鄂尔多斯盆地上古生界岩性气藏形成的主控因素与分布规律

Controlling factors for lithologic gas reservoir and regularity of gas distribution in the Upper Paleozoic of Ordos Basin

鄂尔多斯盆地上古生界天然气成藏条件优越,勘探潜力巨大。对其主要含气层段的天然气分布特点及气水关系研究表明,山西组底部的区域性海退面和石盒子组底部的侵蚀不整合面控制主力气层的发育,气藏平面分布受控于(烃、物)源—(古地)貌—(沉积)相。岩性气藏主要分布于SQ8(山2)、SQ11(盒8下)低位体系域中上部,其中大型—特大型岩性气藏发育在生烃强度大于20×108m3/km2的平缓斜坡区。天然气储层主要为富石英质的粗粒沉积体系,且从东向西含气层位向上迁移。从SQ8(山2)、SQ9(山1)到SQ11(盒8),聚气相带由三角洲前缘向三角洲平原及河流相带迁移。

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 lithologie 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（2nd member of Shanxi Formation）. Giant lithologic gas reservoirs are developed in the gentle slope region, where the hydrocarbon-generating intensity is more than 20 ×10^8 m^3/km^2. 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.