The Reservoir Adaptability and Oil Displacement Mechanism of Polymer Microspheres

Polymer microsphere profile control is a promising approach for the profile control of heterogeneous reservoirs. Matching between polymer microspheres and the reservoir pore throat is crucial for profile control. In this study, the range of the optimal matching factor Ra between polymer microspheres and core porosity was divided through core permeability limit experiments, and the dynamic migration laws and shut-off patterns of microspheres were studied using 9-m-long cores and microscopic models. The oil displacement effect and mechanism of microspheres were analyzed using three cores in parallel. The “injectability limit” and “in-depth migration limit” curves were divided by Ra into three zones: blockage (R(a) < 1.09 ± 0.10), near-well profile control (1.09 ± 0.10 < R(a) < 5.70 ± 0.64), and in-depth fluid diversion (R(a) > 5.70 ± 0.64). During migration in porous media, the microspheres gradually enlarged in size and thus successively shut off in four forms: multi-microsphere bridging shut-off, few-microsphere bridging shut-off, single-microsphere shut-off, and elastic shut-off. Microspheres with a rational combination of sizes versus those with a single particle size further enhanced reservoir oil recovery under certain reservoir conditions. Through “temporary shut-off–breakthrough–temporary shut-off,” the polymer microspheres were able to change the fluid flow rate and streamlines, mobilize residual oils, and enhance the oil recovery rates.