Geochemical Modelling of the Evolution of Caprock Sealing Capacity at the Shenhua CCS Demonstration Project

Abstract

CO2 geological storage is considered as an important measure to reduce anthropogenic CO2 emissions to the atmosphere for addressing climate change. The key prerequisite for long-term CO2 geological storage is the sealing capacity of caprock. This study investigates the evolution of sealing capacity of caprock induced by geochemical reactions among CO2, water and caprock using TOUGHREACT code based on the Heshanggou Formation mudstone at the Shenhua Carbon Capture and Storage (CCS) demonstration site of China. The results show that the self-sealing phenomenon occurs in the lower part of the caprock dominated by the precipitation of dawsonite, magnesite, siderite, Ca-smectite and illite. While the self-dissolution occurs in the upper part of caprock mainly due to the dissolution of kaolinite, K-feldspar, chlorite and Ca-smectite. Sensitivity analyses indicate that the precipitation of dawsonite, magnesite, siderite is highly advantageous leading to self-sealing of caprock, with albite and chlorite dissolution providing Na+, Mg2+ and Fe2+. The dissolution of K-feldspar dominates illite precipitation by providing required K+, and albite affects Ca-smectite precipitation. The self-sealing and self-dissolution of caprock are enhanced significantly with increasing temperature, while the effect of salinity on caprock sealing capacity is negligible perhaps due to the low salinity level of formation water.

Long‐term CO2 sequestration mechanisms and influence of injection mode in Zhujiang Formation of Pearl River Mouth Basin

“…After 5,000 years, the hydrodynamic trapping contributions of injected CO 2 in Cases 2–4 were 1.35%, 1.27% and 1.10%, respectively; the dissolution trapping proportions of injected CO 2 in Cases 2–4 were 18.50%, 17.85% and 17.28%, respectively; and the mineral trapping fractions of the injected CO 2 in Cases 2–4 were 80.15%, 80.88% and 81.62%, respectively. The previous studies also point out that the reaction rate of minerals increases greatly with the increase in temperature, thus strengthening the dissolution and precipitation of minerals 61,62 . It is well known that the greater the proportion of dissolved and mineralized CO 2 , the safer the storage.…”

“…The previous studies also point out that the reaction rate of minerals increases greatly with the increase in temperature, thus strengthening the dissolution and precipitation of minerals. 61,62 It is well known that the greater the proportion of dissolved and mineralized CO 2 , the safer the storage. It is obvious that with the increase of injection temperature, the proportions of dissolved and mineralized CO 2 of the total injected CO 2 increase, and the storage safety also increases.…”

Surface Chemistry and Chemical Structure of Shale Caprocks Exposed to CO2: Implication for Sealing Integrity

“…In recent years, studies have been conducted to evaluate various types of CO 2 storage such as geological storage of CO 2 in the forms of hydrates − and underlying depleted oil and gas reservoirs with caprock seals. − Understanding the role of sealing caprocks during carbon capture and storage (CCS) application is crucial to ensure the safe containment of the stored CO 2 . , Due to the low density of CO 2 compared to formation brine, CO 2 tends to migrate upward and penetrate through the sealing layers resulting in CO 2 breakthrough. − Shale caprocks play a major role in a petroleum reservoir system, as they are considered effective sealing layers due to their ultralow permeability and high capillary pressures, which can either prevent CO 2 leakage or significantly reduce CO 2 migration rate. Previous studies reported that CO 2 /brine injection can be beneficial for enhanced oil recovery (EOR) applications, as CO 2 can generate complex fractures with high conductivity, prevent formation damage, reduce the amount of produced wastewater, , and provide better displacement of the natural preadsorbed methane during fracturing. , However, during storage, CO 2 can cause major changes in the petrophysical and chemical properties of rocks and affect the storage capacity. − Considerable accomplishments were achieved in studying the sealing integrity of shales during CO 2 storage. − Seal integrity of shales is mainly affected by the geochemical interactions between CO 2 –brine and shale mineralogy, which can alter the wetting behavior, pore structure, and surface chemistry.…”

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

“…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).…”

“…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). Nevertheless, the precipitation reaction was observed in anhydrite caprock (Bolourinejad & Herber, 2015; Miri & Hellevang, 2016; Yang et al, 2020; Wolterbeek & Hangx, 2021). This dissolution or precipitation reaction may vary if the CO 2 breaks through the caprock (Llanos et al, 2022; Luquot et al, 2016; Wang & Peng, 2014).…”