DEVELOPMENTAL FEATURES AND THE RELATIONSHIP BETWEEN FRACTURES AND GAS ACCUMULATION IN THE XUJIAHE FORMATION OF GUANG'AN GASFIELD, THE SICHUAN BASIN

The fractures have a great effect on gas migration and accumulation in compacted sandstone of Xujiahe Formation,the Sichuan Basin.Developmental features and mechanical formation process of fractures determined the relationship of effective reservoirs and gas accumulation in compacted sandstone.Based on it,the fractures in sandstone reservoirs of T₃x⁴ and T₃x⁶ in the Sichuan Basin are discusseded according to core observation and imaging logging analysis.According to researches of fractures character and regional stress fields indicated that there are two stages of fractures formation,which are tension fractures associated with folds in the late Yanshanian period,and shear ones associated with faults in the Himalayan period.In Well GAN5 area of T₃x⁴,the first stage of fractures is formed at the same time with peak hydrocarbon-generation period,therefore,the fractures can be favorable to the forming of effective reservoirs and the gas migration.However,in Well GAN124 area,the fractures are formed after the effective reservoirs occurrence,so the fractures must be combinated with the effective reservoirs,and can adjust and reshape the gas reservoir which have already been formed.