鄂尔多斯盆地苏里格西部气田"源控"主导的天然气成藏研究

苏里格西部气田致密砂岩气藏大面积复合连片分布,其主要含气层段二叠系盒8段-山1段为河流-三角洲沉积体系砂体。通过分析研究区天然气地球化学特征,并结合盆地烃源岩分布与生烃特征,揭示了研究区“源控”作用下的天然气成藏特征及成藏过程中的气水关系。结果表明:研究区天然气整体具有从西南向东北、从西向东及自下而上的运移特征,反映了处于生烃中心“三角地带”的研究区接受了来源于生烃中心的异地成因气与现今持续的原地成因气。在源岩控制作用下,苏里格西部气田天然气运聚成藏过程中,天然气驱动地层水区域性向北、向上运移,使研究区具有“南气北水”和地层水“上多下少”的气水分布总格局。

Study of Gas Accumulation under “Source Control” in Western Sulige Gas Field,Ordos Basin

Tight sandstone gas reservoirs are distributed over a wide area in the western Sulige gas field,with interconnected and superposed gas-bearing sands. The main gas-bearing sands occur in the eighth member of the Shihezi Formation and the first member of the Shanxi Formation. These are sand bodies of a river delta sedimentary system. In this study,the geochemical characteristics of the gas from the study area were analyzed together with the characteristics of the source rocks and hydrocarbon generation in the basin to determine the gas accumulation characteristics and the extent to which the gas-water relationship is controlled by the source rocks. It is shown that the gas in the study area mainly migrated from SW to NE,from west to east,and from bottom to top. It was found that the study area,which is located within the triangular zone of three high-intensity hydrocarbon generation centers,produces abundant gas, not only from the three hydrocarbon generation areas but also in the study area itself,which is continually producing gas to this day. The effect of the source rocks is that,as the gas migrates and accumulates,it drives formation water northward and upward regionally. The general pattern in the study area is summed up as "southern gas and northern water, more water above and less below".