Simulation Study for Improving Seawater Polymer Flood Performance in Stratified High Temperature Reservoirs

Polymer flood has achieved technical and commercial success, especially for its large-scale application in the Daqing oilfield in China. However, previous field tests indicated polymer flood was not economically successful for high temperature reservoirs when injected with high salinity, high hardness water. Novel thermal and salinity-resistance polymers have been developed, and their properties are tested via comprehensive lab experiments, which encourage further development of polymer flooding in high-temperature and high-salinity reservoirs.

To achieve a promising recovery effect, numerical simulation, including all significant physicochemical phenomena, must be carried out before field implementation to realize the reservoir response to polymer. An optimized recovery design, which minimizes costs and increases the process efficiency, should be proposed for reservoir models representing real harsh conditions including severe heterogeneity.

In this work, the effects of shear thinning, thermal thinning, degradation of polymer/seawater solution to oil recovery performance in stratified reservoir are studied in various temperature conditions. Also supporting measures for polymer flood, such as mechanical water shutoff and in-depth profile control, are studied to evaluate their ability in harsh reservoir conditions. Thermal thinning and shear thinning properties of polymer/seawater solution were measured by a rheometer, and compared with published data. Degradation and adsorption properties of the polymers, as well as the gelation reaction and resistance properties of the gel were summarized from literature review generating reasonable parameters for simulation.

Simulation results indicate that thermal thinning of polymers has a marginal effect on the final oil recovery. Another property related to temperature, polymer thermal degradation, is obviously influenced by temperature, leading to decrease of the final oil recovery to different extent. Both water shutoff and in-depth profile control can improve waterflood. However deep profile control will be more efficient if polymer flood is applied, and the combination of in-depth profile control and polymer flood carried out with low injection temperature achieve the best recovery performance.