Research and Development of a CO2-Responsive TMPDA–SDS–SiO2 Gel System for Profile Control and Enhanced Oil Recovery

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Abstract
A CO2-responsive TMPDA–SDS–SiO2 gel system was developed and evaluated through formulation optimization, structural characterization, rheological testing, and core flooding experiments. The optimal formulation was identified as 7.39 wt% SDS, 1.69 wt% TMPDA, and 0.1 wt% SiO2, achieving post-CO2 viscosities above 103–104 mPa·s. Spectroscopic and microscopic analyses confirmed that CO2 protonates TMPDA amine groups to form carbamate/bicarbonate species, which drive the micellar transformation into a wormlike network, thereby enhancing gelation and viscosity. Rheological tests showed severe shear-thinning behavior, excellent shear recovery, and reversible viscosity changes under alternating CO2/N2 injection. The gel demonstrated rapid responsiveness, reaching stable viscosities within 8 min, and maintained good performance after 60 days of thermal aging at 90 °C and in high-salinity brines. Plugging tests in sand-packed tubes revealed that a permeability reduction of 98.9% could be achieved at 0.15 PV injection. In heterogeneous parallel core flooding experiments, the gel preferentially reduced high-permeability channel conductivity, improved sweep efficiency in low-permeability zones, and increased incremental oil recovery by 14.28–34.38% depending on the permeability contrast. These findings indicate that the CO2-responsive TMPDA–SDS–SiO2 gel system offers promising potential as a novel smart blocking gel system for improving the effectiveness of CO2 flooding in heterogeneous reservoirs.

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