Laboratory and Modelling Study on Comparison of Geochemical Reactivity in Carbonate Reservoir Due to CO2 Injection With/Without the Presence of H2S at High Temperature and Pressure

Abstract

Carbon Capture and Storage, known as CCS, is a technology that involves capturing CO2 from industrial and energy-related sources such as a power plant before being transported and injected into geological formations for long-term isolation from the atmosphere. There are four types of geological formations that can be used to store CO2: depleted oil and gas reservoirs, deep coal seams, salt caverns and deep saline aquifers. Among these, deep saline aquifers provide the best option for storage as it presents the largest storage capacity. After the injection of CO2 underground, the gas (or, in most cases, the CO2 will be a supercritical fluid) will undergo physical and chemical changes. The CO2 will be trapped in the pore space of the rock by three trapping mechanisms: hydrodynamic trapping, solubility trapping and mineral trapping. The storage security increases over the time with mineral trapping provides both the slowest and the safest process. This is because the injected CO2 will be permanently sequestered as a solid phase. As a result, this prevents leakage of CO2 into the surface. The development of injection process is still in its infancy, especially when it comes to the consideration of CO2 injected with other impurities. To date, most research has only studied the injection of pure CO2. However, allowing impurities in the gas stream reduces the cost of capture – the most expensive step in CCS – and so is an attractive option (Gaus, 2010; Knauss, 2005). Some studies have reported few geochemical effects associated with injecting a mixture of CO2 and H2S (Gunter et al., 2000; Knauss et al., 2005; Xu et al., 2007); however, the details study on kinetics of H2S during and post-injection of CO2 with H2S is still scarce. Previous study by Ahmad et al., 2023 has reported that potential mineral precipitation of sulfide in carbonate reservoirs due to CO2 injection with H2S. The precipitation resulted the reduction of rock porosity and pemerbility which impact on the injectivity and ultimately on the storage capacity (Clark et al., 2018).