Study on mechanical parameters and creep seepage characteristics of different coal and rock combination samples

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. Short bullet pointsThe strength of the composite sample depends on the part of the combination with weak strength, and the permeability characteristics depends on the part of the combination with poor permeability.The stress-seepage coupled creep damage model is established, which can be used to describe the deformation law of each rock sample under different stresses.The permeability model based on porous media theory can be used to predict the influence of creep effects on permeability under different in-situ stresses in engineering.

Automated summary

Based on the lower than expected production of deep coalbed methane in the Yushe-Wuxiang Block, this paper conducted uniaxial strength tests and triaxial rheological tests on coal measure strata reservoirs. The results showed that the stress-strain process of deep coal rock samples was similar to that of shallow ones, but the brittleness of deep coal rock samples was more obvious. The established stress-seepage coupled creep damage model and the permeability model based on porous media theory are of great significance in predicting the influence of creep effects on permeability under different in-situ stresses in engineering.