Chemical eor techniques
Polymer flooding is the injection of water with polymer additives into an oil reservoir in order to improve the sweep of the reservoir by the displacement process. High viscosity improves the mobility ratio of the injected fluid and hydrocarbons in the formation.
The technology has a positive effect on sweep efficiency, allows to increase the productivity of wells, reduce water cut and increase the oil recovery factor.
The most common polymer flooding agents are acrylamide-based high molecular weight polymers (partially hydrolyzed polyacrylamides), used primarily in powder and emulsion form.
Surfactant polymer flooding includes injection of polymer and surfactant into the formation. While the main purpose of polymer injection is to change the mobility ratio of the displacing agent (water and oil) by increasing the viscosity of the former, surfactant is added to mobilize residual oil by reducing interfacial tension at the oil-water interface and/or due to changes in rock wettability.
At alkali-surfactant-polymer flooding the main function of the alkali is to prevent the retention of expensive surfactant on the rock and thereby reduce its loss. The alkali reacts with natural organic acids present in the oil, forming additional surfactants in the reservoir at the oil-water interface, which in turn also reduce interfacial tension.