WATER INJECTION INTO A HYDROCARBON RESERVOIR

The invention relates to the production of hydrocarbons and in particular to waterflooding, or the injection of water into a hydrocarbon reservoir to assist recovery of the hydrocarbons. It is often desirable to use produced water (PW) for waterflooding, whereas seawater (which is often more convenient to use) can cause issues such as undesirable precipitation in the reservoir and associated pipelines and equipment. Often there is insufficient PW and the supply of PW needs to be supplemented. It is also often desirable to reduce the salinity of the PW. The invention contemplates an osmotic process in which the high salinity PW acts as a draw solution and lower salinity seawater is used as a feed. The PW supply may be pressurized in preparation for injecting it into the reservoir and then passed through an osmotic membrane element, whilst low pressure seawater is passed through the osmotic membrane element on the other side. The lower salinity of the seawater leads to an osmotic pressure difference across the membrane causing a pure water permeate to enter the PW stream, whilst maintaining the pressure of the PW stream. In this way, the volume of the PW injection stream is increased without reducing the pressure, the specific energy requirement for injecting water into the reservoir are reduced and undesirable components of the seawater are removed.