Deformation and water transport behaviors study of heterogenous coal using CT-based 3D simulation

Abstract

It is well known that the deformation of coal will implicitly influence the fluid flow transport properties due to the coupled stress-permeability evolution. The stress-induced structural deformation plays an important role in water flow prediction. To define the relationship between the deformation and water transport with multi-scale coal matrix, a micro and meso-scale geometrical coal model was initially reconstructed based on X-ray CT imaging and 3D reconstruction technology. We then carried out 3 kinds of uniaxial compression experiments under displacement loading based on the Mohr-Coulomb constitutive model of LS-DYNA platform. Then we obtained deformable structural model by adding the structure of water and air fields with the built-in ALE algorithm to simulate water injection process of the deformative coal model. The simulation results showed that 1) coal heterogeneity leads to an uneven distribution of strain and displacement during uniaxial compression, 2) the deformation affects not only the distribution of the whole water transport process, but also the velocity change of the unsteady seepage in the pore and fracture structures. In the fracture structure, the axial strain plays a major role in changes of velocity peak, while the interaction of axis strain with radial strain mainly influenced the steady flow. In the pore structure, changes of velocity peak and steady flow are more complex and not obviously corresponded to axial strain and radial strain. Moreover, estimation of the permeability of each deformation structure using Darcy's law showed that with deformation degree increasing, permeability increases after decreases.