Primary recovery
- Also known as
- primary production, natural drive
Primary recovery is the first stage of oil production, in which oil is produced using the reservoir's natural energy, such as gas expansion, water influx and gravity, with help from pumps and other artificial lift. It typically recovers only a small share of the oil in place.
What is primary recovery?
When a well is first drilled into a reservoir, the pressure in the rock pushes oil toward the wellbore. Primary recovery produces oil using that natural energy, supplemented by artificial lift, such as rod pumps, when pressure is no longer enough to lift fluids to the surface.
Natural drive mechanisms
- Solution gas drive. Gas dissolved in the oil comes out of solution as pressure falls and expands, pushing oil out.
- Gas cap drive. A gas cap above the oil expands as pressure drops.
- Water drive. Water from a connected aquifer moves in to replace produced oil.
- Gravity drainage. Oil drains downward in steeply dipping or thick reservoirs.
- Rock and fluid expansion. Rock and fluids expand slightly as pressure drops.
Water drive and gravity drainage generally recover more oil than solution gas drive.
How much oil it recovers
The U.S. Department of Energy estimates that primary recovery typically produces only about 10 percent of a reservoir’s original oil in place. In shale and tight reservoirs, primary recovery factors are typically lower still.
What comes next
- Secondary recovery, usually waterflooding or gas injection to maintain pressure and displace oil, which the DOE says typically raises total recovery to 20 to 40 percent.
- Tertiary recovery, or enhanced oil recovery, which alters the oil or the rock-fluid interactions and can raise total recovery to 30 to 60 percent or more.
Frequently asked questions
Yes. Artificial lift helps bring fluids to the surface but does not add energy to the reservoir, so it is still primary recovery.
As pressure declines, the energy available to push oil falls, and much oil remains trapped in the rock by capillary forces.
Sources
- primary recovery; drive mechanism, SLB Energy Glossary
- Enhanced oil recovery, U.S. Department of Energy, Office of Fossil Energy and Carbon Management