System węglowodorowy z gazem ziemnym w łupkach —północnoamerykańskie doświadczenia i europejskie perspektywy

Abstract

Shale gas hydrocarbon system—North American experience and European potential.m3A b s t r a c t . The last two decades witnessed a significant progress in understanding unconventional hydrocarbon systems, exploration and developments in technology, which led to substantial increase of tight gas and shale gas production. This progress occurred mainly in USA, where unconventional gas production currently stands for ~50 % of annual domestic gas production, and it is forecast to increase to more than 60 % in 2016. Recoverable shale gas resources of USA and Canada are estimated at present for at least ~20 trillion m3 (~750 Tcf). Shale gas is a unique hydrocarbon system in which the same rock formation is a source rock, reservoir rock and seal (Figs. 2, 3). Gas field often appears continuous at a regional scale and does not requires hydrocarbon trap (Fig. 3). For development of shale gas, a high TOC contents (>1–2 %) is required for relatively thick formation (>30–70 m). High thermal maturity is essential for gas generation (>1.1–1.3 % Ro), and relatively low depth of burial (3500–4500 m) is necessary for commercial gas production. Gas is accumulated in isolated pores or adsorbed by organic matter (Fig. 5). Gas exploitation requires dense grid of wells with horizontal intervals and multiple fracturing. Shale gas is currently produced in several basins in USA and Canada. American success in unconventional gas production led to intensive shale gas and tight gas exploration across the world, with Europe being one of the priorities (Fig. 7). At the current stage, a couple of European sedimentary basins were selected as the major shale gas exploration targets. This includes predominantly the Lower Jurassic shale in the Lower Saxony Basin in Germany, the Alum shale in Scania (Southern Sweden), and to a lesser degree, the South-Eastern Basin in France with its Lower Jurassic and Lower to Upper Cretaceous shales, the Paris Basin in France with the Lower Jurassic shale, the Upper Jurassic shale in the Vienna Basin, the Lower Cretaceous Wealden shale in England, the Bodensee Trough in SW Germany with the Permian-Carboniferous shale, and the cenozoic Mako Trough in Hungary. In Europe the most intense exploration for shale gas is currently being carried out in Poland. The major target in that exploration is the Lower Palaeozoic shale at the East European Craton (Baltic and Lublin–Podlasie Basin), mainly the Upper Ordovician and/or Lower Silurian graptolitic shale (Fig. 8) (Poprawa & Kiersnowski, 2008; Poprawa, 2010). For that formation, Wood Mackenzie and Advanced Resources International estimated recoverable gas resources as equal to 1,400 mld m3 and to 3,000 mld m3, respectively. Also the Lower Carboniferous shale of the south-western Poland (area of Fore-Sudetic Homocline; Fig. 8) could potentially accumulate gas, however in this case a limitation to potential for shale gas is a complex tectonic setting. Other black shale formations in Poland appear to have lower potential for shale gas exploration due to insufficient thermal maturity, low TOC, or low thickness.