Impact of Supercritical CO2 and Carbonated Water Exposure on Geomechanical Properties of Carbonate Samples

Abstract

Carbon dioxide (CO2) could be potentially stored in subterranean reservoirs, such as carbonate aquifers. Choosing the optimal aquifer to be used for CO2 sequestration is a challenging task because of many factors, including fluid-rock interactions. As CO2 dissolves in brine, it forms carbonic acid, which may interact with the carbonate minerals and, eventually, alter the rock mechanical and petrophysical properties. The objective of this study is to evaluate the impact of CO2 and carbonated water on geomechanical properties of carbonate samples at different exposure periods. Carbonate samples are first characterized in terms of petrophysical, and mineralogical properties. A high-pressure high-temperature (HPHT) vessel was used to conduct the reactivity (exposure) test. The rock mechanical testing procedure involves a triaxial test with cyclic loading, where a constant effective confining pressure of 1700 psi (12 MPa) is applied, and a cyclic loading-unloading-reloading axial load is applied to evaluate the static and dynamic Young's modulus and Poisson ratio. The reactivity (exposure) experiments were conducted at 2000 psi and 60°C. The samples used in this study consist primarily of calcite mineral. The results revealed that the samples exposed to carbonated water show more changes when compared to those exposed to only supercritical CO2. Exposure to supercritical CO2 does not significantly impact the mechanical behavior of the rock. After 3 months of exposure, less than 4% variation in static and dynamic elastic properties was observed. The results also show that both the static and dynamic Young's modulus of the rock samples decrease with increasing exposure time to carbonated water, highlighting the time-dependent of the chemical reactions between the fluid and the rock minerals. In general, reactivity with carbonated water alters the rock's mechanical properties by reducing the Young's modulus and increasing Poisson's ratio, resulting in a more ductile behavior. This study aims to enhance our understanding of how different fluid types affect the rock mechanical properties. The interaction between CO2, brine, and rock minerals may influence CO2 injection processes, storage capacity, sealing integrity, and long-term stability and safety.