Enhance oil recovery in low permeability reservoirs: Optimization and evaluation of ultra-high molecular weight HPAM/phenolic weak gel system

With the development and application of water flooding technology in low permeability reservoirs, at the later stage, the excessive water cut and the low oil recovery is inevitable. Therefore, it is of great importance to apply chemical flooding technology in the oilfield exploitation. In order to improve the oil recovery, the mechanism of ultra-high molecular weight HPAM/water-soluble phenolic weak gel formulation and the optimization of indepth profile control parameters for low permeability reservoirs are studied in this work. By condensation reaction between -CONH2 in HPAM and -CH2OH in water-soluble phenolic aldehydes, it is found that the weak gel can form a stable network structure under the microscope. The cross-linking kinetics of ultra-high molecular weight HPAM/water-soluble phenolic weak gel system is studied by the viscosity method, and the optimum concentration of HPAM and cross-linking agent are determined as follows: strong thermal stability and shear resistance can be got while concentration of HPAM is above 600 mg/L and the concentration of cross-linking agent is above 1400 mg/L. Based on the core flooding experiment, the displacement pressure and the oil recovery measured are compared at different molecular weights of HPAM, and the optimum molecular weight of HPAM for flooding applied in low permeability reservoirs is screened out as 1100*million. Microscopic displacement experiment indicates that large oil droplets were formed by the remaining oil in the small pores during the process of displacement, and were displaced out in the form of oil flow. The experimental findings were applied in Block Pu125, which is a low permeability reservoir in Daqing. The result shows that the production of a single well increased by 1400t, the comprehensive water cut in the whole area decreased by 7.16%, and the oil recovery increased by 3.58% after the weak gel flooding. Therefore, it is proved that the ultra-high molecular weight HPAM/water-soluble phenolic weak gel flooding system for profile control can effectively improve the oil recovery efficiency of low permeability oilfield.