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The assessment of gas storage capacity is crucial to furthering shale gas exploration and development in the eastern Sichuan Basin, China. Eleven organic-rich shale samples were selected to carry out the high pressure methane sorption, low-pressure N2/CO2 gas adsorption, and bulk and skeletal density measurements to investigate the methane storage capacity (MSC). Based on the relative content of clay, carbonates, quartz + feldspar, we grouped the 11 samples into three lithofacies: silica-rich argillaceous shale (CM-1), argillaceous/siliceous mixed shale (M-2), and clay-rich siliceous shale (S-3). The total porosity of the shale samples varies from 3.4% to 5.6%, and gas saturation ranges from 47% to 89%. The measured total gas amount ranges from 1.84 mg/g to 4.22 mg/g with the ratio of free gas to total gas amount ranging from 52.7% to 70.8%. Free gas with high content in the eastern Sichuan Basin may be the key factor controlling amount of shale gas production. The TOC content critically controls the MSC of shales, because micropore, mesopore volumes and the specific surface areas associated with organic matter provide the storage sites for the free and adsorbed gas. The methane sorption capacities of samples from different lithofacies are also affected by clay minerals and moisture content. Clay minerals can provide additional surface areas for methane sorption, and water can cause a 7.1%–42.8% loss of methane sorption capacity. The total porosity, gas-bearing porosity, water saturation, free gas and adsorbed gas number of samples from different lithofacies show subtle differences if the shale samples had similar TOC contents. Our results suggest that, in the eastern Sichuan Basin, clay-rich shale lithofacies is also prospecting targets for shale gas production. [ABSTRACT FROM AUTHOR]

Time-dependent behaviors of rocks can be attributed to long-term applied stress, which occurs in most underground engineering projects. The creep behavior of granite from the Shuangjiangkou underground powerhouse in western Sichuan Province, China, was investigated via creep tests. It is shown that granite has an obvious creep behavior under different confining pressures and deviatoric stresses. The new dimensionless parameter DPR, which is defined as the ratio of the deviatoric stress to the peak strength, is proposed for experimental analysis. The relationships between the instantaneous strain and final visco-elastic creep strain of granite with DPR are established under different confining pressures. It is shown that when DPR is equal to 0.63, the final visco-elastic creep strain of rocks will reach a minimum value. Based on DPR and the secondary creep strain rate, a unified method for defining the long-term strength of rocks is proposed, and the granite will enter in secondary creep with a nonzero strain rate when DPR > 0.9501. The Nishihara model is improved, and the relationships between the parameters of the improved model with confining pressures and DPR are obtained. The improved creep model can satisfactorily represent the primary creep strain of granite and secondary creep strain of granite with time under a given confining pressure and deviatoric stress. [ABSTRACT FROM AUTHOR]