Accumulation Conditions Of The Chang 7 Tight Oil Reservoir In Chenghao Area, The Ordos Basin

Chang 7 oil-bearing formation group, which was mainly considered to be a reserve source within seldom basement geological research, is becoming a new target in recent petroleum exploration. Based on making full use of the previous studies, this paper integrate geologic data, well log data and outcrop data etc, in order to have a further study of the accumulation conditions of Chang 7 tight oil formation in Cheng hao area. This study analyzed the characteristics and conditions of the Chang 7 tight oil accumulation in Cheng hao area, Ordos basin, according to the characteristics of source, reservoir, shale caprock; the source-reservoir-seal assemblage; and the conditions of charging, etc. This research on the accumulation conditions of tight oil-bearing reservoir contributed to recognize the forming history and the mechanism of tight oil-bearing reservoirs, provided a theoretical basis for future exploration.According to the research of source rock, the result shows that the total organic carbon content of Chang7 is mainly under 4%, the source rock quality of Chang71 is poor-fair while Chang72 and Chang73 are dominated by good-best source rock. Ro value ranges from 1.02% to 1.21%, 1.13% in average, thermal evolution degree of organic matter being mature and within the oil window. Interstitial material is dominated by quartz; the content of illite is the highest in clay mineral, followed by illite-smectite mixed layer and chlorite, while only rarely kaolinite contained in clay mineral. The average of porosity and permeability is 7.14% and 0.17×10-3μm2, respectively. The caprock thickness of Chang 7 in Chenhao area is mainly between 10 to 25 m, and has a decreasing trend from east to west; shale content mainly distributed in 60%~75%. Geochemistry index of shale in Chang 71, Chang 72 and Chang73 is higher than hydrocarbon generation base level indicates a good quality of source rock, especially the Chang 73 black shale. Meanwhile, the reservoir has a favorable accumulate ability which is benefit for the source-reservoir-seal assemblage. The hydrocarbon generation pressurization is the mainly driving force in first migration of tight oil, resistance is dominated by intermolecular force as well as capillary force; the main paths of first and second migration are provided by fractures and sands. Overall, this area is considered to have great conditions for tight oil accumulation, after comprehensive assessment.