Today diminishing oil reserves force us to seek ways of increasing the yield of existing resources.
Some years go oil was mainly recovered by means of the natural pressure of the oil bearing formation. When natural pressure decreased, the source was regarded as exhausted, although considerably more than half of the total oil quantity remained in the fine pores of the oil bearing rock strata. Meanwhile techniques have been developed to exploit a greater part of these neglected reserves.
The principle of all these techniques is that the pressure in the oil reservoir is maintained in order to force the remaining oil towards the well-bore. One of the methods to achieve this is the injection of water under high pressure into the oil-bearing stratum. Depending on the location of the recovery point fresh water or sea-water is used.
A prerequisite condition for successful injection is a water treatment scheme which must be able to produce water of suitable quality. This means that bacteria concentration, oxygen- and suspended solids content must be controlled to prevent plugging of the formation and corrosion in production facilities. Treatment of water for injection involves a combination of physical and chemical treatment. The main process stages are:
Micro-screening Gross solids removal
Pre-chlorination to kill algae and higher organisms
Deep bed filtration for suspended solids removal
Disinfection killing of Sulphate Reducing Bacteria (SRB) and othermicro-organisms