Dewatering is the removal of water from the reservoir during oil and gas production. Petroleum reservoirs often contain a mix of hydrocarbons (oil and gas) and water, typically in the form of formation water or brine that naturally exists within the rock pores alongside the oil. As production begins, this water can be extracted along with the hydrocarbons, especially in reservoirs where water occupies a significant portion of the pore space or where water injection is used to enhance recovery.
Dewatering in this case happens as the reservoir is "drained" during extraction. When a well is drilled and production starts, the pressure drop causes fluids, oil, gas, and water, to flow toward the wellbore. Initially, you might get mostly oil, but over time, the water cut (the proportion of water in the produced fluid) often increases. This is because water from deeper layers or adjacent zones can move in, a process called water encroachment, or because injected water (used in secondary recovery techniques like waterflooding) starts breaking through to the production wells.
