Numerical analysis of improvements to CO2 injectivity in coal seams through stimulated fracture connection to the injection well

Chen, Min; Hosking, Lee J.; Sandford, Richard J.; Thomas, Hywel R.

Abstract

This work presents a hybrid discrete fracture-dual porosity model of compressible fluid flow, adsorption and geomechanics during CO2 sequestration in coal seams. An application of the model considers the influence of hydraulic fractures on CO2 transport and the stress field of the coal. The low initial permeability of coal is compounded by the injectivity loss associated with adsorption-induced coal swelling, which is recognised as the major challenge limiting CO2 sequestration in coal seams. In this model, the natural fracture network and coal matrix are described by a dual porosity model, and a discrete fracture model with lower-dimensional interface elements explicitly represents any hydraulic fractures. The two models are coupled using the principle of superposition for fluid continuity with a local enrichment approximation for displacement discontinuity occurring at the surface of hydraulic fractures. The Galerkin finite element method is used to solve the coupled governing equations, with the model being verified against analytical solutions and validated against experimental data. The simulation results show that the presence of a hydraulic fracture influences the distribution of gas pressure and improves the gas flow rate, as expected. The stress field of a coal seam is disturbed by CO2 injection, especially the vertical stress, and the presence of a hydraulic fracture leads to a reduction in stress with permeability recovery starting earlier.

Citation

Chen, M., Hosking, L. J., Sandford, R. J., & Thomas, H. R. (2020). Numerical analysis of improvements to CO2 injectivity in coal seams through stimulated fracture connection to the injection well. Rock Mechanics and Rock Engineering, 53, 2887-2906. https://doi.org/10.1007/s00603-020-02088-1

• Journal Article Type: Article
• Acceptance Date: Mar 5, 2020
• Online Publication Date: Mar 23, 2020
• Publication Date: Jun 1, 2020
• Deposit Date: Mar 26, 2020
• Publicly Available Date: Mar 24, 2021
• Journal: Rock Mechanics and Rock Engineering
• Print ISSN: 0723-2632
• Electronic ISSN: 1434-453X
• Publisher: Springer Verlag
• Peer Reviewed: Peer Reviewed
• Volume: 53
• Pages: 2887-2906
• DOI: https://doi.org/10.1007/s00603-020-02088-1
• Keywords: Geotechnical engineering and engineering geology; General engineering; Earth and planetary sciences; General Earth and planetary sciences; Geology; Civil and structural engineering; General environmental science; Carbon sequestration; Hydraulic fracture
• Public URL: https://uwe-repository.worktribe.com/output/5816329
• Additional Information: Received: 6 August 2019; Accepted: 5 March 2020; First Online: 23 March 2020; : ; : The authors declare that they have no conflict of interest.