Temporary Plugging Agent System for Thermally Induced Phase Change Fracturing in Shale Gas Reservoirs

In this study, a temporary plugging agent composed of two different types of guest molecules for thermally induced phase change fracturing was constructed for different shale formation temperature ranges. This agent, which was constructed through the screening of the host, guest, and solvent, is in a uniform solution state at room temperature. The solution became cloudy with increasing temperature, and a stable gel was formed when the respective gelling temperature was reached. However, the gel turned into a solution again upon further heating. The temporary plugging agent system developed in this paper could realize the phase transition of "solution–gel–solution" only by changing the temperature. Characterization and evaluation of the basic performance of the temporary plugging agent show that the components of this agent form a long fibrous gel through supramolecular interactions, the constructed thermally induced phase change fracturing system has good thermal stability, and the filter loss is small. These findings indicate that the temporary plugging agent system for thermally induced phase change fracturing could form an excellent temporary plugging agent suitable for formations at 90–120 °C through the unique temperature responsiveness of supramolecular gels. In addition, the gel formation process was described by the host–guest structure combined with SEM characterization. The results of physical simulation experiments reveal that the temporary plugging agent has low viscosity, good fluidity, and good injectability at room temperature. After being injected into the formation, the temporary plugging agent could form a gel with sufficient strength at the target formation temperature to plug the fractures. After the formation was further heated, the formed gel gradually broke and caused slight damage to the core. The whole temporary plugging process does not require the addition of an additional crosslinking agent and a gel breaker. This new type of temporary plugging agent has a potential application value in shale gas refracturing.