Upper Triassic In The Sichuan Region Xujiahe To Be Two, Four Sandstone Reservoirs

Based on the observation of field section and core, the managing data of logging, the research of casting thin sections, core analysis data, scanning electron microscope and capillary pressure curve, this paper discussed the features of strata and sedimentology, petrology characters, percolation and pore structures features of the second and fourth member's sandstone of Xujiahe Formation, Upper Triassic, The middle of Sichuan Basin, we mainly discussed the forming conditions of the advantaged reservoirs from the sediment, diagenesis and sturucture, and provided vital evidences for predicting the advantaged reservoir zones. Finally we confirmed the lower bound of physical property and studied the evaluation and forecasting of the reservoir.Early sediment of Xujiahe Formation was the process that leveled up the rugged geography of Leikoupo Formation. So the strata of the second and fourth member's sandstone of Xujiahe Formation were relatively stabilization, and their lithologys were similar. The sandstones of reservoir were mainly mesograin to macrograin detritus quartz sandstone and fine to mesograin feldspar detritus quartz sandstone. The clastic rocks of investigative area mainly developed in shoreside and shallow lake. The microfacies mainly included bank and dam. It is considered that sandstone reservoir is low porosity and extremely low permeability. The remainder intergranular and solution pores were primary reservoir room. The hole structure belonged to the small hole and thin to tiny throat. We consider the terrains intensively effected by wind sea and lake current were the optimistic zonations of high-quality reservoir, in which the sandstones deposited have coarse grain size, nice separation, good textural maturity and component maturity. The sandstones are in favor of preserving primary intergranular pores for the capability of resist compaction. The well-developed ripidolite loops formed in early diagenesis is good to prevent the quartz secondary enlargment, and saved relatively high porosity and high permeability for the reservoirs. The fracture systems formed by tectonic movements improve the penetrative performance of the reservoir, so some compact reservoirs become to well pay formation. According to the calculation of the existing data, we considered that the lower limit of porosity was 5%, and the rate of percolation was 0.4× 10^-3μm². So we divided the reservoirs into four types. The type of...