Abstract

As part of the screening process for chemical EOR, several polymers have been screened as co-injectants in a surfactant-aided water flood scheme. Due to their higher viscosity, polymers improve sweep efficiency and reduce the permeability of rock matrix, therefore help to improve oil recovery. Aimed at a representative carbonate reservoir in the Middle East, a polymer screening study has been conducted with respect to polymer solubility and viscosity retention in high salinity brines, equivalent to our reservoir parameters. The polymers have to pass through a stringent screening process to meet the harsh conditions encountered in the reservoir: high temperature, high salinities and carbonate nature. Salinity effect was studied in a range of brines that included shallow formation water, produced water, and connate water. Among the polymers studied, six were found compatible and have been short-listed. Based on rheological measurements and flow curves, the concentrations of polymers have been determined to achieve the target viscosity under reservoir conditions. Long-term stability and adsorption tests were conducted to ensure the efficiency of the polymer exposed to reservoir conditions. Oil displacement tests with a selected polymer showed an increased oil recovery factor of 11% by polymer flooding and 18% by surfactant-polymer flooding. This study demonstrates the potential application of polymers under extremely harsh reservoir conditions and their promise to be good additives for chemical flooding.

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