Effect of Geochemical Characteristics on Caprock Performance in Deep Saline Aquifers

Abstract

Sequestration of CO2 in deep saline aquifers has attracted positive attention from the scientific community as a mitigatory measure to reduce anthropogenic CO2 in the atmosphere. Caprock layers/zones, which are saturated with brine and CO2 at different degrees of saturation (DOSs), behave differently. Since the risk of CO2 back-migration through different zones in the caprock varies, the focus of this study is on the effects of injected CO2 on the mineralogical and mechanical behavior of caprock with different DOSs due to chemical alteration. A series of reactivity tests were conducted on siltstone samples under different saturation conditions. The experimental results showed that fast dissolution of minerals such as kaolinite and muscovite due to carbonic acid increases the pore volume of caprock. Therefore, flow paths and porosity increase in the fully CO2–brine-saturated zone compared to other zones in the caprock that are not fully saturated with CO2 and brine. In addition, the caprock layer, which is fully saturated with CO2 and brine, has the highest stress corrosion and shear weakening due to mineral dissolution and wetting softening effects, which occur due to surface energy consumption. The next weakest zone in the caprock is the fully brine-saturated siltstone layer due to quartz hydrolysis and wetting softening effects. Therefore, serious attention should be paid to a caprock layer fully saturated with a CO2–brine mixture during sequestration because the risk of CO2 migration via this caprock zone is high, and this affects the permanence and security of injected CO2, especially during periodic CO2 injections and minor seismic events.

Advances in Carbon Dioxide Storage Projects: Assessment and Perspectives

“… When selecting a well site, caprock integrity should be evaluated and its features should be clearly identified. Additionally, the geological evaluation, especially faults and fractures, is thoroughly explored to prevent any potential CO 2 migration path to the surface. ,− …”

Review on Geopolymers as Wellbore Sealants: State of the Art Optimization for CO2 Exposure and Perspectives

“…Si to Al Ratio. The Si/Al ratio is a key factor controlling GP properties through its impact on the network connectivity (Si−O−T, where T is Al or Si) and the degree of Si(OH) 4 and Al(OH) 4 emancipation. 27,78 In general, the Si content determines the condensation between Si−O−Si and Al−O−Si species and strongly influences late-age compressive strength of the material, while the Al content regulates a GP's type of network formation, framework, and setting time.…”

“…Carbon capture and storage (CCS), with storage in porous geological reservoirs of sedimentary origin, is considered a key technology for the mitigation of climate change. − An important challenge for geological CO 2 storage is the integrity of the wells used during CO 2 -injection (as well as potential pre-existing wells). The main risk to the sealing integrity of these wells is leakage through the cement matrix or along the cement-formation and cement-steel interfaces, which could lead to the uncontrolled release of the injected CO 2 . − In most CCS operations, CO 2 is injected to a depth of 800 m or greater, where required conditions for the supercritical state of CO 2 (scCO 2 ) are met (i.e., pressures greater than 7.38 MPa and temperatures above 31.04 °C).…”

Comprehensive Review of Sealant Materials for Leakage Remediation Technology in Geological CO2 Capture and Storage Process

“…Geological leakage problems mean that CO 2 mainly leaks through natural leakage pathways, which are not caused by human activities. , Figure shows that geological leakage problems mainly include CO 2 leaking across caprock through either natural fractures or faults, unconfined lateral migration, or volcanic and tectonic activities . CO 2 leaks through caprock mostly through the following three mechanisms.…”

“…50,51 Figure 2 shows that geological leakage problems mainly include CO 2 leaking across caprock through either natural fractures or faults, unconfined lateral migration, or volcanic and tectonic activities. 52 CO 2 leaks through caprock mostly through the following three mechanisms. First, CO 2 can migrate via fractures in the caprock caused by the compressible flow of free CO 2 gas and molecular diffusion.…”