Characterization, Screening and Feasibility Assessment of Depleted Gas Reservoirs and Saline Aquifers for CO2 Storage in Nigeria: A Pilot Case Study

Abstract Carbon Capture and Storage (CCS) involves capturing carbon dioxide (CO2) emissions from industrial, oil, and gas operations and securely storing them deep underground. By preventing CO2 from entering the atmosphere, CCS helps reduce emissions. It enables permanent, quantifiable, and verifiable CO2 storage in geological formations. As the world transitions to cleaner energy and strives for net-zero targets, focused CCS feasibility studies and strategic implementation are crucial. Energy companies in many countries are already building CCS hubs, although this process requires dedicated effort and time. With the emerging energy transition drive and ever-increasing company and country net zero targets; it has become paramount to set the scene for more focused CCS feasibility study and future implementation. In most countries, energy companies have commenced building CCS hubs. But doing this organically takes years, dedicated efforts, and strategic focus. To demonstrate potential for pilot development and operation of the CCS project in Nigeria, many depleted gas reservoirs and saline aquifers were subjected to detailed technical screening and feasibility assessment for CO2 storage in depleted gas reservoirs and saline aquifers. Of the 40 reservoirs screened, 3 reservoirs were selected as potential candidates for CO2 storage. Material Balance model and reservoir parameters for the SeaGen field were used to quantify storage capacity, while implementing the material balance calculations, with similar rock properties used to estimate CO2 storage capacity for the depleted reservoirs. PVT properties of the reservoirs and CO2 properties (density and viscosity) at reservoir conditions were used to estimate for the volumetrics estimations. This paper presents key technical considerations for CO2 storage in depleted gas reservoirs and saline aquifers in Nigeria; including storage capacity characterization, screening criteria, volumetric-based and production-based CO2 storage estimation methodologies as well as voidage modelling workflow in depleted gas reservoirs. It also focused on both the static and dynamic characteristics of the rock that determine the feasibility in Nigeria. Finally, the paper highlights standard screening workflow for selected depleted gas fields and saline aquifers in Niger Delta, and the results of quantitative subsurface storage capacity and Material balance estimations.