Injection-Rate-Controlled Dynamic Gelation and Flow-Resistance Evolution of Hydrogels for CO₂ Conformance Control in Parallel Microtubes

Static gelation tests are insufficient for evaluating hydrogel placement and resistance development during rate-controlled injection for CO₂ conformance control. In this study, a parallel-microtube dynamic gelation method was developed to simultaneously monitor segmented pressure drop, dynamic gelation time, residual resistance factor, and apparent viscosity under restricted-flow conditions. Chromium-crosslinked hydrogel (Cr-gel) and phenolic resin hydrogel (PFR-gel) were compared to clarify how injection rate regulates gelation timing, structural retention, and flow resistance. Cr-gel showed an accelerated-gelation but weakened-structure response: as the injection rate increased from 0.050 to 0.150 mL/min, the initial dynamic gelation time decreased from 4.00 to 1.33 h, whereas the stable pressure drop, residual resistance factor, and apparent viscosity decreased markedly. In contrast, PFR-gel showed delayed gelation and better structural retention, with a longer stabilization time but a nearly stable pressure-drop plateau. Calibrated simulations further linked these experimental trends to the spatial coupling among pressure gradient, shear rate, structure conversion, effective viscosity, and local resistance enhancement. The results indicate that injection-rate optimization should balance gelation-position matching and post-gelation resistance retention, providing a dynamic screening basis for hydrogel conformance-control design under the tested microtube conditions.