion von unkonven- das Land weder über eine Vision noch über tionellen Kohlenwasserstoffen meist private eine Strategie der Nutzung seines geologi- Akteure. Die Risiken erscheinen als Risiken schen Untergrundes verfügt. Sodann fehlen zu Lasten der Bevölkerung. Entsprechend ist die zur Umsetzung notwendigen rechtlichen die Akzeptanz von Projekten zur Erschlies- Grundlagen sowie die Instrumente, um diese sung von unkonventionellen Kohlenwasser- Nutzung im Sinne der nachhaltigen Entwick- stoffen sehr schlecht. Der Widerstand kann lung zu steuern und zu begleiten. regional bezüglich seiner Intensität mit jenem gegen Kernkraft verglichen werden. Vor diesem Hintergrund scheint die Schaf- fung öffentlicher Kompetenzzentren und kompetenter öffentlicher Kontroll- und Überwachungsbehörden als einziger Aus- weg, um die Vertretung öffentlicher Interes- sen kompetent zu vertreten.
Diskussion
Wie die obigen Ausführungen aufzuzeigen versuchen, sind in der Schweiz heute die Voraussetzungen für die Produktion unkon- ventioneller Kohlenwasserstoffe mit Hilfe von Fracking nicht gegeben. Fakten, wie ungenügende rechtliche Regelung, fehlende wissenschaftlich-technologische Beherr- schung aufgrund mangelnder Nachwuchs-
127 2-2014_geologi 2.06 12.02.15 15:21 Pagina 128
Referenzen
Brink, H. J., Burri, P., Lunde, A. & Winhard, H. 1992: Hydrocarbon habitat and potential of Swiss and German Molasse Basin: a comparison. Eclogae geol. Helv. 85/3, 715−732. Burri, P., Chew, K., Jung, R. & Neumann,V. 2011: The Potential of Unconventional Gas – energy bridge to the future (with a review of European uncon- ventional gas activities). Swiss Bull. angew. Geol. 16/2, 3−55. Burri, P. & Häring, M. 2014: Ressourcen-Explo- ration: Risiko oder Chance? – Das Spannungs- feld zwischen wissenschaftlichen Fakten und öffentlicher Wahrnehmung. Swiss. Bull. angew. Geol. 19/1, 33−40. Heitzmann, P. 2007: Kapitel 12, Gesetzliche Grund- lagen für die Rohstoffnutzung und für andere geologische Aktivitäten. Die mineralischen Rohstoffe der Schweiz. Schweiz. Geotech. Komm. IRGC 2013: Risk governance guidelines for uncon- ventional gas development. Report Int. Risk gov- ernance Council. ISBN 978-2-9700-772-8-2, Lausanne, 94 p. Ketelaar, V. B. H. 2009: Satellite Radar Interferome- try; subsidence monitoring techniques. Springer. Leu, W. 2008: Potential der Kohlenwasserstoffres- sourcen; Schweizer Mittelland und subalpiner Bereich. NAGRA, NAB 08-03, Wettingen. Leu, W. 2014: Erdöl-Erdgasexploration in der Trendwende: Potenzial der unkonventionellen Ressourcen in der Schweiz und Europa – Anstrengungen und Kontroversen. Swiss Bull. Angew. Geol. 19/1, 29−32. Schnyder, S. 2013: In Europa spricht vieles gegen Schiefergas. Der Bund, 10.09.2013. Titz, S. 2013: In Europa sitzen die Bedenken gegen Schiefergas tief. NZZ, 23.04.2013. United Nations 1987: «Brundtland Report». Report of the World Commission on Environment and Development. Official Records of the General Assembly, Forty-second Session, Supplement No. 25 (A/42/25).
128 2-2014_geologi 2.06 12.02.15 15:21 Pagina 129
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 129-139
The Global Impact of Unconventional Hydrocarbons (Hydraulic Fracturing on the way to a clean and safe technology). AAPG Annual Convention Houston, April 2014 – Selected highlights Peter Burri1
Comments and additions by the author in italics.
Key words: AAPG, natural gas, unconventional gas, unconventional oil, hydraulic fracturing, fracking, global energy, climate, CO2, coal, US energy, gas reserves, peak oil, peak gas
1 General impressions and highlights
The convention: The convention was held in reluctant to invest in exploration activities out- Houston, the centre of the US oil and gas side N-America. An additional reason may be industry and drew, with over 8.000 attendees the disappointment of many US companies almost twice the crowd of the Pittsburgh meet- with the progress of unconventional activities ing last year. outside America, especially in Europe, even The focus of the talks has been very much on though high gas prices in Europe, and espe- domestic business: never in the past years cially in Asia, are most attractive. US compa- have there been so few contributions by US nies see Europe increasingly as a high-risk companies on plays outside America. There area with low legal security. This mood has were many very specialized technical talks been triggered by the moratoria on shale gas (many by Chinese scientists) but disappoint- and the revoking of valid exploration licences ingly few overviews of large new international (also in Switzerland) as well as short term plays. Especially the independents are retreat- changes in tax regimes and very slow and ing to domestic activities. The other general unpredictable approval processes. observation is the still increasing importance Gas in the US was in April 2014 valued around of unconventional exploration and develop- 4.0−4.5 $/MCF, i.e. about half the prices in ment, a topic that had an absolutely dominant Europe and 3−4 times lower than in the Far role at this year’s conference. East. Prices of 4−5 $/MCF do allow breakeven production in most of the plays but the main US E&P Industry: Amongst US companies profits are presently made on associated liq- the move «back home» to the US onshore is uids. European Majors who had invested heav- still on-going. This may also be a matter of ily in unconventional gas acreage in the US funding: unconventional domestic activities (e.g. BP, Shell, Statoil) have grown more cau- have attracted a very large part of the world- tious. Most of these companies have been late- wide E&P investment and fewer companies comers to the game, have overpaid corporate can afford to dance on too many shows. In acquisitions and acreage and often only man- addition, banks and private capital are still aged to get second grade blocks. The most suc- cessful companies in the US unconventional business remain the smaller independents. 1 Holbeinstrasse 7, 4051 Basel, Switzerland The low energy prices continue to have a strong [[email protected]] positive effect on the US economy. Energy inten-
129 2-2014_geologi 2.06 12.02.15 15:21 Pagina 130
sive industries and/or industries with a large ing NGL) compared to 6.8 Mio BOPD in 2006 demand for gas as a raw material are relocat- (Fig. 3). ing back to the US. The US draws a major com- Energy self-sufficiency for the US is still a petitive advantage from the gas boom and the prominent topic. Though it is very question- recovery of the US economy over the past years able whether the US will reach self-sufficiency is at least partly driven by energy costs. in oil, imports are steeply decreasing and the The Obama administration has called uncon- US do in principle not need any imports from ventional gas «America’s answer to Fukushi- the Middle East or N-Africa. The US will ma». The switch to gas, mainly the substitution become a net exporter of gas in 2020 (Fig. 5). of coal in power generation, has led to a fur- ther decrease in CO2 emissions in 2013 in Unconventional hydrocarbons strong contrast to Germany where CO2 emis- Unconventional oil in US: Unconventional oil sions are rising (Figs. 1, 2). Gas will also exploration is today in the US as important as impact the transport sector: by 2030 over 10 unconventional gas – and more profitable. million vehicles in the US, especially diesel Contrary to gas where the biggest plays have trucks are expected to run on natural gas. This probably been identified, unconventional oil will have a major positive impact on the envi- plays continue to emerge. The production of ronment. In spite of not having signed the the Bakken oil shale in Montana has already Kyoto Protocol the US may eventually be one changed the US energy landscape and has led of the few countries achieving the Kyoto target to a situation where the domestic oil produc- reductions (reducing greenhouse gases emis- tion now exceeds imports for the first time in sions until 2020 to 18% below 1990 levels). 20 years (Fig. 3).
Reserve and Production growth: Gas Unconventionals US: There is a conspicuous reserves and oil reserves of the US continue to move away from the «drilling the hell out of it» grow. The country added over 35 TCF in 2013 approach to a sweet spot exploration. The (production 24 TCF). Proven gas reserves are brainier part of the Industry has realized that therefore about double of those 20 years ago. 80% of the production came from only 20% of Oil reserves and -production grew even the wells and that many wells (possibly up to stronger. The country is approaching about 9 50%) were not or only marginally commercial. Mio BBL/D in total liquids production (includ- The new approach gives much more weight to
Fig. 1: CO2 emissions in US per capita are at present back to levels of 1960s (contrary to Europe).
130 2-2014_geologi 2.06 12.02.15 15:21 Pagina 131
geological thinking, reservoir analysis, geo- There are also some technical/geological con- chemistry and rock mechanics. Parallel to this, cerns: e.g. China, seen after Argentina as prob- the drilling performance and well comple- ably the next major development area for tion/stimulation technology are continuously unconventional gas, has geological settings improved. Thanks to these improvements one that are very different from N-America. Most year drilling delivers today in the Marcellus basins have a lacustrine source rock. Lacus- 10 × more production than 6 years ago. Oil pro- trine shales are often rich source rocks but duction in the Eagle Ford has risen 20 × in 5 may provide lower quality shale gas plays years (see Fig. 4). The often heard statement since proximal intracratonic settings produce that in general unconventional production per much more variable lithology and a more well is low, not sustainable and thus not com- mineralogically immature clastic input. Lacus- mercial, is clearly incorrect. Production does trine source rocks are also generally more drop steeply in the first year in most wells but shaly than marine ones and may thus be less it stabilizes thereafter and economic produc- brittle and less suited for hydraulic fracturing. tion can reach far over 10 years. Environmental concerns with hydraulic Unconventionals worldwide: There is no fracturing are still part of the public discus- doubt that the success of unconventionals will sion, especially in the State of New York, the be repeated in many other parts of the world. only state where a development of the Marcel- There is, however, at present more caution in lus play is still banned, though interestingly the forecasts as to how fast this will happen. New York is the biggest gas consumer of Nowhere else are unconventional hydrocar- unconventional gas. In depth studies by the US bons tackled in the determined approach of Department of Environment show conclusive- the US and nowhere else will there be the ly that the very large majority of water con- same huge resources in money and technolo- tamination by drilling fluids and gas is not gy dedicated to such exploration. In addition related to hydraulic fracturing. Extensive action by regulators in almost all countries water analyses in Pennsylvania identify and especially in Europe is slow and unpre- methane as a very common constituent of dictable. Unconventional gas and oil will be drinking water from water wells (some 36% of developed worldwide but it will most likely wells in W Pennsylvania contain natural take decades rather than years. methane). Most methane stems from coal
Fig. 2: US CO2 emissions and shale gas production. Shale gas allows emission reductions that are not achieved in any other indu- strialized country. (Source US DOE).
131 2-2014_geologi 2.06 12.02.15 15:21 Pagina 132
Fig. 3: US oil imports vs. exports 1994 to 2013 (source US DOE).
Fig. 4: Dramatically improved production per drilling rig (liquids left, gas right). The graph gives daily pro- duction added per rig active in the play. The growth reflects reduced drilling times as well as higher pro- duction per well as a result of sweet spot location and better completion/stimulation (Source US EIA).
132 2-2014_geologi 2.06 12.02.15 15:21 Pagina 133
seams, some rise naturally from deep ther- drilling, multilaterals and multifracs have mally mature Marcellus Shale. There is still no become very affordable routine tools. These case in North America where a direct contam- technologies are increasingly applied to ination of groundwater, or the surface envi- mature areas that were previously deemed to ronment, by the actual fracturing has been be in tail-end production. Prime example is proven, this in spite of several hundred thou- the highly mature Permian Basin where oil sand stimulations/fracks every year. Proven production from old fields has been rising by contaminations were caused by poor well over 30% since 2007 and is expected to double integrity (e.g. poor cement jobs) or by poor to about 1.3 MMBOPD by 2018. Plenty of other handling of completion fluids in the surface similar revivals of old conventional plays installations. Contaminations can also stem exist in the US and the added volumes may from old historical wells that were not proper- even exceed those of the new unconventional ly abandoned. Best practice operations are liquids production. being developed by several operators in the Marcellus Shale; they allow operations with- Worldwide Gas Market and LNG: The out excessive water use (thanks to total recy- world gas market continues to be bolstered by cling) and without the use of toxic additives. the rising imports in South Korea, China and Cluster drilling has reduced the land use by a the after-effects of Fukushima. Though almost factor 20−30. half of the global LNG production goes still to Large water use is always mentioned as a Japan and Korea, China is soon likely to main criticism for hydraulic fracturing. In this become the main importer and Europe may context it is important to know that burning follow in a desire to diversify its energy gas produces CO2 and water, an average Mar- sources. cellus well produces therefore over its lifetime LNG exports will start from the US in 2015 and 15 × more water than all the water needed for from Canada in 2016; considering also the still drilling and fracturing of this well. Biofuels, ongoing imports from Canada this will lead to praised as renewables, use one order of mag- the US becoming a net gas exporter before nitude more water than HC production. 2020. At present four LNG export projects The only major environmental problem have been approved by the DOE, others will remaining is the flaring or venting of gas in follow. The American Petroleum Institute unconventional oil production. Very large vol- (API) has published an export forecast for the umes of gas are being flared in the Bakken period 2015−2035, giving a cumulative total of Shale of North Dakota or in the Eagle Ford in 41 TCF or 1.15 BCM (Fig. 5). This amount is Texas since gas-gathering nets are lacking and relatively small compared to the US domestic flaring is more cost effective. This is an enor- gas production (some 7%) but is significant for mous waste of energy (about 10 BCM/y) and the world LNG market. On average the US LNG has a negative environmental impact. Flaring exports will add almost 60 BCM/y to the pres- and venting have been largely eliminated in ent LNG world market (18% of the 2012 global most oil fields worldwide and there is no tech- volume). Larger volumes would be possible nical reason to flare in unconventional pro- but are unlikely in view of the strong political duction. This harmful practice can only be opposition against export of domestic energy. stopped with clear guidelines and laws by the Similar LNG export volumes can be expected regulator. from Canada; in total N-America is thus likely to add some 120 BCM LNG per year to the Application of unconventional technolo- world market (over 1/3 of the 2012 world LNG gies to mature conventional plays: market). At present the world LNG market is Through the unconventional boom the previ- still characterized by very large regional price ous advanced technologies, like horizontal differences, ranging from 3.15 to 16.40
133 2-2014_geologi 2.06 12.02.15 15:21 Pagina 134
USD/MMBTU. The new LNG volumes for N- East Africa, the big discoveries in Mozam- America will, however, greatly add to the glob- bique, with reserves of > 100 TCF, are being al availability and will have a moderating and repeated in neighbouring Kenya and Tanza- equalizing effect on gas prices. With increas- nia with similar volumes. By 2020 Mozam- ing global gas to gas competition the link of bique is expected to become one of the gas to oil prices will further weaken. world’s largest LNG exporters after Australia and Qatar. The reserves offshore Mozam- Conventional gas has in many parts of the bique could cover the demand of Switzerland world been neglected in exploration, especial- for some 1.000 years. ly where pipeline transport was not possible and where volumes were assumed to be too CO2 Sequestration and Climate (see also marginal for LNG. It is therefore not surprising Figs. 1, 2): CO2 sequestration was only a few that very large amounts of conventional gas years ago a prominent topic at the AAPG and continue to be found. The important new gas was seen by many as the final solution to the volumes discovered in the last 5−6 years in CO2 emission problem. Few talks were dedi- many parts of the world are being confirmed cated to this theme now. Not only in the US but and keep growing, e.g. in the Eastern Mediter- worldwide the hope pinned on sequestration ranean Levante Basin, where the proven appears to be waning. This is partly due to the reserves offshore Israel have now exceed 40 very high unit costs of sequestration: they TCF (over 1.100 BCM). Israel is likely to would kill the economics of any coal power- export up to 23 BCM/year. The total potential plant (which might actually be a positive of the Levante (incl. Lebanon and Cyprus) is thing). Reasons for skepticism come also from estimated at > 100 TCF (about 1 year present the very modest volumes handled so far in world gas consumption). Additional upside pilot plants and the fact that public opposition will soon be tested offshore Cyprus. Offshore and NIMBY («not in my backyard») attitude
Fig. 5: US natural gas resources (left side) and domestic consumption and LNG Exports 2015−2035 (right side). All in TCF (1 TCF = 28 BCM). Total US LNG exports 2015−2035: 1.15 BCM (Source EIA).
134 2-2014_geologi 2.06 12.02.15 15:21 Pagina 135
are increasingly affecting the support for new tion, which, in turn, has been triggered by the projects. Energy projects of any kind, also availability of abundant cheap fossil energy. renewables are in today’s society more and Oil and gas people have shaped the last 100 more difficult to realize. This is unlikely to years of the earth’s development, they have a change as long as people have access to responsibility for the next 100 years. ample and cheap energy supply. One of the best ways to sequestrate CO2 is still in the enhanced oil recovery. With aging fields 2 Presentations of special interest this is a growing opportunity, especially in the for the topic hydraulic fracturing US where CO2 pipelines from e.g. coal power- and unconventional production plants to oil fields already exist. Pumping CO2 into depleted oil and gas fields will also meet 2.1 Unconventional gas and oil, with less public resistance since the existence general aspects of the old fields is proof that the system is seal- ing. Leakage of CO2 back into the atmosphere The Future of US Shale (Scott Tinker, Bureau is one of the main concerns in the public. of Economic Geology, Texas University) • The energy need grows with people: world Renewables: As last year, the US E&P indus- population will grow by 1 Billion every 13 try is so focused on the technical and financial years. challenge of the unconventional revolution • Over 50% of world population live in Chi- that renewables were not really a theme at the na, India, SE Asia. 85% of their energy conference. The much higher profitability in needs are covered by fossil fuel. hydrocarbons has led to a drain of financial • Wrong perceptions distort public discus- and technical resources away from geother- sion: mal, wind and – to a lesser degree solar. - High water use: Hydraulic fracturing and Geothermal use of well fluids in oil and gas unconventional drilling consume < 1% of fields is still being pursued. New technologies Texas water needs. that would allow a much more efficient heat - Fracs contaminate drinking water: fracs extraction, especially at lower temperatures, are 5−6 Eiffel Towers below ground water. would give a much needed boost to these Heavy frac waters do not rise (gravity!). efforts. Deep geothermal activities are concen- - Land use: 15.000 wells of Barnett shale trated in volcanic areas with little investment or would be only 800 locations if clustered. research going into true enhanced geothermal The productivity of wells is rising every systems (EGS), designed to artificially create year (fewer and fewer wells are needed). deep heat exchangers. Given the large areas - Unconventionals are not economic: Most with shallow volcanic heat in the US, the more presently produced plays are economic or complex and less proven artificial stimulation break even at 4$/MCF. methods are not a prime target and develop- - The recovery factor is negligible: Average ment is much slower than in Europe. RF is 10% but some areas achieve 50%, the RF is rising in all plays. A philosophical thought by the director of the • Global aspects: Smithsonian’s National Museum of Natural His- - Peak Oil and Peak Gas: Oil peak estimate tory: The 21st century is unique in the 200.000 2060, coal 2070, gas next century? years of humans on earth. In the last 200 years - Unconventional gas could eventually the population of our planet has increased reach 4 × the conventional volume (Fig. 6). 700% to 7.1 Billion. Since the birth of our grand- - Shale gas will require 2.000 Billion $ fathers the increase has been 3−4 ×. This explo- investment globally until 2040. sive growth is the effect of the industrial revolu- - The world will produce 40−50 TCF/y of
135 2-2014_geologi 2.06 12.02.15 15:21 Pagina 136
shale gas by 2050 (equivalent to 33−42% of field installations can all be driven by gas. present world production). • Fresh water should no longer be used. • Worldwide do-ability of unconventional There is plenty of saline, brackish water gas developments: available, including oilfield waters. - Russia and Middle East: negative (not yet, too much cheaper gas). Panel on shale gas - Europe: mixed to negative. • US lessons for overcoming resistance in - Rest of world: positive. other countries: - Education and communication. Demon- Assessment of Technically Recoverable stration of positive economic impact. Resources (John Browning, Bureau of Eco- - Positive involvement of government rep- nomic Geology [BEG], Texas University) resentatives. • The statement that unconventional gas - Local people must benefit. production levels are not sustainable is - Industry must realize that regulations are incorrect. There is generally a rapid positive. decline of production in the first year but - Show best practice cases and especially production stabilizes thereafter in most that land use has been dramatically wells with low further decline rates. Most reduced. Barnett Shale wells produce over 5 years, - Show consequences of saying NO: Saying Haynesville wells produce 5−10 years and NO to gas is saying YES to something else: for Fayetteville up to 20 years appears to e.g. more coal and more CO2. be possible. • Transport can be the main bottleneck: • The Barnett shale will require some addi- trains should be used for LNG or CNG tional 90.000 wells for complete drainage. (trains are more flexible than pipelines). • Reserve estimates and remaining Ultimate • One well in the Marcellus produces over Recovery in TCF (GIIP / Recoverable): its lifetime out of the gas 15 × more water - Barnett → 440 / 86 than what it uses for drilling and fractur- - Fayetteville → 80 / 38 ing (burning gas produces water and CO2). - Haynesville → 487 / 138 • Decline rates: The Marcellus production Recoverable volumes have kept increas- can keep building capacity for another ing, driven by technological and geologi- 10−20 years. cal (e.g. sweet spot) improvements; recov- • The drilling effort decreases since wells ery factors are likely to increase further. deliver continuously higher flow rates and ultimate recoveries (The Industry has Shale Gas sparks Innovation (Vikram Rao, been too successful, resulting in a gas bub- Research Triangle Energy Consortium) ble and low prices). But unconventional • Almost anything that can be produced by production uses still in average 10 × more oil can be produced by gas. wells than conventional production for • 5 TCF/y are flared worldwide, a tremen- equivalent ultimate volumes. dous waste and pollution that must stop. • Economy: Cheap gas due to unconvention- All venting and flaring should be aban- al production has so far triggered > 100 Bil- doned. Flexible, temporary pipelines will lion USD investments in new industry help to do this. The co-produced gas can plants. Repatriation of industry back to be processed/used in the field. the US is continuing. Without shale gas the • Mini LNG plants (producing about 200 m3 gas price in the US would be at 10−12 LNG/day) exist and could be deployed in USD/MCF (actual is 4−5 USD/MCF). Shale fields. gas has given stability to gas prices. • Diesel must be eliminated from operations:
136 2-2014_geologi 2.06 12.02.15 15:21 Pagina 137
2.2 Expulsion efficiencies in source rocks 2.3 Water use and potential groundwater contamination Determining Oil-Expulsion Efficiencies of Source Rocks by Hydrous Pyrolysis The Prevalence of Methane and Solutes in (Lewan, Michael, US Geological Survey, Den- Shallow Ground Water (Siegel, Donald et ver) al., Syracuse University, NY.; Groundwater & • Expulsion processes have in the past Environmental Services, Altoona, PA). probably not adequately been understood • A geochemical synthesis of ~20.000 sam- and expulsion efficiency was therefore ples of shallow ground water from north- generally overestimated. RockEval can e.g. eastern and western parts of the not handle a mixed system of oil and gas. Appalachian Basin were collected 3−6 For the determination of expulsion effi- months prior to drilling for Marcellus ciency RockEval should therefore be Shale gas. In addition detailed temporal replaced by a process called hydrous studies on the variability of methane and pyrolysis. other parameters in ground water of 11 • The initial porosity of a source rock and to water wells in different hydrogeological a lesser degree clay mineralogy have the settings was carried out in northeastern biggest effect on expulsion efficiencies. Pennsylvania. Higher TOC values (greater than 4 wt%) • Mineral content: The results of the study have no clear effect on expulsion efficien- show that the natural mineral content of cies. High clay-mineral content can reduce drinking water is generally much higher expulsion efficiencies by 88%. than previously assumed. The spatial and • Oil expulsion needs a continuous bitumen temporal variability in concentrations of network in the SR. A 1−2% TOC SR never constituents (e.g. Na, CH4, Fe, Mn, Sr, and expels. Ba) span factors of an order of magnitude • Increasing porosity in the SR decreases or more. Concentrations of these elements (sic) the expulsion efficiency (organic commonly exceed regulatory maximum porosity soakes up the oil)! The effect of levels because of natural geochemical porosity is best observed in carbonate- processes. rich source rocks where chalky marl- • Methane: Tap water contained methane in stones with porosities of > 30% can reduce 24% of analyzed samples in N-Pennsylva- expulsion efficiencies by 35%. nia and in 36% of samples in W-Pennsylva- • Expulsion Efficiency increases with over- nia. Traces of heavy metal are very com- burden. Without overburden a SR would mon. grow 33% in volume during maturation • In the absence of clear baselines, an obser- due to creation of porosity in Kerogen dur- vation of higher solute and gas concentra- ing maturation. tions in domestic well water after gas drilling cannot be considered as com- The talk of Lewan confirmed again that the pelling evidence for contamination by expulsion efficiency of most SR has in the past shale gas development. Additional inde- been grossly overestimated. The higher per- pendent isotopic data and other forensic centage of non-expelled HC creates the large geochemical tools are needed. opportunity of unconventional oil and gas. • Best practice: - Sample 3−6 months prior to drilling. - Have analysis done by State certified labs. - Measure not only chemical composition but also temperature, turbidity, pH.
137 2-2014_geologi 2.06 12.02.15 15:21 Pagina 138
- Collect water samples in houses after ventional gas will in future be less than flushing lines and taps (naturally occur- double the average production costs of ring high mineral content turbidity and conventional gas. Unit production costs methane accumulations occurs when have been steadily decreasing. water wells are not used continuously. • Between 1/3 and 1/2 of the known uncon- - Take unfiltered samples. ventional gas plays can today be produced at prices of 6 USD/MCF or lower. At least 25% The study confirms previous findings by the can be produced below 5 USD/MCF. These Department of Environment that water from figures are for dry gas, wet gas improves domestic wells in many cases do not corre- commerciality substantially (Fig. 7). spond to official standards for drinking water quality. Only in very rare exceptions a possi- Economic Evaluation of Unconventional ble link to gas drilling can be established. Cas- Plays (Clarke, Robert, Wood Mackenzie, es with clear proof of contamination by uncon- Houston) ventional gas wells are still lacking. • It is unlikely that there are big unconvention- al gas plays in the US that have not yet been 2.4 Economics of unconventional plays identified. The remaining plays are mainly for niche players but can still be very attractive. Scott Tinker Bureau for Economic Geology • In the US the economics for unconvention- (Texas University) al gas are still marginal. The profits • On a global scale unconventional gas achieved in unconventional gas are only resources (tight gas, shale gas, coalbed about 1/10th of profits in conventional gas methane) have a volume potential that could plays. Better well placement and better be 4 × the volume of all so far produced and stimulation may improve this. The main remaining conventional resources (Fig. 6). profit comes from associated liquids. • Unconventional gas is becoming more • Internationally the development of uncon- competitive with technical progress and ventional resources is a very slow experience. Production costs for uncon- progress. The road to unconventional suc-
Fig. 6: Estimated produc- tion costs and resource volumes of unconventional and conventional gas sup- plies. Unconventional gas resources may be 4x larger than the produced and remaining conventional reserves. (Source IEA and Scott Tinker 2014).
138 2-2014_geologi 2.06 12.02.15 15:21 Pagina 139
Fig. 7: Breakeven econom- ics for different US shale gas plays. Reading exam- ple: some 2/3 of the wet gas (high BTU) Barnett Play can be produced at prices below 6 USD/MCF, at least half can be pro- duced at gas prices < 5 USD/MCF. (Source: Bureau of Economic Geology, Texas University).
cess will be much longer, more risky and more expensive by up to a factor 2 than in the US. Regulators do often not under- stand the business and the progress of regulation is very slow, especially in Europe. • Number of shale gas or shale oil explo- ration wells drilled outside US by end 2013: - Europe 25 - Russia 20 - Australia 25 - Asia (mainly China) 165 Acronyms and terms - Argentina 250 Argentina is likely to be the first country B: Billion (109); BBO: Billion Barrels Oil; BOE: Bar- rel Oil Equivalent; BOPD: Barrel Oil per day; BBL: outside the US to have a substantial Barrel; BCF: Billion Cubic Feet (109); BCFD: Billion unconventional oil and gas production, Cubic Feet per Day; BCM: Billion Cubic Metres; followed by China. BTU: British Thermal Units (mostly as Million Btu − MMBtu); CBM: Coal Bed Methane; CF: Cubic Foot; • Role of Majors: Majors will be the domi- CNG: Compressed Natural Gas; DHI: Direct Hydro- nant players in international unconven- carbon Indications (from seismic); DOE: Depart- tional activities. This contrasts with the ment of Energy (US); E&P: Exploration and Produc- tion; EIA: Energy Information Administration (US); US where the Majors came late, were often GIIP: Gas initially in place; IEA: International Ener- overpaying for the acquisition of acreage gy Agency; Industry: here always meant as the Oil or companies and frequently ended up and Gas Industry; M: Thousand; MCF: Thousand with second-rate acreage. Plays like the cubic feet; MM: Million; Majors: the category of the largest multinational private oil and gas compa- Vaca Muerta of Argentina, the Bazhanov nies; mD: Millidarcy (permeability measure); Nm: source rock of Siberia or the Cooper Basin Nano metre; RF: Recovery Factor; SR: source 12 are too big to be tackled by independents. rocks; TCF: Trillion Cubic Feet (10 ); TCM: Trillion Cubic Metres (1012); TOC: Total Organic Carbon; Majors are already well placed in e.g. the USD: US Dollar; USGS: US Geological Survey; 3D: UK or China. three dimensional seismic.
139 2-2014_geologi 2.06 12.02.15 15:21 Pagina 140 GEBÄUDE- HEBUNG RISSE? SENKUNGEN? FUNDAMENT- STABILISIERUNG URETEK Injektionen schnell und einfach! BAUGRUND- VERSTÄRKUNG GEBÄUDE- AUFSTOCKUNG Kostenlose Angebote: URETEK Schweiz AG 6052 Hergiswil 041 676 00 80 Tel. - [email protected] www.uretek.ch
140 2-2014_geologi 2.06 12.02.15 15:21 Pagina 141
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 141-142
Energie aus dem Untergrund – who cares? Ueli Seemann1
Am 7. Oktober 2014 fand ein Symposium menden erfreulich hoch. Die hohe Anzahl unter obigem kryptischem Titel im neu von SASEG- und SFIG-Mitgliedern war eben- erstellten Konferenzpavillon auf Berns Haus- so bemerkenswert. Andererseits war die berg, dem Gurten statt. Das Symposium war Präsenz der Politik (nicht?) überraschend der erste Anlass, welcher in diesem wunder- niedrig. Immerhin hatten zwei prominente baren Pavillon mit einer faszinierenden Aus- Politiker den Weg auf den Gurten gefunden: sicht auf die helvetische Hauptstadt abgehal- der Präsident der nationalrätlichen Umwelt- ten wurde. Eine andere Schweizerische Pre- Raumplanung und Energiekommission miere war auch der Themenkreis, welcher (UREK) und der Präsident der kantonal-ber- während eines vollen Tages integral abge- nischen Grünen Partei. handelt wurde. Vereinfacht zusammenge- fasst handelte es sich dabei um eine techni- Die Themen, welche während des Symposi- sche und operationelle «state of the art ums behandelt wurden waren breit abge - review» bezüglich Untergrundgeologie und deckt und ausgewogen: Energie in der Schweiz mit «Hydraulic Fractu- Nach einer kurzen Einleitung durch die Sym- ring» als aktuellem Trigger und Buzzword. posiumsleiterin Marianne Niggli ergriff Oli- Das Symposium wurde von der Eidgenössi- vier Lateltin – Leiter der Landesgeologie bei schen Geologischen Kommission EGK initi- swisstopo – das Wort. Er präsentierte ein iert. Dieses Gremium berät den Bundesrat in feuriges Plädoyer für die strukturierte Fragen der Geologie und des Untergrundes. Weitererforschung «seiner» (schweizeri- Die Kommission hat den Auftrag, dem schen) Untergrundgeologie und für eine pro- Bundesrat bis zum Frühling 2015 eine Emp- minentere Rolle, welche Geologen in ener- fehlung zur Methode des Hydraulic Fractu- giepolitischen und technischen Angelegen- ring in der Kohlenwasserstoffexploration heiten spielen sollten. und der Geothermie zu unterbreiten. Das Prof. Kurt Reinicke (Technische Universität Gurten-Symposium sollte dazu eine breite Clausthal) beeindruckte mit seiner Keynote Basis von Fakten und Meinungen liefern. Lecture: «Hydraulic Fracturing – Technologie, Das Symposium stand unter dem Patronat Herausforderungen und Chancen in Gas- von CHGEOL, SASEG, swisstopo und sc | nat. Exploration und Geothermie». Martin Bach- Dabei trug die SASEG in entscheidendem mann (Leiter E & P Wintershall Holding Masse bei der Zusammenstellung des Pro- GmbH) referierte in der Folge zum Thema gramms und vor allem bei der Rekrutierung Schiefergas, Fracking und zu «Best Practices». von hochkarätigen Referenten aus der Indu- Bei beiden Referenten war deutlich spürbar, strie bei. dass sie Personen aus der operationellen Angesichts der Tatsache, dass es sich bei Praxis repräsentierten. Sie relativierten die diesem Anlass um den ersten seiner Art han- oft zitierten und übertrieben dargestellten delte, war die Anzahl von über 150 Teilneh- Risiken im Zusammenhang mit Schiefergas- exploration und Fracking (Seismik, Grund- wasserverschmutzung etc.) in einer wohl- tuend bestimmten und auf Fakten basieren- 1 Vorstandsmitglied SASEG den Art und Weise.
141 2-2014_geologi 2.06 12.02.15 15:21 Pagina 142
Prof. Peter Huggenberger, Beauftragter der lights zu verzeichnen hatte: absolute Akzep- Universität Basel für Kantonsgeologie, plä- tanz durch die Bevölkerung und exzellentes dierte in seinem Vortrag für mehr «Ordnung» Bohrmanagement, um nur zwei zu erwäh- im Untergrund, will heissen: mittelfristig nen. sollte die Möglichkeit geschaffen werden, landesweit alle Untergrundressourcen (bei- Das Symposium wurde durch zwei Podiums- spielsweise Geothermie, Schiefergas) syste- gespräche bereichert, welche durch Karin matisch und konsistent zu erforschen und Frei vom Schweizer Fernsehen souverän zu priorisieren. moderiert wurden. Die Diskussionen und Prof. Walter Wildi, em. Prof. Institut F. A. Frage-Antwortrunden konzentrierten sich Forel Université de Genève befasste sich in erwartungsgemäss auf geologisch-techni- seiner Präsentation mit Umweltaspekten im sche Themen. Bemerkenswert war aller- Zusammenhang mit der Erforschung der dings, dass trotz der technischen Fokusse Untergrundgeologie, speziell mit denjenigen weiteren Themenkreisen wie Umwelt, gesell- der Exploration nach Schiefergasvorkom- schaftspolitischen und anderen Aspekten men. Auf Grund eines ausführlichen Kata- ebenfalls genügend Raum und Zeit gegeben logs von umweltrelevanten Beurteilungskri- wurden. Das Symposium wurde dadurch in terien kommt Wildi zum Schluss, dass laut einem gesunden «bipolaren» Klima abgehal- dem bestehenden Regelwerk und dem Feh- ten – ungleich anderen Veranstaltungen zu len von entsprechenden Experten die Bedin- denselben Themenkreisen, welche öfters zu gungen zur Exploration nach Schiefergas in Polarisierungen tendieren. Die lange Podi- der Schweiz nicht gegeben seien. umsdiskussion zeigte aber auch einen fun- Nga Le (CFO ver.de München) wagte sich in damentalen Unterschied in den Erwartun- das problematische Gebiet der Versicher- gen zum weiteren Vorgehen. Während die barkeit – oder Nicht-Versicherbarkeit – von Vertreter der Industrie, aber auch von swiss- Untergrundprojekten. Die in diesem Zusam - topo oder SASEG dafür plädierten, dass nur menhang relevanten Umweltrechte wurden gut kontrollierte Pilotprojekte eine sachliche erst in den letzten Jahren entwickelt. Nga Le Evaluation und Weiterentwicklung der Tech- kommt zum Schluss, dass Umweltrechte nologie ermöglichen würden, verlangten die noch nicht genügend ausgereift sind, um ein Vertreter der Universitäten ausgedehnte, komplexes Haftungsgebiet wie dasjenige des theoretische Grundlagenforschung als Vor- Untergrundumweltrechts adäquat abzude - aussetzung für weitere Schritte. cken. Die Präsentationen von Fredy Brunner, Dr. Franz Schenker, Präsident der Eidgenös- Stadtrat St. Gallen und Dr. Michel Meyer, Ser- sischen Geologischen Kommission, bedank- vices Industriels de Genève SIG, befassten te sich mit einer launigen Ansprache bei sich beide mit aktuellen Geothermieprojek- allen Anwesenden und Referenten für das ten. Es war interessant festzustellen, dass Erscheinen an diesem doch denkwürdigen bezüglich dem Approach zu Geothermiepro- Symposium. Was der Schreibende den präsi- jekten, insbesondere der damit verbunde- dialen Worten noch beifügen möchte wäre nen Fracking-Methode, kein «Röschtigraben» der Wunsch, dass dieses erfolgreiche Sym- zwischen dem St. Gallischen und dem Gen- posium absolut eine Fortsetzung verdient. ferprojekt zu bestehen scheint, trotz der in diesem Zusammenhang verfänglichen Bedeutung des englischen Ausdrucks «Frack» (= Bruch, Riss, [«Röschti»]-Graben). Hervorzuheben ist auch die Präsentation des St. Gallerprojektes, welches einige High-
142 2-2014_geologi 2.06 12.02.15 15:21 Pagina 143
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 143-150
Hydraulic Fracturing – Postscriptum. A geologist's attempt to sum- marize what we know and where we go Peter Burri1
P. Burri is Co-author of the 2014 Study of the German National Academy of Science and Engineering (Deutsche Akademie der Technikwissenschaften, acatec) on Hydraulic Fracturing and is a member of the Expert Group on Hydraulic Fracturing of EASAC (European Academies Science Advisory Council) that has in September 2014 formulated a recommendation on this technology for the EU Member States.
Key words: hydraulic fracturing, natural gas, unconventional gas, global energy, global climate, methane, CO2, coal, greenhouse gas
1 Introduction
During my professional life as a geologist aware that talking to the media, the politi- there has never been a geoscience topic so cians and the greater public has become a hotly and emotionally debated as is the case must in order to be heard beyond the «ivory with the concept and application of tower». This applies not only to hydraulic hydraulic fracturing, the only likely excep- fracturing but also equally to other geosci- tion being the geological concepts surround- entific activities that are in the public focus ing nuclear waste disposal. There has also (e.g. waste disposal, mining, large engineer- rarely been a topic in geology and subsur- ing works, exploration for fossil fuels). In face-engineering that has led to such violent Europe the time of innocence of the geo- opposition and attacks. Many geoscientists science community appears to be definitely – grown up in the belief that science was gone and it will take a long, tedious effort at largely a matter of logical debate where all levels to re-establish a new base of confi- rational arguments, empirical facts and dence. observations prevailed – were caught off- guard by this wave of rejection and had diffi- A second aspect of the discussion on culties adapting to a new world in which the hydraulic fracturing is the speed with which knowledge of scientific facts and arguments opposition to the technology has spread. was not good enough anymore. Scientists During over 60 years hydraulic fracturing discovered that there was a need to explain was practiced in Europe with many thou- their lines of thought to a large, often scepti- sand frac jobs carried out in Germany, NL, cal – if not hostile – public. They also dis- UK, Denmark and Norway. This occurred covered that the trust of the public in scien- without any known accidents or any impair- tific judgment and wisdom had been seri- ment to the environment and was accepted ously impaired; a loss of credibility caused by the authorities as a routine process, nec- to a large extent by the scientific community essary for increasing flow rates from poor itself which did not deem necessary to «sell» reservoirs, be it oil, gas or water. As recently its arguments outside its own circles. The as five years ago, hydraulic fracturing was a scientific community has now become process unknown to anybody outside the technical world and the mining authorities. This changed after 2010 when the film 1 Holbeinstrasse 7, 4051 Basel, Switzerland «Gasland» stirred up opposition against [[email protected]] hydraulic fracturing and unconventional gas
143 2-2014_geologi 2.06 12.02.15 15:21 Pagina 144
in some parts of the US. The pictures in the 2 Hydraulic Fracturing: Criticism vs. feature play in an emotionally very sugges- Facts tive way to the fears of the broad public. Unease exists in the greater public with any- The process of hydraulic fracturing is con- thing that impacts the ground under our feet fronted with the following main points of or the quality of our drinking water as the criticism: lifeline of humans. The approach of the film • Artificially created fractures can reach the is best characterized by the cover picture, surface or intersect aquifers of drinking showing the author playing banjo in front of water, thus creating pathways for possible a drilling rig with a gas mask on his face. pollutants. Although in the meantime most of the accu- • Additives to fracturing or drilling fluids sations of the film have proven to be wrong are toxic and a hazard to drinking water as – not by industry but by the environmental well as to the water in the fractured reser- authorities in the US – the pictures of burn- voirs. ing water taps, gas seeps in scenic streams • Hydraulic Fracturing uses large quantities and murky water samples have long started of freshwater. to lead their own life. Within a year the pic- • Hydraulic Fracturing causes earthquakes. tures had spread to Europe and – true to the • Unconventional gas production leads to rule: only bad news is good news – there is excessive land use. today no television debate without a diligent • In the course of the hydraulic fracturing replay of the alleged horror pictures. Many and the later gas production large quanti- unfounded ideas prevail even though in the ties of methane leak into groundwater, the meantime a second film by an Irish Journal- soil and into the atmosphere. ist («Fracknation») has tried to confront • Hydraulic fracturing leads to heavy traffic «Gasland» with the real facts. It is possible during the operations. that without the film «Gasland», hydraulic • Wells stimulated by hydraulic fracturing fracturing would still be a technical term, have high decline rates, dropping to negli- known to few technical insiders only and we gible levels within months. Shale gas pro- could devote ourselves to the more urgent duction requires continuous high levels of environmental problems of this planet. drilling and unconventional gas is, there- Having said this, it is fully understandable fore, not sustainable and largely uneco- that the public is concerned by the many nomic. accusations and doubts raised about the technology. The scientific community has, Some of the above issues have indeed been therefore, the duty to provide insight and areas of concern during the earlier «gold contribute as much as possible to factual rush» boom time of unconventional gas arguments. Getting back to a rational discus- exploration in the US. Most of the problems sion is also essential since a potential ban on have in the meantime been resolved (partly hydraulic fracturing would also severely due to more severe regulations, partly endanger deep geothermal projects that through self-control of industry in an effort have to rely on creating artificial heat to keeping the licence to operate). It has to exchangers, requiring extensive fracturing be noted that the majority of the critical of the reservoir rock. points have never been issues in Europe, given the fact that European legislations have already introduced a much stricter control and regulation of deep-well-drilling, well integrity and hydraulic stimulations. At the risk of duplicating the statements in
144 2-2014_geologi 2.06 12.02.15 15:21 Pagina 145
some of the other papers in this special vol- practice in Europe and many parts of the ume of the Bulletin, I like to sum up briefly the US and should become compulsory stan- present state of knowledge, relating to the dard practice worldwide. above criticism. The factual arguments for the Conclusion: Hydraulic fracturing can today statements below can be found in the follow- be carried out without any harmful addi- ing publications: Emmermann (editor) 2014, tives. EASAC 2014, Reinicke 2014, Reichetseder 2014, Burri & Leu 2012, Burri & Häring 2014 Large water use and Burri 2014. • Hydraulic fracturing requires indeed large quantities of water: several 100 m3 per frac Hydraulic fractures reach the surface and cre- in gas wells, 10.000−20.000 m3 in geother- ate pollution pathways to the drinking water mal wells (smaller volumes in future multi- aquifers fracs). • Microseismic measurements allow a very • A large part of these fluids is recovered in precise mapping of the extension of artifi- backflow and production. cial hydraulic fractures. • Burning of gas produces CO2 and water. • Fracture volume cannot exceed the vol- The gas from an average Marcellus shale ume of fluid injected. With the limited well produces over its lifetime some 15 injected volumes and pressures, a cre- times the water needed originally for ation of vertical fractures over 1.000 and drilling and the frac job (AAPG convention more metres is physically not possible. 2014, panel on shale gas). • In the very rare cases where leaks into • Companies in the US with best practice aquifers have been observed, they have operations recycle up to 100% of the back- been caused by poor well integrity, defect flow. casings or poor cement jobs. • Hydraulic fracturing does not need fresh- Conclusion: There is no proven case where water. It can equally use saltwater, brack- hydraulic fracturing has created a vertical ish water or even wastewater. fissure as a pathway extending from depths Conclusions: Hydraulic fracturing still uses of > 1.000 m to surface. relatively large quantities of water but does not require freshwater. Water use is being Toxic additives in fracking and drilling fluids significantly reduced through recycling. Water • Potentially harmful substances have availability is a potential problem only in indeed been used in some of the US opera- very arid climate with no access to brackish tions. Recent developments in Europe water. have, however, led to a reduction to only two additives, both non-toxic and Induced seismicity, earthquakes biodegradable (recent publication Exxon • Any artificial fracturing of rock causes Germany). microseismicity. Seismic magnitudes cor- • Additives used in Germany in the past are relate directly with injected volumes and classified by the authorities at the lowest fracture size. water-hazard level (in concentrated form); • In shale gas and other sedimentary fracs liquid agricultural manure belongs to the the induced seismicity lies generally below same category. In contrast to manure M 1 (Magnitude), i.e. far below the thres- (spread at a few 10 m above groundwater) hold noticed by human beings. The highest the frac additives are, however, diluted by magnitude known and related to shale gas a factor of about 1:100 and are injected in fracturing has reached M 2.5 (Quadrilla reservoirs at a depth of several 1.000 m. UK). In geothermal wells, injecting into • Disclosure of additives is today common basement or close to basement, seismicity
145 2-2014_geologi 2.06 12.02.15 15:21 Pagina 146
of up to M 3.5 has been observed, largely • Except for very few and yet unproven cases caused by shear movements, releasing ten- with damaged wells, where gas could leak sions in pre-existing tectonic stress fields. into neighbouring sediments, there is no • Induced seismicity has in several areas leakage from shale gas wells into groundwa- been observed in wells where large fluid ter and the sediments. All alleged methane volumes were being injected. contaminations in the film «Gasland» have Conclusions: In spite of some 3 Million frac been proven to be of natural origin. jobs that have been carried out globally for Conclusion: Where high drilling standards oil and gas production from sedimentary and good maintenance of the surface equip- rocks, there has been no recorded case of a ment are observed there is no risk of con- damage quake. Seismicity in injection wells tamination of groundwater or sediments can be eliminated by avoiding disposal of with methane. High standards of regulations fluids through recycling. In deep geothermal for well design and operations in Europe stimulation the risk of higher magnitude have led to a situation where methane leaks seismicity can be mitigated by replacing are not an issue. very large volume single fracs by much smaller volume multifrac jobs. Heavy traffic during hydraulic fracturing oper- ations Land use • This has been a serious issue in areas of • Land used has been intensive in the early intense drilling and stimulation efforts stages of shale gas developments when that often have led to thousands of truck- exclusively vertical wells were drilled. loads within a few months of operations. • The use of horizontal drilling and the • Trucking can be reduced significantly development of cluster drilling with up to where recycling of backflow (with recov- 30 wells from one drilling location have led ery of water and chemicals) is applied. to a drastic reduction in land use. Up to Several US companies have a 100% recy- 10 km2 or more of reservoirs in the sub- cling target. Also the reduction of addi- surface can be drained from one location. tives leads to a lower transport intensity. Drilling sites can now be spaced at several • Using local groundwater of non-drinking km intervals. quality can further reduce traffic. Conclusions: Land use is no longer an issue • Temporary water pipelines are increasing- in modern cluster shale gas development. ly used to replace trucking. Geothermal projects have the lowest foot- Conclusion: Trucking remains an issue with print of any renewable energy. local communities during the drilling and fracturing phase. It is not an issue during Methane leaks (see also «Methane as a cli- production. Traffic intensity needs close mate gas» below) attention and further improvement. Recy- • In large gas generating basins mature source cling and temporary pipelines go a long way rocks and mature coal seams produce tril- to mitigate the impact. lions of m3 of methane of which a significant part migrates to surface and leaks out into High decline rates of fractured wells requires the atmosphere. In prolific basins, e.g. in the continuous drilling Marcellus Shale of Pennsylvania thousands • In most hydro-fractured wells production of natural gas seeps occur and studies by is highest in the weeks after the stimula- environmental authorities reveal that, tion and shows then a steep decline within depending on the area, between 24% and the first year. 36% of all drinking water wells contained sig- • After the initial decline phase the wells nificant amounts of methane. enter a phase with very slow further
146 2-2014_geologi 2.06 12.02.15 15:21 Pagina 147
decline and most wells continue produc- Europe, where tight regulations for produc- tion over many years. Production lifetimes tion operations and maintenance prevent of 10 years and more are known even in gas to escape into the atmosphere. In Ger- old, not optimally treated wells. many 53% of the total methane originates • Focus on geological sweet spots and bet- from agriculture, 3% from the energy indus- ter completion has led to lower decline try and only 0.1% from gas production. Since rates, considerably longer production life 1990 the methane emissions in Germany and an up to tenfold increase of ultimate have been decreasing by 55%, mainly recovery per well. Drilling time per unit through closing coal mines (Umweltbunde- gas produced has decreased by a factor 10 samt 2014). between 2008 and 2014 (US EIA Drilling It is scientifically incorrect to use individual Productivity Report, March 2014). Over US worst case examples and extrapolate the same period the number of rigs drilling them to a global scale. Such an extrapolation for gas has fallen by 80% while total uncon- has recently been presented by Howarth ventional gas production kept growing. 2014. His assumptions for methane emis- • 25% of all the Marcellus shale gas reserves sions from unconventional gas production can be produced at gas prices below 5 range from 3.6% to 7% of total gas produc- USD/1.000 cubic feet. For the more valuable tion. Emissions at such high levels would wet gas the percentage is much higher. imply leakage of millions of m3 of gas from Conclusion: Fractured wells do show high one location. Leaks at such levels would initial decline rates but stabilize later for cause a very high level of explosion risk that many years at still commercial levels. would be incompatible with even low safety Recent technological progress has multi- standards. Gas concentrations at produc- plied ultimate recovery per well. Drilling tion locations are routinely monitored and time per unit gas produced has in the Mar- emissions in the several % range would auto- cellus operations been reduced to as little as matically lead to a shut down of the plant. 10% of the time required 6 years ago. Uncon- What is certainly not tolerable in today’s ventional gas production has therefore world is the widespread flaring and partly become increasingly sustainable and com- venting of associated gas in oil fields and mercially robust. particularly in unconventional oil produc- tion where the initial lack of infrastructure makes a gathering of the associated gas eco- 3 Methane as a climate gas nomically not attractive. US flaring and vent- ing has reached the highest level since the Methane is a potent greenhouse gas (over a early 70’s with almost 7.5 Billion m3/y (over time frame of 100 years it is 28 × more effec- 2 × annual gas consumption of Switzerland). tive than CO2) and should therefore not Flaring and venting is banned in Europe enter the atmosphere. There is no doubt except for production tests. Such wastage of that in the past methane leaks from the oil gas needs to be eliminated through stringent and gas industry have significantly con- regulations. Flaring, as occurring in some tributed to the amount of greenhouse gases. parts of the US is, however, not a valid argu- Source of the emissions are mostly leaks ment to ban gas production – we do not ban during testing and from poorly maintained cars because they cause accidents, we regu- production installations as well as pipeline late the traffic and carry out technical systems and venting. Again, these emissions inspections. are still a concern in parts of the US and in The level of methane emissions in European some other oil and gas producing countries gas fields lies well below 1% and is thus an but methane leaks are today insignificant in order of magnitude below the Howard esti-
147 2-2014_geologi 2.06 12.02.15 15:21 Pagina 148
mates. The European experience demon- 5 Gas, fossil fuels and the world strates that methane emissions can be suc- energy supply cessfully eliminated. In well run and well maintained gas fields the risk of methane The likely link between manmade green- leakage is minimal. house gases and the burning of fossil fuels suggests that it is wise to reduce our depend- ence on non-renewable energy, no matter 4 Gas production and CO2 emissions where we stand in the discussion on global warming. Requests for reduction range from Doubts are regularly surfacing on whether «no investment into fossil energy after 2017» the new availability of much larger gas to a reduction of CO2 by 40−70% until 2050 resources can have an impact on climate and zero fossil fuels by 2100 (Press release change at all. Proof of this is relatively sim- IPPC, 2 November 2014). Reaching these tar- ple: from 2008 to 2013 the US were able to gets will require transformations at an reduce CO2 emissions by 600−700 million t, extremely high speed that is not in line with i.e. by over 12% or 15 × the annual CO2 emis- the statistical experience of the last decade. sions of Switzerland. The lion share of this In spite of a very impressive growth of over reduction was achieved through replace- 300% in the last 10 years, renewables w. o. ment of coal by gas in power plants. With hydro provide today only 2.4% of the global this, the US have achieved the largest CO2 energy supply while the share of fossil fuels reduction of any industrial country and have has decreased since 2004 only very marginal- almost reached the 1990 emission levels, tar- ly from 87% to 86% (Reinicke 2014). Only 7% get of the Kyoto Protocol (not signed by the of the energy growth in the same 10 years US). During the same time CO2 emissions in period could be covered by the large rise in Germany have been rising against a back- the new energies. This implies that, while we drop of a politically strangled gas produc- make most impressive progress in develop- tion and its replacement by coal. ing renewables, we are still decades away from even covering the growth in energy, let alone replace fossil fuels. In addition the sup- ply may have to cover an approximate dou- bling of world energy demand within 50 years (assuming the present growth can be halved).
Fig. 1: US CO2 emissions and shale gas production. The availability of shale gas allows emission reductions that are not achieved in any other industrialized coun- try. The 1990 CO2 emis- sions of the US were 5.100 million t (Kyoto Protokoll target). Source US DOE.
148 2-2014_geologi 2.06 12.02.15 15:21 Pagina 149
It will be important to structure the transi- would be required, probably in the form of a tion to a renewable energy world in a way CO2 tax, which ideally should be comple- that protects economic development and mented with an additional pollution tax for does not put the burden on a few countries coal. alone. We should not forget that only pros- perous countries can afford a high level of environmental protection. Where countries 6 Scientific advice and decision and people are in survival mode there is lit- makers tle concern about the state of the world that we may leave to future generations. A proper assessment of chances and risks of In the absence of a major technological new technological applications requires in- breakthrough that would revolutionize the depth knowledge and profound experience in global energy supply (like nuclear fusion) the sciences involved. In the case of the world has two options: hydraulic fracturing and unconventional gas production this calls for geologists and geo- The «pure renewables scenario»: political physicists with expert knowhow of the barriers will be used to block the develop- processes in deep sedimentary basins and ment of unconventional gas in many parts of for engineers, specialized in drilling and in the world. Growth of renewable energies will the very sophisticated subsurface engineer- cover an increasingly larger share of the ing technologies. Unfortunately decision market but – given the likelihood of rising makers have often ignored the need for com- NIMBY public opposition to windfarms, petent specialists, with very unfortunate hydro dams, geothermal powerplants and results: most of the bans declared on the solar farms – renewables may take well into technology have not been introduced on the the next century to cover the global needs. grounds of technical expertise but were large- The remaining energy will predominantly be ly emotionally and politically motivated. supplied by coal, the cheapest and most abundant fossil energy. Oil will gradually Today we have a very peculiar situation make place to renewables, especially in where there is not a single scientific organi- transport and heating. The consequence will zation or institution worldwide (with com- be a very slow improvement of the global petence in these technologies), that advo- CO2 balance (see developments in present cates a ban on hydraulic fracturing, neither day Germany) and a severe deterioration of in gas nor in geothermal applications. All air quality in most of the Asian, African and these institutions, private as well as state Latin American megacities with millions of controlled, recommend that the technology fatalities caused by respiratory diseases. be properly regulated and that adequate standards and controls be introduced. In The «mixed gas – renewables scenario»: The Europe they also stress the need for pilot present abundance of gas resources (reach projects without which there will be no 250−300 years at present day demand) is learning and no scientific progress. being deliberately used for a rapid replace- ment of coal power stations and of diesel- The worrying aspect is that the advice of all driven heavy vehicles by gas. This could these highly competent scientific bodies within two decades lead to a very drastic has, so far, been almost totally ignored by reduction in global CO2 emissions (several decision makers. France has banned the 10%) and would improve the air quality in technology at the very moment when the most megacities of the developing coun- Academie des Sciences de France and the tries. Political steering of the energy use Bureau des Recherches Geologiques et
149 2-2014_geologi 2.06 12.02.15 15:21 Pagina 150
Minières advised to the contrary; Germany References and several other countries show similar Burri, P. 2014: AAPG Annual Convention Houston behaviour patterns. It is time that geoscien- April 2014. The Global Impact of Unconventional tists regain their voice and make themselves Hydrocarbons (Hydraulic Fracturing on the way heard. Important decisions, like the future of to a clean and safe technology). Swiss Bull. angew. Geol., 19/2, 129-139. our energy supply and the quality of our Burri, P. & Leu, W. 2012: «Unkonventionelles Gas – environment, should not be left to politi- Brückenenergie oder Umweltrisiko?». Aqua & cians, pressure groups and sensation-hun- Gas, Vol. 9, 54−63. Burri, P. & Häring, M. 2014: «Ressourcen Explo- gry media alone. ration: Risiko oder Chance? – Das Spannungs- feld zwischen wissenschaftlichen Fakten und öffentlicher Wahrnehmung». Swiss Bull. angew. Geol., 19/1, 33−40. EASAC (European Academies Science Advisory Council) 2014: Shale gas extraction: issues of particular relevance to the European Union. www.easac.eu. Emmermann, R. (Projektleitung) 2014: Bericht aus dem Projekt «Hydraulic Fracturing – eine Tech- nologie in der Diskussion». acatech − DEUTSCHE AKADEMIE DER TECHNIKWIS- SENSCHAFTEN, Stand: 4. September 2014. Howarth, R. 2014: A bridge to nowhere: methane emissions and the greenhouse gas footprint of natural gas. Energy Science & Engineering (Open Access). Reichetseder, P. 2014: Clean Unconventional Gas Production: Myth or Reality? The Role of Well Integrity and Methane Emissions. Swiss Bull. angew. Geol., Vol. 19/2, 39-52. Reinicke, K 2014: The Role of Hydraulic Fracturing for the Supply of Subsurface Energy. Swiss Bull. angew. Geol., Vol. 19/2, 5-17. Umweltbundesamt Deutschland 2014: «Methane- missionen». http://www.umweltbundesamt.de/ daten/klimawandel/treibhausgas-emissionen- in-deutschland/methan-emissionen (retrieved 08.09.2014).
150 2-2014_geologi 2.06 12.02.15 15:21 Pagina 151
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 151-156
High Pressure (HP) and Ultrahigh Pressure (UHP) metamorphism in continental crust and oceanic lithosphere («subduction metamorphism») Roberto Compagnoni1
Abstract of the talk given on June 21, 2014, in Aosta, Hotel Europa, at the 81st SASEG Convention.
Subduction and eclogite-facies metamorphism
According to Plate Tectonics, the unifying and the African (or Adria) plate to the south) Earth’s Science theory, the lithospheric were separated by an ocean (the Mesozoic plates may be subjected to three main rela- Tethys) which favoured the subduction of tive movements: oceanic lithosphere below continental litho- 1. At passive boundaries, the plates slide sphere. With advance of subduction, the horizontally past each other (see Fig. 1 ocean basin progressively disappears until left), such as the San Andreas fault in Cal- the two continental blocks (plates) collide ifornia; (Fig. 2). However, remnants of the former 2. At divergent boundaries, plates move oceanic basin – squeezed between the two apart and create new lithosphere (see Fig. blocks – are preserved and allow to recog- 1 center), such as in the mid-ocean ridges; nize the «oceanic suture», i.e. the original 3. At convergent boundaries, plates collide location of the disappeared ocean. These and one is pulled down (subducted) into oceanic remnants are known as «ophiolites». the mantle and recycled (see Fig. 1 right). In the Alps, the Piemonte zone of Calcschists Three different types of subductions may with meta-ophiolites (Fig. 5) is the remnant of be distinguished: the former Mesozoic Tethys oceanic basin. a. oceanic plate sinking below oceanic plate, During subduction, within the subducting b. oceanic plate sinking below continental plate the isotherms are deflected down- plate (Fig. 1 right), or wards, because the rock thermal re-equili- c. continental plate colliding against an- bration is slower than the velocity of the other continental plate (Fig. 2). sinking lithospheric plate (see Figs. 1, right, and 2). As a consequence, in the subducting This last type of collision produces the so- plates the geothermal gradients (i.e. the rate called «collisional orogens», such as the of increasing temperature with respect to Himalayan-Alpine mountain belt. It is impor- increasing depth in the Earth's interior), tant to point out that, before collision, the which are normally ~ 25 °C/km, may two continental plates (in the case of the decrease down to ~ 5 °C/km, depending on Western Alps the European plate to the north the speed of the subducting plate. Most minerals or mineral assemblages, sta- ble at «normal» gradients (i.e. within the fields of greenschist, amphibolite and gran- ulite facies, Fig. 3), become unstable and 1 Department of Earth Sciences, the University of Torino transform into new minerals as a conse- (Italy) quence of the pressure increase.
151 2-2014_geologi 2.06 12.02.15 15:21 Pagina 152
Fig. 1: The three main relative plate movements expected by the Plate Tectonics Theory. Left: passive plate boundaries; center: Divergent plate boundaries, where new ocean floor is generated by uprising basaltic magma; right: convergent plate boundaries, where lithospheric plates sink (subduct) into the mantle and andesitic magma (in yellow) is generated. Grey: oceanic (thinner) and continental (thicker) crust; brown: rigid lithospheric mantle, forming the prevailing part of the lithospheric «plates»; red to yellow: ductile upper (asthenospheric) mantle. T is progressively increasing with depth (from red to yellow) [from Press et al. 2003].
Fig. 2: The best example of a collisional orogen is the Himalaya chain, formed by the collision of the Indian- Australian Plate against the Eurasian Plate. In grey the continental crust of the two plates, in brown the lithospheric mantle, and in red the asthenospheric mantle [from Press et al. 2003].
Fig. 3: The downward deflection of the isotherms in a subducting slab is well exemplified by the Japan Islands subduction zone. The T distribution is high- lighted by different colours, at constant intervals of 400 °C. The black dots show locations of the earthquake foci.
152 2-2014_geologi 2.06 12.02.15 15:21 Pagina 153
The subduction metamorphism corre- – is the stable silica phase (Fig. 4). Rocks sponds to P-T conditions of the blueschist recrystallized under the quartz-eclogite sub- facies and of the eclogite facies (green in Fig. facies are said to belong to the High Pres- 4), which is named after eclogite, the most sure (HP) metamorphism (darker green in typical rock type. The eclogite facies has Fig. 4), whereas those recrystallized under been further subdivided into the quartz- the coesite-eclogite subfacies to the Ultra eclogite subfacies, where quartz is the sta- High Pressure (UHP) metamorphism (lighter ble silica phase, and coesite-eclogite subfa- green in Fig. 4). cies, where coesite – its higher-P polymorph The basalt to eclogite transformation
Because the eclogite is the most typical HP rock, mineral reactions leading to its forma- tion are useful to understand the process of the subduction metamorphism. The eclogite is a mafic rock with the bulk chemical composition of a basalt (or a gab- bro, its equivalent plutonic rock). The most significant reactions, leading to the conver- sion of basalt (or gabbro) to eclogite, are triggered by the P increase and accompa- nied by a density increase from 3.0 (basalt) to 3.5 (eclogite). Basalt (or gabbro) consists of two igneous minerals: plagioclase (anorthite-rich) and clinopyroxene, and eclogite of two main metamorphic minerals, garnet and omphacite (a Na-clinopyroxene). However, each phase is a complex solid solution of two or more pure end-members. Plagioclase is a solid solution of albite (NaAlSi3O8) and anorthite (CaAl2Si2O8), the clinopyroxene of diopside (CaMgSi2O6) and hedenbergite (CaFeSi2O6). Garnet is a solid solution of three main end-members, alman- dine (Fe3Al2Si3O12), pyrope (Mg3Al2Si3O12), and grossular (Ca3Al2Si3O12), and omphacite is a solid solution of jadeite (NaAlSi2O6), Fig. 4: P-T diagram which shows in green the diopside (CaMgSi2O6) and minor aegirine eclogite-facies field, characterized by low- (10−20 3+ °C/km) to very low (down to ~ 5 °C/km) geothermal (NaFe Si2O6). gradients. In darker green the quartz-eclogite sub- The eclogite usually includes, in addition to facies [i.e. the field of High-Pressure (HP) meta- the anhydrous minerals garnet and morphism], and in lighter green the coesite-eclog- omphacite, accessory rutile (TiO ), quartz ite subfacies [i.e. the field of Ultra-High-Pressure 2 (UHP) metamorphism] where diamond may be or coesite. However, locally other hydrated present at the higher-pressure portion. In grey the mineral phases may be present, which are «forbidden zone», bounded by the 5 °C/km geo- useful to infer the peak eclogite-facies condi- therm line, which corresponds to extremely low geothermal gradients so far never observed in tions: they are amphiboles (mainly glauco- nature (drawn by Jane Gilotti). phane, ~ 2 wt % water), zoisite (0.5−2 wt %),
153 2-2014_geologi 2.06 12.02.15 15:21 Pagina 154
lawsonite (12–13 wt %), white micas (phen- low-P metamorphism, which develops dur- gite and/or paragonite, ~ 4 wt %), etc. The ing the subsequent rock exhumation. Usual- hydrated minerals are also very important ly, in most orogenies this second event per- for the transfer to depth and later release of vasively obliterates, especially in continen- water during subduction, which favours the tal crust, the minerals formed during the HP andesitic magma generation of the volcanic event. However, in the western Alps, the arc (cf. Fig. 1 right). Eclogitic Micaschist Complex of the Sesia The basalt to eclogite transformation, there- Zone shows extraordinary fresh HP mineral fore, may be summarized by the following assemblages, well preserved most likely simplified mineral reactions (in black the because a very fast exhumation prevented igneous and in red the metamorphic miner- retrogression. Between Ivrea and Châtillon als): (Fig. 5) both the continental crust of the «Eclogitic Micaschist Complex» (EMC) of the Sesia zone (Fig. 5, Stops 1 to 4) and the ocean-derived Piemonte zone of «Calc- schists with meta-ophiolites» (Fig. 5, Stop 5) are extensively exposed on fresh surfaces polished by the Val d’Aosta Quaternary gla- cier. For the stops description we refer to the Field Excursion Guide-book.
An interesting consequence of the albite breakdown is the release of free silica (lack- ing in the original basalt), which may crys- tallise as either quartz (at lower P) or coesite (at higher P) (see Fig. 4).
The geologic cross section of the lower Val d’Aosta
This short introduction to the subduction metamorphism is essential to the under- standing of the outcrops visited in the first day of the 2014 SASEG field excursion along the lower Val d’Aosta cross section.
During mountain building, deformation processes – folding, thrusting and faulting – are accompanied by metamorphism and magmatism. In the western Alps, magmatism is limited to the small Oligocene intrusions of Brosso-Traversella (Fig. 5) and of Valle del Cervo with related andesitic dykes and flows. On the contrary, two main types of orogenic metamorphism are observed: an earlier high-P metamorphism, which gener- ates during subduction and collision, and a
154 2-2014_geologi 2.06 12.02.15 15:21 Pagina 155
Fig. 5: Geotectonic map of the lower Val d’Aosta with location of the stops visited during the 2014 SASEG excursion. Stops 1 to 4 are within the eclogite-facies continental crust of the Eclogitic Micaschist Complex of the Sesia Zone, Stop 5 within the eclogite-facies Piemonte zone of Calcschists with meta-ophiolites [from Compagnoni et al. 2014].
155 2-2014_geologi 2.06 12.02.15 15:21 Pagina 156
References
Compagnoni, R., Engi, M. & Regis, D. 2014: Val d’Aosta section of the Sesia Zone: multi-stage HP metamorphism and assembly of a rifted con- tinental margin. 10th Int. Eclogite Conference, Syn-Conference Excursion, 5 September 2013, GFT – Geological Field Trips, 6 (1.2), 1−44. http://www.isprambiente.gov.it/it/pubbli- cazioni/periodici-tecnici/geological-field- trips/valle-daosta-section-of-the-sesia-zone Press, F., Siever, R., Grotzinger, J. & Jordan, T. H. (2003): Understanding Earth. Freeman & Com- pany (4th Ed.).
156 2-2014_geologi 2.06 12.02.15 15:21 Pagina 157
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 157-167
Bericht der 81. Jahresversammlung der SASEG vom 21. bis 23. Juni 2014 in Aosta (Italien) Heinz M. Bürgisser1
Teilnehmer (91): Baumgartner, Walter; Béguelin, Karim (StN); Belgrano, Thomas (StN); Bolliger, Werner & Renate; Bollinger, Daniel; Boulicault, Lise (St); Brumbaugh, William & Michele; Burckhardt, Jenny; Bür- gisser, Heinz & Trudy; Burri, Peter; Carmalt, Sam; Christe, Fabien (StN); Compagnoni, Roberto (E, R); De Loriol, Jean-Pierre & Mary; Do Couto, Damien (StN); Fankhauser, Kerstin (StN); Fischer, Andreas & Eva; Fomin, Ilya (StN) & Kozhina, Ekaterina; Franks, Sibylle; Frei, Walter; Glaus, Martin; Grossen, Viktor & Friederike; Guggiari, Orlando (StN); Gunzenhauser, Bernhard & Censier, Kathrin; Hansen, Wolfgang; Häring, Markus; Häusler, Mauro (St); Heckendorn, Werner; Heitzmann, Peter & Anni; Hemsted, Tim; Hynes, Pierre (StN); Kalbskopf, Reinhard (N); Kaufmann, Manuela (StN); Keller, Franz; Knup, Peter; Leu, Werner; Massaras, Dimitri & Schurtenberger, Heidi; Matter, Albert; Meier-Senn, Beat; Mermoud, Cédric (StN); Meylan, Benjamin; Minnig, Christian; Moscariello, Andrea & Mondino, Fiametta, with Camilla; Pittet, Céline; Pümpin, Volkmar & Anne; Scherer, Frank; Schmid, Stefan (E, R) & Jacobs, Inge; Schmidt, Thomas & Martina (Sp); Schwendener, Brigitte; Schwendener, Heinrich; Seemann, Ulrich; Siddiqi, Gunter (R); Stäuble, Albert & Tilda; Stäuble, Martin (R); Stenger, Bruno & Roux, Pauline, with Louis, Paul and François Stenger; Stumm, Fred & Margrit; Suana, Michael; Tangtuengtin, Pakorn (StN); Teumer, Peter & Renate; Trümpy, Daniel; Vimpere, Lucas (StN); Walter, Patric (St); Wicki, Antonia (StN); Wyss, Roland & Wyss-Böh- ni, Kristina; Zanoni, Giovanni (StN); Ziegler, Martin; Zürcher, Benjamin (StN); Zwaan, Frank (StN). (E) Exkursionsleiter 22. und 23.6.; (R) Referent 21.6.; (St) Studentenmitglied; (StN) Neues Studentenmit- glied; (N) Nichtmitglied (Gast); (Sp) Vertreter des Sponsors des Apéros
Samstag 21. Juni: Administrative und einigung in der Pause und am Ende des wissenschaftliche Sitzungen Nachmittags zum Verkauf anbieten wird. (Biblioteca Regionale), Partnerausflug, Apéro und Nachtessen (Restaurant Bataclan) 1 Genehmigung des Protokolls der GV vom 22. Juni 2013 in Chamonix I Generalversammlung Der Protokollentwurf der letztjährigen Ver- (Protokollentwurf, zu genehmigen am 20. sammlung, publiziert im Swiss Bulletin für Juni 2015 an der GV in Baden) angewandte Geologie (18/2, 2013, 95−99) wird diskussionslos genehmigt. Um 13:50 Uhr begrüsst Präsident Peter Burri die anwesenden Mitglieder im gut besetzten Konferenzsaal des Bibliothekgebäudes, 2 President’s Report, June 2013 − einer ehemaligen Kirche, die nun jedoch June 2014 komfortable Sitze aufweist. Er erklärt auf englisch, dass traditionsgetreu die Geschäf- P. Burri started his report by showing the te der Vereinigung auf deutsch durchgenom- excellent development on membership: men würden; da nun aber zahlreiche Neu- mitglieder nicht gut deutsch verständen, werde er seinen Jahresbericht auf englisch vortragen. P. Burri preist kurz das Buch «Swiss Gang» – Pioniere der Erdölexploration an, das die Ver-
1 Vorstandsmitglied SASEG
157 2-2014_geologi 2.06 12.02.15 15:21 Pagina 158
The increase by 8 members contrasts with month for lectures, papers and panel discus- the decreases in the two previous years sions, which causes the Committee to consi- (-7, -8); main contributor is the higher joi- der an increase in Committee members. The- ning rate (+ 80%, caused especially by more re was much positive feedback on the sym- students joining), though there were also posium organised by SASEG and the Univer- fewer resignations. sity of Berne to honour Peter Lehner. Also During a period of silence the assembly’s the themed Bulletin issue (on climate chan- thoughts went to the four members who ge) received praise, both from supporters died during the past 12 months: and critics. The only negative observation • Carl Eduard Burckhardt (member for 60 was that the AAPG Distinguished Lectures years, died at age 99) that SASEG organised in Geneva were atten- • Peter Lehner (member for 43 years) ded only by people from the Geneva region, •Heino Lübben (member for 17 years) not from other parts of Switzerland. • Helmut Niko (member for 9 years) P. Burri reiterates that SASEG has no politi- The merits of Peter Lehner, VSP president cal agenda; as per by-laws discussions are preceding Peter Burri, get specially mentio- conducted on the basis of facts, not political ned, as well as those of Heino Lübben, for- beliefs. The Annual Convention will remain mer CEO of BEB, and also of Charles Mer- important, and although the Association is canton, who left the association shortly changing face, Convention attendance has before his death. been good, with more than 90 participants at the rather remote Aosta. P. Burri urges Five members are honoured for their long members to talk to earth scientists with an membership: Fritz Burri and Edouard Lan- interest in energy issues to become mem- terno for 65 years, Mrs. Greti Büchi (to- bers of the Association. gether with her deceased husband U. P. Finally, P. Burri reads the names of all 29 Büchi) and Peter Diebold for 60 years, and members that joined SASEG in the past 12 Martin Ziegler for 50 years. Martin Ziegler months, whereby each member present receives his commemorative membership rises from his/her seat, to be seen by all certificate, signed by the President, perso- members of the assembly. nally from Peter Burri, whereas the others There are no questions from members regar- will receive it by mail, together with a perso- ding the President’s Report. nal cover letter.
Then P. Burri reviews the past year. SASEG 3 Bericht des Kassiers experienced many positive developments: The Association has managed to be placed Kassier W. Heckendorn charakterisiert die on the distribution list of all consultations of Finanzen der SASEG als gesund, was durch Switzerland’s Federal Department of the die mit einem Überschuss von Fr. 4‘342 abge- Environment, Transport, Energy and Com- schlossene Gewinn- und Verlustrechnung munications; SASEG was invited to give sig- für 2013 demonstriert wird (Tab. 1): nificant input to a positioning paper by the German Academy of Science on hydraulic fracturing for both hydrocarbons and geo- thermal energy and will also be the co- patron of a one-day symposium in Bern this October on the same topic, together with Der Überschuss erklärt sich vor allem aus Swisstopo and the Swiss Academy of Scien- viel tieferen Ausgaben für die Website gegen- ce. SASEG has received 2−3 requests per über 2012 (als die Transformation von der
158 2-2014_geologi 2.06 12.02.15 15:21 Pagina 159
VSP zur SASEG durchgeführt wurde) und aus 6 Décharge des Vorstandes einem kleinen Überschuss der Tagung Cha- monix (gegenüber einem Verlust der Tagung Durch Handmehr erteilen die Mitglieder Luzern 2012). Das Konto zum Sponsern von dem Vorstand Décharge und sprechen ihm Studenten enthielt zu Beginn von 2014 bei- damit ihr Vertrauen aus. Es standen keine nahe Fr. 6‘000, wonach noch Honorare für Vorstandswahlen an. Referate, die P. Burri im Namen der SASEG hielt, diesem Konto gutgeschrieben wurden. Mit Applaus wird W. Heckendorn’s Arbeit 7 Tagung 2015 verdankt. Der Tagungsschwerpunkt Geologie der nuklearen Endlagerung bleibt unverändert, 4 Bericht des Redaktors jedoch beschloss der Vorstand an der Sit- zung am Morgen der GV, auf der Montag- Bulletin-Redaktor D. Bollinger erinnert die Exkursion das Mont-Terri Felslabor bei St. Mitglieder an den Höhepunkt der letzten 12 Ursanne zu besuchen. Vize-Präsident B. Gun- Monate, das Erscheinen des 164-seitigen zenhauser erläutert dazu, dass deswegen Themaheftes «Klimawandel», das ein exklu- der Tagungsort von Baden nach Westen ver- sives Gespräch mit Prof. Thomas Stocker, legt werden wird (nach Aarau oder Solo- Co-Vorsitzender der IPCC Working Group I thurn). Die Exkursion am Sonntag, der Geo- des 5. Sachstandberichts, enthielt. Er infor- logie des Jura im Querschnitt Brugg – Rhein miert, dass Heft 19/2 ebenfalls ein Hauptthe- gewidmet, bleibt unverändert. ma haben werde, nämlich Fracking. Im Weiteren zeigt D. Bollinger, dass der Mix der Bulletin-Artikel nur wenig gegenüber 8 Tagung 2016 dem Vorjahr änderte (je ungefähr 25% über Energie & Klimawandel, geologisch-wissen- Der Vorstand hat sich für eine Tagung im schaftliche Artikel und über Naturgefahren, nördlichen Oberrheingraben entschieden und 18% zu Ingenieurgeologie). Von der (Tagungsort entweder Heidelberg oder eine Anzahl Seiten der wissenschaftlichen Artikel kleinere Stadt in der Umgebung). Das vorlie- in den letzten zwei Heften des Bulletins gende Konzept umfasst eine geologische waren 49% durch die Autoren aus eigenem Exkursion zum Kohlenwasserstoff-System Antrieb eingereicht und 51% auf Anfrage des des nördlichen Oberrheingrabens und eine Vorstandes; dies ist ähnlich des vorherge- Exkursion mit Besuchen von Energie-Pro- gangenen Jahres. duktionsstätten (mehrere Möglichkeiten sowohl für Öl/Gas als auch für Geothermie).
5 Bericht der Revisoren 9 Varia Revisor W. Frei liest den auch von Revisorin D. Decrouez unterzeichneten Bericht vor, P. Burri erwähnt, dass die Firma Stump Fora- der beantragt, dem Kassier Décharge zu tec AG die Cocktails am Abend sponsert und erteilen. Mit Handmehr und Applaus wird auch ein gutes Honorar für P. Burris Referat die Décharge erteilt und damit die Rechnung beim Rotary Club in Zürich bezahlt hatte, 2013 genehmigt sowie Kassier W. Hecken- das dem Studenten-Sponsoring zugute kam. dorn entlastet. Vize-Präsident B. Gunzenhauser ergreift das Wort, um der Versammlung mitzuteilen, dass an der AAPG Annual Convention im
159 2-2014_geologi 2.06 12.02.15 15:21 Pagina 160
Tab. 1: Bilanz SASEG per 31. Dezember 2013; Gewinn- und Verlustrechnung.
160 2-2014_geologi 2.06 12.02.15 15:21 Pagina 161
April P. Burri den Distinguished Service and temperatures. Then he zoomed in on Award der AAPG erhalten habe. Grosser minerals found in the Western Alps and Applaus folgte auf diese Mitteilung. the excursion area, which indicate specific V. Grossen fragt den Vorstand, wie die Ver- fields of the phase diagrams (see p. 153 of bindung der SASEG zu den eidgenössischen this Bulletin for the extended abstract of Räten sei. Er erwarte keine plötzliche Verän- this presentation). derung, aber würde die Vereinigung «politi- • Prof. Dr. Stefan Schmid (Prof. em. Basel sche Leute» aufnehmen? Wie kritisch sind University and SASEG committee mem- wir bei der Aufnahme von neuen Mitglie- ber): Geodynamic aspects of high-pressure dern? P. Burri repliziert, dass nur Geowis- metamorphism; how do subducted rocks senschafter und Fachleute im Energiebe- reach the earth’s surface again? reich aufgenommen werden. Da ein Einzel- Also this presentation was related to the mitglied nicht für die SASEG spricht, ergä- excursions of our Annual Convention. S. ben sich Probleme höchstens bei den Schmid presented, energetically and Vorstandsmitgliedern. Im Weiteren lehne die enthusiastically, different models publish- Redaktionskommission des Bulletins ten- ed within the last 30 years on how exactly denziöse (z. B. polemische, mit politischen the formerly deeply subducted continen- Zielen) und nicht wissenschaftlich fundierte tal crust near the Africa-Europe plate Artikel ab. V. Grossen zeigt sich von den Ant- boundary could have reached the surface worten befriedigt, warnt jedoch in seinem again. Experts don’t agree on the validity Schlusswort vor Gruppierungen, die wissen- of a series of dynamic models (e.g. exten- schaftliche Vereinigungen desavouieren wol- sion, extrusion and slab extraction), all of len. which have shortcomings or contradict Daraufhin wird die Generalversammlung um actual observations also to be made in the 14:40 Uhr geschlossen. wider excursion area.
• Dr. Gunter Siddiqi (Swiss Federal Office of II Technical and Scientific Meeting Energy): The role of Geo-Energies in Swit- zerland’s Energy Strategy 2050. The Technical and Scientific Meeting that G. Siddiqi described the Energy Strategy followed the General Assembly straight 2050, based on a scenario characterized by away were conducted in English. The pre- a major decrease in demand despite conti- sentations were the following: nued population and economic growth. The strategy rests largely on a massive improve- • Prof. Dr. Roberto Compagnoni (Torino Uni- ment in energy efficiency, a much bigger versity): High Pressure (HP) and Ultrahigh share of renewable energy, imports and Pressure (UHP) metamorphism in continen- more research and development to enable tal crust and oceanic lithosphere («subduc- the implementation of the strategy. He then tion metamorphism»). focussed on the stimulation of the search The first part of this talk was to the many for geothermal energy in Switzerland: the non-metamorphic geologists in the feed-in tariffs, the geothermal guarantee audience a welcome introduction / scheme, more funds for pilot and demon- refresh er to subduction and metamor- stration projects and more coordinated geo- phism at plate boundaries, whereby R. thermal research and development. The Compagnoni also showed the progress in discussion showed that some members are the past 20 years in extending the petrolo- concerned about the envisaged decrease of gy phase diagrams to greater pressures energy demand in Switzerland driven by efficiency targets and more regulation.
161 2-2014_geologi 2.06 12.02.15 15:21 Pagina 162
• Dr. Martin Stäuble (MD Shell China und back to the initial layout of the town by the Vice President Shell China EP): China Romans. Unconventionals. The pursuit of unconventionals is driven by China’s huge predicted increase of IV Evening energy demand. M. Stäuble characterized China’s numerous basins as having (1) Convention participants gathered under the generally complex geological histories and arcade of Bataclan restaurant, near the Arch therefore complicated structures, (2) lacu- of Augustus, the perfect location for esta- strine shales as the source for unconven- blished and new SASEG members and their tional oil and gas, and (3) a regulatory fra- partners to meet and to enjoy the cocktails mework for exploration based on a very sponsored by Stump Foratec AG (Fig. 1/1). supportive government. He then present- President Peter Burri welcomed all in the ed the many issues during the initial years traditional short address (Fig. 1/2), in which of Shell’s operations in the densely popu- he first warmly welcomed partners; through lated Sichuan Basin (see p. 69-74 of this their presence the SASEG Annual Conven- Bulletin for the extended abstract of this tion distinguishes itself from conventions of presentation). Also here the discussion other Swiss earth science associations. He time was fully used. then talked passionately about the distor- tion of scientific facts in the present Europe- • Dr. Bernhard Gunzenhauser (SASEG Vice- an campaign against shale gas and hydraulic President): Logistic details of the further fracturing, pointing out that no scientific convention programme. organisation in Europe supports a ban of The meeting closed at 6 p.m., leaving suffi- fracturing. He pleaded to members to be, as cient time to get ready for the cocktail scientists, ambassadors (not lobbyists) for a reception and dinner. scientifically correct discussion of our ener- gy options. Finally P. Burri touched on the history of the Aosta valley and on its inhabi- III Partners’ Programme: Guided tour tants who have kept the French language of Aosta and their autonomy much alive; he compa- red their single-minded character to those of Whilst members convened for the General geologists. Assembly, nineteen partners of members The subsequent dinner was served in the explored on foot, with a German- and an open air in the back garden of the restau- English-speaking guide, the many architectu- rant, whereby participants not only enjoyed ral jewels of Aosta’s more than 2.000 years of excellent food, but also the views of the history: the Town Hall (Hôtel de Ville) in mountains surrounding the venue (see Fig. neoclassical style, completed in 1841; the 1/2), with the sun slowly setting. collegiate church of Saint Orso and its Romanesque cloister; the eastern entrance to the town during Roman times, the Porta Excursions Praetoria; the Roman theatre with its back wall rising to the impressive height of 22 m; Both Sunday and Monday excursions belon- and the cryptoporticus, part of the market ged to the same theme and were led by Prof. of the Romans, situated today partly under- Dr. R. Compagnoni and Prof. (em.) Dr. S. neath the town’s cathedral. Many of the city Schmid (SASEG board member). An excel- centre’s streets through which the SASEG lent 17-page excursion handout with nume- partners walked on their guided tour go rous colour illustrations of maps, cross-sec-
162 2-2014_geologi 2.06 12.02.15 15:21 Pagina 163
tions, outcrops and thin-sections was prin- across (Fig. 1/6). Jadeite, a rare mineral ted free of charge for each participant by (NaAlSi2O6) of the pyroxene family, forms Proseis AG. This handout has been the sour- when albite (NaAlSi3O8) of a granitoid rock ce for most of the descriptions and interpre- breaks down to form jadeite + quartz at high tations below. pressures and relatively low temperatures. Donnas: This outcrop contains a spectacular feature of the Roman era: A 221 m long expo- Sunday 22nd June: Sesia Zone and sure of the Roman consular road from Ivrea internal part of the Piemonte-Liguria to Aosta and the Gallic provinces (modern- Zone (Lower Valle d’Aosta, northwest day France), with furrows and an impressive of Ivrea) arch (Fig. 1/7). The road was cut into rocks At 8 a.m. 87 participants climbed in Aosta typical of the northernmost (most external) into three coaches. In a beautiful morning part of the Eclogitic Micaschist Complex of light we made our way downvalley towards the Sesia Zone. These rocks have Early Terti- Ivrea, on the motorway. ary pervasive greenschist-facies metamor- phism that overprints the earlier eclogite Quincinetto: We reached the «outcrops», facies mineral assemblages. Visible eviden- which were large fallen blocks, by an easy ce of this overprint are garnet relics preser- yet invigorating morning walk along a minor ved at the core of iron-rich chlorite masses, road on the valley floor. Here Roberto Com- the outline of which indicated they were pagnoni introduced the Sesia Zone, its tecto- pseudomorphs after garnet porphyroblasts. nic setting and its metamorphism (Figs. 1/3, Soon afterwards we enjoyed, on three long 1/4) before explaining the actual rocks seen tables, a five-course lunch with local flavour at this spot of the Eclogitic Micaschist Com- at La Kiuva restaurant in Arnad (Fig. 1/8). plex of the Sesia Zone: continental-crust Hillock west of the Clapey house: In the shade sediments of a large block that rifted off the near the isolated house, Roberto Compagno- Adria plate in Jurassic times and became ni introduced the setting of the Piemonte- subducted underneath the Southern Alps in Liguria Zone, representing the spreading late Cretaceous time. Minerals indicate P-T ocean north of the Sesia Zone (Penninic conditions of 15−20 kbar at 550−600 °C (eclo- Domain). Then we scrambled to the top of gite metamorphic facies, high pressure/rela- the hillock (Fig. 2/9), a «roche moutonnée» tively low temperature), suggesting subduc- shaped in the Quaternary by the Valle d’Ao- tion of this continental crust to 50−70 km sta glacier. Glacial evidence included stria- depth. As co-leader Stefan Schmid emphasi- tions and an erratic boulder of a porphyritic zed, the rocks themselves were not eclogi- granite from the Mont Blanc massif, resting tes; we observed phengite micaschists with on the polished surface and aligned in the garnets and other metasediments in eclogite direction of the former ice flow. A lot of facies. observations could be made on the well- Montestrutto: About 50 participants hiked exposed bedrock itself, a foliated antigorite- 150 m up to a glacially polished terrace bearing serpentinite, i.e. a high-pressure above the village (Fig. 1/5), whilst the others metamorphic ultramafic rock. Perhaps most walked to a rock-climbing park at the foot of spectacular were veins of rodingite, which the cliffs where similar lithologies were visi- were folded and boudinaged, with the ble. Also these rocks belong to the Eclogitic yellow ish rodingite being preserved only in Micaschist Complex of the Sesia Zone; para- the central parts of the largest boudins. schists dominate the outcrop, with a few lay- Rodingite is the product of metasomatism ers of leucocratic orthogneiss containing altering an original basaltic dyke, which roundish jadeite megablasts several cm intruded a peridotite and formed during the
163 2-2014_geologi 2.06 12.02.15 15:21 Pagina 164
serpentinization at the ocean floor. This out- Viewing terrace in front of St. Nicolas church: crop led to a discussion initiated by Stefan At this panorama stop we overlooked the Schmid (Fig. 2/10) on the initial definition of entire southern flank of the upper Valle d’Ao- ophiolites by the Penrose Conference, which sta, including the Gran Paradiso Massif. First was guided by outcrops on Cyprus, where Stefan Schmid demonstrated the 1937 Carta sheeted dyke complexes are common. geologica Alpi Nord-Occidentale by F. W. However, the latter are missing in Alpine Hermann, the most beautiful geological map ophiolites. of the area (Figs. 2/11, 2/12). Then he embar- At 5:30 p.m. the coaches brought us back to ked on explaining the paradox of the schi- Aosta, where the participants had time to stosity dipping to the foreland, which Stefan further explore the town and enjoy in small Bucher, a student of Stefan Schmid, found to groups dinner in one of the many restaurants. have been caused by re-folding of nappes at a large scale during the Oligocene. This re- folding was preceded by subduction (to Monday 23rd June: Geotraverse across blueschist metamorphism) at 50−43 Ma and the major tectonic units exposed in the by subsequent exhumation. Blown-ups of upper Valle d’Aosta (between Aosta the guidebook illustrations helped explai- and Courmayeur) ning the complex geological history of the At 8 a.m. 59 participants left Aosta in three area. small coaches and five private cars. The six Roadside outcrop SE of village of Cérellaz stops, of which the first four were on the (Figs. 2/13, 2/14): Crenulation and tight fold- north-eastern slope of the upper Valle d’Ao- ing in the gneisses of the Nappe du Ruitor. sta, were spaced out at relatively short This gneiss belongs palaeogeographically to distances. the Briançonnais basement and tectonically is part of the Grand S. Bernard nappe St. Pierre castle: This beautiful outcrop was system. just underneath the castle, along the track Cascata di Lenteney: We parked off the main to the church. It comprised calcareous schi- road at the valley bottom and walked up a stes lustrées with a layer of the white horn- trail to a bridge just below the spectacular blende, tremolite. The outcrop belongs to Lenteney cascades, produced by a stream the Combin Zone of the Piemonte-Liguria from a hanging valley. The geological inte- Zone, which is the part of the Piemonte-Ligu- rest in this stop was a small outcrop of Zone ria Zone that did not reach the eclogite Houillère rocks: metamorphosed pebbly metamorphic facies, in contrast to yester- sandstones in which elongated quartz peb- day’s last outcrop which represented the bles manifest the intense deformation. The internal part of the Piemonte-Liguria Zone Zone Houillère represents the fill of Permo- that did reach eclogite metamorphic facies. Carboniferous troughs within the Briançon- Outcrop near the road to S. Nicolas: This nais basement; (Alpine) metamorphism is small outcrop, also in the Combin Zone, lowermost greenschist facies. comprised a fine-grained meta-basaltic rock Morgex, outcrops within vineyards off rue des with the greenschist facies mineral assem- Condemines (Fig. 2/15): These impure carbo- blage actinolite-chlorite-epidote-albite (pra- nates belong to yet another palaeogeogra- sinite), overprinting earlier blueschist facies phic unit, the Valais trough. Stefan Schmid parageneses. Excursion leader Stefan explained the development of this palaeo- Schmid explained that these were intercala- graphic element that straddles the northern ted within the schistes lustrées metasedi- parts of the Western Alps in Valais and ments and discussed a mafic dyke vs. basal- Savoy. The small outcrops featured sandy tic pillow lava origin of these rocks. limestones and dolomites of the Couches de
164 2-2014_geologi 2.06 12.02.15 15:21 Pagina 165
l’Aroley, deposited above an unconformity interpreted as the break-up unconformity, formed after rifting of the passive continen- tal margin of the Briançonnais facing the Valais Ocean. The Couches de l’Aroley repre- sent therefore the earliest part of the post- rift phase (Barremian-Aptian) of the Valaisan Unit. We continued driving towards Courmayeur, where we took the steep and winding road up to the Val Vény. Along the road we obser- ved strongly deformed schistose limestones that are part of the root zone of the Helvetic nappes and the Chaînes Subalpines. Later we had good views onto a lateral moraine with large erratic blocks. Shortly before 1 p.m. we reached Restaurant Petit Mont- blanc, at an elevation of 1.500 m a.s.l. (Fig. 2/16). Before the five-course lunch was ser- ved, P. Burri thanked organizers and excur- sion leaders for a very successful Conven- tion, and the participants for the good atten- dance. Before 3 p.m. we hurried back into the coaches in order to reach Aosta in time, to allow some participants to catch the last postal coach to Martigny in Switzerland.
Acknowledgments
Sincere thanks to P. Burri for contributions to the report and S. Schmid, G. Siddiqi and M. Stäuble for suggestions to improve an earlier draft.
165 2-2014_geologi 2.06 12.02.15 15:21 Pagina 166
Fig. 1: Selected photographs of the 2014 SASEG Convention in Aosta. [1-2] 21st June, Restaurant Bataclan, Aosta. 1] SASEG treasurer Werner Heckendorn (centre) and Prof. Dr. Andrea Moscariello of the University of Geneva (right) with six of his students, all of them new members sponsored by SASEG for the Conven- tion, raise the glass at the cocktail reception (Photo: H. M. Bürgisser); 2] President Peter Burri welcomes all in the traditional short address (Photo: B. Gunzenhauser); [3-8] 22nd June, excursion Sesia Zone. 3] Prof. Dr. Roberto Compagnoni introduces the Sesia Zone geology … (Photo: I. Fomin); 4] … to an attentive audience (Photo: H. M. Bürgisser); 5] Stop 2, high above the vineyards of the village of Montestrutto; … 6] … featured jadeite in an orthogneiss dyke within the paraschists (both photos: H. M. Bürgisser); 7] Roman consular road with furrows and an impressive arch (Photo: I. Fomin); 8] Lunch at La Kiuva restaurant (Pho- to: W. Heckendorn).
166 2-2014_geologi 2.06 12.02.15 15:21 Pagina 167
Fig. 2: Selected photographs of the 2014 SASEG Convention in Aosta. [9-10] 22nd June, afternoon: Hillock near Clapey house, Piemonte-Liguria Zone. 9] Roche moutonnée outcrop; Montjovet Castle in background (Photo: H. M. Bürgisser); 10] Prof. Dr. Stefan Schmid explains the complex history of this Zone (Photo: W. Heckendorn). [11-16] 23rd June, excursion Geotraverse Upper Valle d’Aosta. 11] On the terrace of the church of S. Nicolas, S. Schmid presents the 1937 map of the area … (Photo: F. Stumm); 12] … which every- one admires (Photo: B. Gunzenhauser); 13/14] Participants align at the roadside near Cérellaz to listen to S. Schmid’s explanation of the Ruitor gneiss (Photos: B. Gunzenhauser); 15] A walk through vineyards was required to reach the Couches de l’Aroley outcrop outside Morgex (Photo: H. M. Bürgisser); 16] Lively dis- cussions at lunch at restaurant Petit Mont Blanc in Val Vény (1.500 m a.s.l.), where the convention ended (Photo: B. Gunzenhauser).
167 2-2014_geologi 2.06 12.02.15 15:21 Pagina 168
168 2-2014_geologi 2.06 12.02.15 15:21 Pagina 169
Swiss Bull. angew. Geol. Vol. 19/2, 2014 S. 169-170
Heini Schwendener 1952 − 2014
Ich habe Heini Schwendener relativ spät kennengelernt, auf einer VSP-Tagung im Unterengadin vor etwa 15 Jahren, wo der Dauerregen uns zwang, statt der geologi- schen Exkursion bei einem Glas Wein lange Diskussionen zu führen. Als ich nach 35 Jah- ren im Ausland 2005 in die Schweiz zurück - kehrte, war Heini Schwendener derjenige, der mich in das Tiefengeothermie-Projekt Basel holte. Daraus wurden 9 Jahre enge Zusammenarbeit in der Energieszene der Schweiz und ein Kontakt, der weit über das Professionelle hinausging.
Es ist nicht leicht, ein Leben zusammenzu- fassen, das trotz seiner viel zu kurzen Dauer so vielschichtig und reich war wie dasjenige von Heini Schwendener. Er hat viele von uns von Heini zugeschnitten und liess noch Zeit gerade mit seiner Lebensintensität faszi- für Segelfliegen und die Reisen auf Fischkut- niert; mit seiner Leichtigkeit und anschei- tern in der Nordsee. Und in diesen Projekten nend unerschöpflichen Energie, sich allem war er auch der Perfektionist, der erst zufrie- widmen zu können: seiner Familie, seinem den war, wenn alles hundert Prozent in Ord- Beruf, seinen vielen Interessen und daneben nung war. Die Leidenschaft für das Segelflie- noch immer da zu sein für seine Kollegen gen und auch das Hochseesegeln sollten ihn und Freunde, wann immer man Heini das ganze Leben begleiten, und als Bündner brauchte. Vielleicht war das auch für Heini behielt er auch eine spezielle Liebe zum zu viel, aber er hat in kurzer Zeit mehr Hochgebirge. bewegt und mehr Spuren hinterlassen, als manche andere in einem viel längeren Heini konnte seine Kenntnisse nach dem Leben. Doktorat bald in die Praxis umsetzen. Er nahm 1984 eine Stelle als Geophysiker an bei Das Bedürfnis, sich breit für die Welt um ihn der Exxon/Shell-Tochter BEB in Hannover, herum zu interessieren und zu engagieren, dem grössten Gasproduzenten Deutsch- prägte schon seine Schulzeit, wo er einer- lands. Er kam im richtigen Moment in die seits ein begabter Schüler war und ander- Gas-Industrie. Es war die Zeit, in welcher die seits doch nur gerade so viel machte wie es 3D-Seismik in der Exploration für eine Revo- brauchte, um zur Matur zu kommen, was lution sorgte, was die Qualität der Abbildung ihm aber genügend Reserven gab, um sich des Untergrundes betraf und in der die Geo- für die vielen anderen Dinge einzusetzen, die physiker ins Zentrum der Geo-Aktivitäten ihn faszinierten. Das Studium der Geophysik rückten. Der neue Job führte ihn auch zu sei- mit Schwerpunkt Gravimetrie war mit Feld- ner Frau, Brigitte, die ebenfalls als Geophysi- arbeiten und Reisen auf die Vielseitigkeit kerin in der Exploration von BEB arbeitete.
169 2-2014_geologi 2.06 12.02.15 15:21 Pagina 170
Frisch verheiratet kehrte er 1988 in die alten Profession, der Erdgasexploration, da Schweiz zurück, um beim Stanford Research er die Beteiligungen der Swissgas in Nor- Institute für internationale Energie- und Che- wegen, in Dänemark und in der Schweiz mie-Firmen als Unternehmensberater zu betreute. Daneben ging es um Erdgasspei- arbeiten, vor allem im Bereich von Techno- cher und um neue Herausforderungen, wie logie-Management und Strategie. In dieser Power to Gas. Heini war nicht mehr an eine Zeit kamen die zwei Söhne Martin und Dario Stadt gebunden, sein Tätigkeitsfeld war nun zur Welt, und die wachsende Familie zog auf wieder die ganze Schweiz und Europa und er einen Bauernhof hoch über dem Zürichsee, lebte in dieser neuen Weite sichtlich auf. wo sie sich äusserst wohl fühlten. Heini Schwendener war über seine Frau Bri- 1996 kam Heini Schwendener nach Basel zu gitte seit 1991 mit dem damaligen VSP und IWB, den industriellen Werken der Stadt der heutigen SASEG verbunden und wurde Basel als stellvertretender CEO und verant- 2009 zusätzlich separates Mitglied. Wir freu- wortlich u.a. für die Bereiche Beschaffung, ten uns an seiner treuen Teilnahme an fast Marketing und Verkauf. Hier liess sich Heini allen Tagungen und an den meisten SASEG für die Deep Heat Mining Idee von Markus Vorträgen. Häring begeistern und – mit IWB als Haupt- Heini Schwendener hat uns alle viel zu früh aktionär der Geopower Basel – war er der und zu plötzlich verlassen. Die Energie-Indu- eigentliche Förderer des Projektes. Ohne strie der Schweiz hat kaum mehr jemanden, Heini Schwendener wäre die Bohrung mögli- der so sehr auf «zwei Beinen» steht wie er cherweise nie realisiert worden. Als das Pro- das konnte, da er sowohl auf der techni- jekt wegen der verursachten Seismizität ein- schen Seite der Energiegewinnung, wie auch gestellt werden musste, realisierte Heini, kla- auf der wirtschaftlichen Seite bestens rer als viele andere, den grossen Wert der zuhause war. Sowohl die Wissenschaftler generierten Daten und die Notwendigkeit, wie die kommerziellen Kollegen werden sei- die Anstrengungen für die Entwicklung der nen Rat vermissen. Und vor allem wird uns Tiefengeothermie in der Schweiz, trotz Rück- eines fehlen: Heini hatte ein enormes schlägen, weiterzuführen. Er war denn auch Geschick, in schwierigen Situationen Brü- wesentlich beteiligt an der Gründung der cken zu bauen und mit Imagination Lösun- neuen, schweizweiten Firma Geo-Energie gen zu finden. Er tat dies mit grosser Lie- Suisse und gehörte bis zuletzt dem wissen- benswürdigkeit und Diplomatie, aber auch schaftlichen Beirat dieses Unternehmens an, mit zäher Hartnäckigkeit, und er hatte damit mit ein Grund, weshalb wir intensiv mitein- fast immer Erfolg. Viele von uns aber verlie- ander zu tun hatten. Heini war überzeugt, ren einen fröhlichen, stimulierenden und dass die unerschöpflichen Wärmeressour- vor allem sehr lieben und herzlichen Freund. cen der Erde gerade in der Schweiz genutzt werden konnten und mussten und er setzte Peter Burri sich mit dem für ihn typischen Enthusias- mus bis zuletzt dafür ein. Genau so engagiert wehrte er sich in den vergangenen Jahren gegen die für ihn unwissenschaftliche Ver- teufelung von unkonventionellem Gas. 2010 gab Heini Schwendener das tägliche Pendeln nach Basel auf und wurde stellver- tretender CEO und Mitglied der Geschäfts- führung von Swissgas. In dieser Firma war er wenigstens teilweise wieder näher bei seiner
170 2-2014_geologi 2.06 12.02.15 15:21 Pagina 171
171 2-2014_geologi 2.06 12.02.15 15:21 Pagina 172
172