Assessment and Challenges of CO2 Injection in a Depleted Reservoir and Interactions With The Design of a Platform Under Conversion

Re-using the depleted reservoirs for CO2 storage offers advantages over saline aquifers because the geological characteristics required for CO2 storage have been pre-determined with high accuracy throughout the reservoir production life, plus a proof of secure containment. Additionally, re-using the production facilities and offshore platforms for the injection of CO2 would be economically and environmentally winning fact, which is the case in this study. This study, based on intensive bibliographic research, gave support to the MISE project regarding the challenges and concerns of CO2 storage in depleted oil and gas reservoirs and selecting the optimum solution for converting the offshore platform GREEN1 in the Adriatic Sea to be re-used instead of decommissioning. It also highlights the interactions between the reservoir parameters and the design of surface facilities. Accordingly, the design of all the upstream components, i.e., transportation pipeline diameter, compression capacity, and maximum allowable pressure is mainly based on the rock and fluid interactions in the reservoir porous media. Nevertheless, storage capacity has a vital role on the candidate sites screening process, accompanied by an economic feasibility study. From here, CO2 storage capacity of ‘Porto Corsini Mare’ reservoir , as a candidate site for GREEN1, is estimated based on returning the depleted reservoir to its initial pressure before production. Furthermore, a methodology for comparing and selecting the suitable reservoirs for CO2 geo-storage is introduced, for the purpose of identifying the optimum storage site for GREEN1 platform. This screening criterion is divided to three main categories: storage capacity, injectivity, and containment, in the shape of logic flow charts with the relevant parameters to each category, in order to help the analysts and decision makers to identify and compare candidate sites for CO2 storage, so that they are easily able to exclude the unsuitable reservoirs and proceed with the right candidates for economic and risk assessment studies.