To address the problems of steam channeling caused by the nonhomogeneity and fluid compatibility of the reservoir in heavy oil reservoirs and the permanent damage to the reservoir easily caused by traditional plugging agents, this study adopted polyaluminum chloride (PAC) as the main agent, urea as the coagulant promoter, and thiourea as the stabilizer and prepared a high-temperature-resistant (up to 350°C) degradable inorganic aluminum gel with excellent performance. Initially, scanning electron microscope (SEM) tests were conducted on gels with and without urea. Energy-dispersive X-ray spectroscopy (EDS)-mapping analysis of gels immersed in water with different mineralization levels for 5 days was then performed. The results revealed that the addition of urea led to a tighter and more complete crosslinked structure, significantly enhancing the mechanical strength of the gel. As water mineral content increased, the gel’s microstructure became denser and smoother. Metal cations on the cross-sectional surface increased gradually and distributed uniformly, further confirming the mechanism of the synergistic salt effect of soluble strong electrolytes and urea in strengthening the gel. Finally, the plugging and degradable properties of the gel were evaluated, and the results showed that the plugging percentage of the gel could still reach 97.6% after aging at 350°C for 30 days, and the gel had excellent plugging and diversion in dual sandpack experiments where the permeability ratio was less than 44. At 250°C, the degradation percentage of the gel was more than 98% at 5 days under the nonacid degradation system and 94% at 5 days under the acid degradation system. The gel showed good degradability and effectively reduced the damage to the reservoir.

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