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

Abstract：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.