Enhanced oil recovery

Enhanced oil recovery uses injected fluids or heat to mobilize oil left behind after primary production and waterflooding. It can improve recovery by changing reservoir pressure, fluid properties, or rock–fluid interactions.

Thermal enhanced oil recovery: Oil-recovery methods that heat reservoir fluids to reduce oil viscosity and improve flow. Steam and other heat sources make heavy oil easier to move through the reservoir.
Primary oil recovery: Oil production driven by a reservoir’s natural energy and, sometimes, artificial lift. Enhanced recovery follows the decline of production driven by natural reservoir energy.
Steam-assisted gravity drainage: A thermal method that injects steam between horizontal wells so heated bitumen drains to a lower producer. It applies heat and gravity drainage to recover bitumen from thick oil sands.
Hydraulic fracturing: A method that creates or enlarges fractures in rock by injecting pressurized fluid. It improves access to hydrocarbons by changing rock permeability, rather than primarily mobilizing residual oil.
Gas injection: The injection of gas into an oil reservoir to maintain pressure or mobilize hydrocarbons. Injected gases can swell oil, lower its viscosity, or displace it toward production wells.
Secondary oil recovery: Oil production supported by pressure-maintenance methods such as water or gas injection. It is the conventional stage that typically precedes enhanced oil recovery.
Cyclic steam stimulation: A thermal method that alternates steam injection, soaking, and oil production through the same well. It is used to heat heavy oil where continuous steamflooding is unsuitable.
Artificial lift: Methods that help produced fluids rise through a well when reservoir pressure is insufficient. Artificial lift moves fluids up the well; enhanced recovery targets oil movement within the reservoir.
Chemical enhanced oil recovery: Oil-recovery methods that inject chemicals to alter fluid flow or oil–water interactions. Polymers, surfactants, and alkaline agents can improve sweep or release trapped oil.
Waterflooding: The injection of water into an oil reservoir to maintain pressure and displace oil toward producing wells. Waterflooding is a common secondary method; enhanced recovery targets oil it leaves behind.

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