Petroleum Geology Characteristics Of Continental Strata In Puguang Area

The previous exploration and development in Puguang area, Neortheastern Sichuan are mainly dolomite reservoirs of reef flat pore type in marine Changxing-Feixianguan Formation, and a good exploration development effect has obtained., but the degree of exploration in continental strata is low. Good indications of oil and gas of continental strata are found generally, showing the exploration potential that can become an important replacement sequence for the long-term and steady development of Puguang gas field. But because of the limited data of continental strata in the study area predecessors has not studied it extensively. According to this situation, based on many literatures, the abundant data of core analysis and gas testing data of well Pulul and the available basic geological data of Puguang area, this paper studies on the basic geological questions of hydrocarbon source rocks and cap layers characteristics, reservoir characteristics and some influence factors of continental strata in Puguang area through various methods such as the description and analysis of cores and thin sections, lithology and physical and chemical analysis of the data and source rock pyrolysis analysis, maturity and other geochemical index information and so on. Further, petroleum accumulation conditions of continental facies in the area are discussed, as the continental strata exploration provides a new basis.According to Puguang Gas reservoir, This paper has studied the following several aspects and the main achievements are as follows:1%Continental strata in Puguang area is of appreciable thickness and large coverage, and can provide a favorable geological basis for the gas accumulation. Dark mudstone, coal bed, carbonaceous mudstone in the Member1,3,5of Xujiahe Formation, Upper Triassic and.dark mudstone in Ziliujing and Qianfoya Formation, Jurassic are the main gas source kitchen. Organic matter in Xujiahe Formation, whose type is type Ⅲ Kerogen, with high abundance of organic matter, and belongs to the stage of high to post-maturity, can be served as gas source rock because of a great biogas potential, and the hydrocarbon generation capability is the best In terrestrial clastic source rock. Organic matter in Qianfoya formation and Ziliujing formation is abundance, with type Ⅱ1n Ⅱ2Kerogen, which although is in a mature stage, but the hydrocarbon generation capacity is poor.2、The brown-red mudstone of the Jurassic-Cretaceous becomes the effective regional cap rocks for it’s pure quality and strong plasticity. Mudstone in the Member1,3,5of Xujiahe Formation is the direct cap rock of Xujiahe reservoir, and provide a favorable sealing condition for gas reservoirs in the area. The cap rock is composed of thick tight sandstone and mudstone, which is tight、pure and plasticity, with wide distribution and good continuity and large thickness. Therefore, there is good preservation condition that provides favorable closed condition for the reservoirs.3-. The terrigenous clastic rock is with the characteristics of lower compositional maturity and higher texture maturity, and reservoir lithology are widely spread from mudrock to conglomerate, which mainly distribute over the distributary channel sand bodies of delta facies. The pore types include intragranular dissolved pore-. intergranular dissolved pore and fracture, and the pore structure of reservoir is poor, with the characteristics of low porosity and microthroat, which is difficult displacement and low displacement efficiency. The reservoir, with large thickness, are poor development and mainly type Ⅱ and type Ⅲ, but the physical property is poor, and belongs to super-low porosity and super-low permeability reservoir, although develop high quality reservoir with relatively high porosity. All above shows that sedimentary microfacies have controlled the distribution and development of reservoir bodies, lithogenesis has made the tight reservoir, fractures have improved the reservoir physical properties and percolation ability.4、The gas accumulation has good source-reservoir-cap combination.The district is located in hydrocarbon generation center, and continental strata is a set of thick sand and mud interstratification, with characteristics of self-generation and self-accumulation.The sandwich type can provide a solid foundation for terrestrial gas accumulation, which source-reservoir-cap combination can not only acquire high quality gas source, but also can avoid the loss of natural gas because of short migration distance. Natural gas migration channel is expedite, main development natural gas near distance vertical migration, the two migration distance is short, beneficial gas reaches the reservoir.5、Although reservoir is tight and with characteristics of poor physical properties, but develops high-quality reservoir with relatively high porosity (φ≥4%) and improved by fractures. According to the oil and gas shows, Xujiahe formation has the characteristics of thick hydrocarbon showings layer and high total hydrocarbon content, and the high porosity reservoir, with good gas production test after fracturing, is the main natural gas enrichment horizon in the sandstone with hydrocarbon show. And fractures plays a very important role on natural gas accumulation, because the two party is often consistent. This high-quality reservoirs are mainly developed in the Xujiahe formation, with characteristics of great thickness and widespread distribution, therefore, it’s the key factor of the forming of natural gas reservoir. 6、According to the oil and gas shows and distribution of high-quality reservoir, The gas mainly enriched in the Xujiahe formation, the reservior quality and gas accumulation are significantly best in the other section in member2、4and6of Xujiahe formation, Qianfoya formation is the better, and Ziliujing formation is the worst.Overall, this paper, based on numerous literature under the premise and comprehensive use of various geological data, through a large number of basic geological work, finds out characteristics and distribution of hydrocarbon source rock, reservoir, caprock in Puguang area, discusses reservoir forming conditions of continental gas reservoir and enrichment regularity of oil and gas, prociding a new theoretic for the exploration and development of continental strata.