Assessing the Impact of CO2-H2S at 400 ppm for Storage: A Geochemistry Perspective

Abstract

Abstract The presence of impurities, such as H2S, in CO2 injection carries a higher risk of sulfide mineral precipitation. This can have detrimental effects on rock properties, leading to a reduction in rock porosity and permeability. Consequently, it affects the injectivity and storage capacity of the reservoir. In addition, the reliability of fluid-rock reaction simulations is uncertain and requires calibration using laboratory data. However, there is a scarcity of published experimental data on the geochemical effects of CO2-H2S under reservoir conditions. The objective of this study is to measure the key parameters of geochemical reaction kinetics between injected CO2-H2S at 400 ppm concentration level, brine, and carbonate reservoir rocks, and their effects on fluid and rock properties. Carbonate core samples from the X Field have been selected as a case study due to their identification as potential CO2-H2S storage sites, and the availability of the core samples. In this study, H2S gas with a concentration level of 400 ppm is pre-mixed with CO2 and brine water. The CO2-H2S-brine mixture is aged with core samples under X Field reservoir conditions using two different setups: high-pressure chamber (static) and core flood (dynamic) for a duration of 30-days and 14-days respectively. These setups were designed to represent two different scenarios during injection: far from the wellbore and near wellbore scenario. At the end of the ageing period, cores and effluent were collected for analysis to measure changes in key geochemical parameters, including rock porosity, permeability, mineralogy, and images from CT scans, between the post-ageing and pre-ageing stages. The findings offer valuable insights into the behavior and stability of carbonate rocks within near wellbore and far from the wellbore environments during CO2-H2S interactions. Understanding the geochemical processes involved is crucial for evaluating the long-term stability and containment of CO2 or natural gas containing impurities such as H2S in geological storage scenarios.