Which are the three categories of enhanced oil recovery?

• A. Chemical Flooding, Gas Injection and Thermal Recovery
• B. Primary Recovery, Secondary Recovery and Tertiary Recovery
• C. Water Flooding, Steam Injection and Gas Cap Formation
• D. Hydraulic Fracturing, Acidizing and Enhanced Recycling

Answer: (A)

The idea being tested is how enhanced oil recovery methods are grouped. Enhanced oil recovery uses three main approaches to push more oil out after primary production: chemical flooding, where polymers, surfactants, or other chemicals are injected to alter the oil–water interface and increase mobility; gas injection, where a gaseous agent like CO2, natural gas, or nitrogen is injected to displace oil and improve sweep efficiency; and thermal recovery, where heat (typically steam) lowers the oil’s viscosity so it flows more easily toward the well.

These three categories capture the distinct mechanisms by which oil is mobilized or displaced in the reservoir, regardless of the specific agent or process used within each method. The other choices mix stages of production or list techniques that aren’t grouped into the three broad EOR categories, such as primary/secondary/tertiary recovery (stages rather than methods), or individual methods like water flooding, steam injection on its own, gas cap formation, hydraulic fracturing, or acidizing.