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.
Highlights
The increasing concentration of anthropogenic CO2 in the atmosphere has caused significant global climate change
This study investigates the evolution of seal capacity of caprock induced by mineral alteration using
TOUGHREACT based on the Heshanggou Formation mudstone at the Shenhua carbon capture and storage (CCS) demonstration site of China
Summary
The increasing concentration of anthropogenic CO2 in the atmosphere has caused significant global climate change. Among the existing emission reduction ways, carbon capture and storage (CCS) in geological formations such as deep saline aquifers, oil and gas reservoirs, and un-minable coal beds, is considered to be the most promising options for lowering anthropogenic emissions of CO2 to the atmosphere on a large scale [2,3]. Minerals 2020, 10, 1009 have been extended to CCUS (carbon capture, utilization and storage) technologies, which can reduce. For the implementation of a large-scale CCS/CCUS project, the primary concern is the sealing capacity of caprock overlying the CO2 storage reservoir, which improves the long-term safety of CO2 geological storage [13]. The injected CO2 can accumulate with time under the caprock due to its low permeability and high capillary entry pressure [14,15,16]. CO2 may infiltrate into the initially water-saturated caprock when buoyancy pressure is higher than the capillary entry pressure
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