Experimental study on the characteristics, injection damage, and oil displacement efficiency of alkali-free ternary composite flooding extracted wastewater

Suspended solids, oil droplets and residual polymers can easily lead to the blockage of the produced water reinjection reservoir. However, its influence on the permeability damage mechanism, the recovery degree after damage, and the optimization of the efficiency of alkali-free ternary oil displacement remains unclear. In this study alkali-free ternary produced water quality based on analysis of fixed permeability loss classification standard, evaluation of the impact on the core permeability mechanism, establish reinjection chart. An innovative evaluation method for the recovery mechanism after core permeability loss was proposed. There was transitional blockage, and the feasibility of preparing a polymer system with alkali-free ternary produced water for reinjection oil displacement was clarified. Experiments show that for 200 mD cores, the risk of reinjection is significant when the oil content is ≥ 60 mg/L or the suspended solids content is ≥ 60 mg/L. The permeability of the 1000 mD core recovered by 4.95 % and 6.65 % after flushing, with the most significant effect. The polymer preferred system formulated with the produced water increased the recovery rate by approximately 17 %, confirming its good reservoir compatibility and resource reuse potential.