Polymer flooding

Polymer flooding works by changing the mobility ratio between the oil in the reservoir and the water that is injected. Only a small amount of polymer (c. 0.25%) is added to the injection water to increase the water viscosity (from about 1cP to 25cP). The viscosified water can then sweep the oil with a more stable flood front towards producing wells, accelerating production and increasing recovery.

The mobility ratio depends upon the ratio between the fluid viscosities and the ratio of oil and water relative permeabilities at the fluid interface. If the mobility ratio is high, because the oil is less mobile, the water fingers through the oil, bypassing much of the oil in place, and potentially leaving the bypassed oil unrecovered. If the oil and the water are equally mobile the water can sweep the oil from the reservoir in a very efficient piston-like fashion

When compared with a waterflood, for every barrel of water injected a polymer flood will produce significantly more oil, so fluid handling requirements are substantially reduced and the energy required to recover the oil is significantly less.

As a result, the practical recovery factor for a polymer flood will be much higher than a water flood, and the key to an economically successful polymer flood is to have a close enough well spacing that the time from injecting polymer to producing the incremental oil is short. When well spacings are too wide the cost of the polymer is not recouped quickly enough and the economic advantage is lost.

In our process design all produced water will be reinjected, thereby avoiding the possibility of releasing any polymer into the sea, but the polymer we add to our injection water is commonly used as a flocculant in water and wastewater treatment, and as a soil conditioner, so is not considered terribly damaging to the environment.