Waterflooding
- Also known as
- waterflood, secondary recovery, water injection
Waterflooding is the injection of water into an oil reservoir through injection wells to maintain reservoir pressure and push oil toward producing wells. It is the most common method of secondary recovery.
What is waterflooding?
When a reservoir is first produced, natural pressure drives oil to the wells. As that pressure declines, production falls. Waterflooding restores the drive by injecting water, usually produced water or another available source, through dedicated injection wells. The water maintains pressure and sweeps through the rock, displacing oil toward producing wells.
Waterflooding is the most widely used form of secondary recovery. According to the U.S. Department of Energy, primary recovery typically produces about 10 percent of the original oil in place, and secondary recovery methods such as waterflooding bring total recovery to about 20 to 40 percent.
How a waterflood works
Injection and producing wells are usually arranged in repeating patterns, such as the five-spot pattern of four injectors around a producer, or in lines. Engineers design the pattern, injection rates and water quality to push oil evenly through the reservoir. Over time, injected water reaches the producing wells, called breakthrough, and the water cut of the produced fluid rises until the wells become uneconomic.
Why waterflooding leaves oil behind
- Capillary trapping. Water cannot move oil droplets held in pores by capillary pressure, leaving residual oil.
- Poor sweep. Water follows the most permeable paths and bypasses parts of the reservoir, especially when oil is much more viscous than water; see sweep efficiency and mobility ratio.
- Wettability. Oil-wet rock holds oil more tightly.
Enhanced oil recovery methods target this remaining oil.
Operating a waterflood
Waterfloods require large volumes of water handling, water treatment to prevent plugging, mineral scale and corrosion, and monitoring of injection well injectivity.
Frequently asked questions
Primary recovery relies on the reservoir’s natural energy to produce oil. Secondary recovery adds energy, most commonly by injecting water to maintain pressure and displace oil.
Usually not. Waterflooding is classed as secondary recovery. Enhanced oil recovery refers to methods, such as gas injection, heat or chemicals, that change how oil and rock interact.
Sources
- waterflooding, SLB Energy Glossary
- Enhanced Oil Recovery, U.S. Department of Energy, Office of Fossil Energy and Carbon Management
- Waterflooding, SPE PetroWiki