The United States Department of Energy (DOE) has previously supported unconventional storage projects to work towards achieving low-, net-zero-, and net-negative-carbon oil, focusing on optimizing carbon dioxide (CO2) storage associated with enhanced oil recovery (EOR), residual oil zones (ROZs), and tight oil formations (TOFs). DOE is not currently supporting any hydrocarbon production including those used in unconventional storage.
Storage of CO2 in association with EOR offers a means to help offset capture costs and thereby accelerate the implementation of geologic storage. Carbon dioxide-EOR is commercially active, whereas ROZs and TOFs present a new opportunity for CO2 injection for oil production and associated storage. Primary production of these reservoirs may have as low as 5% of original oil-in-place.
Associated storage field laboratory projects focused on unconventional ROZs and TOFs will demonstrate their potential as an additional type of carbon storage resource and support deployment of unconventional storage technology by industry. Field laboratories will also provide data to improve estimates for storage capacity of CO2 in conjunction with EOR and will provide validation of modeling, simulation, and monitoring tools specific for associated storage in unconventional ROZs and TOFs.
EOR involves injecting CO2 into existing oil fields. As CO2 dissolves in oil, it acts as a solvent and swells the oil and reduces its viscosity. These effects help to improve the efficiency of the oil displacement process. Reginal Carbon Sequestration Partnership (RCSP) projects have injected more than 10 million metric tons of CO2 in conjunction with EOR projects. Carbon dioxide-EOR can add value by offering a bridge to a reduced carbon emissions future. Carbon dioxide-EOR effectively reduces the cost of storing CO2 by earning revenues for the CO2 emitter from sales of CO2 to oil producers.
ROZs are immobile areas of oil located below the oil-water contact of a reservoir, commonly located at the base of oil reservoirs. Carbon dioxide flooding mobilizes the residual oil, allowing it to be produced. Removal of the oil results in additional CO2 storage capacity. Some studies have proposed that ROZs may also occur laterally beyond the boundaries of existing oil reservoirs and are termed “fairways.”