CO2 storage in depleted oil and gas fields in the Gulf of Mexico

Depleted oil and gas reservoirs are one of the prime-candidate formations for geologic CO2 storage. Although both the geological structure and the physical properties of most of them have been extensively studied and characterized, there is limited data on the assessment of the CO2 storage capacity, especially in the offshore fields. The purpose of this study is to develop a high-level quantitative assessment of the CO2 volume that can be stored in depleted oil and gas fields in the Federal offshore regions of the Gulf of Mexico (GOM), both on a field-by-field and on a reservoir-by-reservoir basis. In this study, we simulated CO2 storage in 461 of the depleted oil and gas reservoirs (73 fields) among 3514 reservoirs (675 fields) in the GOM (2013 BOEM Reserves database). Based on the simulation results, we improved the Department of Energy (DOE) CO2 Storage Resource Estimate Equation to make more refined and accurate estimates of storable CO2 volumes. Newly revised efficiency factor (E-Roil/gas) correlates better with hydrocarbon recovery factor (HCRF), which is found to be a strong indicator of the CO2 storage capacity of the reservoir. The higher HCRF results in higher E-Roil/gas. The further investigations resulted in an improved, material balance-based correlation-which is called the Production-CO2 Storage Correlation-between cumulative production (free gas, oil and water) at reservoir conditions and CO2 storage volume at standard conditions. This relationship, which is unique for all three types of reservoirs (gas, oil and combination), allows for making direct estimates of CO2 storage volume using only existing production data. Application of these correlations to all of the depleted fields (3514 reservoirs) yields CO2 storage capacities of 4748 MMtons, and the CO2 storage capacity in all 1295 depleted and active fields (13,289 reservoirs) in the GOM calculated to be 21.57 Billion tons. If a 5000 psia surface injection pressure constraint was applied, these volumes would be reduced to 4075 MMtons for all depleted fields only and to 15.80 Billion tons for all depleted and active fields in the GOM. The production-CO2 storage correlations can be used to make more accurate CO2 storage volume estimates in all onshore and offshore depleted oil and gas fields.