Heat-Resistant Hydrogel for Temporary Plugging in High-Temperature and High-Pressure Fractured Reservoirs

Polymer hydrogels have shown considerable potential as materials for lost circulation control. Nevertheless, implementation in high-temperature and high-pressure (HTHP) formations has been challenging due to their poor thermal stability and strength. To overcome this limitation, a heat-resistant hydrogel (HT-Gel) composed of a terpolymer (PAAA) and chromium (III) acetate was developed in this study. PAAA was produced from acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), and N-acryloyl morpholine (ACMO). The sulfonated groups of AMPS and the ring structure of ACMO endowed HT-Gel with favorable temperature resistance and pressure-bearing performance. HT-Gel gelled at 150 °C could effectively plug fractures of 0.1–5.0 mm, and the breakthrough pressure exceeded 4.0 MPa. After aging at 150 °C for 7 days, the elastic modulus only decreased by 14.29%. The gel strength and gelation time of HT-Gel could be adjusted by terpolymer concentration, cross-linker concentration, temperature, and salinity, which was beneficial for HT-Gel to enter and plug fractures smoothly. Additionally, HT-Gel exhibited exceptional resistance to shear and contamination. The viscosity of the gelants decreased by less than 16 mPa·s at high shear rates, and the elastic modulus of HT-Gel changed by less than 13% when combined with various drilling materials. Extensive laboratory experiments indicated that HT-Gel had outstanding thermal stability and pressure-bearing performance, making it a promising candidate for lost circulation control in high-temperature and high-pressure formations.