Enhanced Salt-Resistant and Shear-Resistant Gel Particles with Core–Shell Structure for In-Depth Permeability Control

Preferential flow channels significantly diminish the sweep efficiency of displacement fluids. Polymer gel particles are commonly employed as in-depth profile control agents to block these high-permeability pathways, thereby improving sweep efficiency and enhancing oil recovery. However, conventional gel particles expand relatively quickly during the initial stage of injection. This characteristic is considered unfavorable for the in-depth migration of gel particles into the formation. Additionally, formation shear forces acting on the swelled particles can degrade the gel structure, thereby hindering effective plugging. Moreover, the electric interaction of gel particle functional groups is compressed by metal salt ions in formation water, reducing their final swelling factor. To address these challenges, this study developed a novel core–shell structured gel particle that combines a delayed swelling mechanism with a sodium alginate-based multicross-linked network. This integrated design not only improves in-depth migration but also significantly enhances shear and salt resistance. The surface shell layer limited the initial swelling rate of the gel particles─the swelling onset was delayed from 3 days to 12 days, and the time to reach maximum swelling was extended to 28 days with increasing shell thickness─thereby facilitating in-depth migration. The core exhibited a volume swelling factor exceeding 20 in high-salinity formation water (18 × 104 mg/L) at 70 °C after the addition of sodium alginate. Atomic force microscopy (AFM) was employed to measure the Young’s modulus of different gel particles. Results indicated that sodium alginate-enhanced gel particles exhibited a higher Young’s modulus than conventional gel particles, with minimal variation after shear, confirming their superior resistance to shear degradation. Core flooding experiments further demonstrated the particles’ migration and permeability control capabilities. Before shell degradation, the permeability reduction rate was below 20%, whereas after degradation, it exceeded 90%. These core–shell gel particles show great potential for enhancing oil recovery by enabling efficient in-depth permeability control.