Research and application of low-flow partial injection technology for polymer flooding of class III oil layers

Abstract

The geological reserves of the third type of oil layers in a certain oilfield account for as high as 52.76%. Whether they can be effectively utilized is of vital importance to the sustainable development of the oilfield. Class III oil reservoirs feature prominent inter-layer heterogeneity, thin individual pay zones, narrow inter-bed intervals, and low injection volume per single layer. The conventional separate injection technologies deliver limited throttling pressure drop at low injection rates (5-20 m3/d), failing to achieve precise flow control for single layers with low injection volume. A symmetrical structure double offset hole injector and a new type of throttling element were developed. By means of finite element numerical simulation, the spatial flow channel layout was reconstructed and key mechanical parameters were optimized, so as to widen the flow regulation range under low-injection operating conditions. The experimental results show that at an injection rate of 5 m3/d, the throttling pressure drop rises from 0.2 MPa to 0.8 MPa compared with the original scheme. The adjustable flow range for a single layer is extended from 20-70 m3/d to 5-70 m3/d, enabling accurate flow regulation under low-injection working conditions. Field application results demonstrate that the utilization of the effective thickness of the reservoir has been effectively improved, and the utilization ratio has significantly increased by 9.7%. Efficient utilization of medium and low permeability formations has been realized.