Reservoir Permeability Evolution during the Process of CO2-Enhanced Coalbed Methane Recovery

Abstract

In this study, we have built a dual porosity/permeability model through accurately expressing the volumetric strain of matrix and fracture from a three-dimensional method which aims to reveal the reservoir permeability evolution during the process of CO2-enhanced coalbed methane (CO2-ECBM) recovery. This model has accommodated the key competing processes of mechanical deformation and adsorption/desorption induced swelling/shrinkage, and it also considered the effect of fracture aperture and effective stress difference between each medium (fracture and matrix). We then numerically solve the permeability model using a group of multi-field coupling equations with the finite element method (FEM) to understand how permeability evolves temporally and spatially. We further conduct multifaceted analyses to reveal that permeability evolution near the wells is the most dramatic. This study shows that the farther away from the well, the gentler the evolution of permeability. The evolution of reservoir permeability near the injection well (IW) and the production well (PW) are very different, due to the combined effects of effective stress changes and gas adsorption and desorption. Furthermore, adsorption is the main controlling factor for the change of permeability for regions near the IW, while the change in effective stress is the main cause for the change in permeability near the PW. Increasing the injection pressure of CO2 will cause the reservoir permeability to evolve more quickly and dynamically.

Multiscale model for flow and transport in CO2-enhanced coalbed methane recovery incorporating gas mixture adsorption effects

“…The set of equations (9), (10) and (11) forms the pore-scale model for fluid transport in the matrix.…”

“…In this paper, we aim at clarifying this issue by developing a new multiscale model for flow and transport in dual porosity coalbed methane reservoir, which is coupled with the three-scale poromechanical model reported in a previous work [8]. Modeling of the coupling between transport and poromechanics problems in coal seam is well reported in the literature and classically described by dual porosity type models combined with Langmuir isotherm to compute gas adsorption in the coal matrix [9,10,11,12,13]. Moreover, modeling of CO 2 -enhanced coalbed methane recovery has showed important improvement of methane production curve and matrix swelling phenomena inducing cleat closure [10,11,12,14].…”

Numerical analysis of drainage rate for multilayer drainage coalbed methane well group in Southern Qinshui basin

“…CH 4 in matrix is composed of the adsorbed CH 4 and the free CH 4 , which can be defined as follows (Ren et al., 2017; Wang et al., 2018a, 2018b; Yin et al., 2017) where, ρ s is the density of coal matrix, kg/m 3 ; P s is the standard atmospheric pressure, 101325 Pa; T s is the standard temperature, 298.15 K; φ m is the matrix porosity.…”

“…There is a cube law between coal permeability and porosity. Therefore, the permeability can be defined as follows (Li et al., 2016; Palmer and Mansoori,1998; Pan and Connell, 2007; Wu et al., 2010b; Wang et al., 2018a, 2018b) where, k 0 is the initial permeability of coal seam.…”

“…In this study, a multi-physical field fully coupled mathematical model was defined to describe coal seam deformation, fluid flow, and energy transmission and conversion in coal seam during CBM exploitation (Xia et al, 2015;Zhang et al, 2008). The mathematical model is established based on the following assumptions (Guo et al, 2015;Li et al, 2016;Wu et al, 2010a;Zhu et al, 2011): (1) coal is a homogeneous elastic medium with "dualporosity" composed of matrix and fractures; (2) the fractures are saturated with CH 4 and water; (3) CH 4 exists and migrates in pores and fractures, and water exists and migrates in fractures; (4) the adsorption, desorption, and diffusion of CH 4 mainly occur in matrix; (5) CH 4 adsorption and desorption follows Langmuir's law, and CH 4 diffusion follows Fick's law; (6) the migration of CH 4 and water in fractures follows the Darcy's law; (7) the coal deformation conforms the small elastic deformation, and the gas adsorption, desorption and pressure changes will cause changes in volumetric strain of coal (Fang et al, 2019a;Kumar et al, 2014;Langmuir et al, 1916;Wang et al, 2018aWang et al, , 2018b.…”