High-strength and controllable thermal degrading hydrogel for temporary plugging in ultra-high-temperature reservoirs

Abstract

The efficacy of temporary plugging and diverting fracturing techniques critically depends on the performance of temporary plugging agents. However, conventional gel-based temporary plugging agents are typically limited to application temperatures below 160°C. This study developed a gel-based temporary plugging agent that exhibits high strength and tunable degradation performance at 180°C. The agent is formed in situ through free-radical polymerization of acrylamide and 2-acrylamide-2-methylpropane sulfonic acid(AMPS), using triallylamine as the crosslinker. The effects of monomer concentration, crosslinker content, AMPS ratio, and salinity on gel strength and degradation time were systematically investigated. Additionally, the gel's plugging performance was assessed. Its degradation mechanism was elucidated through SEM, FT-IR, and XPS analyses. Results show that when the gelling solution is prepared using deionized water, the gel achieves high strength(G’﹥400 Pa), with degradation time adjustable between 20–140 h by adjusting formulation parameters. In high-salinity environments (NaCl ≤100,000 mg·L⁻¹ and CaCl₂ <20,000 mg·L⁻¹), the system maintained excellent gel strength and degradation performance. In fractures with a width of 1 mm, the gel achieved a pressure gradient of 51.6 MPa/m. The degradation solution exhibits low viscosity and negligible residue. Passage of the degradation fluid through the fractures resulted in a differential pressure of only 0.01 MPa. The degradation occurs in two stages: rapid hydrolysis of amide groups followed by chain scission, leading to molecular fragmentation and conversion into a low-viscosity liquid. This study extends the applicable temperature limit of gel-based temporary plugging agents, providing a useful reference for advancing temporary plugging and diverting fracturing technologies in ultra-high-temperature reservoirs.