Some water is produced from all reservoirs. Wellstreams comprise a blend of oil, condensate, gas and water. One way of dealing with the last is to inject it back below ground. The other options are either to treat the water before discharging it to the sea, or to store it in tanks before shipping to land.
Work has long been pursued by the Norwegian government and the petroleum industry to reduce discharges of environmentally harmful substances to the sea. A zero-discharge concept was introduced in the 1997 White Paper on an environmental policy for sustainable development. On that basis, the goal of zero environmentally harmful discharges was established in 2005.
The biggest contributor to such discharges was oil and other damaging components found in produced water.
Injecting the latter back below ground was long under consideration, and this was the solution proposed in the plan for development and operation (PDO) of the Ekofisk Growth project. When the company studied this solution more closely, however, it found that the water was unsuitable for being returned because it posed too great a probability of acidifying the reservoir.
A hunt for new options was accordingly launched, and ended up with CTour. This process involved injecting natural gas liquids (NGL) into the produced water stream in a coalescer. Mixing these components had a combined effect, where the polluting components were both collected and extracted from the water phase. The NGL containing these components was then removed in a separator. CTour was configured so that all the NGL used was returned to the Ekofisk production stream.
This project has reduced oil particles in treated water to only a third of the maximum level specified in Norwegian legislation.Female platformEkofisk Growth start-up with 2/4 M