Enhanced Oil Recovery

Part 11, Chapter 11: Wells, Recovery, and Displacement

Going After What Water Leaves

After a waterflood most of the oil is still underground: trapped as residual oil SorS_{or} where the water swept, and bypassed where it did not. Enhanced (tertiary) recovery attacks both losses.

Enhanced oil recoverywaterfloodrecovered 28%remaining 72%with enhanced recoveryrecovered 42%remaining 58%+15% EORwaterflood oilEOR incrementPolymer lifts the sweep factor and a miscible or surfactant flood lifts the displacement factor; the increment over the waterflood is the prize and must pay for itself.

The Mechanisms

Mobility control, such as polymer, thickens the injected water to improve the sweep. Lowering interfacial tension, with surfactant or a miscible gas like CO2, frees the trapped residual oil to improve the displacement. Thermal methods such as steam cut the oil viscosity for heavy oil. Each lever lifts one factor of the recovery product.

The Increment Has to Pay

The prize is the increment over the waterflood, and it must cover the cost of the injected chemicals or gas. Enhanced recovery is screened against the oil price, the reservoir quality, and the residual-oil target before a barrel of solvent is bought.

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