Low-salinity water (LSW) flooding 

LSW flooding involves injecting brine with a lower salt content or ionic strength. The latter is typically in the range of 500–3,000 parts per million of total dissolved solids (TDS), and no more than 5,000 ppm (parts per million).

This can be compared with salinities for seawater or formation water, which are about 30,000 ppm or higher.

The introduction of LSW in an equilibrium system of high salinity appears to cause a shift to a new system equilibrium, which tends to favour improved oil recovery (IOR).

Although the mechanisms have not yet been verified, the solution and surface chemistry as well as rock/fluid interactions play important roles.

Reservoir minerals are sensitive to small changes in solution properties, which can have important implications for the IOR processes.

Statoil is evaluating the IOR potential of this method through in-house activities and external cooperation.

The main practical challenge for offshore application is the availability of large volumes of low-saline water and the sustainability of these supplies.

Project progress demands on securing a better grip on the weights and dimensions of the desalination facilities – for instance, by evaluating the impact of using existing platforms versus new ones.