Modified EOR Screening Criteria as Applied to a Group of Offshore Carbonate Oil Reservoirs

Abstract

AbstractThis screening study has been applied on a group of offshore carbonate oil reservoirs. The methodology is based on the EOR screening criteria set forth by Taber et. al.1,2 enriched with additional screening criteria. The EOR techniques screened included solvent flooding (miscible, immiscible hydrocarbon and CO2 Gas flooding), chemical flooding (Polymer flooding, and Surfactant and Polymer flooding), as well as Thermal flooding (Steam injection and In-situ combustion) techniques. The screening study investigated the challenging and the killing parameters of each technique if any, indicating the most applicable EOR technique.By comparing the depth and API gravity data of the reservoirs under study to that of the worldwide producing EOR projects, it was possible to define at a glance which EOR methods have been already experienced for the same conditions of reservoir depth and API oil gravities. Furthermore, by considering the relatively high pressure and temperature of the heterogeneous carbonate reservoirs under study, with its low viscosity oil, and the associated high salinity formation water, several EOR methods can be discarded including: Steam Injection, In Situ Combustion, and Polymers.Two methods were found to be most suitable for most of the reservoirs: Miscible Hydrocarbon and CO2 Gas injection. Minimum Miscibility Pressure (MMP) has been estimated using correlations. A miscible gas injection could be achieved in most of the reservoirs by adding 2 to 13% C3-C4 to processed gas. CO2 mimimum miscibility pressure, MMP, is expected to be about 1000 psi lower than most of the reservoir pressures, making CO2 miscible flooding to be easily achieved.Surfactant Polymers flooding could reduce Remaining Oil Saturation in reservoirs with more than 50mD permeability. This technology is less mature, than other EOR technologies. It is yet too challenging due to the high salinity, high temperature and carbonate formation.