鄂尔多斯盆地西南缘长8段油藏成藏动力条件探讨

RESERVOIR ACCUMULATION DYNAMIC CONDITIONS OF CHANG 8 MEMBER IN THE SOUTHWEST MARGIN OF ORDOS BASIN

基于大量的新井钻探测试、声波测井及流体包裹体分析等资料,针对鄂尔多斯盆地西南缘长8段油气运移成藏动力机制不清的问题,以环县-彭阳及周缘地区深部异常压力为重点开展研究.结果表明:长7底部与长8上部普遍存在一定的剩余压力差,平面上压力分布特征与全盆地流体压力由中心向拗陷边缘逐渐减低的趋势相吻合.长7段烃源岩生烃作用产生的异常高压可驱使烃类向下以较大规模运移充注至长8储层,流体包裹体古压力模拟恢复出原油在充注进入长8段储层后仍具有一定的异常高压.整体上,与盆地内部相比,研究区源储剩余压差较小,但仍然是作为西南缘长8段油气成藏动力的主要机制.期待该研究能更进一步认识盆缘低渗致密油的成藏机理和分布规律,为拓展勘探领域提供参考.

Based on massive data from new well drilling tests,acoustic logging and fluid inclusion analysis,the deep abnormal pressure in Huanxian-Pengyang area and its surroundings are studied to find out the dynamic mechanism of hydrocarbon migration and accumulation of Chang 8 Member in the southwest margin of Ordos Basin.The results show that there is a certain residual pressure difference between the bottom of Chang 7 and the top of Chang 8 members.The plane distribution characteristics of pressure show a gradually decreasing from the center to depression margin,which are consistent with the trend of whole basin fluid pressure.The abnormal high pressure from hydrocarbon generation of source rocks in Chang 7 Member can cause the hydrocarbon to migrate downward on a large scale and charge into Chang 8 reservoir.The restored paleopressure of fluid inclusion by simulation shows that the crude oil still remains a certain abnormal high pressure after charging into Chang 8 reservoir.Compared with the interior of basin,despite the low residual pressure difference between source and reservoir on the whole,it is still the main hydrocarbon accumulation dynamic mechanism of Chang 8 Member in the southwest margin.It is expected that the study can help further understand the accumulation mechanism and distribution rule of low permeability tight oil in the basin margin,and provide reference for expanding exploration fields.