Speaker
Description
Coalbed methane (CBM) reservoirs store gas primarily by adsorption in nanoporous coal matrices while flow occurs through stress-sensitive cleat networks. During CO2-enhanced coalbed methane recovery (CO2-ECBM), preferential CO2 sorption promotes CH4 desorption and enables long-term CO2 sequestration through competitive adsorption effects [1]. However, field operations often face a progressive loss of injectivity driven by coupled hydro-mechanical effects: sorption-related nanoscale fluid–solid interactions and matrix swelling alter the local stress state and promote cleat closure, reducing near-well permeability [2,3,4].
We develop a multiscale mechanical skin-factor formulation that captures evolving, pressure-dependent near-well additional flow resistance and can be embedded in reservoir-scale well models. The approach links three scales: (i) nanoscale solvation forces computed via Density Functional Theory (DFT) to quantify adsorption-related stresses responsible for matrix swelling, (ii) mesoscale coupled flow–deformation in the cleat–matrix system governed by a Barton–Bandis joint law for cleat closure, consistent with non-linear cleat deformation mechanisms, and (iii) field-scale upscaling to an equivalent well index (WI) and a non-linear mechanical skin factor defined relative to a reference (non-deforming) configuration. The coupled problem is solved in a preprocessing step on the well-block scale to generate WI and skin factor as functions of injection pressure for coarse-grid cells intersecting the injection well.
Numerical experiments show a marked, non-linear decline of WI with increasing bottom-hole pressure and a corresponding increase of the mechanical skin factor to values of order 10², indicating substantial injectivity deterioration driven by hydro-mechanical coupling. When integrated into coarse-grid simulations, the WI/skin upscaling reproduces direct numerical simulation (DNS) trends for pressure fields and CO2 storage rates with small cumulative storage errors. Compared with DNS, the proposed approach avoids near-well mesh refinement and fully resolved coupled calculations, delivering approximately a tenfold reduction in computational cost while retaining the key physics required for designing and optimizing CO2 injection strategies in coal seams.
References
[1] White, Curt M., et al. "Sequestration of carbon dioxide in coal with enhanced coalbed methane recovery a review." Energy & Fuels 19.3 (2005): 659-724.
[2] T. D. Le et al, Multiscale model for flow and transport in CO2-enhanced coalbed methane recovery incorporating gas mixture adsorption effects, Advances in Water Resources, volume 144, 103706- (2020).
[3] Q. D. Ha et al., Upscaling poromechanical models of coalbed methane reservoir incorporating the interplay between non-linear cleat deformation and solvation forces, International Journal of Solids and Structures, 262-263, 112083- (2023).
[4] Q. D. Ha et al, Solvation force and adsorption isotherm of a fluid mixture in nanopores of complex geometry based on Fundamental Measure Theory, Journal of Physics: Condensed Matter, volume 33, 335002- (2021).
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