Accumulation condition for Wufeng-Longmaxi Formation shale gas of Yanjin-Gongxian area

The formation conditions of shale gas in Wufeng-Longmaxi Formation of Yanjin-Gongxian area were analyzed on the basis of field observation and experimental data,and then the main factors for shale gas accumulation were discussed. Results show that black shale at the bottom of Wufeng-Longmaxi Formation is a deep-water shelf deposit product. The dessert shale gas from the first stage of Wufeng to the fourth stage of Longmaxi was complete. The organic carbon content is between 2.7%-6.0%. Mainly for the high organic carbon content,the thickness of black shale rich in organic matter is 30-50 m. In the high gas horizon,nanometer organic pores and pyrite intracrystalline pores are abundant,and the average rate of porosity is 2.28%-3.48%,providing a good reservoir space for the adsorbed gas and free gas. Structural strength in the research area is weak and large faults are less. There are good conditions of roof and floor. The pressure coefficient is more than 1,which reflects the suitable preservation condition. The main factors for shale gas accumulation are as follows:deep shelf sedimentary environment,high organic carbon content,abundant nanometer pores,high level porosity,and high pressure coefficient.