CO2-responsive preformed particle gels with high strength for CO2 conformance control in heterogeneous reservoirs

Preformed particle gels (PPGs) are extensively used to address the challenges of early CO2 breakthrough and excessive CO2 production in heterogeneous reservoirs during CO2 flooding. However, the acidic environment induced by CO2 will seriously affect the swelling behavior, stability and plugging strength of PPGs, and even lead to dehydration and degradation of PPGs. Herein, a type of CO2-responsive preformed particle gels (CR-PPGs) with high strength was designed, strengthened by the nano-crosslinking agent vinyl silica nanoparticles (VSNPs). Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) respectively confirmed the expected functional group structures and morphological characteristics of VSNPs and CR-PPGs. CR-PPGs exhibited a swelling ratio of approximately 3200 % in acidic CO2 environments, compared to 750 % in water-only conditions. The CO2 response mechanism of CR-PPGs was elucidated by conductivity test. Rheological tests indicated that, CR-PPGs maintained considerable strength in acidic CO2 environments, with an elastic modulus of 41,823 Pa. Gel stability tests showed that CR-PPGs could maintain satisfactory swelling ratio and strength even under high temperature (100 degrees C) and brine (10,000 ppm NaCl) acid environments. Lowtemperature Differential Scanning Calorimetry confirmed that the superior stability and strength of CR-PPGs stemmed from an increase in the proportion of bound water in the system. Finally, the plugging experiments demonstrated that CR-PPGs provided a high breakthrough pressure (1.91 MPa) and plugging efficiency (99.92 %) for the fractured core. Oil displacement experiments further underscored the effective Improved Oil Recovery (IOR) capability of CR-PPGs, with a crude oil recovery rate of 52.74 % from fractured cores treated with CRPPGs. This work introduces an appealing alternative for CO2 conformance control in heterogeneous reservoirs during CO2 flooding.