Reservoir Characteristics And Prediction Of The Carboniferous-Permian System In Jiyang Depression

Experience of exploration in recent years reveals that Permo-Carboniferous formation in Jiyang depression has good oil and gas exploring promising. Favorable target areas for exploration are put forward through researches and evaluation of sedimentary facies, petrologic features, diagenesis, characteristics of microscopic structure of pores, and factors influencing reservoirs of Carboniferous- Permian System in Jiyang depression.There are three sedimentary environments including epicontinental littoral environment , continental-marine environment and continental environment ;. four sedimentary systems including lagoon-plateau sedimentary system, barrier land-tidal flat-lagoon sedimentary system, shallow delta sedimentary system and fluvial-lake sedimentary system; seven sedimentary faces including lagoon, platform, tidal flat, barrier island, shallow delta, meandering river and shallow lake occurred in Carboniferous- Permian System of Jiyang depression.It can be found that the sandstone can be considered as the available reservoir of Carboniferous-Permian System in this area according to the compare of all kinds of stone. The sandstone reservoir mainly distributes in Shanxi, Xiashihezi and Shangshihezi formation. The reservoirs'lithology of the Shanxi formation is mainly middle-fine grained feldspathic quartzose sandstone, lithic quartzose sandstone ; that of the Xiashihezi formation is middle-coarse grained feldspathic and lithic quartzose sandstone ; and that of the Shangshihezi formation is gritstone and pebbly gritstone. The composition maturity and the texture maturity of clastic reservoir are both high. The main diagenesis types include compaction, cementation, metasomatism, and dissolution. The Diagenetic stage of Shangshihezi, Xiashihezi Formation is from the mesodiagenetic stage A to the mesodiagenetic stage B, that of Shanxi, Taiyuan, Benxi Formation is from the mesodiagenetic stage B to the telodiagenetic stage. Primary pores are decreasing whereas secondary pores and fractures are increasing downward. Physical property and mercury penetration indicate that the reservoir pore throat structure characterized by mini pore throat, poor sorting, poor connectedness and poor infiltrating ability, and the reservoir sand bodies belong to low porosity and permeability to extremely low porosity and permeability. Comparing to Shanxi Formation, reservoirs of Shangshihezi and Xiashihezi Formation have the features of skewing bold pore throat size distribution, more secondary dissolution pores, improving infiltrating ability and lower displacement pressure. The macroscopic element , which controls the reservoir's extent , is tectonism. Diagenesis controls the changing of reservoir character on verticality, and sedimentary facies on plane, i.e. the characteristics of main fluvial channels'distributions. Considering these controlling factors, the evolution standard of reservoir is established, and the primary formations are evaluated. On the basis of reservoir physical properties affected by sedimentary condition, diagenetic evolution and tectonic process, it can be forecasted that the most favorable exploration targets are the west of Gubei, Gaoqing ,the west of Chezhen, the east of Yihezhuang, Huagou and Pancanzhen areas and the secondly favorable exploration targets are Shaojia, Wangjiagang and the south of Huimin sag areas.