Which EOR method uses polymers or detergent-like surfactants to lower surface tension and mobilize oil droplets?

• A. Gas Injection
• B. Thermal Recovery
• C. Chemical Injection
• D. Waterflood

Answer: (C)

This is about chemical injection, a type of Enhanced Oil Recovery that uses additives to modify how the displacing fluid interacts with oil. Polymers and detergent-like surfactants are the agents involved. Polymers thicken the injected water, increasing its viscosity so it pushes more oil and reduces fingering, which helps sweep more oil from the reservoir. Surfactants lower the interfacial tension between the oil and the water, making it easier for oil droplets trapped in the tiny pores to become mobilized and displaced. They can also help shift the rock’s wettability toward the oil-waiting side, further aiding oil flow. In contrast, gas injection relies on pushing oil out with gas pressure, thermal recovery uses heat to lower oil viscosity, and a basic waterflood uses water without these chemical additives.