The effect of stepwise increasing of water injection rates on enhanced oil recovery after preformed particle gel treatment

Abstract

In the past ten years, preformed particle gel (PPG) has been widely applied in oil fields as an effective conformance control agent for reducing water cut in oilfield. However, there is little research on the injection rate of subsequent water flooding after PPG injection on recovery. In this paper, the swelling, scanning electron microscope, rheological and viscoelasticity tests were performed to investigate into the characteristics of PPG and explore the mechanism of enhancing oil recovery by stepwise increasing subsequent water injection rate. In the homogeneous and heterogeneous cores, the plugging effect of PPG was judged according to different pressures, and the subsequent water injection rate is 0.5–0.75, 1, 1.25, and 1.5 mL/min after the water cut of each injection rate reaches 100% stage. The distribution of residual oil in different displacement stages was studied by nuclear magnetic resonance (NMR). The experimental results show that the PPG has high viscoelasticity and can be fully swelled within 42 h in 70 °C. The subsequent increase in flow rate can promote the previous phase of the PPG particles remaining in the pore throat to move, and then have a better effect to drive the oil droplets attached to the rock surface. Stepwise increasing the subsequent water flooding injection rate in the homogeneous formation can improve the oil washing efficiency and reduce the residual oil saturation. In the heterogeneous formation, the recovery factor is improved by stepwise increasing the sweep coefficient.