EOR (Enhanced Oil Recovery) is the term for a wide range of proven methods, engineering practices and production technologies used for recovering oil from existing oil fields.
EOR is the acronym for ENHANCED OIL RECOVERY which – along with IOR (Improved Oil Recovery) – comprises the technologies employed to extend the life of an otherwise depleted oil reservoir. It is often regarded as the third phase (tertiary recovery) after the primary stage (post discovery phase) and secondary stage (e.g. water flood or gas cycling) and currently accounts for approximately 10% of oil produced in the USA. EOR technology can take one of four forms: gas injection, chemical injection, thermal processes, and other less conventional. Carbon dioxide (CO2) at miscible conditions currently accounts for half the EOR production (5% of the total oil production) in the USA. Applied to fields that have undergone primary and secondary recoveries to produce 35%-40% of the original oil in place (OOIP), miscible CO2 flood technology can add a further 15%-20% incremental recovery.
CO2 injection can take the form of simple immiscible flooding or miscible (solvent) flooding with immiscible displacements which are generally not as efficient as miscible displacements of crude.
Miscible CO2 flooding involves CO2 mixing with the residual oil in the reservoir to effectively eliminate the interfacial tension between the oil and water to release the otherwise immobile oil. The CO2 causes the oil-CO2 miscible phase to swell and viscosity to reduce and thereby allow the miscible phase to flow to producing well bores. Flooding of oil fields with CO2 is generally limited by the availability of a source of CO2.
Waterflood EOR is the use of water injection to increase the production from oil reservoirs. Use of water to increase oil production is known as “secondary recovery” and typically follows “primary production,” which uses the reservoir’s natural energy to produce oil. In this EOR technique, water is injected into the reservoir and the flood of water sweeps the remaining oil in the reservoir to production wells. Waterflood EOR can recover anywhere from 5% to 50% of the oil that remains in the reservoir, and greatly enhance the productivity and economics of the development.
Chemical flooding of oil fields generally involves an alkaline water base to which a polymer and/or a surfactant and polymer have been added. The addition of polymer as a thickening agent increases the viscosity of the water phase in the reservoir thereby lowering the mobility ratio of the oil and achieving an improved oil recovery. The inclusion of a surfactant (detergent) to an alkaline-polymer injection fluid has the additional benefit of reducing the oil-water interfacial tension and releasing otherwise immobile oil from the reservoir.