Water Soluble Gas in Deep Carbonate Reservoir Sichuan Basin, Southwest China

Based on temperature and pressure of fluid inclusion, phase of organic inclusion in calcite and quartz filled in vug in the deep carbonate reservoir and the natural gas composition in Weiyuan (sic) gas field in Sichuan (sic) basin, research indicates that water soluble gas exists in deep carbonate reservoir, which reconstructs development and effusion process of water soluble gas. The overpressure formed during oil thermal cracking can reach 105-170 MPa in Sinian and Cambrian reservoir in Central Sichuan and 78-86 MPa in Cambrian reservoir in Southeast Sichuan. The high temperature caused by deep burial and overpressure caused by thermal cracking make thermal cracking gas dissolve in water so that it becomes water soluble gas. The ratios of gas to water can reach 50-90 m(3)/m(3) and 10-30 m(3)/m(3), respectively, in deep carbonate reservoir in Central and Southeast Sichuan. Methane dissolving in water exists in form of liquid phase. Until now, the decreases in temperature and pressure due to the uplift during 74 Ma make water soluble gas separate from water, water soluble gas pool or mixed gas pool of thermal-cracking gas and water soluble gas are modified or even destroyed in varying degrees. This may be the case of Weiyuan gas field.