Water Injection Enhanced Oil Recovery
Also known as water flooding, this is usually the first type of EOR used as there is plenty of water about offshore.
However seawater is not the first choice. Produced water is used in most cases, and as this contains hydrocarbons, it needs to be treated before being disposed of overboard. This is a cheap means of getting rid of it, but it still requires cleaning up and filtration before use.
Produced water, as the name suggests, is water removed from the oil, gas, and condensates during production processing.
It is supplied to the injection wells by high pressure and by flow-dedicated water injection pumps that can be to sixteen stage pumps running at 5000 RPM. If seawater is to be used, it is normally taken from the platforms deoxygenating unit as an anti-corrosion precaution.
Water injection is used for two purposes;
1. Pumped directly into the oil reservoir it sinks to the bottom where it gradually builds up pressure, displacing the oil floating on top and forcing it up the production well.
2. Pumped into injection wells drilled in selected locations throughout the reservoir rock. Being under high pressure it pushes any oil trapped in the porous rock towards the production wells.
Both methods require a substantial amount of time to begin to show improvements, however once established, represent a long-time investment, extracting up to 35% of oil which would otherwise remain stored in the reservoir.