4.: In-Situ Factors Influencing Recovery Efficiency Available to Purchase

While the inherent properties of the reservoir cannot be changed (although compaction can worsen them), they have a significant impact on recovery. It is important to understand how they affect recovery because this strongly influences whether a waterflood project can be economically justified.

It is important to understand the proportion of the in-place oil that is mobile because this represents the maximum amount of oil that could be recovered if all the reservoir could be contacted by injection water and if a large-enough pore volume of water could be injected to displace all the oil to producing wells. Therefore, the key saturation parameters in this respect are the residual oil saturation (the saturation that will never be moved under the waterflood) and the initial oil saturation. The residual oil saturation is often found to be up to 30%, or even greater. In many reservoirs, the initial saturation is very high, but some waterfloods are deployed in low-permeability reservoirs where all the oil is found within the transition zone. In such cases, the initial oil saturation might be only 40 to 50%. It can be expected that as the proportion of the mobile in-place oil reduces, it will become more difficult to justify a waterflood development.