CO ₂ sequestration potential in Depleted Hydrocarbon fields - A geochemical approach

The CO ₂ emissions reduction is crucial for the energy transition. New technologies for CO ₂ capture and storage are under development, such as CEEGS ^{1, 2}. Porous media and rock caverns are geological formations of high interest for such technology. Among them, depleted hydrocarbon fields (DHF) gain ground due to existing reservoir knowledge and already established infrastructure which decreases the cost. However, one of the major problems caused during CO ₂ storage in DHF is the interactions between the injected CO ₂ and the remaining fluids.

In this study, the potential CO ₂ storage in DHF was investigated. Marismas 3 was used as a hypothetical model area for the examination of CO ₂ interactions with a carbonate-silisiclastic reservoir. PHREEQC software ¹ was used to investigate reservoir rock/water/remained gas (CH ₄) interactions followed by interactions taking place after the CO ₂ injection. Different scenarios were used for the CO ₂ concentration and behaviour in the reservoir. To make the system more complex and generic, the CMG-GEM software ³ was utilized to examine the long-term sequestration of CO ₂ through dissolution trapping, residual trapping, and lateral migration in a reservoir analogue to the Marismas field, but at higher depth, compatible with the CEEGS technology.

During the CO ₂ injection, carbonic acid was formed, causing a dissolution of several minerals, leading to siderite and clay minerals precipitation, which may cause problems to the permeability of the system. The colloidal nature of siderite and the Ca-montmorillonite swelling properties are of high concern for pore throat clogging. The other newly formed mineralogical phases are not threatening the reservoir quality. CMG-GEM validated the critical phase of CO ₂ plume establishment.

The proposed DHF is promising for real-world underground applications fitting to CEEGS technology as the newly formed minerals that could cause failures can be easily controlled by anthropogenic changes in the reservoir parameters.