Geologic Storage of Carbon Dioxide and Enhanced Oil Recovery II: Cooptimization of Storage and Recovery
Geologic sequestration of carbon dioxide (CO2) in oil and gas reservoirs is one possibility to reduce the amount of CO2 released to the atmosphere. Carbon dioxide injection has been used in enhanced oil recovery (EOR) processes since the 1970s; the traditional approach is to reduce the amount of CO2 injected per barrel of oil produced. For a sequestration process, however, the aim is to maximize both the amount of oil produced and the amount of CO2 stored. It is not readily apparent how this aim is achieved in practice. In this study, several strategies are tested via compositional reservoir simulation to find injection and production procedures that “cooptimize” oil recovery and CO2 storage. Flow simulations are conducted on a synthetic, three dimensional, heterogeneous reservoir model. The reservoir description is stochastic in that multiple realizations of the reservoir are available. The reservoir fluid description is compositional and incorporates 14 distinct components. The results show that traditional reservoir engineering techniques such as injecting CO2 and water in sequential fashion, a so-called water-alternating-gas process, are not conducive to maximizing the CO2 stored within the reservoir. A well control process that shuts in (i.e. closes) wells producing large volumes of gas and allows shut in wells to open as reservoir pressure increases is the most successful strategy for cooptimization. This result holds for both immiscible and miscible gas injection. The strategy appears to be robust in that physics simulations employing multiple realizations of the reservoir model all confirmed that the well control technique produced the maximum amount of oil and simultaneously stored the most CO2.