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The Accumulation Mechanism Of Lithologic Gas Reservoir Of The Upper Paleozoic In Eastern Ordos Basin

Posted on:2009-12-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:X S LiuFull Text:PDF
GTID:1100360242988511Subject:Mineral prospecting and exploration
Abstract/Summary:PDF Full Text Request
Aimed at lithologic gas reservoir of the upper Paleozoic in eastern Ordos Basin, this paper analyzes the course, the mechanism and the main control factors of tight lithologic gas reservoir synthetically. The accumulating regularities of different gas zones are recognized. The research is based on the studies of tectonic evolution, thermal and hydrocarbon generation, sediment and diagenetic evolution, accumulating history, and dynamics of gas accumulation by means of the geochemistry and fluid history analyzing.There are three different gas zones in research area, including lower, middle and upper gas zones. The studies of alkane carbon isotope and gas-source rock correlation indicate that the natural gas originate from coal-derived gas mainly, and in very few areas, a little quantity oil-type gas is mixed in. The obvious relationship between the quantity of methane gas and itsδ13C1 and maturity of the hydrocarbon source rock reveals the reservoir feature of close-migration and accumulation.Through investigation of main hydrocarbon-expulsion epoch, fluid inclusion, K-Ar isotope of authigenic illite and isotope dynamic fractionation of methane, it can be drawn a conclusion that lower and middle gas layers experienced two times injection, and the main gas injection occurred from late Jurassic to early Cretaceous. Whereas, the main filling of upper gas zone only occurred in early Cretaceous.During the deepest buried period, abnormal high pressure was developed at large in upper Paleozoic of eastern Ordos basin, and the overpressure between reservoir and hydrocarbon source rock was the dominating driving-force of gas migration. Powerful filling and high saturation in lower and middle gas zone was resulted from exceed overpressure. Whereas, far distance between reservoir and hydrocarbon source rock restricted the supply of gas in upper gas layers."Compact firstly, hydrocarbon accumulation secondly" characterize the process of the upper Paleozoic reservoir. For lower layers, rational matching of reservoir factors brought on efficient accumulation and formed large-scale gas field. As for the upper gas layers, immoderate framework of reservoir factor resulted in inefficient assembly, and formed small reservoirs. Accordingly, Large-middle scale reservoirs were fashioned in the middle layers usually for it's accumulation condition lies between the upper and the lower gas layers.The hydrocarbon enrichment in the east of basin was mainly controlled by such geological factors as gas generation intensity of source rock, the overpressure between reservoirs and source rocks at accumulation stage, the type of passage system, the distribution of high quality reservoir, the thickness of cap socks and displacement pressure, etc. The different gas zones are of the different accumulation rule. Based on the study mentioned above, four favorable exploration targets are obtained. Aimed at Lower gas zone, Shenmu and Yuxingzhuang regions are well evaluated. To the middle and upper gas zones, Dafusi and Wangjiabian regions are prospective.
Keywords/Search Tags:Ordos Basin, Upper Paleozoic, Nature gas, Lithologic gas reservoir, Accumulation mechanism
PDF Full Text Request
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