鄂尔多斯盆地吴堡地区延长组长8致密砂岩油藏成藏主控因素

The distribution of Chang-8 tight sandstone oil reservoir of Yanchang Formation in Wubao area, central-south of Ordos Basin

鄂尔多斯盆地三叠系延长组长8油层组为近年来发现的勘探开发新层系,勘探实践证实其成藏条件优越,勘探潜力大。本文以盆地中南部志丹县吴堡地区为例,对该区长8油藏成藏条件及分布规律进行了研究,结果表明:长8油藏油源主要来自于上覆长73烃源岩、长8内部烃源岩和长9顶部烃源岩,具有良好的生储层组合配置;主成藏期运移动力主要为生烃增压等形成的异常高压,油气充注到长8致密储层后主要以近距离垂向和侧向运移为主;成岩作用加剧了储层非均质性,形成成岩遮挡型准连续型油气聚集。长8油藏平面及层位分布主要受控于有效烃源岩展布、储层质量和有效盖层的控制,多种地质因素共同形成现今长8油藏分布格局。

Chang-8 oil-bearing bed of Yanchang Formation was found in recent years in the exploration and development of new Triassic reservoirs in Ordos Basin.Exploration practice has proved that it has good accumulation conditions and favorable exploration potential.With Wubao area in Zhidan County in the central south part of the basin as an example,the authors studied the conditions and distribution regularity of Chang-8 reservoir,and the results show that the Chang-8 oil source mainly came from the overlying Chang-73 source rocks,Chang-8 internal hydrocarbon source rocks and Chnag-9 top hydrocarbon source rocks,thus having a good oil-generating and oil-accumulating reservoir configuration.The migration force of main reservoir producing stage resulted mainly from hydrocarbon generation pressurization and abnormal high pressure,and the injection of oil and gas into Chang-8 tight reservoir was mainly caused by nearly vertical and lateral migration.Diagenesis exacerbated the reservoir heterogeneity and resulted in the formation of diagenetic occlusion type and quasi-continuous type oil gas accumulations.Chang-8 reservoir plane and horizontal distribution are mainly controlled by the effective hydrocarbon source rocks,reservoir quality and the effective cover layer,and hence various geological factors have resulted in the present Chang-8 reservoir distribution pattern.