Analysis On Reservoir Formation Condition Of Xujiahe Formation In Zizong Depression, Western

Zitong depression located in the northwest of Sichuan Basin, in Zitong syncline and Sichuan uplift transitional zone, having good exploration potential. This paper based on petroleum geology, oil and gas exploration geochemistry and related disciplines theory, Systematic study on the main factors for the forming of oil and gas reservoirs of Xujiahe formation in Zitong depression, accumulation conditions of the study area will be confirmed, the establishment of reservoir forming model and analyze the main controlling factor reservoir forming.Three kinds of source rocks of Xujiahe formation is development in study area, which had been third member hydrocarbon source rocks greatest potential, the dark mudstone organic carbon content of 0.29% to 1.32%, averaging 1.46%; third member source rocks kerogen most of Ⅱ2 type. Source rock evaluation consider that the third source rocks have better conditions, greater developmental class I source rocks, having resource potential.Xujiahe reservoir lithology is mainly lithic quartz sandstone, lithic sandstone followed. The sandstone porosity is generally less than 15%, the permeability is generally less than 10× 10-3μm2, overall belongs to the low porosity and low permeability reservoir, the local development of high hole section. The reservoir space are mainly primary intergranular pore, secondary pore, local area development within a matrix of micro hole and micro fracture, fracture pore type reservoir. According to reservoir evaluation the second member of Xujiahe formation reservoir in Ⅱ, Ⅲ, the forth member of Xujiahe formation is mainly Ⅱ reservoirs.The varied types of trap in zone, mainly construction-lithologic traps, developmental stratigraphic, lithological traps and so on. Structural-lithological traps mainly in Zitong slopes slow wing with depression; stratigraphic traps are mainly distributed in the Zhongba-Liya temple constructed at the area; and lithologic traps are located in Zhongba-Weicheng structure area. Formation water in the study area is mainly CaCl2 type, belonging to the more stable hydrodynamic tape, storage conditions better. The third member and fivth member of Xujiahe formation of mudstone caprock in southern West Sichuan Shifang-Deyang-Santai along the thickness, having a good cover.The main factors of accumulation is ancient structure, effective reservoir and related fractures. First of ancient high band, the ancient slope restricts hydrocarbon migration; secondly is the basis of the size of the effective oil and gas accumulation, especially in high porosity and fracture zones; once again crack is the communication of hydrocarbon source and reservoir outlet window, which also is gas high and stable yield of the key.Comprehensive analysis:south of the study area in Mianzhu-Mianyang slopes with distance Xujiahe source rocks close, the existence of local tectonic uplift, vertical reservoir is developed, relatively developed cracks near the fault may be a good migration path conducive to migration and accumulation of gas, is favorable zones of oil and gas exploration.