Geothermal Exploration Best Practices IGA ACADEMY
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Report 01/2013 Geothermal Exploration Best Practices Geology Exploration Drilling Geochemistry Geophysics IFC - International Finance Corporation Developers Workshop Izmir, Turkey, 18.-19.11.2013 IGA ACADEMY global.geothermal.knowledge IGA ACADEMY Report Vol. 1 / Dec. 2013 Geothermal Exploration Best Practices – Geology, Exploration Drilling, Geochemistry, Geophysics Editors R. BRACKE, C. HARVEY, H. RUETER Publisher IGA Service GmbH, Bochum, Germany © 2013 by IGA Service GmbH. All rights reserved. IGA ACADEMY Report comprises textbook materials of advanced trainings for geothermal professionals conducted by lecturers who are approved by the International Geothermal Association - IGA. These materials and the individual contributions contained in are protected under copyright by IGA Service GmbH and by the contributors. Photocopying and Derivative Works Single photocopies of single articles may be made for personal use as allowed by national copyright laws. Permission of the Publisher and payment of a fee is required for all other photocopying, copying for advertising or promotional purposes and all forms of document delivery. Permission of the Publisher is required for all derivative works, like compilations and translations. For information on how to seek permission call the IGA Secretariat: +49 234 32 10712 (Germany). Electronic Storage or Usage Electronic storage and usages of any material, including any article or part of an article, contained in this report requires permission of the Publisher. Notice of Publication No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the training material herein. About IGA ACADEMY is a Trademark of the IGA Service GmbH, Bochum, Germany; IGA Service GmbH is the business and service company of the International Geothermal Association. Cover Images GZB – International Geothermal Centre, Bochum, Germany. Further information www.geothermal-energy.org Contents Report-Nr. Author Title 0101-2013 I. MOECK Classification of geothermal plays according to geological habitats 0102-2013 I. KARAMANDERESI Characteristics of Geothermal Reservoirs in Turkey 0103-2013 T. BACKERS Borehole Geomechanics and Well Design 0104-2013 R. BRACKE, Geothermal Drilling Best Practices: The Geothermal translation of D. VOLLMAR, conventional drilling recommendations - main potential challenges V. WITTIG 0105-2013 H. RÜTER, Geothermal Exploration Best Practices, geophysical methods, A. DONAT, seismic, general aspects S. BAUER 0106-2013 H. RÜTER, Geothermal Exploration Best Practices, geophysical methods, A. DONAT, seismic, equipment S. BAUER 0107-2013 H. RÜTER, Geothermal Exploration Best Practices, geophysical methods, A. DONAT, seismic, data acquisition S. BAUER 0108-2013 H. RÜTER, Geothermal Exploration Best Practices, geophysical methods, A. DONAT, seismic, data processing S. BAUER 0109-2013 H. RÜTER, Geothermal Exploration Best Practices, geophysical methods, A. DONAT, seismic, geological interpretation S. BAUER 0110-2013 G.P. HERSIR, Resistivity surveying and electromagnetic methods Ó.G. FLÓVENZ 0111-2013 C.C. HARVEY Water-Rock Interaction, Alteration Minerals and Mineral Geothermometry 0112-2013 N. GÜLEC Isotope and gas geochemistry of geothermal systems Moeck: Classification of geothermal plays according to IGA Academy Report 0101-2013 geological habitats Supported by: Classification of geothermal plays according to geological habitats I. Moeck Faculty of Science, University of Alberta, Edmonton, AB T6G 2E3, Canada Abstract: Geothermal resources can be found in a large variety of geological environments ranging from volcanic arcs to sedimentary basins to crystalline rock provinces. Two large groups can be distinguished between all geothermal resources types: Either the heat transport is dominated by convection leading to accumulated heat, or the heat transport is conduction dominated leading to distributed heat. Considering the source of heat, heat transport, and thermal energy storage capacity of rock to store heat or to host hot fluids, it becomes obvious that geologic controls influence significantly the placement and formation of geothermal resources. The new geothermal play concept follows the basic approach of general resources assessment to group exploration targets according geologically controlled tiers, connected by similar geodynamic, sedimentary, magmatic and/or tectonic evolution. This lecture introduces into the geothermal play concept, play analysis and play assessment comprised by meaningful natural groups placing this concept directly into a geologic context. Worldwide case studies are demonstrated and exemplify the application of this new geothermal play concept. and it does not help in decision making for the 1 The play type concept appropriate exploration strategy. Two major In his article about exploration plays, well known problems rise from such an unspecific classification petroleum explorationist Harry Doust (2010) refers to scheme: the first problem is that these criteria are not the almost mythical status of “plays” in the known prior to exploration, therefore we cannot hydrocarbon industry. Playmakers are considered as classify a geothermal resource before exploration and heroes of the industry, and the successful play feeds therefore we cannot estimate the success of an everlasting legends about incredible discoveries, exploitation venture. The second problem is that low, exploration efforts and glory men. Basically, the play shallow, medium, deep are adjectives that invite us to type concept is a fundamental part of resources guess a whole suite of subjective interpretations and assessment in hydrocarbon industry. The analysis and ultimately numbers. understanding of play types is recognized as essential to strategically focused and successful exploration Let us have a look to one example: “moderate ventures. temperature” is described as between 90-150°C (Muffler, 1979), 125-225°C (Hochstein, 1988), 100- Amazingly, the geothermal community is lacking 200°C (Benderitter and Cormy, 1990) and 180-230°C such a concept although the utilization of geothermal (Sanyal, 2005). Global explorationists may struggle heat and energy looks back to a much longer history with a classification scheme that leads to such a wide than hydrocarbon production. Instead we range of temperature between 90-230°C. Obviously exhaustingly try to classify geothermal resources this concept is globally not applicable: in a standard according to temperature (low-, medium-, high- sedimentary basin 230°C is not in economically temperature), to depth (shallow, medium-shallow, drillable depth while at volcanic systems this medium-deep and deep) or to hydrothermal versus temperature might be accessed in a few couples of petrothermal systems. Obviously such a classification hundreds of meters. Important factors as porosity, focuses on the end-user or the probable utilization permeability, type of heat source, distribution of heat concept that may be demanded at a certain site. It (vertical or horizontal) are completely neglected in clearly prevents, however, from analog comparisons such an approach. The ultimate question is: what are because a certain temperature can be found in all we actually looking for? Is it temperature, or flow kinds of geological environments at various depths rate, or fluids in place? What answers need to be Moeck: Classification of geothermal plays according to IGA Academy Report 0101-2013 geological habitats provided by geothermal exploration, and how can we and permeability enhancement. There are clearly learn from geothermal field to field worldwide? physical limits to extract thermal fluids from any Eventually how to avoid over-estimates and under- rock types and main focus of play assessments is estimates of resources? on the description of the reservoir unit therefore. An alternative way to categorize geothermal The heat charge system, comprising the type of resources may be based on a globally applicable play heat source and the heat transport, expelling heat type concept (Moeck, submitted). A play type in from deeper to shallower parts in a geothermal petroleum geology represents a particular system. stratigraphic or structural geological setting, defined The regional topseal or caprock, a low by source rock, reservoir rock and trap. Translated to permeability unit which traps the thermal fluids at geothermal systems, a play type might be defined by a (litho)stratigraphic level and concentrates steam, the heat source and the geological controls on heat liquids or thermal fluids in specific locations, transport and thermal energy storage capacity. The allowing commercial exploitation either without or geological setting not only controls the play type but with EGS treatments. also the most appropriate exploration and heat recovery technologies. The timely relationship of the above four ingredients, for example that a pluton intrudes into Certainly the geothermal community would benefit a porous rock formation, which is then covered by from a consistent globally applicable framework. low-permeability rock as fine grained mélange at a Moreover a logical and consistent framework for a forearc region of a subduction zones. geothermal play type catalog needs to be simple enough to communicate important aspects of The play fairway, the geographic area over which geothermal energy potential to both