关键词: 鄂尔多斯盆地, 上古生界, 岩性气藏, 低位体系域, 不整合面, 古地貌, 沉积相, 天然气分布

Abstract:

The hydrocarbon source rocks of coal-bearing strata are widely distributed in the Upper Paleozoic of Ordos Basin.There exist multiple layers of fluvial-deltaic reservoir sand bodies, which forms the favorable reservoir-seal combinations.The main part of the basin is a large gentle slope tilting westward and develops large lithologic traps. There are favorable gas reservoir-forming conditions and great exploration potential.Two regional unconformity surfaces including the regional marine regression surface at the bottom of Shanxi Formation and the erosion unconformity surface at the bottom of Shihezi Formation control the formation of the main gas reservoirs.Analysis on gas distribution and gas-water relationship of the main gas-bearing strata showed that three factors of provenance, palaeogeomorphology and sedimentary facies controlled the distribution of gas reservoir.Lithologic gas reservoirs are mainly developed in the middle-upper part of the low system tracts of SQ11(lower part of 8^th member of Shihezi Formation) and SQ8(2^nd member of Shanxi Formation). Giant lithologic gas reservoirs are developed in the gentle slope region, where the hydrocarbon-generating intensity is more than 20×10⁸m³/km². Natural gas are mainly distributed in quartz-rich coarse depositional systems, and the gas-bearing strata transfer upward from east to west. From SQ8 to SQ9(1^st member of Shanxi Formation)and to SQ11, gas-accumulating facies transfer from delta front to delta plain and fluvial facies.

Key words: Ordos Basin, Upper Paleozoic, lithologic gas reservoir, low system tract, unconformity surface, palaeogeomorphology, sedimentary facies, gas distribution