Question

Which of the following is/are conventional Enhanced Oil Recovery (EOR) method(s)?

• A. Water flooding
• B. In situ combustion
• C. Surfactant flooding
• D. Steam flooding

Hint:

EOR methods change oil viscosity, interfacial tension, or wettability, unlike plain water flooding which is a secondary recovery method.

Answer 1

The Correct Option is B, C, D

Step 1: Recall how oil recovery is classified:
Oil recovery from a reservoir is normally grouped into three stages. Primary recovery uses the natural energy already present in the reservoir, such as rock and fluid expansion or a natural water drive. Secondary recovery involves injecting a fluid, most commonly water or gas, simply to maintain reservoir pressure and physically push additional oil toward the producing wells. Enhanced Oil Recovery, or EOR, goes a step further and involves injecting a fluid or energy source that actually changes the properties of the oil or the rock oil interaction, for example by lowering oil viscosity, reducing interfacial tension, or altering wettability, so that oil which would otherwise remain trapped can be mobilized.
Step 2: Evaluate option A, water flooding:
Water flooding involves injecting water into the reservoir mainly to maintain pressure and sweep oil toward the producing wells through simple immiscible displacement. It does not change the viscosity of the oil, does not reduce the interfacial tension between oil and water in any special way, and does not alter the rock wettability by design. Because of this it is classified as a secondary recovery method rather than a conventional EOR method, so option A is not correct.
Step 3: Evaluate option B, in situ combustion:
In situ combustion is a thermal EOR method in which air or oxygen is injected into the reservoir and a portion of the oil is ignited downhole. The resulting heat lowers the viscosity of the surrounding oil considerably and generates additional drive mechanisms such as steam and flue gas, making the oil far easier to mobilize and produce. This is a well recognized conventional thermal EOR technique, so option B is correct.
Step 4: Evaluate option C, surfactant flooding:
Surfactant flooding is a chemical EOR method in which surface active agents are injected to sharply lower the interfacial tension between the oil and the displacing water. This reduction in interfacial tension allows oil droplets that are normally trapped in the pore spaces by capillary forces to be mobilized and swept out. This is a standard conventional chemical EOR method, so option C is correct.
Step 5: Evaluate option D, steam flooding:
Steam flooding is a thermal EOR method in which steam is continuously injected into the reservoir. The heat carried by the steam substantially reduces the viscosity of heavy or viscous crude oil, making it flow much more easily toward the producing wells, and the method also provides an additional pressure drive. This is one of the most widely used conventional thermal EOR techniques, so option D is correct.
Final Answer:
\[ \boxed{\text{In situ combustion, Surfactant flooding, and Steam flooding are conventional EOR methods}} \]