Hydrocarbon reservoirs are comprised of natural rock formations which are permeated with a mixture of hydrocarbons and water. Due to their underground nature and temperature, reservoirs are usually under considerable pressure.

As fluid is extracted from a reservoir, the pressure underground often slowly reduces, having the consequence of reducing the flow to the producing well area. In addition, and specific to each reservoir, the rate at which the fluid migrates to the well may also reduce.

Water injection is the action of injecting water into a reservoir to maintain pressure and encourage hydrocarbons to the producing well.

In many situations, the most convenient fluid for injection is the produced water from the well. Injection is also a convenient method of produced water disposal. In an offshore environment, seawater is often the preferred source of injection water.

The quality of the water for injection, from whatever source, will be required to be of a standard that will not cause problems such as plugging and/or scaling of the injection equipment. This is an important issue, especially offshore, where drilling a new well is extremely expensive.

In addition, because a reservoir is effectively sterile, injecting water containing oxygen and bacteria can cause'souring' of the reservoir. A'sour' reservoir is one where there is the presence of hydrogen sulphide (H₂S) in the hydrocarbons.

Souring reduces the value of the produced hydrocarbons and requires expensive production equipment and materials to cope with the aggressive nature of the produced fluids.

Typical contaminants that need to be removed from injection water are:

• Hydrocarbons
• Solids
• Scaling compounds such as sulphate
• Sulphate reducing bacteria (SRB)

The VWS Westgarth turnkey package

VWS Westgarth engineers, procures and project manages the complete seawater system including:

• Coarse filtration
• Chlorine generation
• Process pumps
• Pre-treatment systems (membrane and traditional media)
• Deaeration packages (vacuum, gas strip and nitrogen blanketing)
• Chemical storage, dosing and injection (inc. nitrogen generation and blanketing)
• System Healthcare