What is waterflooding?
Waterflooding is a low cost secondary production solution to increase the amount of oil that can be recovered from an oilfield. The process involves converting some oil production wells into water injection wells by injecting (sea) water into the reservoir to encourage oil production from the remaining producers. The injected water helps to increase pressure within the reservoir; it also helps to move the oil in place increasing the amount of oil that can be recovered from the reservoir rocks. Although the effectiveness of water injection varies according to formation characteristics, a waterflood can recover anywhere from 5% to 50% of the oil that is remaining in the reservoir, greatly enhancing the productivity and economics of the development.
Illustration of a Typical Waterflood
Water-floods are a method of secondary recovery in which water is injected into the reservoir formation to dis-place residual oil. The water from injection wells physically sweeps the displaced oil to adjacent production wells. Water is injected (1) to support pressure of the reservoir (also known as voidage replacement), and (2) to sweep or displace oil from the reservoir, and push it towards a well.
Normally only 30% of the oil in a reservoir can be extracted, but water injection increases that percentage (known as the recovery factor) and maintains the production rate of a reservoir over a longer period. Flooding an oil field with extraneous water has been a widely accepted method for increasing a reservoir’s recovery since the 1950’s.
Most oil reservoirs are solution gas drive reservoirs. This means as the oil is produced the reservoir’s pressure is reduced and the gas that was held in solution begins to breakout and expand thus, “driving” the oil towards the producing wells. This is a familiar process we see when opening a can of soda (Mentos added for emphasis).
The problem with a solution gas drive reservoir is when the gas breaks out of solution it is free to flow to the producing well and be produced. Typically a solution gas drive reservoir will only recover up to 20% of the reservoir’s original volume of oil leaving a large portion behind. By injecting water in a controlled manner, the loss of reservoir pressure can be controlled and reversed. Water is injected into dedicated injection wells strate-gically located throughout the reservoir, and the water itself can be used to displace the remaining oil towards the producing wells. If properly designed and operated a water-flood can double the reservoir’s oil recovery.