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Development of N.W. Europe's Southern Permian Gas Basin

Development of N.W. Europe's Southern Permian Gas Basin

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Development of N.W. 's Southern Gas Basin

K. W. Glennie

Shell U.K. Exploration and Production

SUMMARY: The Southern contains over 4.1 × 1015 m 3 of recoverable non-associated gas, most of which is found in Early Permian sandstones. The most important source of this gas is coal deposited in a proto-Tethys foredeep basin. Where the coals were overlain by Rotliegend desert sands and by Late Permian halite, the scene was set for creating important reservoirs for gas. Deformation of the reservoir and seal to create a trap, and the generation and migration of Carboniferous gas, resulted from the structural history of the area, which was shaped in part by underlying crustal blocks and zones of crustal weakness. Much of this history was related to events most clearly expressed beyond the limits of N.W. Europe in the North Atlantic and Tethys: (1) E.-W. tension, which gave rise to the oblique-slip-induced of many sub- basins within the Southern Permian Basin, caused the consecutive creation of the Viking-Central system and Rockall Trough, and ended with the crustal spreading of the ; and (2) the early opening of Tethys, its closure and ensuing Alpine , which induced in many areas of the Southen Permian Basin that are now gas bearing.

Introduction beyond the limits of N.W. Europe, which were the cause of three major mountain-building North-West Europe's Southern Permian Basin episodes that affected the area to a greater or contains over 4.1 × 1015 m 3 of recoverable lesser extent, the Caledonian, Variscan and reserves of non-associated gas, most of which is Alpine . found in Early Permian Rotliegend sandstones, with minor quantities in reservoirs of Late There have always been slow changes in global Permian, Early , Cretaceous and mean surface temperature that were related to Tertiary ages (Fig. 1). By far the most important changes in the location and the relative propor- source of this gas is the underlying coals and tions of land and sea, and in the freedom of carbonaceous of the Carboniferous Coal movement of oceanic currents. Superimposed Measures. The maturation of this source rock on these have been long-term changes in climate and the migration and entrapment of the that were to effect the post-Caledonian deposi- generated gas is intimately connected with the tional environments of the area. structural and depositional history of this part These climatic changes were brought about by of Europe. the slow, apparently passive, drift of the North The Southern Permian Basin is both under- American-Eurasian land mass from a location lain and surrounded by an assortment of rocks, that was south of the Equator during the both sedimentary and crystalline, whose origins , that straddled the Equator during the stretch back to the early Palaeozoic and beyond. Carboniferous, and that today have their During the course of the basin's long history, separate locations centred some 50°-55 ° north vertical and horizontal movement of the older of the Equator (see e.g. Habicht 1979). These cratonic blocks continually influenced the struc- climatic changes had no direct effect on the tural and depositional history of their sedi- cratonic structural development of the Southern mentary cover as well as that of their sur- Permian Basin, but without those changes there roundings. Because many of these ancient would have been an entirely different set of blocks were not firmly welded together, the hydrocarbon source-rock, reservoir and seal zones that separated them were inherited as lines parameters to deal with, especially with respect of weakness that were activated repeatedly to the rocks of terrestrial and shallow-marine during the later history of the area in response to environments of deposition. changes in tensional, compressive and tangential It is clear from the foregoing that no sedimen- forces. Many of these forces were themselves tary basin should be studied in isolation, but induced by changes in crustal (plate) geometry rather should be considered in the context of its

From BROOKS, J., GOFF, J. C. & VAN HOORN, B. (eds), 1986, Habitat of Palaeozoic Gas in N. W. Europe, Geological Society Special Publication No. 23, pp. 3-22. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

4 K.W. Glennie / DISTRIBUTION OF GAS IN SOUTHERN PERMIAN BASIN OF N W EUROPE

I RESERVOIR FIELDS CRETACEOUS K TRIASSIC T PERMIAN : ZECHSTEIN z : ROTLIEGEND CARBONIFEROUS c SIGNIFICANT GAS DISCOVERY •

T~ Esmond T ° ~T z c L %wos, so,o C.B•C ~-p O~, Barque~ :~Viking ee'~KlO ~ • Ameland o Clipper~ ~:~Q~nde. ee eC Valiant %~- ~T~T ~e~ • ~ lezu'dwal• ..;~

. L .... S.... • ~P6 ~'~T~T ~T. Z =~e .. 01 1OOL 2OOkml T Bergen• e Wijk .e_~Coevorden e j ~ 52. ~ oo ~o

FIc. 1. Distribution of gas fields in the Southern Permian Basin that are known or presumed to contain gas of Carboniferous origin; the reservoirs, however, are of varying age. The reservoir age in many of the single well discoveries has not been published. surroundings. The Southern Permian Basin is seaway () trending roughly no exception for, as its name implies, its origin is W.N.W.-E.S.E. between southern and associated, at least in time, with that of its the -derived microcontinents of northern partner, the Northern Permian Basin. London-Brabant, Armorica-Bohemia and Both basins have, to a greater or lesser extent, Silesia (Cocks and Fortey 1982; Ziegler 1982). been affected by plate-tectonic events that resul- For the most part, the sediments of the Torn- ted in the opening and closing of the southern quist Sea are deeply buried beneath a cover of ocean Tethys, and in the long period of gesta- Devonian, Carboniferous and younger sedi- tion that eventually led to the opening of the mentary rocks (Fig. 3). Along the southern edge North Atlantic Ocean (Fig. 2); and both basins of Fenno-Scandia in Poland and northern are associated with rocks that are considerably (Flensburg), however, well data indi- older than the basins themselves. cate that there is a change from crystalline base- ment in the northeast, through a (protected?) zone of unmetamorphosed Lower Palaeozoic Early Palaeozoic Origins sediments to a zone in which the sediments are During the early Palaeozoic, the major slightly metamorphosed (Frost et. al., 1981). A S.W.-N.E. trending separated the little further to the north in southern Sweden, a old cratonic shield areas of and source rock, the Alum , overlies Baltica (Harland and Gayer 1972). Late the basement and is still not closure of the Iapetus Ocean gave rise to the mature for oil (Cornford 1984). If hyrdocarbon Important Caledonian mountain system, sub- source rocks are present within the zone of slight merged relics of which extend beneath the metamorphism mentioned above, like the post- northern North Sea between North Britain and mature source rocks of the Lake District (Fig. 3). Long before this major (Parnell 1982), they will probably have a rank orogeny, however, there existed a deep-marine approaching that of graphite. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Ha. REGIONAL EVENTS NORTH SEA PERMIAN BASINS ML PERIODS TETNYS-RELATED ATLANTIC-RELATED NORTHERN SOUl'HERN 0 ...... 0

Hiccene REGIONAL SUBSIDENCE OVER GIRABEN SYSTEM SPREADING ALPINE OF PRESENT HID ATLANTIC RIDGE I OROGENY Plateau ba.~lts Zechstein diapirism Palecc~ne-- - PLATE COLLISION SPREADING OF ROCKALL TROUGH Renewed faulting Inversk~ in of i Inversion of NW.SE trending Late EXTENDING NORTH TO GRADUAL Rotation NORWAY- SEA Central Danish : sub-basins CLOSURE of A Graben i Embayment J~ OF Iberia I SUBSIDENCE Extrusives I TETHYS ~i I SEA-FLOOR SPREADING IN in I Early CENTRAL Danish [ I IBERIA - NEWFOUNDLAND I GRABEN Embayrnent Zechstein diapirism ONSET OF SEA-FLOOR SPREADING LATE CIMMERIAN UNCONFORMITY Indefatigable erosion IN CENTRAL ATLANTIC DOMAL COLLAPSE & HAIN PHASE Rapid Sole Pit subsidence Late I OF GRABEN FORHATION u SEA-FLOOR SPREADING A IN TETHYS 1 & WRENCH TECTONICS Mid I ~e A DOMING AND I I LIMITED VOLCANIC ACTIVITY Early I 2~ I I -2~ I RIFTING IN Earliest Zechstein diapirism CENTRAL ATLANTIC 400m Triassic in RIFTING PHASE Polish Trough HARDIEGSEN UNCONFORMIrrY I DEVELOPMENT OF N.W. EUROPEAN I BASINIGRABEN SYSTEM Late I I Zechstein ,',~,~:n t | of sub-seal~vel I~slns Early I LATE HERCYNIAN I SUBSIDENCE OF SOUTHERN & NORTHEI~N PERHIAN BASINS BEGAN WRENCH TECTONICS Stephanian EARLY COLLAPSE OF VARISCAN 1 300- [ Extrusion of I- Rotllegend volcamia began .300 FOLD BELT IN EUROPE D Rifting in Right-lateral faulting: inver~on of Sole Pit Basin Westphal. Norway-Greenland Sea 250Om U. Carbemiferous A VARISCAN OROGENY Namurian T I VARISCAN FOREDEEP PLATE COLLISION INITIATION OF 1 NORTH ATLANTIC Dinantian FRACTURE PATTERN STEP-WISE CLOSURE I BACK-ARC RIFTING Z Probable strike-slip < Late OF PROTIO TETHYS I 2 movement of Great Glen Fault Marine Ur~,,sto~ in i & Extention in N. Atlantic Auk & Argyll I ~.~ Hid I Early I Volcanics in S. Scotland i Granites in Lake District I df~mAI I=IqU~IbIIALII ~f~.glklY

FIG. 2. A simplified evolution of the Tethys and Atlantic oceans tentatively related to some post-Caledonian structural events within the Northern and Southern Permian basins (Modified from Glennie, 1984b. Table 1). Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

6 K. IV. Glennie

During the late Cambrian-early Collision between Gondwana and took closure of the Tornquist Sea, the sedimentary fill place south of Armorica in the Late Visean and was deformed and consolidated into continental marked the start of the Variscan orogeny (Fig. crust but without, apparently, creating a moun- 2). tain range. This failure might be attributed to a With the slow northerly drift of Laurasia, relatively weak and oblique west-east conver- Early Carboniferous sediments represent the gence of the microcontinents towards Baltica transition from a relatively arid climate with without an intense , the only seasonal rainfall during deposition of the strongest deformation perhaps being concen- , to the more humid equa- trated along a narrow and steep zone of torial conditions that were to support the low-grade metamorphism such as that described prolific growth of coal-forming vegetation from Poland, parallel with the southern margin during the later Carboniferous. The earliest of the Fenno-Scandian-Baltic . Of coals were deposited during the Visean in the importance to our thesis, however, is that this north of and in the Midland Valley of axis of convergence is possibly now marked by a Scotland (Scottish Limestone Coal Group) buried zone of deformation that extends west- where they are underlain by lacustrine lime- ward from the Polish Anticlinorium (the north- stones and oil shales. Marine limestones repre- eastern margin of which coincides with part sent occasional encroachments of the sea from of the Tornquist-Teisseyre line of strike-slip the west. movement), along the southern edge of the Fyn- South of the Southern Uplands and its north- RingkObing highs to the Mid North Sea High, eastern extension below the modern North Sea, where it possibly merges with the younger coals form members of the late Visean-early deformation products of the Iapetus Ocean (Fig. Namurian Yoredale cyclic sequences; these also 3.). involve the sediments resulting from marine If this interpretation is correct, then already incursions of Proto-Tethys, which lay to the during the Ordovician, the scene had been set south and southwest. Over most of the future for the early Permian creation of the two southern Permian Basin, however, the start of separate Permian basins by the presence of a coal-forming conditions was delayed until later zone which in some way resisted the crustal in the Namurian, and was to reach its zenith stretching and subsidence that took place to the during the earlier half of the Westphalian. north and south following the Variscan orogeny. Subsidence within the basin permitted the The deformed of the zone may have accumulation of up to 2500 m of Westphalian given the added rigidity needed to prevent it strata, of which some 3-4°-/o (75-100 m) com- from shearing, stretching and subsiding to the prises coal, the potential source of very large same extent as the basins to the north and south. volumes of gas. In addition to the coal, asso- ciated carbonaceous shales are believed to have acted as a poorer but still significant source of Devono-Carboniferous History additional gas (Cornford 1984). The orogenic uplift of the Scottish-Norwegian The widespread interbedded horizons of Caledonian Mountains at the end of the Silurian marine fossils within the Namurian and West- period resulted in considerable erosion, and in phalian coal-beating sequences are evidence of the fluvial transport of large volumes of sedi- the generally low relief of this basin. And ment southwards across the adjacent plains because of this low relief, they are also evidence towards the margin of the Proto-Tethys Ocean. of relative changes in sea level that may in part During the Devonian and early Carboniferous, be the result of structural downwarp or of subsi- north-south stresses between the former dence in response to crustal loading with Laurentian Continent and the young Cale- sediment. The marine fossils may also, however, donian mountain chain resulted in an unknown reflect eustatic rises in sea level caused by the amount of left-lateral displacement across the contemporaneous melting of Southern Hemis- line of the , which crossed the phere ice caps over Gondwana. Nineteen marine subsiding basin of Lake Orcadie, and possibly bands have been recognised within the British across another fault or faults in what now Coal Measures (Anderton et al. 1979); within the underlies the Atlantic ocean (Ziegler 1985). Parana Basin of South America alone, 12 Farther south, the Devonian and early Permo-Carboniferous glaciations have been Carboniferous development of a large area of recorded (Martin 1981), and undoubtedly there Europe was dominated by subduction of Proto- were others as Gondwana drifted slowly across Tethys along the southern margin of Laurasia. the South Pole. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 7

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~x~o~ .Y S"AL'-.O'-"A"'NEI

---v -- ~ N ~ ~pMEMNATRSINE [LOWER VARlSCA ~'------I SED|MENTS ~ PALAEOZO)C '~_~"L ~'-"- ~ CRYSTALLINE I ~ i ~ [~/~"~*"'] METAMORPHICS J ~ ~ PRECAMBRIANAND I~:::.:-:..::l CADOMIAN BASEMENT

...... oo~ ~ ORIGIN OF MID NORTH SEA- RINGK~BING-FYN HIGH

FIG. 3. The locations of the Mid North Sea-Ringk0bing-Fyn High and the Central, Horn and Grinsted graben system that cuts it, are superimposed on a pre-Permian map of N.W. Europe. The Southern Permian Basin north of the Variscan Deformation Front and east of the Dowsing Fault is shown without ornament. Here, the deeply buried Carboniferous and Devonian strata are believed to be underlain by deep-marine sediments deposited in the early Palaeozoic Tornquist Sea, which contrast with the coeval shallow-marine sedimentary rocks of the High east of the Central Graben (Modified after Ziegler, 1982, and others).

Although the environment of deposition in ments within the main coal basin were derived the north and flanking the north slope of the largely from northern (Caledonian) sources. By London-Brabant Platform was essentially terres- the late Westphalian, however, sediment was trial, a N.W.-S.E. trending marine embayment also transported northward across the southern followed a Devonian line of weakness across the part of the basin, thus providing evidence of the area of the southern North Sea. As with a closer proximity of the newly created southern similar marine facies of Namurian age in highlands during the closing stages of the England (Widmerpool Basin; 1985), source orogeny. Furthermore, the mid Westphalian C rocks for oil or condensate may be present at dating of the youngest of the marine bands in depth (Fig. 4). The North Sea Namurian embay- England and Wales indicates that by then, Varis- ment had a depocenter just east of the Ruhr can folding was about to involve the permanent (Katzung and Krull 1984), where it joined the exclusion of the sea from the area. marine foredeep basin that separated the rising Westphalian C and D sequences in Britain can Variscan fold belt from its northern foreland. In occur in both coal-measure and red-bed facies. the east, this foredeep basin extended in an arc This is thought to reflect a generally increasing, to the north of Berlin and around Bohemia to perhaps seasonal, aridity, with coal-forest the Upper Silesian Basin. To the west, the fore- deposition being maintained in the well-watered deep passed south of the Wales-London- basin centres and sediment reddening taking Brabant Massif, where its sediments (Culm place below the surfaces of the better drained Measures) contain finely comminuted evidence basin flanks. Within the more southerly located of the coalfields that lie immediately to their Variscan Mountains local downwarps such as north. the Saar and Saale basins provided the sites for During the earlier Westphalian, fluvial sedi- depositing considerable thicknesses of coal- Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

8 K.W. Glennie

¢////,~ PROBABLE POST-MATORE SOORCE~OCKS

POSSIBLE OIL SOURCE ROCKS

LIMIT OF COAL DEPOSITION

f

0o

~o~a

O I00 200 300 KM Ir CARBONIFEROUS SOURCE ROCK

FIG. 4. Distribution of Carboniferous strata ranging in age from Visean to Stephanian with source rock potential for hydrocarbons. Visean oil shales in the Midland Valley of Scotland and Namurian marine shales in the southern parts of the basin are oil prone. Coal Measures are gas prone but adjacent to the Variscan Deformation Front are locally of anthracite grade and thus post-mature for major gas generation. Similarly, coals are unlikely to have produced much gas during the where they are buried beyond about 6000 m or are intruded by Permo-Carboniferous or younger igneous rocks. Stephanian coals are limited mostly to intra- montane depressions within the Variscan fold belt. bearing sequences (see e.g. Sch~fer 1983), which between Britain and Poland being subjected to there continued into the early Permian. These right-lateral wrench movements and the mountains were to form an effective climatic development of a complex pattern of conjugate divide between the relatively humid equatorial faults (Fig. 6). These movements brought about areas to the south and the decidedly arid the rapid collapse of especially the Central Euro- Permian deserts to their north. pean part of the Variscan fold belt. On the mega scale, the Variscan orogeny Coincident with the collapse of the Variscan resulted in the union of Laurasia and Gondwana Mountains, its northern foreland seems to have into the single super-continent (Fig. 5). been subjected to E.-W. tension. This tension The union was not a very stable one, however, probably began as far back as the late Dinantian as almost before it had been completed, other with early attempts to create an Atlantic Ocean events had already begun the process of its and bring about the crustal separation of North destruction. America and Eurasia. Indeed, Surlyk et aL (1984) present evidence of E.-W. extensional Creation and Early Development of rifting in E. Greenland, where Permian faults developed to the west of those of Carboniferous the Permian Basins origin; and Haszeldine (1984) reasons that a The Variscan orogeny was followed, and indeed nominal width of axial could have probably accompanied, by an east-west relative been emplaced in this proto-Atlantic Ocean movement between the Laurasian and Gon- before the end of the Westphalian, and might dwanan parts of Pangaea. This resulted in both have expanded to a strip some 200-300 km wide the Variscan fold belt and its northern foreland by the mid Permian. Others (e.g. Ziegler 1982; Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 9

LATE PERMIAN PANGAEA

.... HERCYNIAN .... MOUNTAINS

ROTLIEGEND ~ BASINS I

EQUATOR PROTOTETHYS

FIG. 5. Location of the Northern and Southern Permian basins within the megacontinent Pangaea. The lines of crustal separation in the future Atlantic and Tethys oceans are indicated. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

10 K. W. Glennie

Flc. 6. Pattern of important faults in Permian basins and surrounding areas. Note the contrast in trend direction between the N.W.-S.E. pattern within the Southern Permian Basin, the N.N.W.-S.S.E. trend of the Central Graben and Permo-Triassic basins of west-central England and the Irish Sea, and the S.W.- N.E. trend of the basins between southern and Brittany. BF Broad Fourteens Basin; CG Central Graben: G Grinsted Graben; GL Glt~ckstad Graben; H Horn Graben; MNS Mid North Sea High; NPB Northern Permian Basin; RFH Ringk0bing-Fyn High; S Sole Pit Basin; SPB Southern Permian Basin.

Hanisch 1984), however, would be inclined to (Fig. 7). The character of these Lower Rotlie- delay this latter event until the Cretaceous or gend volcanics is described by Dixon et al. early Tertiary (see also Fig. 2). Nevertheless, the (1981). At about the same time, zones of local evidence for a considerable degree of E.-W. transpression in the area of the Southern North tension in the proto-Atlantic area during the late Sea, such as North Yorkshire (Kent 1980) Sole Palaeozoic is very strong, even though it may Pit (Glennie and Boegner 1981) and the Broad not have resulted in the creation of new oceanic Fourteens (Oele et al. 1981) were subjected to crust at that time. inversion and subsequent erosion. Regional stresses associated with this tension Regional extension of the earlier areas of seem to have affected many parts of N.W. subsidence resulted eventually in the two east- Europe. Indeed, Russell and Smythe (1983) west trending Northern and Southern Permian relate the mid-Carboniferous conception and Basins. These basins are separated by the late Carboniferous birth of the Oslo Graben, Mid North Sea-Ringk0bing-Fyn system of with its widespread extrusion of basalts, to highs. Just why there are two Permian basins extensional stresses associated with crustal separated by a ridge that failed to subside with separation between Norway and Greenland. them is not known. The creation of both basins Also under conditions of tension, latest are coeval post-Variscan events. The suggestion Carboniferous (Stephanian) and early Permian was made earlier that in some way this may (Asselian) volcanics were extruded over other mark a zone of greater rigidity resulting from associated pull-apart structures, especially in the closure of the Tornquist Sea against the area of the North German-Polish plain, and southern edge of Fenno-Scandia. If so, then it intruded into dykes and sills within N.E. Britain took over 100 × 106a to make itself felt, for it Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

FIG. 7. Distribution of Stephanian to Autunian volcanics and volcanogenic sediments of the Lower Rotliegend and the dyke trends in Scotland and Sweden.

FIG. 8. The Early Permian sediment fill of the Moray Firth and Northern and Southern Permian Basins. The Rotliegend sandstones form important reservoir rocks, whereas the non-porous lacustrine claystone and halite may act as a seal for underlying Carboniferous or older reservoirs. Bedded halite has not been found in the Rotliegend of the Northern Permian Basin. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

12 K. W. Glennie seems to have had no obvious Devonian or thickness of over 8 km in the Glfickstadt Trough earlier Carboniferous expression. Possibly the at the southern end of the Danish peninsula. The setting was there but it required the addition of crustal weakness associated with this depocenter Stephanian volcanics to make it effective. This must have been established already early in the system of highs also roughly coincides with the Permian, where it was the site of accumulation northern limit of the Upper Carboniferous Coal of over 1500 m of Rotliegend (mostly desert Measures, a coincidence of critical importance lake) sediments. This inference is also supported for the development of gas fields in Rotliegend by the difference in number of halite horizons and younger reservoirs in the Southern Permian found in the Rotliegend, up to 16 in German Basin, and for the absence of gas of known offshore wells (Hedemann et al. 1984) compared Carboniferous origin in its northern neighbour. to five in British waters far to the west (see The Mid North Sea-Ringkc~bing-Fyn High is Glennie 1984c, Fig. 5). now cut by the Central, Horn and Grinsted Areas of more local subsidence (e.g. Sole Pit, (Fig. 6). Because of their consider- Broad Fourteen's Basins, Fig. 6) were also estab- able fill of Rotliegend volcanics and sedi- lished early in the Permian in response to right- ments and Zechstein halite, the writer believes lateral wrenching. These wrench movements that these grabens were already forming early in seem to have involved only limited lateral dis- the Permian, if not in the latest Carboniferous, placement on any one fault but, to judge from and were probably a tensional response to that the close spacing of faults recognised on seismic post-Variscan pattern of conjugate faults men- lines, may have been active over relatively broad tioned above. fault zones. The Southern Permian Basin extends almost Wadi and dune sands, which were to become 1500 km from eastern England to the Polish- the main reservoir for gas, accumulated pre- Russian border, and has a maximum width of ferentially along the southern flank of the basin about 400 km. Within the basin, post-Carboni- (Fig. 8). This was the natural outcome of a ferous sediments have accumulated to a relationship between a linear basin whose axis of

FIG. 9. Distribution of halite of Zechstein Cycle II, the most important seal for Rotliegend reservoirs. Shallow- marine carbonates of Zechstein cycles I, II and III were deposited around the margins of the salt basin and locally form reservoirs for both oil and gas. (Adapted from Ziegler 1982.) Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. IV. Europe's Southern Permian Gas Basin 13

subsidence lay north of centre, the northward that there seems to have been virtually no marine transport of fluvial sediment away from its erosion of the linear dunes of Durham, source area in the Variscan Highlands, and the England, so that their former relief is still largely deflation of these fluvial deposits by N.E. Trade preserved. Indeed, there is little or no reworked Winds, which resulted in redeposition of the sand in the interdune hollows between the basal sands in dunes farther to the west. Zechstein Marl Slate and the underlying By contrast, in the Northern Permian Basin, Carboniferous surface. A similar Rotliegend both aeolian and fluvial sediments were derived dune relief is believed to be preserved under the mostly from the Caledonian Mountains. North Sea (Glennie and Buller 1983b), but there, Because of a different relative distribution of the the dunes are probably of transverse type areas of subsidence and of wind direction (Glennie 1983a). (Glennie, 1983a) aeolian and wadi sediments A continuation of the hot and essentially arid tend not to coincide; the former accumulated in climate into the late Permian ensured that within considerable thickness against the northern the almost enclosed Northern and Southern flanks of the Mid North Sea and Ringk~bing- marine Zechstein basins, basin-margin sedi- Fyn highs in response to winds from the N.W., mentation was dominated initially by shallow- with the latter being concentrated closer to the marine carbonates (Fig. 9). Later, as these Caledonian Highlands. inland seas became more saline, deposition of Dune sands generally form the best reservoirs gypsum (anhydrite after burial), was concen- for Rotliegend gas, whereas, unlike the deposits trated around the basin margins and halite was of constantly-flowing rivers, wadi sands are precipitated in the deeper basin centres, where it commonly tightly cemented and thus cannot be accumulated to a thickness that locally reached good reservoirs. This is because once the surface some 3000 m (Taylor 1984). This halite was to be waters have dried up, evaporation of water still especially important in providing the top seal for percolating through the sediment just below the gas accumulations. surface results in the precipitation especially of Zechstein carbonates, mainly the second and carbonate cement. In areas of sand dunes, how- third cycle Haupt and Plattendolomites, provide ever, the water table is generally so far below the the reservoir for relatively small oil and gas surface that the evaporation of ground water is accumulations scattered between eastern virtually zero. In two fields of the Southern England and Poland (Taylor 1984, Fig. 4.16). Permian Basin, however, Groningen (St~iuble The common presence of some hydrogen and Milius 1970) and Rough (Goodchild and sulphide in the hydrocarbons associated with Bryant, this volume) the reservoir properties of these reservoirs is probably connected with the the wadi sands and gravels are virtually as good widespread occurrence of sulphate minerals as those of the dune sands. The writer suspects within the Zechstein. that in these two cases, because the sands and Although early Permian subsidence was in gravels were deposited on alluvial fans near the response to post-Variscan crustal stretching, late margins of the basin, they were well above the Permian subsidence resulted mostly from local level of the water table. By the time they isostatic adjustment of the crust to the initial were buried to that level, they must have been load of Zechstein marine water and the ensuing protected from evaporation by a fairly thick accumulated sediment and evaporite. Zechstein cover of sand and gravel. depositional cyclicity may have been in response Because the Permian was a time of consider- to eustatic changes of sea level caused by the able aridity in both the northern and southern waxing and waning of the last of Gondwana's basins, there was a relatively low rate of sedi- Permo-Carboniferous glaciations (Smith 1979; ment influx, and sedimentation failed to keep up Glennie 1983a, 1984b). with subsidence. At the time of the mid-Permian Zechstein marine transgression, the surface of the desert lake in the Southern Permian Basin is Triassic and estimated to have lain some 200 to 300 m below The advent of the Triassic period brought a global sea level (Smith 1979; Ziegler 1982), and a return to terrestrial conditions of deposition similar depth to the floor of the new Zechstein over especially the western half of the basin, Sea may also have been present in the northern with a marine influence extending slowly west- basin. ward from Tethys via the Polish Trough during Under these basinal conditions, once started, mid Triassic time (Muschelkalk). the Zechstein transgression appears to have been The red-brown anhydritic mudstones of the achieved exceedingly rapidly; so fast, in fact, Bacton Group Bunter Shale, which completely Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

14 K. W. Glennie lack marine fossils, indicate deposition in a The R6t halite, in particular, is important to major desert lake that extended from eastern the hydrocarbon industry as it provides the England to Poland, where there was a possible upper seal for many accumulations of gas that tenuous connection with Tethys. The lake was have found their way into reservoirs of Bunter rimmed by mostly fluvial deposits. With time, Sandstone. however, the marginal coarse clastics (Bunter A late Triassic-early Jurassic global rise in sea Sandstone) prograded into the centre of the level resulted in a more widespread trans- basin, where they included the local occurrence gression, the deposition of Liassic source rocks, of aeolian sands in its eastern half. After the and the linking of the Tethys and Arctic oceans Rotliegend sandstones, the Bunter Sandstone is across the Southern Permian Basin. This the next most important reservoir for gas in the connection was broken during the mid-Jurassic Southern Permian Basin. uplift of the Central Graben and Mid North Sea A change in the depositional pattern was system of highs, only to be followed during the brought about by a eustatic lowering of sea level late Jurassic by another global rise in sea level associated with the late Early Triassic Hardegsen with its attendant deposition of the Kimmeridge Unconformity, which affected basin margins Clay source rock. Within the Central and Viking and areas of slower subsidence (Ziegler 1982). grabens, this source rock draped older reservoir Local fault movements at about this time sequences that had subsided and rotated during probably triggered the start of diapirism in areas the final phases of important crustal stretching, where both salt and overburden were relatively and thus provided upper seals for many prolific thick. They also resulted in local areas of uplift oil fields that later were to be sourced by the and erosion, and in the development of same rock unit deep within the grabens. subsiding basins that on three occasions became Some of the sub-basins of the southern North the sites of halite deposition (R6t, Muschelkalk Sea area also underwent considerable subsidence and Keuper halites), the depositional area during the late Jurassic (e.g. Sole Pit, Broad becoming smaller with each succeeding cycle of Fourteens), which resulted in the generation of subsidence. These halites are probably all of considerable volumes of gas from the underlying marine origin, as is indicated by the high boron Coal Measures. content of the R6t halite (Holser and Wilgus 1981), with their degree of 'marineness' increasing eastwards towards Poland. Late Cimmerian and Laramide Local depocenters were related to subsidence Tectonism and Intervening of the Central and Horn grabens and the Glt~ck- stadt and Polish troughs. Halite was also Sedimentation deposited in other smaller basins to the west and The Jurassic -- Cretaceous time boundary south of England, as well as over that post- roughly coincided with a world-wide regression, Variscan zone of weakness on continental but in areas of active subsidence within N.W. Europe, the Hessian Trough. Europe, the conditions that caused deposition of

SW NE

DOWSING -ZECHSTEIN SHELF ZECHSTEIN BASIN ~- I: A ~ L ¥ --lIB- ~'~'~ SOLE PIT HIGH ~--~ zo.~ I ~E..N I t ,.oE I o T t~------~,, .~ ", . . ~ r ~.._~,.~ ~.~

KU Upper Cretaceous ~) KL Lower Cretaceous ~.~ J Jurassic "~U Upper Triassic 1L Lower Triassic pz P ...... zec...,° o ', RO Permian - Rotliegend km i

FIG. 10. Section across the U.K. southern North Sea illustrating an increasing degree of Late Cimmerian erosion towards the northeast, where virtually the total Jurassic and Triassic sequence is now missing. Uplift is believed to have resulted from crustal heating associated with E. - W. extension across the south Central Graben. Subsidence and deposition of thick Upper Cretaceous and Cenozoic sequences followed crustal cooling; these strata provide some measure of the amount of former uplift. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 15 the Kimmeridge Clay source rock for oil con- of Zechstein halite, the start of which can be tinued into the earliest Cretaceous (Ryazanian). deduced from the age of sediment in the first rim In many parts of the Southern North Sea, . Especially within the U.K. Southern however, this time span seems to have been one North Sea, many of these diapirs are oriented of considerable uplift and erosion of the basin N.W.-S.E. ,and are underlain by faults having flanks (see, e.g. Oele et al. 1981, Fig. 12). In the same trend (compare Fig. 6 with Taylor, British waters, erosion in the Sole Pit area exten- 1984, Figs. 4.11, 4.15). The effect on gas ded down to the Lias and, locally, to strata of reserves resulting from the Zechstein seal having Keuper age. East from Sole Pit, erosion pene- been breached by major wrench faults or by trated progressively more deeply into the Trias diapiric salt withdrawal has not been properly (Fig. 10), reaching the Upper Permian assessed. (Zechstein) in what is known as the Cleaver The succeeding Cretaceous history in this part Bank High. Here, up to possibly 2000 m of of N.W. Europe was one of a slow transgression Jurassic and Triassic strata may have been that reflected a rising global sea level with a eroded in a relatively short time. The regional steady retreat of the shore lines. The deposition pattern of erosion is well expressed in the Top of chalk was widespread from the Cenomanian Triassic and Top Bunter maps of Day et al. onward. Late Cretaceous land areas were limited (1981). to the Precambrian and Palaeozoic massifs of To judge from the age of the Delfland conti- the western and Armorica in nental to paralic clastics in the Rijswijk province the west, and Fenno-Scandia in the northeast; to of The (Bodenhausen and Ott 1981) the south, the Rhenish-Thuringian-Sudetic or the time of initial deposition of the Spilsby islands were all that remained of a much more Sandstone off the coast, uplift had extensive Rhenish-Bohemian land mass that had begun before the end of the Jurassic (Volgian). existed earlier in the Cretaceous. Although major folding was not involved, these The slow closure of Tethys resulted in the movements were sufficiently important to have . The Southern Permian Basin, been referred to as the Late Cimmerian tec- had long been associated with deposition in local tonism, and the resulting erosional surface as the sub-basins under the influence of E.-W. late Cimmerian Unconformity (Fig. 2). tension, and of erosion from the effects of The Cretaceous was a period of almost con- E.-W. compression. The area now came under tinous rise in global sea level. In the area of the influence of N.-S. compression and the former maximum erosion flanking the Broad reactivation of right-lateral movement across the Fourteens Basin, the subsequent transgression dominant N.W.- S.E. faults. This resulted in the seems to have begun by the Hauterivian. inversion of former basinal areas: the creation Sedimentation then onlapped progressively of the Polish Anticlinofium during the westward towards the Late Cimmerian Sole Pit Coniacian -- Santonian (Ziegler 1982), uplift of High, parts of which were not covered until after the Sole Pit (Glennie and Boegner 1981) and the start of Chalk deposition. Broad Fourteens -- West Netherlands basins The complex pattern of Early Cretaceous (Oele et al. 1981) during the latest Cretaceous uplift and subsidence, coupled with the obvious and earliest Tertiary, to be followed by The activity of some major faults, indicates that in the later Eocene. these movements were probably caused by wide- spread strike-slip activity of the Dowsing and Structural Control of Generation, other N.W.-S.E. oriented faults. The initial left-lateral compressive wrench movements that Migration and Entrapment of Gas induced the uplifts were possibly activated by These days it is axiomatic that any occurrence of stresses originating with the onset of sea-floor oil or gas must be the result of a fortuitous spreading in the Central Atlantic between New- association of source rock, reservoir and seal foundland and Spain (Figs. 2 and 5). (Fig. 11) coupled with the creation of trapping Apart from the global rise in sea level, the conditions prior to its generation and migration. later transgression may also reflect a relaxation The gas found in the Rotliegend and other reser- of these stresses as continental S.W. Europe voirs of the Southern Permian Basin is no excep- began to move in harmony with the newly- tion. By utilising a combination of Figs. 4 and 7 formed oceanic crust of the Central Atlantic to 9, the outcome, Fig. 2, gives an indication of area. those parts of the Southern North Sea Basin that The occurrence and timing of fault activity can be considered as prospective for gas. It high- can also be inferred from the diapiric movement lights those areas where the Carboniferous Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

16 K. W. Glennie

AGE SOURCE ROCK RESERVOIR SEAL

CENOZOIC PALEOCENE SST. PALEOCENE SH. CHALK CRETACEOUS HOLLAND MARL U VLIELAND SST.

~ JURASSIC 0

TRIASSIC ROT HALITE BUNTER SST.

Zechstein Zechstein /shale dolomite PERMIAN ~.:.:.:.:.:.:~:.:.:.:.:.:.:.!:!:!:!:!:i:i:i:i:i:!:i:i:i:i:i:i:i:i:i:!:!:!:!:i:i:i:!:i:i:i:i:i:i:i:i:~ i~::i::i::iliiiii::i::~::i::~ROTLIEGEND !i ii!iii!i!i!i!i!i!i!~!~iI Rotliegend :::::::::::::::::::::SANDSTONE :::::::::::::::::::::::::: halite/shale

COAL MEASURES Fluvial sands Shales

CARBONIFEROUS

Marine shales

DEVONIAN Old Red Sandstone

SILURIAN ORDOVICIAN Marine shales CAMBRIAN

FIG. 11. The stratigraphic distribution of known and presumed Palaeozoic source rocks within the Southern Permian Basin, and of reservoirs and seals associated with gas fields. The most important of these are the Carboniferous Coal-Measure source rocks, the Rotliegend sandstone reservoir and the Zechstein halite seal. There are no confirmed Lower Palaeozoic source rocks within the basin, and the few tests of Old Red Sandstone reservoirs found no hydrocarbons. The Palaeozoic gas found in younger reservoirs results from failure of Zechstein seals. source rocks are mature for the generation of top of the Coal Measures are now found at gas and are overlain by differing combinations depths ranging from the surface to as great as of reservoir and seal. This approach has already 8000 m or so. been applied to the gas prospects of part of the At this latter depth, with a modern tempera- Southern North Sea Basin by Lutz et al. (1975) ture gradient that varies between about 2.5 and and van Wijhe et al. (1980). 4.0°C per 100 m (Carstens and Finstad 1981), a The temperature at which the generation of temperature in the range 200 to 320°C can be gas begins will differ with the composition of its expected. This temperature range is considerably source rock and is probably also influenced by greater than that expected at the rule-of-thumb the length of time that the rock has been kept depth of 4000 m (100-160°C) which Oele et al. at any particular pre-maturation temperature. 1981 suggest can be taken as a guide for Thus these temperatures cannot be known with outlining the main areas of current gas any degree of accuracy for a source rock as old generation. as the Carboniferous. In practical terms, to Taking the gas drainage area around the Sole judge from the experimental work of Higgs (this Pit Basin as an example, Cornford (1984, p. volume), generation from coal can begin at 184), has shown that the proven reserves of some Vitrinite Reflectance values as low as 1.0070 R 693 × 109 m 3 (24.5 × 10 '5 ft 3) of gas could have and some gas can still be generated from anthra- been generated from a sheet of coal only 1.3 m cite with a VR of around 3.0°70 R (see also Corn- (4 ft) thick. With a cumulative thickness of up to ford 1984, p. 184). 75 or 100 m of coal, not to mention the much The Carboniferous Coal Measures have a thicker associated carbonaceous shale, it is clear thickness in the range of 1000 to 2000 m, and the that in general within the Southern Permian Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 17

Basin there was no shortage of gas to fill the because, with regional subsidence still con- available traps. tinuing, there has probably been more than In areas of relatively rapid subsidence, some enough gas generated during the Cenozoic to of the older Carboniferous source rocks were replace losses through leakage several times possibly already buried deeply enough to over. generate gas before the end of the Permian, but The preservation of gas in reservoirs that have with little or no chance of it being trapped in undergone great amounts of uplift relative to quantity. In those areas where the depth of their surroundings testifies to an exceptionally burial is now in excess of 6000 m, gas generation good seal. As may be expected, however, the is probably already in decline if it has not seal failed locally. In the Hewett field, for already ceased. And because these are precisely instance, which is flanked by the Dowsing Fault, the areas that underwent maximum crustal the thin evaporites at the margin of the Zech- stretching, not only were they probably affected stein salt basin failed to seal the fault conduits by a higher than normal heat flow, but very and gas escaped from the Rotliegend into the locally were also subjected to additional cooking Triassic Hewett and Bunter sandstones (see Fig. in proximity to dykes feeding the extensive 11). Lower Rotliegend volcanics. Later in their burial Further north, where the Zechstein halite is history, the rank of the coal must have been regionally much thicker, seal failure was raised and gas generated in the vicinity of large achieved by its local complete withdrawal during intrusions such as the Bramsche and Vlotho diapiric movements (see, for example, Taylor Massifs in Germany (Teichmi~ller, this volume). 1984, Fig. 4.14); Triassic Bunter sandstones The youngest Carboniferous source rocks again provide the reservoirs for gas of Carboni- beneath the giant are not ferous origin (Bifani, this volume). Over the mature for gas generation. This field is flanked central part of the basin where the Zechstein by depressions, however, which probably acted halite was thick, these diapirically-induced struc- as source areas. The main supply of gas is tures are large and numerous. Most have no gas, believed to have come from the west, where and those that do are far from being filled to there were two periods of gas generation, late capacity. This lack of gas may be explained in Triassic -- early Jurassic and Cenozoic, part by the limited areas over which withdrawal separated by a period of uplift with no genera- was complete, but also by the lack of an under- tion of gas. In the Ems Graben to the east, the lying Rotliegend reservoir to act as a feeder Westphalian source rocks are capped by red channel to the areas of salt withdrawl. In the shales of Stephanian age that are considered to area of the Esmond, Forbes and Gordon gas have been an impediment to the vertical migra- fields, the Rotliegend is in a shaly desert-lake tion of gas into Rotliegend sandstones, which facies complete with its own halite beds (see, e.g. should then have provided a permeable path to log of well 44/21-1 in Glennie 1984b, Fig. 5), the adjacent Groningen structure. To the north, which would impede the vertical migration of the Coal Measures are post-mature, possibly in gas from the Carboniferous. In this respect, the part because of their burial history, but perhaps variable but relatively high percentages of also because of proximity to Early Permian or Nitrogen (8-16°70; Bifani, this volume) in these earliest Cretaceous volcanism (Van Wijhe et al. fields may indicate a difficult migration path. 1980; Kettel, 1983). In the Dutch offshore block K/13, on the Burial graphs indicate that in progressively flank of the Broad Fourteens area, gas, as in the subsiding areas like the Sole Pit and Broad Four- Hewett area, was first reservoired in Rotliegend teens basins, gas generation will have been active sandstones. Late Cretaceous inversion move- during the Jurassic and Cretaceous, with the ments helped to breach the Zechstein seal, which migration of gas to the basin flanks or into had already been thinned by the diapiric with- adjacent highs which had a slower rate of subsi- drawal of halite, and the gas remigrated along dence such as that now represented by the Inde- reverse faults into the shallower Bunter Sand- fatigable area. The Rotliegend reservoir in the stone reservoir (Roos and Smits 1983). Indefatigable field is capped by up to 1000 m of On land in The Netherlands, failure of the Zechstein halite which, because of its ability to Zechstein seal is probably also responsible for flow and reseal fractures caused by faulting, the occurrence of gas in the multiple Triassic and must always have been a very efficient seal. It is Paleocene reservoirs of the de Wijk and Wanne- not known, however, if this seal has been able to perveen fields (Gdula 1983), and in the early retain gas that was generated during the Jurassic Cretaceous sandstones of the Zuidwal or Cretaceous. Pragmatically, it matters little (Cottencon 1975) and Chalk of the Harlingen Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

18 K. W. Glennie fields (van den Bosch 1983). In the Bergen con- quantity occurs only where there is a combina- cession (van Lith 1983) Rotliegend, Zechstein tion of Carboniferous source rock and Zechstein and Bunter reservoirs are all gas bearing within halite. This is found in the Fourth Approaches close proximity to each other, and locally with area of the Northern Permian Basin (Fig. 12), in stacked gas accumulations. the Antrim Basin area of the North Channel Zechstein reservoirs in the Southern Permian (Illing and Griffith, this volume), and in the Basin occur in carbonate rocks. Most of the gas Morecambe field of the Irish Sea where addi- is believed to have migrated from Carboniferous tionally, the Triassic reservoir has a top seal of sources through poor bottom seals. In contrast, Triassic halite (Ebbern 1981; Bushell, this much of the oil in the Zechstein reservoirs of this volume). Small gas accumulations occur within basin is thought to have been sourced from fine- Carboniferous reservoirs such as at Cousland, in grained rocks of basin and slope facies Scotland (Fig. l) or in the midlands of England, belonging to the same depositional cycle as the where there is no cover of Zechstein halite. With reservoir (Taylor 1984). seals consisting only of overlying Carboniferous Gas seems not to occur in any quantity where shale, the potential size of these fields is there is no Zechstein halite in the system, and probably severely limited by leakage along indeed, the Triassic reservoirs of the Southern faults. Basin probably exist only because of upper seals With the step-by-step opening of the Atlantic, of R6t, Muschelkalk or Keuper halites. The lack first along the Rockall Trough and then along of a halite seal over the Zuidwal (Cottenqon et the Reykjanes-Iceland spreading axis during the al. 1975) and Harlingen (v.d. Bosch 1983) reser- Cretaceous and early Cenozoic, compressive and voirs may indicate that they received their charge tensional stresses largely ceased over most of the of gas only recently. North Sea area. Steady cooling of the thinned Beyond the limits of the Southern Permian continental crust beneath the axis of the Viking- Basin, the prospect of finding gas in any Central graben system (which probably began ( ?

f

©

J 0 ° / ZECHSTEIN SEAL .....~r__ __...~ ~ ROTLIEGEND RESERVOIR CARBONIFEROUS SOURCE ~ ROTLIEGENDSEAL CARBONIFEROUS RESERVOIR 8= SOURCE ZECHSTEIN SEAL CARBONIFEROUS RESERVOIR 6 SOURCE

0 Io0 ZOO 300 KM I PROSPECTS FOR PALAEOZOIC GAS

FIG. 12. Areas prospective for the generation, entrapment and preservation of gas. (1) where a Carboniferous source, Rotliegend reservoir and Zechstein seal are all present, (2) where the Rottiegend, and (3) where the Zechstein provides the seal for gas that is both sourced and reservoired within the Carboniferous. Only where these seals have failed has gas migrated into younger reservoirs. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 19 already during the early Cretaceous) caused the It is possible to have an accumulation of North Sea Basin to subside along the line of this hydrocarbons only if the reservoir and seal are axis. The greatest amount of subsidence (> 3000 deformed to form a trap before the start of m) was concentrated over the N.W.-S.E. migration. The size, geometry and temperature trending portion of the Central Graben within history of the Southern Permian Basin is such the Northern Permian Basin, which is roughly that gas generation possibly began locally before the area of maximum crustal stretching and of the end of the Permian and has been generating the greatest former heating by early to mid- somewhere within the basin more or less ever Jurassic volcanics. since. Differential rates of subsidence from the In the northern half of the North Sea, this early Permian onwards ensured that limited subsidence was sufficient to carry the rich trapping in Rotliegend sandstones was possible Kimmeridgian source rocks to depths where the from the moment the regional seal of Zechstein temperatures were high enough to mature them halite was deposited. The halite seal is not only m hence the distribution of oil (and gas) fields thick, it also posseses the physical property of along the flanks of the Central and Viking being able to flow and reseal any fracture caused grabens. In the Southern Permian Basin, how- by faulting. Nevertheless we know that in several ever, Cretaceous and Tertiary subsidence was areas this seal must have been breached from insufficient to carry the Kimmeridge Clay to the time to time, by fault activity and by diapiric salt required maturation depth of around 3000 m withdrawal, to permit the upward migration of and, indeed, it was only locally in areas such as gas into younger reservoirs. Major breaches the Broad Fourteens sub-basin that the deeper probably occurred when the Zechstein halite of Liassic source rocks were buried sufficiently former basinal areas such as Sole Pit and Broad deeply to become mature for oil generation (see Fourteens were uplifted some 2000 m or more e.g. Bodenhausen and Ott 1981). In some areas, during Late Cimmerian faulting and Late Creta- however, Tertiary subsidence has been great ceous inversion, but there was so much source enough to carry Carboniferous source rocks rock stil! capable of generating gas that, with back into the gas-generating window (e.g. Broad fractures rapidly healed, the underlying reser- Fourteens Basin and S.W. of the Groningen voirs are now gas fields. The effects of compac- High; van Wijhe et al. 1980) following the tion and the growth of authigenic minerals various phases of inversion uplift that seem to within the pore spaces during deep burial prior have been so widespread during the late Jurassic to uplift, has rendered these particular reservoirs and late Cretaceous. much less useful to industry than those of adjacent areas that underwent a smaller amount Conclusions of vertical movement. Beyond the limits of the Southern Permian It is obvious that the entrapment of Palaeozoic Basin, the combination of Carboniferous source gas within the younger reservoirs of N.W. rocks and Zechstein halite is found only in the Europe is a product of the long geological Forth Approaches area of the Northern Permian history of the area. It is not so obvious, but just Basin, the Antrim Basin of the North Channel, as likely, that this history has been influenced by and in the Manx-Furness Basin, where the the varying stresses, tensional, compressive and Permian is not gas bearing but the Triassic reser- torsional, associated with the ever-changing voir of the Morecambe field is capped by sali- geometry of crustal plates, the boundaries of ferous beds. some of which are beyond the limits of N.W. Older Palaeozoic source rocks may be buried Europe. deep beneath the Southern Permian Basin, but More directly pertinent to the origin of the most are probably so strongly post-mature that known gas fields, however, was the deposition they can be of interest only as a potential source of a sequence of source rocks, reservoirs and of graphite for the pencil-making industry. seals within the same general area and in the correct order to permit the upward migration and entrapment of generated gas. By far the most important of these are, respectively, the ACKNOWLEDGEMENT: This paper is published by Carboniferous Coal Measures, Rotliegend sand- permission of Shell U.K. Ltd. and Esso U.K. stones and Zechstein halite. Exploration and Production Limited. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

20 K. W. Glennie

TABLE 1. Publications on Fields Containing Gas of Known or Probable Carboniferous Origin, N. W. Europe

AGE RESERVOIR FIELD AUTHOR TE RT. de Wijk Gdula 1983

C R E T. Chalk Harlingen v.d. Bosch 1983 Vlieland Sandstone Zuidwal, Harlingen, Cottenqon et al. 1975 Leeuwarden

JUR.

TRIASSIC Muschelkalk (et al.) De Wijk Gdula 1983 Bunter Sandstones Hewett Cumming & Wyndham 1975 Esmond Bifani This volume Bergen Concession V. Lith 1983 K 13 Roos & Smits 1983 Hewett Sandstone Hewett Cumming & Wyndham 1975 Morecambe (Irish Sea) Ebbern 1981 This Bushell volume

PERMIAN Zechstein Coevorden Schermer & Alkmar V. Lith 1983 Eskdale Kent 1985 Rotliegend Groningen Bungener 1969 St~iuble & Milius 1970 K. & L. blocks Oele et al. 1981 West Sole Butler 1975 Leman Bank V. Veen 1975 Indefatigable 1975 Viking Gray 1975 Rough Goodchild & Bryant This volume Sean Ten Have & Hillier This volume Victor Conway This volume

CARB. Coal Measures/ Eakring Area Kent 1985 Millstone Grit Dukes Wood, Egmanton (Oil) Calciferous Cousland (Gas) Kent 1985 Sandstone Midland Valley Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

Development of N. W. Europe's Southern Permian Gas Basin 21

References ANDERTON, R., BRIDGES, P. H., LEEDER, M. R. & EBBERN, J. 1981. The of the Morecambe gas SELLWOOD, B. W. 1979. A Dynamic stratigraphy field. In: (eds L. V. Illing and D. G. Hobson). of the , 299. George Allen and The Petroleum Geology of the Continental Shelf Unwin. of N. W. Europe, Heyden, 485-493. BIFANI, R. (this volume). Esmond gas complex. FRANCE, D. S. 1975. The geology of the Indefatigable BODENHAUSEN, J. W. A. & OTT, W. F. 1981. Habitat gas field. In: (ed A. W. Woodland). Petroleum of the Rijswijk Oil Province, onshore The and the Continental Shelf of N.W. Europe, Netherlands. In: (eds L. V. Illing and D. G. Volume 1. App. Sci. Publ., 233-41. Hobson). The Petroleum Geology of the FROST, R. T. C., FITCH, F. J. & M/LEER, J. A. 1981. Continental Shelf of N.W. Europe, 301-309. The age and nature of the crystalline basement of Heyden. the North Sea Basin. In: (eds L. V. Illing and D. BOSCH, W. J. VAN DEN 1983. The Harlingen Field, the G. Hobson). The Petroleum Geology of the only gas field in the Upper Cretaceous Chalk of Continental Shelf of N.W. Europe, Heyden, The Netherlands. Geologie en Miinbouw 62 (1), 43-57. 145-56. GDULA, J. E. 1983. Reservoir geology, structural BUNGENER, M. J. A. 1969. Le Champ de gaz de framework and petrophysical aspects of the de Groningen. Revue de l'Assoc. Franc. des Wijk field. Geologie en Miinbouw 62 (1), Tecniciens du P~trole 196, 19-32. 191-202. BUSHELL, T. (this volume). The geology of the GLENNIE, K. W. 1983a. Early Permian (Rotliegendes) Morecambe gas field. paleowinds of the North Sea. Sedimentary BUTLER, J. B. 1975. The West Sole gas-field. In: (eds Geology 34, 245-65. L. V. Illing and D. G. Hobson). The Petroleum 1983b. Lower Permian Rotliegend desert Geology of the Continental Shelf of N.W. sedimentation in the North Sea area. In: (M. E. Europe. Heyden, 213-223. Broodfield and T. S. Ahlbrandt eds.) Eolian sedi- CARSTENS, H. 8~ FINSTAD, K. G. 1981. Geothermal ments and processes. Elsevier, Amsterdam, gradients of the northern North Sea Basin, 521-41.

59-62°N. In: (eds L. V. Illing and D. G. -- 1984a. In: (ed K. W. Glennie). Introduction to Hobson). The Petroleum Geology of the Conti- the Petroleum Geology of the North Sea. nental Shelf of N. W. Europe, Heyden, 151-61. Blackwells-Oxford, 236.

COCKS, L. R. M. & FORTEY, R. A. 1982. Faunal -- 1984b. The structural framework and the pre- evidence for oceanic separations in the Permian history of the North Sea area. In: (ed K. Palaeozoic of Britain. J. geol. Soc. London 139 W. Glennie). Introduction to the Petroleum (4), 465-478. Geology of the North Sea. Blackwells-Oxford, CORNFORD, C. 1984. Source rocks and Hydrocarbons 17-39.

of the North Sea. In: (ed K. W. Glennie). -- 1984c. Early Permian-Rotliegend. In: (ed K. Introduction to the Petroleum Geology of the W. Glennie). Introduction to the Petroleum North Sea. Blackwells-Oxford, 171-204. Geology of the North Sea. Blackwells-Oxford, CONWAY, A. (this volume). Geology and petrophysics 41-60. of the Victor gas field. 8~ BULLER, A. T. 1983. The Permian COTTENCON, A., PARANT, B. & FLACEL1ERE, G. 1975. Weissliegend of N.W. Europe: the partial Lower Cretaceous gas fields in Holland. In: (ed deformation of aeolian dune sands caused by the A. W. Woodland). Petroleum and the Continen- Zechstein transgression. Sedimentary Geology tal Shelf of N. W. Europe, Volume 1. Appl. Sci. 35, 43-81. Publ. 403-12. t~ BOEGNER, P. 1981. Sole Pit inversion CUMMING, A. D. & WYNDHAM, C. L. 1975. The tectonics. In: (eds L. V. Illing and D. G. geology and development of the Hewett gas field. Hobson). The Petroleum Geology of the Conti- In: (ed A. W. Woodland). Petroleum and the nental Shelf ofN. W. Europe, Heyden, 110-20. Continental Shelf of N. W. Europe, Volume 1, GOODCHILD, M. & BRYANT, P. (this volume). The App. Sci. Publ. 313-325. geology of the Rough gas field. DAY, G. A., COOPER, B. A., ANDERSON, C., BURGERS, GREY, I. 1975. Viking gas field. In: (ed A. W. W. F., RONNEVIK, H. C. & SCHONEICH, H. 1981. Woodland). Petroleum and the Continental Shelf Regional seismic structure maps of the North of N. W. Europe, Volume 1. Appl. Sci. Publ., Sea. In: (eds L. V. Illing and D. G. Hobson). The 241-49. Petroleum Geology of the Continental Shelf of HABICHT, J. K. A. 1979. Palaeoclimate, Palaeomag- N.W. Europe, Heyden, 76-84. netism and continental drift. Am. Assoc. Pet. DIXON, J. E., FITTON, J. G. & FROST, R. T. C. 1981. Geol. stud. Geol., 1-31. The tectonic significance of post-Carboniferous HANISH, J. 1984. The Cretaceous opening of the activity in the North Sea Basin. In: (eds L. V. Northeast Atlantic. Tectonophysics, 101, 1-23. Illing and D. G. Hobson). The Petroleum HARLAND, W. D. & GAYER, R. A. 1972. The Arctic Geology of the Continental Shelf of N.W. Caledonides and earlier oceans. Geol. Mag. 109, Europe, Heyden, 121-37. 289-314. Downloaded from http://sp.lyellcollection.org/ by guest on October 10, 2021

22 K. W. Glennie

HASZELDINE, R. S. 1984. Carboniferous North RUSSELL, M. J. & SMYTHE, D. K. 1983. Origin of the Atlantic palaeogeography: stratigraphic evidence Oslo Graben in relation to the Hercynian- for rifting, not megashear or subduction. Geol. Alleghenian orogeny and lithospheric rifting in Mag. 121 (5), 443-63. the North Atlantic. Tectonophysics 94, 457-472. HEDEMANN, H. A., 1VIASCHEK, W., PAULUS, B. & SCHAFER, A. 1983. Lower Rotliegend fluvio-lacustrine PLEIN, E. 1984. Mitteilung zur lithostrati- sequences in the Saar-Nahe Basin. Geol. graphischen gleiderung des Oberrotliegenden im Rundschau 73 (3), 1135-46. Nordwesdeutschen Becken. Nachr. Dt. Geol. SMITH, D. B. 1979. Rapid marine transgressions and Ges. 30, 100-107. regressions of the Upper Permian Zechstein Sea. HIGGS, M. D. (this volume). Laboratory simulation J. Geol. Soc. London 136, 155-56. studies into generation of coals. ST.~UBLE, A. J. 8£ I~IILIUS, G. 1970. Geology of the ILUNG, L. V. & GRIFFITH, A. E. (this volume). Gas Groningen gas field. Am. Assoc. Petrol. Geol. prospects in South Antrim, North Ireland. Memoir 14, 359-369. -- & HOBSON, D. G. 1981 (eds). The Petroleum SURLYK, F., PIASECKI, S., ROLLE, F., STEMMERIK, L., Geology of the Continental Shelf of N.W. THOMSON, E. & WRANG, P. 1984. The Permian Europe, Heyden, 521. Basin of East Greenland. In: (ed A. M. Spencer). KATZUNG, G. & KRULL, P. 1984. Zur tektonischen Petroleum Geology of the North European Entwicklung Mittel und Nordwesteuropas Margin. Norwegian Petroleum Soc. Graham and w~hrend des Jungpalaozoikums. z. angew. Geol. Trotman, 303-15. 30 (4), 163-73. TAYLOR, J. C. M. 1984. Late Permian-Zechstein. In: KENT, P. 1980. Subsidence and uplift in East (ed K. W. Glennie). Introduction to the Yorkshire and Lincolnshire: a double inversion. Petroleum Geology of the North Sea. Blackwells- Proc. Yorks. Geol. Soc. 42, 505-524. Oxford, 61-83.

-- 1985. U.K. onshore oil exploration, 1930-1964. TEICHMt3LLER, M. (this volume). Coalification and Marine and Petroleum Geology 2 (1), 56-64. natural gas deposits -- a new coalification map KETTEL, D. 1983. The East Groningen Massif: detec- for the top surface Carboniferous in north- tion of an intrusive body by means of coalifi- western Germany. cation. Geol. M(inbouw 60 (1), 203-210. TEN HAVE, A. & HILLIER, A. P. (this volume). Scan LITH, J. G. J. VAN. 1983. Gas fields of Bergen Con- North and South: Peakshaver gas fields, cession, The Netherlands. Geologic en M(inbouw Southern North Sea Basin. 62 (1), 63-74. VEEN, F. R. VAN. 1975. Geology of the Leman gas LUTZ, M., KAASSCHIETER, J. P. H. & WIJHE, D. H. field. In: (ed A. W. Woodland). Petroleum and VAN. 1975. Geological factors controlling Rotlie- the Continental Shelf of N. W. Europe, Volume gend gas accumulation in the Mid-European 1. Appl. Sci. Publ., 223-33. Basin. Proc. 9th World Petroleum Cong. 2, 93-7. WIJHE, D. H. VAN, LUTZ, M. & KAASSCHIETER, J. P. MARTIN, H. 1981. The Late Palaeozoic Gondwana H. 1980. The Rotliegend in The Netherlands and glaciation. Geol. Rundschau 70 (2), 480-96. its gas accumulations. Geol. M~inbouw 59, 3-24. OELE, J. A., HOL, A. C. P. J. & T~EMANS, J. 1981. WOODLAND, A. W. (ed). 1975. Petroleum and the Some Rotliegend gas fields of the K and L blocks, Continental Shelf of N. W. Europe, Volume 1. Netherlands offshore (1968-1978) -- a case Geology. App. Sci. Pub. London, 501. history. In: (eds L. V. Illing and D. G. Hobson). ZmGLER, P. A. 1984. Caledonian and Hercynian The Petroleum Geology of the Continental Shelf crustal consolidation of western and central of N. W. Europe, Heyden, 289-300. Europe -- a working hypothesis. Geologic en PARNELL, J. 1982. Genesis of the graphite deposits at M(inbouw 63 (1), 93-108. Seathwaite in Borrowdale, Cumbria. Geol. Mag. ZIEGLER, P. A. 1982. Geological atlas of Western and 119 (5), 511-12. Central Europe. Elsevier, Amsterdam, 130. ROOS, B. M. 8£ SM1TS, B. J. 1983. Rotliegend and Main gas fields in block K 13 -- a case history. Geologie en M(inbouw 62 (1), 75-82.

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