Daqing Oilfield has carried out a high viscelasticity polymer flooding pilot in LMDN4-4 Block, demonstrating that the high viscoelasticity polymer flood has bigger capability to further increase oil recovery over moderate viscoelasticity polymer flood. The bulk viscosity of produced polymer solution taken from a monitoring well is around 140 mPa.s, using the high viscosity data as input parameters to conduct history matching by commercial simulator indicated that injection pressure from simulation is much higher than that from observation data, resulting from the higher bulk viscosity together with having no take polymer elasticity process mechanism into account. Therefore, how to successfully conduct simulation for high viscoelasticity polymer flood is a big challenge.
We have conducted a series of lab and reservoir engineering studies to further realize and characterize the polymer elasticity process mechanism so as to achieve a good history matching. Polymer flooding capillary desaturation curve at different polymer elasticity level is established, relative permeability curve for high viscoelasticity polymer flooding is obtained, and the flowing viscosity in porous media for polymer solution with high viscoelasticity is estimated based on the polymer flooding performance data. All these research results provide very accurate input parameters for the simulation model, running by an in-house simulator that has incorporated polymer elasticity process mechanism model.
Based on these newly methods above, the production performance for the high viscoelasticity polymer flood pilot has been matched very well, showing that: (1) High viscoelasticity polymer flood simulation should take the polymer elasticity process mechanisms of reducing residual oil saturation and increasing oleic phase relative permeability into account, (2) It is the flowing viscosity of polymer solution that acts on the flow process in polymer flooding rather than the bulk viscosity, and the flowing viscosity is dramatic lower than the bulk viscosity for high viscoelasticity polymer solution.