鄂尔多斯盆地姬塬地区延长组中段岩性油藏成藏规律研究

Hydrocarbon accumulation law of lithologic reservoirs of middle Yanchang Formation in Jiyuan area,Ordos Basin

通过对延长组中段各油层组沉积特征、物源及沉积相演化规律的详细分析,结合各油层组油藏的分布特征,认为姬塬地区长8—长4+5油层组主要发育岩性油藏和构造-岩性复合型油藏2种基本类型,这2类油藏主要发育在三角洲前缘、水下扇及临近湖岸线的三角洲平原位置。姬塬地区长8—长4+5油层组油藏的类型及分布规律主要受物源控制,向北东及南东方向尖灭的砂体容易形成岩性油藏,油藏的规模取决于砂体的大小;而向南西及南部尖灭的砂体一般需要与鼻状构造叠合才能形成构造-岩性复合型油藏,油藏的规模同时受控于砂体和鼻状构造的大小。长8—长4+5油层组沉积时期,研究区西部物源逐渐减弱而北部及北东部物源逐渐加强,导致主要油藏类型及分布特征发生改变,长8油层组以岩性油藏为主,而长7—长4+5油层组则以构造-岩性复合型油藏为主。

Based on sedimentary characteristics,provenance analysis,sedimentary evolution and reservoir distribution,the reservoir types of middle Yanchang Formation in Jiyuan area,Ordos Basin are studied.The result shows that Chang 8 to Chang 4＋5 oil layers of Yanchang Formation are mainly dominated by lithologic reservoirs and lithologic-structural reservoirs,which mainly developed in delta front,subaqueous fan and delta plain close to lakeshore line.The types and distribution of Chang 8 to Chang 4＋5 reservoirs in Jiyuan area are mainly controlled by sedimentary provenance.The sand bodies that pinch-out to northeast and southeast are likely to form lithologic reservoirs,and the scale is controlled bythe size ofsand body.However,the sand bodies that pinch-out tosouthwest and south only form lithologic-structural reservoirs when superimposed with nose structures,and their scale is controlled by the size of sand body and nose structure at the same time.The sedimentary provenance in the west of the study area are weakened gradually while the sedimentary provenance in the north and northeast are strengthened gradually during the deposition stage of Chang 8 to Chang 4＋5 oil layers,which causes the change of reservoir types and distribution.It indicates that lithologic reservoirs mainly developed in Chang 8 oil layers,and lithologic-structural reservoirs mainly developed in Chang7 toChang4＋5 oil layers.