COUPLING RELATIONSHIP BETWEEN OVERPRESSURE EVOLUTION AND HYDROCARBON ACCUMULATION PROCESS IN THE KARASU STRUCTURAL BELT IN KUQA DEPRESSION, TARIM BASIN, CHINA

As the core content of reservoir-forming dynamics research, overpressure is a key element for controlling oil and gas enrichment and distribution in petroleum-bearing basins. The Kuqa Depression is the most typical overpressured petroleum basin in China. The early rapid settlement and the strong uplift since the late 5 Ma have led to extremely complicated genesis and evolution of overpressure. In this paper, through the fluid inclusion tests and. PVTX simulation results of the overpressured development segments of the Karasu Structural Belt in Kuqa Depression. we reconstructed the overpressure evolution process in the study area, that is, the three-stage change process (pressure increase-pressure relief-pressure increase). 5-3 Ma is the stage of under compaction and pressure increase, 3-1.2 Ma is the stage of pressure relief caused by faulting, and 1.2 Ma is the stage of late structural compression and pressure increase. At the same time, for each overpressure development stage, we discussed the coupling relationship between the overpressure evolution process and hydrocarbon accumulation in terms of trap formation time, shallow oil and gas display, and oil and gas charging characteristics. In the 5-3 Ma stage, due to the gradual weakening of the squeezing stress from north to south, the difference in the formation time of traps in the Karasu Structural Belt was significant, and a large amount of low mature crude oil began to be charged into the reservoir. In the 3-1.2 Ma stage, with the increase of squeezing stress, uplifting leads to the activation of faults, a large amount of crude oil in Well Kela 2 was adjusted and migrated to the shallow part for accumulation, while highly mature crude oil did not accumulate in the Kara area. The Keshen area is far away from the Tianshan Mountain and has a large burial depth and good storage conditions. Not only did the crude oil in this area not migrate to the shallow part. but it also experienced a secondary filling process of highly mature crude oil. From 1.2 Ma to now, tectonic compression is still the main cause of overpressure, but with the occurrence of overpressure conduction, a large amount of natural gas flows into the Cretaceous reservoirs, forming the Kuqa gas field. Finally, through the study in this paper, we proposed a compound hydrocarbon accumulation model, namely early crude oil accumulation, medium-term crude oil adjustment controlled by faults, and rapid natural gas filling in the late stage.