Sedimentary And Diagenetic Evolution Of Permo-Carboniferous In Jiyang Depression

Experience of exploration in recent years reveals that Permo-Carboniferous formation in Jiyang depression has good oil and gas exploring promising. Base on the data of geology, geophysics, geochemistry and the tectonic evolution history of north and south border orogenic zones of North China plate, stratigraphic distribution, sedimentation, diagenetic evolution, characteristics and controlling factors of reservoir of Permo-Carboniferous in Jiyang depression have been studied.The result show that three sedimentary environments that are epicontinental littoral environment, continental-marine environment and continental environment; four sedimentary systems that are lagoon-plateau sedimentary system, barrier land-tidal flat-lagoon sedimentary system, shallow delta sedimentary system and fluvial-lake sedimentary system; seven sedimentary facies that are lagoon, plateau, barrier land, tidal flat, shallow delta, meandering river and shallow lake occurred in Permo-Carboniferous of Jiyang depression. And five to six times marine transgressions occurred in late Carboniferous period (along the transgression passageway from south to north, then, from east to west), and two accumulating coal models that are epicontinental littoral environment and shallow delta environment, five accumulating coal environments that are delta plain peat swamp, lagoon peat flat, barrier land peat flat, tidal peat flat and carbonate plateau peat flat existed. From late Carboniferous to late Permian, Jiyang depression developed epicontinental littoral environment coal-bearing sedimentary successions, continental-marine environment shallow delta facies coal-bearing sedimentary successions and continental environments fluvial and lake facies poor coal -bearing sedimentary successions, and the provenance always lay in the east area of the Yinshan orogenic zone, the ability of providing sediments gradually strengthened. Accompanying with seawater's fallback and climate becoming to dry, the coal-forming environment becoming poor, continental sediment of oxidizing environment gradually played a main role in sedimentary successions. The tectonic evolution history of boundary orogenic zones and remnant sea basins are the main controlling factors to all the sedimentary process.Based on the analysis of routine physical properties and pore throat structure in sandstone reservoirs in Permian of Jiyang depression, shallow delta facies sand body of Shanxi Formation and meandering river facies sand body of Shang, Xiashihezi Formation are the main efficient reservoir in this area, and the reservoir sand bodies belong to low porosity and permeability to extremely low porosity and permeability, and the main reservoir space is the secondary dissolution pores. The reservoir pore throat structure characterized by mini pore throat, poor sorting, poor connectedness and poor infiltrating ability. Comparing to Shanxi Formation, Shang, Xiashihezi Formation reservoirs have the features of skewing bold pore throat size distribution, more secondary dissolution pores, improving infiltrating ability and lower displacement pressure.On the basis of reservoir physical properties affected by sedimentary condition, diagenetic evolution and tectonic process, it can be concluded that the main geological factor to control reservoir properties is sedimentary condition, i.e. the characteristics of distributions of sedimentary main fluvial channels (geometric shape of sand body). And finally, the classification criteria of the deeply buried reservoirs are established making use of the three factors-porosity, permeability and fractal dimension. Based on above analysis, it can be forecasted that the most favorable exploration targets are the west of Chenzhen, the east of Yihezhuang, Luojia, Gubei, Wangjiagang, Jinjia, Gaoqin and Pancanzhen areas and the more favorable exploration targets are Shaojia and the south of Huimin sag areas.