CO2 sequestration potential in Depleted Hydrocarbon fields – A geochemical approach

The reduction of CO2 emissions is crucial for the energy transition. New technologies for the CO2 capture and storage are under development to achieve this goal. CO2 based electrothermal energy and geological storage system (CEEGS) is a novel technology trying to combine renewable energy storage system based on the transcritical CO2 cycle with CO2 storage in geological formations and geothermal heat extraction. Porous media and rock caverns are the geological formations of high interest for such technology. Among them, depleted hydrocarbon fields gain ground due to the experience of reservoir characterisation, sealing performance, storage operability, and already established oil or gas well infrastructure which critically decreases the cost. However, one of the major problems caused during the CO2 storage in depleted hydrocarbon fields is the interactions between the injected CO2 and the remaining fluids. In this study, the potential CO2 storage in the depleted gas fields was investigated and the Marismas 3 was used as an hypothetical model area for the examination of CO2 interactions with a reservoir representing by carbonate-silisiclastic rocks and sands.PHREEQC computer simulation software was used for the investigation of reservoir rock/water/remained gas (CH4) interactions followed by the interactions taking place after the CO2 injection. Two different scenarios were used for the CO2 concentration in the reservoir representing the minimum and the maximum ratio of reservoir storage efficiency factor. During the CO2 injection, carbonic acid was formed, causing a dissolution of several minerals, leading to the precipitation of siderite and clay minerals such as kaolinite, Ca-montmorillonite and illite, which may cause problems related to the permeability of the system. The colloidal nature of siderite and the swelling properties of Ca-montmorillonite are of high concern for the pore throats clogging. However, in this study area, the other new formed mineralogical phases are not threatening the reservoir quality. To make the system more complex and generic, the CMG software utilized to combine dynamic fluid flow and geochemistry, examining the long-term sequestration of CO2 through dissolution trapping, residual trapping, and lateral migration.