Anisotropy characteristics of coal shrinkage/swelling and its impact on coal permeability evolution with CO₂ injection

Abstract

Coal deforms with gas depletion during coal bed methane (CBM) primary recovery and CO2 storage for purposes of sequestration or enhanced recovery. The sorption‐induced deformation associated with gas adsorption and desorption has been experimentally and theoretically studied and is considered to be a unique feature of coal. The results of a series of experimental measurements of coal deformation with gas injection and depletion using helium, methane, CO2, and various mixtures of methane and CO2 revealed that the coal sorption‐induced deformation exhibits anisotropy, with larger deformation in direction perpendicular to bedding than those parallel to the bedding planes. Furthermore, the deformation of coal is reversible for helium and methane with injection/depletion, but not for CO2. Aiming at improving the understanding of enhanced CBM process, a coal deformation experimental study on methane displacement with CO2 was performed as well, where incremental swelling was measured for each CO2 displacement step. The total induced swelling strain (1.68%) with CO2 saturation was less than that for pure CO2 injection‐induced strain (1.87%) at same pressure of 5.9 MPa (850 psi). The measured deformation with CO2 injection was applied to a constant‐volume based analytical coal permeability model, which is capable of accommodating the anisotropic sorption‐induced deformation. Based on the modeling results, it was found that application of isotropic deformation in permeability model can overestimate the permeability loss compared to anisotropic deformation. This demonstrates that the anisotropic coal deformation should be considered to predict the permeability behavior of CBM as well as CO2 sequestration/ECBM projects. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Numerical study on enhancing coalbed methane recovery by injecting N2/CO2 mixtures and its geological significance

“…CO 2 ‐ECBM benefits not only an additional recovery ratio but also greenhouse gas (GHG) controlling . In deep and unmineable coal seams, CO 2 ‐ECBM recovery has received significant attention due to its ability to permanently sequester greenhouse gases …”

“…Injection of pure CO 2 into coal seams usually has a negative effect—coal swelling‐induced permeability decreasing, due to the greater adsorption affinity of CO 2 to coal than of CH 4 . Related studies show that CO 2 injections will cause a reduction in coal permeability by nearly two orders of magnitude, especially near the injection well .…”

Experiment study on the correlation between the CO2 adsorption capacity and electrical resistivity of coal with temperature effect

“…Carbon dioxide as a primary greenhouse gas is largely considered to be the main cause of global warming . Therefore, carbon dioxide sequestration in coal seams has attracted wide attention in the last few decades since it not only can limit climate change but can also effectively improve methane production by CO 2 displacement . At present, the gas content of coal can be determined by several direct and indirect measurement techniques .…”

“…1,2 Therefore, carbon dioxide sequestration in coal seams has attracted wide attention in the last few decades since it not only can limit climate change but can also effectively improve methane production by CO 2 displacement. [3][4][5][6][7][8][9][10][11] At present, the gas content of coal can be determined by several direct and indirect measurement techniques. 12 However, there are few effective methods to monitor carbon dioxide adsorption.…”

Analysis of Analytical Models Developed under the Uniaxial Strain Condition for Predicting Coal Permeability during Primary Depletion

“…These cleats, namely, the face cleat and butt cleat, determine the mechanical properties of coal and provide flow paths for methane another set of fractures, bedding planes, can be observed in coal. However, bedding planes do not normally have a role in conducting fluids due to the large stress caused by overburden weight [4].…”