Comprehensive Study On The Geochemistry Of Oil And Gas In The Northwest Qaidam Basin

Petroleum geochemistry is an important research area of petroleum geoscience, it serves for the petroleum exploration and development. Nowadays, Comprehensive and quantitative development of multidisciplinary and multitechnique has gradually been an important research clue and tendency of petroleum geochemistry. The northwest area is one of the crucial target of petroleum exploration in Qaidam Basin, it is also a hot but difficult research area, there are many controversy problems about it, among which is the hydrocarbon sources.By combining classical petroleum geochemistry with reservoir geochemistry and hydrocarbon generation kinetics, we try to get a breakthrough based on the previous investigation, including ascertaining the hydrocarbon generation potential of source rock, understanding the oil-gas-rock relations, and then built the hydrocarbon generation and accumulation model, which are prepared for the next evaluation and choice of petroleum exploration targets.Since the source rock in the northwest Qaidam Basin is greatly heterogeneous, it shoud be aimed at the valid when we evaluate it. Comprehensive evaluation of the source rock demonstrate that there are plentiful valid source rock in all strata, and the main one is in E₃² and N₂¹. The most important hydrocarbon generation zone is Xiaoliangshan-Nanyishan-Youquanzi; According to the oil-source correlation, instead of originating from Mangya depression, the oil in the northwest Qaidam Basin originate from indigenous source rock of N₂¹ or E₃², and mainly from the zone of high-quality source rock, which accord with the evaluation on the source rock. oil and gas in the area can be divided into several relevant types. The oil and gas form reservoirs mostly by self-generating and self-preserving, or by short distance migration vertically or horizontally, which is determined by the migration pathway; Reservoir geochemical research shows that the hydrocarbon of N₂² in the Nanyishan oilfield originate from the Xiaoliangshan depression, which meets the result of the oil-source correlation; By means of hydrocarbon generation kinetics research, we built the hydrocarbon generation model, which accord with the traditional model and fit the local geologic condition, and the simulation of hydrocarbon maturation and generation also verify the fact that the matching of the formation stage of traps and the stage of hydrocarbon generation is a key factor of reservoir forming, which in turn confirm the applicability of the hydrocarbon generation kinetics model. Through comprehensive petroleum geochemical study, we can make a conclution that Xiaoliangshan depression is an important hydrocarbon generation center.