鄂尔多斯盆地东南部上古生界过剩压力与气藏关系研究

Study on the Relationship Between Overpressure and Gas Reservoir in Upper Paleozoic of Southern Ordos Basin

为了揭示鄂尔多斯盆地东南部古生界天然气运移与富集规律,利用测井声波资料计算上古生界本溪组至石千峰组最大埋深期泥岩过剩压力,分析流体过剩压力的分布特征及其与已发现气藏的关系。结果表明:研究区上古生界普遍发育两个欠压实带,石盒子组—石千峰组过剩压力普遍较高,主要分布在3.00~15.00 MPa之间,最高可达到22.20 MPa;本溪组—山2段过剩压力主要分布在1.02~10.00 MPa之间,最高为17.38 MPa。充足物源、快速沉积导致的"欠压实"和烃源岩大量生排烃"膨胀压"是研究区过剩压力带形成的主要原因。过剩压力带发育与天然气富集关系密切,下部过剩压力是天然气运移的主要动力,同时局部对下部本溪组、山2段气藏起到一定的遮挡作用,上部过剩压力发育带是山1段、盒8段气藏富集的重要区域性盖层。

In order to reveal natural gas migration and enrichment, we applied acoustic interval data to calculate over- pressure of mudstone in the Upper Paleozoic of southern Ordos basin, also analyzed the distribution characteristics of overpressure and their relation to discovered gas reservoirs. The results indicated that it develop two overpressure regions in study area, Shiqianfeng formation--Shihezi formation and Benxi formation--Shan-2 member of Shanxi formation. The overpressures of the former are generally higher, mainly range from 3.00 to 15.00MPa, even peak at 22.20MPa. The values of the latter are mostly between 1.02 to 10.00MPa, maximum value is 17.38MPa. The primary causes of two overpressure regions are the uncompaction results from sufficient sediment supplement and rapid deposition, and the expansion caused by the mass generation and expulsion of hydrocarbons from source rock. Natural gas accumulation is closely related to the development of overpressure, the lower overpressure regions is the main driving force for migration of natural gas and local cover for gas reservoirs of the Shan-2 and Benxi formations. The upper overpressure region is the significant regional seal for He-8 and Shan-1 gas reservoirs.