Definition - What does Depleted Zone mean?
A Depleted Zone is a reservoir zone that does not have enough reservoir pressure left to push the hydrocarbons towards the surface by itself and thereby halting the production. In order to bring this hydrocarbon to the surface, an operator requires implementation of oil recovery techniques to buildup the reservoir pressure. A depleted zone can at times signify the end of the presence of hydrocarbons in a reservoir and thus it can be abandoned since no hydrocarbons can be produced further.
Petropedia explains Depleted Zone
Over a period of time, the pressure inside a reservoir declines making hydrocarbons difficult to rise to the surface and thus the oil and gas production rate declines.
This happens due to lack of pressure and reduction in the volume of hydrocarbons inside a reservoir. As a result, the reservoir tends to form a depletion zone which is left with low levels of hydrocarbons as well as low formation pressure. In a depleted zone, the intensity of depletion depends on the type of fluid, type of drive used during drilling, drawdown pressure and production rate.
However, the interest of an oil E&P organization lies in the extraction of even the last drop of precious hydrocarbons from a drilled location. In order to bring the crude oil stored at lower levels of a reservoir zone of crude oil to the surface, enhanced oil recovery techniques are implemented such as:
- Gas injection
- Steam and hot water injection
- Chemical injections such as polymer flooding, microbial injection & liquid CO2 super fluids.