COUPLING RELATIONSHIP BETWEEN OVERPRESSUREEVOLUTION AND HYDROCARBON ACCUMULATIONPROCESS IN THE KARASU STRUCTURAL BELTIN KUQA DEPRESSION, TARIM BASIN, CHINA

摘要

As the core content of reservoir-forming dy-namics research, overpressure is a key element for controlling o il 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 up-lift since the late 5 Ma have led to extremely com pli-cated genesis and evolution of overpressure. In this paper, through the flu id inclusion tests and PVTX simulation results of the overpressured development segments of the Karasu Structural Belt in Kuqa De-pression, we reconstructed the overpressure evolu-tion 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 com-paction 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. A t the same time, for each overpressure de-velopment stage, we discussed the coupling relation-ship between the overpressure evolution process and hydrocarbon accumulation in terms of trap for-mation time, shallow o il and gas display, and o il 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 sig-nificant, and a large amount of low mature crude o il began to be charged into the reservoir. In the 3-1.2 Ma stage, w ith the increase of squeezing stress, up-liftin g leads to the activation of faults, a large amount of crude o il in W ell Kela 2 was adjusted and m i-grated to the shallow part for accumulation, while highly mature crude o il 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. N ot only did the crude o il in this area not migrate to the shallow part, but it also experienced a secondary fillin g process of highly mature crude oil. From 1.2 Ma to now, tectonic com-pression is s till the main cause of overpressure, but w ith 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 com-pound hydrocarbon accumulation model, namely early crude o il accumulation, medium-term crude o il adjustment controlled by faults, and rapid natural gas fillin g in the late stage.