Process Evaluation of Staged Self-Diverting Acidizing and Cationic Polymer Sand Stabilization in Unconsolidated Sandstone

Unconsolidated sandstone gas reservoirs often suffer from near-wellbore plugging, permeability contrast, and sand production after acid stimulation. This study evaluates a staged chemical process that couples limited cationic polymer sand stabilization with reaction-induced self-diverting acidizing, instead of direct premixing or simultaneous co-injection of acid and sand control fluids. Residual acid viscosity tests, core flooding experiments, dynamic sand production tests, scanning electron microscopy/energy-dispersive spectroscopy, and low-field nuclear magnetic resonance measurements were used to investigate viscosity building, diversion, permeability retention, and pore structure evolution. The 5 wt% EAB self-diverting acid exhibited the strongest reaction-induced viscosity-building behavior, reaching a residual acid viscosity of 134 mPa·s. The selected HCl + HF acid system produced a clear temporary-plugging response during core flooding, and the optimized 0.2 wt% cationic polyacrylamide stabilizer increased the critical sand production flow rate to 1.8 mL·min−1 while maintaining acceptable permeability recovery. Microscopic evidence indicates improved pore connectivity without large-scale skeletal collapse. A comprehensive synergy index showed that medium-permeability cores (300–500 mD) achieved the best balance among acid diversion, sand stabilization, and permeability retention. The proposed process provides a laboratory-scale foundation for coupled stimulation and sand control design.