In terms of ultimate recovery which expansion would prove to be more efficient, free or solution gas or oil?

• A. Oil expansion
• B. Water expansion
• C. Solid expansion
• D. Free or solution gas

Answer: (D)

The driving energy for ultimate oil recovery comes mainly from gas expansion. Gas expands far more than oil or water when pressure drops, especially when gas is dissolved in oil and then comes out of solution as pressure falls. This expansion helps push oil toward the well and maintain reservoir pressure, which boosts how much oil can be recovered.

Oil expansion is limited because oil is less compressible, so its volume increases only modestly as pressure drops and it provides relatively little pushing energy. Water expansion is even less effective because water is nearly incompressible, offering little additional drive. Solid expansion doesn’t contribute to moving fluids in the reservoir at all.

So, expanding free gas (and the dissolved gas that comes out of solution) provides the strongest drive and leads to the most efficient, higher ultimate recovery.