Based on the analyses of generation, migration and accumulation of oil and gas in the structures of Kela 1, Kela 2 and Kela 3 in Kasangtuokai anticlinal belt using a series of geological and geochemical evidence, this paper proposes that the rapid rate of hydrocarbon generation, main drain path for over-pressured fluid flow and converging conduit system are indispensable conditions for the rapid, late-stage gas accumulation in the Kelasu thrust belt in the Kuqa depression. Due to structural over-lapping and the resultant rapid burial, the maturity of the source rocks had been increased rapidly from 1.3 to 2.5% Ro within 2.3 Ma, with an average rate of Ro increase up to 0.539% Ro/Ma. The rapid matura-tion of the source rocks had provided sufficient gases for late-stage gas accumulation. The kelasu structural belt has a variety of faults, but only the fault that related with fault propagation fold and cut through the gypsiferous mudstone cap could act as the main path for overpressured fluid release and then for fast gas accumulation in low fluid potential area. All the evidence from surface structure map, seismic profile explanation, authigenic kaolinite and reservoir property demonstrates that the main drain path related with faults for overpressured fluid and the converging conduit system are the key point for the formation of the giant Kela 2 gas field. By contrast, the Kela 1 and Kela 3 structures lo-cated on both sides of Kela 2 structure, are not favourable for gas accumulation due to lacking con-verging conduit system.
ZOU HuaYaoWANG HongJunHAO FangLIU GuangDiZHANG BaiQiao
The effectiveness of gas accumulation processes is controlled by several main geological factors in-cluding charging force,features of gas conduit,sealing properties of caprock,etc. Based on the analysis and statistics of the large-medium size gas accumulations in China,the main parameters,in-cluding the excess pressure difference between the source rock and reservoir bed,the area coefficient of the gas conduit,and the thickness or displacement pressure of caprock,and the criteria for the as-sessment of gas accumulation processes have been established. Using the parameters and the criteria above,the effectiveness of gas accumulation processes in the Kuqa depression was quantitatively evaluated. By integrating the parameters of the excess pressure difference between the source rock and reservoir bed,the area coefficient of fault conduit system,and the caprock thickness in gas charging period,a comprehensive assessment of the effectiveness of gas accumulation in the Kuqa depression has been made. The result reveals that the Tubei-Dawan area,the Central Kelasu area and the Dongqiu-Dina area are three highly-effective areas for gas accumulation in the Kuqa depression.
LIU GuangDi1,SUN MingLiang1,L YanFang2 & SUN YongHe2 1 State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum,Beijing 102249,China
