Optimization of polymer flooding design in conglomerate reservoirs

The polymer flooding can be a very promising, cost-effective enhanced oil recovery (EOR) strategy in the development of conglomerate oil reservoirs, especially when the reservoirs reach very high water-cut in production. The key to success for a polymer flooding is to use the full potential of mobility control under the premise of good compatibility between polymer and reservoirs. Polymer is easy to be adsorbed and also potentially clogs the formations especially when the pressure gradient is small in the reservoir. Meanwhile, polymer efficient viscosity has a huge impact on polymer mobility control. The method of polymer flooding optimization design is described in a formation of interest called Karamay conglomerate reservoir (Xinjiang Province, China). We've compared the pore structure difference between conglomerates and sandstones, measured hydrodynamic characteristic sizes of polymer molecular and ensured the maximum polymer molecular weight and concentration for corresponding permeability. Then different pore structure cores were used to investigate the rheology of polymer transport in conglomerates and sandstones. A model were built by using the water-oil relative permeability curves and polymer rheology experimental data, which was utilized to calculate the minimum viscosity of the polymer solution required for a high-performance mobility control in polymer flooding. In the study we have found that 1) conglomerate with the shallower depth and tortuous pore structure has about three times shear rates than single pore structure sandstone in the same flow velocity; 2) the viscosity range of a high-performance polymer for conglomerate reservoirs is determined to be 25.1 cP−29.4 cP at shear rate of 7.34 s−1 for Upper Karamay formation, and 8.6 cP−12.8 cP s at shear rate of 7.34 s−1 for Lower Karamay formation. It implies that polymer flooding should be using by injection of polymer solutions in each layer.