Swelling‐induced changes in coal microstructure due to supercritical CO₂ injection

Abstract

Enhanced coalbed methane recovery and CO2 geostorage in coal seams are severely limited by permeability decrease caused by CO2 injection and associated coal matrix swelling. Typically, it is assumed that matrix swelling leads to coal cleat closure, and as a consequence, permeability is reduced. However, this assumption has not yet been directly observed. Using a novel in situ reservoir condition X‐ray microcomputed tomography flooding apparatus, for the first time we observed such microcleat closure induced by supercritical CO2 flooding in situ. Furthermore, fracturing of the mineral phase (embedded in the coal) was observed; this fracturing was induced by the internal swelling stress. We conclude that coal permeability is drastically reduced by cleat closure, which again is caused by coal matrix swelling, which again is caused by flooding with supercritical CO2.

Gassmann Theory Applies to Nanoporous Media

“…This phenomenon is known as adsorption‐induced deformation and is well documented in the literature (see the review Gor et al, , and references therein). Adsorption‐induced deformation is notorious for causing coal swelling and shrinkage in enhanced coal bed methane recovery (Espinoza et al, ; Yang et al, ; Zhang et al, ).…”

Impact of salinity on CO2 containment security in highly heterogeneous reservoirs

“…1 Among the various types of possible CO 2 storage sites (i.e., deep saline aquifers, depleted hydrocarbon reservoirs, and unminable coal beds), saline aquifers have the largest storage capacity. 2,3 Generally, CO 2 would likely be injected at depths below 800 m, where formation temperature and pressure will maintain the CO 2 in a Many factors affect the CO 2 storage efficiency, for example reservoir heterogeneity, 23-36 rock wettability, 7,37-39 injection well configuration, 40 the ratio of vertical to horizontal permeability, 41 stratum dip angle, 42,43 key model parameters (i.e., outer boundary condition, reservoir size, and CO 2 effective permeability), 44 cap rock properties, 7 or aquifer depth and leakage-pathway. 45 However, although it is well established that brine salinity can vary widely between prospective storage reservoirs, [46][47][48][49] there is a knowledge gap in terms of how this can influence storage efficiency.…”

Damage Effects and Fractal Characteristics of Coal Pore Structure during Liquid CO2 Injection into a Coal Bed for E-CBM

“…The coal pore structure was also damaged by the prestressing and shearing stress in the infiltration process, performed the coal matrix shrinkage and the surface was more rough and complex under low temperature by LqCO2 infiltration [25]. This result was different from the study of Zhang et al [23,24], and Zhang's article mainly used Discrete Element Method (DEM) model to simulate the cleats' variation in the swelling process under high temperature and high pressure conditions [24]. To accurately determine the effect of LqCO2 infiltration, further analysis is based on the pore structure parameters of the coal samples [5].…”