Combined Effects of CO2 Adsorption-Induced Swelling and Dehydration-Induced Shrinkage on Caprock Sealing Efficiency

Abstract

Carbon dioxide (CO2) may infiltrate into the caprock and displace brine water in the caprock layer. This causes two effects: one is the caprock swelling induced by the CO2 adsorption and the other is the caprock dehydration and shrinkage due to CO2–brine water two-phase flow. The competition of these two effects challenges the caprock sealing efficiency. To study the evolution mechanism of the caprock properties, a numerical model is first proposed to investigate the combined effects of CO2 adsorption-induced expansion and dehydration-induced shrinkage on the caprock sealing efficiency. In this model, the caprock matrix is fully saturated by brine water in its initial state and the fracture network has only a brine water–CO2 two-phase flow. With the diffusion of CO2 from the fractures into the caprock matrix, the CO2 sorption and matrix dehydration can alter the permeability of the caprock and affect the entry capillary pressure. Second, this numerical model is validated with a breakthrough test. The effects of the two-phase flow on the water saturation, CO2 adsorption on the swelling strain, and dehydration on the shrinkage strain are studied, respectively. Third, the permeability evolution mechanism in the CO2–brine water mixed zone is investigated. The effect of dehydration on the penetration depth is also analyzed. It is found that both the shale matrix dehydration and CO2 sorption-induced swelling can significantly alter the sealing efficiency of the fractured caprock.

Nanoscale Analysis of Shale Matrix Alteration after Supercritical CO2 Treatment: Implications for scCO2 Fracturing in Shales

“…Illustration showing the dehydration of shale matrix surrounded by a fracture network due to CO 2 infiltration (adapted from the work of Shang et al Copyright: 2022 by the authors. Licensee MDPI, Basel, Switzerland, and distributed under the terms and conditions of the Creative Commons Attribution (CC BY) License).…”

“…In his research, Shang et al introduced a multiphysical coupling model to investigate the impact of dehydration and CO 2 adsorption on caprock sealing. 59 He detailed the process wherein CO 2 diffuses from the pre-existing fracture network into the shale matrix, displacing pore water and leading to matrix dehydration shrinkage. Figure 21, extracted from Shang's study, visually represents a shale matrix block surrounded by fractures.…”

A multiphysical‐geochemical coupling model for caprock sealing efficiency in CO2 geosequestration

“…As an effective mitigation strategy for the reduction of CO 2 concentration in the atmosphere, CO 2 geosequestration has received more and more attention (Bachu & Bennion, 2008; Beerling et al, 2020; Huisingh et al, 2015; Isah et al, 2022; Lehmann & Possinger, 2020; Xie et al, 2022). CO 2 injected into the deep ground layer generally migrates in two stages: the first stage is the CO 2 transport within the storage reservoir; the second stage is the CO 2 accumulation beneath caprock (Cai et al, 2021; Heath et al, 2012; Hou et al, 2012; Shang et al, 2022). More and more studies have shown that CO 2 possibly migrates to shallow aquifers and pollutes freshwater resources (Carroll et al, 2014; Keating et al, 2013; Ruggieri & Gherardi, 2020; Smith et al, 2013; Takaya et al, 2017; Wang & Wang, 2018).…”

“…The CO 2 migration and interaction in caprocks are complicated (Hu et al, 2022; Zhang et al, 2021). The CO 2 migration in the caprock under the multiphysical‐geochemical interactions may be self‐enhancing or self‐limiting (Gherardi et al, 2007; Hou et al, 2022; Shang et al, 2022; Wang et al, 2015; Wang & Peng, 2014; Yang et al, 2020). Experimental observations showed that the pH value of CO 2 ‐enriched brine decreases and thus leads to calcite dissolution (Huerta et al, 2016; Martín et al, 2022; Niu et al, 2022).…”

“…Particularly, this study developed a multiphysical‐geochemical coupling model through a corrected porosity to consider the effects of geochemical reactions of dissolved CO 2 in the fracture network on caprock sealing efficiency. This could primarily modify and extend the previous multiphysical coupling model on caprock sealing efficiency for CO 2 storage (Shang et al, 2022; Wang et al, 2015; Wang & Peng, 2014; Wang & Wang, 2018). In this model, porosity is corrected through the volumetric strain induced by geochemical reactions.…”