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

Abstract

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.

Improved nonlinear Burger creep model for soft rocks based on the fractional-order theory and considering viscoplastic deformation

“…The creep constitutive models, as one of the key topics in the time-dependent studies of rocks, have attracted significant research (Sharifzadeh et al 2013). In previous decades, many constitutive models were proposed through empirical, component, and mechanism-based models, and scholars demonstrated that the creep behavior of rock shows significant nonlinear properties (Li et al 2020b;Zhao et al 2023).…”

Simulation Experimental Investigations into the Mechanical Response and Failure Mechanisms of Coal–Rock Combinations

“…Liu et al established a damage constitutive model of rock-coal and rock-coal-rock composite samples by connecting the damage body with Newtonian body [23]. In addition, the effects of interface angle, prefabricated fractures, confining pressure, and loading rate on the strength and failure characteristics of rock-coal composite samples were studied [24][25][26][27][28]. The lithology, strength, and combined forms of coal and rock bodies have an important influence on the deformation and failure of CRCs.…”