Core- and pore-scale investigation on the migration and plugging of polymer microspheres in a heterogeneous porous media

Abstract Polymer microspheres (PMs) can be a very promising, cost-effective in-depth fluid diversion strategy in the development of heterogeneous reservoir. The key to success for the PMs application is to fully understand the PMs-migration and -plugging mechanisms through the confined space. The plugging rate is widely used to evaluate the performance of PMs-plugging. But it always presents a large value using the conventional measurement method even PMs cannot transport through the porous media. The impact factors of PMs-migration and-plugging in previous work based the conventional plugging rate may not be reliable in the reservoir. In this study, three kinds of polymer microspheres (PMs-1, PMs-2, PMs-3) with different particle sizes were synthesized, and their matching relationship with cores and impact factors of plugging were investigated using a new proposed measurement method. Flowing experiment at core- and pore-scale were performed to reveal PMs-migration and -plugging mechanisms. The synthesized PMs had a shape of the regular spheres with initial sizes of 9.8 μm, 6.2 μm and 3.1 μm respectively. They can swell from 3.44 to 2.68 times. The optimal matching factors between PMs sizes and pore sizes were obtained by the redefined plugging strength, which were 1.0–1.2 for PMs-2 and 0.5–0.8 for PMs-3. In the range of the optimal matching factors, PMs-plugging and -migration is affected by PMs sizes rather than the PMs concentration and injection rate. Two plugging patterns of direct-plugging by one single PM and bridge-plugging by multi-PMs were observed in the micromodel. Large PMs was tendency to the direct-plugging, which has much stronger plugging efficiency than the bridge-plugging of multiple small PMs.