Laboratory evaluation of an inorganic gel for conformance control in high-temperature gas reservoirs

Water invasion is a widely encountered challenge in deep fractured gas reservoirs. Gel treatment is an effective method for controlling excessive water production, yet existing gel systems cannot fully meet the requirements of long-term, large-volume injection in terms of cost, injectivity, gelation time control, and stability. In this study, a high-temperature, high-salinity-tolerant inorganic gel system based on polyaluminum chloride (PAC) was developed, and the factors influencing gelation time and gel strength were systematically evaluated. The injectivity and plugging performance of the PAC gel were also investigated using sandpack and fracture models. Results indicate that the addition of methyl lactate effectively delays gelation at high temperatures, allowing gelation time at 150 °C to be controlled from a few hours to several days. The PAC gelant can be easily injected into the rock matrix with an injection pressure gradient below 1.2 MPa/m, achieves over 99% plugging efficiency for 1.2 mm open fractures, and delivers a water breakthrough pressure gradient of 2.6 MPa/m. A 50-m long-tube dynamic gelation test further confirmed that the PAC system can gel in open fractures under dynamic conditions, with gelation time effectively regulated at high temperatures. The PAC gel exhibits excellent thermal stability at high temperatures, with only slight syneresis observed at 150 °C over a 200-d stability test. Overall, the PAC inorganic gel system developed in this study addresses the key bottlenecks of traditional gels applied in high-temperature, high-salinity fractured gas reservoirs, provides a low-cost, high-performance solution for water invasion control in gas reservoirs, and lays a solid laboratory foundation for subsequent field pilot tests and large-scale industrial application.