Synthesis and performance evaluation of multi-crosslinked preformed particle gels with ultra-high strength and high-temperature and high-salinity resistance for conformance control

Preformed particle gels (PPGs) have been identified as an effective method to control conformance and mitigate excessive water production. However, the weak strength of swollen PPGs makes them susceptible to shear failure during formation migration in harsh reservoir conditions. To address this issue, a novel type of multi-crosslinked preformed particle gels (MC-PPGs) with ultra-high strength, exceptional temperature and salinity resistance has been developed. Vinyl silica nanoparticles (VSNPs) were first prepared and used as nano crosslinking agents and enhancing agents in constructing multiple cross-linking structures with macromolecules, functional monomers, and crosslinking agents. MC-PPGs have an elastic modulus up to 110,000 Pa, which is significantly higher than other existing PPGs. Additionally, when exposed to high-salinity environments (e.g., 20 % NaCl and 10 % CaCl2 + 10 % MgCl2), MC-PPGs remain for an extended period at elevated temperatures (80 degrees C for 24 months, 120 degrees C for 13 months, and over one month at 160 degrees C). Furthermore, the degradation products of MC-PPGs have minimal impact to reservoir permeability, with a core damage rate below 5 %. MC-PPGs are pH-adaptable (1 < pH < 12), which makes them a promising candidate for reservoirs with supercritical CO2 flooding. Laboratory coreflooding tests have demonstrated that MC-PPGs provide excellent plugging efficiency (>99.9 %) for fractured cores and ultra-high breakthrough pressure gradients (>14 MPa/m) at varying test temperatures (20 degrees C, 80 degrees C, and 120 degrees C). Considering these unique features, MC-PPGs are ideally suited for oilfield applications.