Two-phase flow effects on the CO₂injection pressure evolution and implications for the caprock geomechanical stability

Abstract

Abstract. Geologic carbon storage is considered to be one of the main solutions to significantly reduce CO2 emissions to the atmosphere to mitigate climate change. CO2 injection in deep geological formations entails a twophase flow, being CO2 the non-wetting phase. One of the main concerns of geologic carbon storage is whether the overpressure induced by CO2 injection may compromise the caprock integrity and faults stability. We numerically investigate the two-phase flow effects that govern the overpressure evolution generated by CO2 injection and how this overpressure affects the caprock geomechanical stability. We find that fluid pressure increases sharply at the beginning of injection because CO2 has to displace the brine that fills the pores around the injection well, which reduces the relative permeability. However, overpressure decreases subsequently because once CO2 fills the pores around the injection well, CO2 can flow easily due to its low viscosity and because the relative permeability to CO2 increases. Furthermore, the pressure drop that occurs in the capillary fringe due to two-phase flow interference decreases as the CO2 plume becomes larger. This overpressure evolution induced by CO2 injection, which remains practically constant with time after the initial peak, is very beneficial for maintaining caprock stability. Thus, the sealing capacity of the caprock will be maintained, preventing CO2 leakage to occur across the caprock.

Proceedings of the 8th International Congress on Environmental Geotechnics Volume 3

“…In contrast, it is the other way around for water injection (Zhang and Agarwal, 2012). For CO2 injection through a vertical well, pressure buildup peaks at the beginning of injection, but subsequently drops (Vilarrasa et al, 2016). However, pressure builds up continuously when injecting CO2 through a horizontal well, which induces a higher pressure buildup in the long term (Zhang and Agarwal, 2012).…”

Impact of Regional Pressure Dissipation on Carbon Capture and Storage Projects: A Comprehensive Review

“…While the initial injection of CO 2 contributes to the pressure increase, a substantial portion of the injected CO 2 is expected to undergo phase changes over time [72]. Gaseous CO 2 injected into the formation can dissolve into the formation fluids, forming a carbonic acid solution.…”

Effects of Impurities on CO2 Sequestration in Saline Aquifers: Perspective of Interfacial Tension and Wettability

“…In two-phase flow, fluid is divided into wetting and nonwetting phases according to the contact angle. For processes involving CO 2 and water in geological formations, generally, water is considered to be the wetting phase, and CO 2 is considered to be the nonwetting phase . The process by which the nonwetting phase displaces the wetting phase gradually reduces the wetting-phase saturation and is called the drainage process.…”

“…Ensuring safety and long-term stability and preventing CO 2 leakage are key points in CCS. The main pathways of CO 2 leakage are caprocks, faults, cracks, and abandoned wells. − Interfacial tension and wettability mainly affect caprock leakage. When capillary pressure reaches or exceeds a threshold, part of the CO 2 leaks through the caprock to the upper strata.…”

“…For processes involving CO 2 and water in geological formations, generally, water is considered to be the wetting phase, and CO 2 is considered to be the nonwetting phase. 19 The process by which the nonwetting phase displaces the wetting phase gradually reduces the wetting-phase saturation and is called the drainage process. In contrast, the process by which the wetting phase displaces the nonwetting phase results in a gradual increase in the wetting-phase saturation and is called the moisture process.…”