Based on the fact that the production of deep coalbed methane (CBM) in Yushe-Wuxiang Block is lower than expected, the paper is carried out uniaxial strength test and triaxial rheological test on coal measure strata reservoirs (mudstone, coal, sandstone and their composite sample) deeper than 1300 m in the block. In the uniaxial strength test, it is found that the stress–strain process of deep coal rock sample was similar to that of shallow one. The brittleness of deep coal rock sample is more obvious. It can also serve as described by the four stages of shallow coal rock sample in the compression process. The compressive strength of the coal in the combined samples will be improved in a small range, while the mudstone will be driven to produce radial tensile failure at the moment of failure. Creep characteristics of the composite sample are similar to those of the single one, and the axial deformation characteristics under lower stress (14 MPa, 18 MPa, 22 MPa) are close to those of coal. The axial deformation characteristics under extreme stress (26 MPa, 30 MPa, 34 MPa) are close to those of sandstone. The established stress-seepage coupled creep damage model can be used to describe the deformation law of each rock sample under different stresses. The permeability characteristics of the composite sample are determined by the poor permeability of the composite formation. There is a great correlation between the volume deformation and permeability evolution of the sample in the test. The permeability model based on the theory of porous media can be well fitted the relationship between volumetric strain and permeability. It is of great significance to predict the influence of creep effect on permeability under different in-situ stresses in engineering.
The slippage effect is an important phenomenon of coalbed methane (CBM) migration. As the exploitation of CBM, the slippage effect becomes more and more obvious. For exploring the evolution of the slippage effect as CBM extraction by heat injection, the thermal expansion test and the temperature increasing desorption test under different stress states, as well as the seepage test under variable temperature conditions, were conducted by operating the hightemperature multifunctional triaxial test system. The effect rules for temperature and pore pressure on the slippage effect were analyzed, and then the evolution mechanism of the slippage factor at the united action of pore pressure and temperature was comprehensively analyzed based on thermal expansion deformation and adsorption characteristics. The results showed that: first, the influence of pore pressure on the slippage effect is mainly caused by the molecular mean free path and effective stress when pore pressure is greater than 0.8 MPa in the range of 30−150 °C. With the pore pressure increase, the slippage effect decreases. Second, the temperature influence on the slippage effect is mostly induced by the variation of cracks in coal due to thermal expansion deformation created by temperature. With the increase in temperature, the slippage factor average increases first from 30 to 60 °C is 19 times and then decreases from 60 to 90 °C is 36%. Finally, at the combined influence of temperature and pore pressure, the slippage effect is mainly influenced by thermal expansion deformation, desorption deformation, and effective stress. At 30−60 °C, the slippage factor is principally affected by thermal expansion deformation. At 60−90 °C, the slippage factor is mostly influenced by desorption deformation and effective stress. The research results provide a foundation for the technology of CBM exploitation by heat injection.
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