Analysis of the Wellbore Temperature Field and Influencing Factors During Shale Gas Fracturing Injection

During shale gas fracturing operations, large volumes of low-temperature fracturing fluid carrying proppant are injected into the high-temperature wellbore, resulting in intense transient heat exchange between the fracturing fluid, the wellbore structure and the surrounding formation. To predict the wellbore temperature field during fracturing, this paper treats proppant-laden slurry as a homogeneous fluid and considers the effects of temperature and proppant concentration on the fluid’s equivalent thermal properties. Based on the energy conservation equation, a transient wellbore heat-transfer model was developed by coupling axial convective heat transfer within the casing, radial heat transfer through the multi-layer wellbore media, and transient thermal conduction in the formation. The radial heat-transfer process was solved using the equivalent thermal resistance method, and the model was validated through finite element simulation. The computational results indicate that under base operating conditions—with an injection temperature of 20 °C, an injection flow rate of 12 m3/min, and an injection duration of 90 min—the bottomhole temperature rapidly drops to the 20–25 °C range, subsequently entering a low-temperature quasi-steady-state phase; following pump shutdown, the bottomhole temperature gradually recovers, reaching approximately 40 °C 120 min after shutdown. The computational results of this theoretical model regarding the variation pattern of the bottomhole temperature, the vertical temperature distribution, and the radial temperature response show good agreement with the finite element simulation results. Parameter analysis indicates that increasing the injection rate from 8 to 16 m3/min shortens the cooling time to below 25 °C from approximately 13–14 min to 8–9 min, while the stable bottomhole temperature only decreases slightly from 23.0 to 21.3 °C. Increasing proppant concentration from 6% to 15% has a weak influence on temperature evolution. In contrast, injection temperature is the dominant factor: when the injection temperature is 5, 15, and 30 °C, the stable bottomhole temperatures are approximately 8, 17, and 31 °C, respectively. The sensitivity analysis indicates that injection temperature is the dominant factor affecting the wellbore temperature field, followed by injection rate, while proppant concentration is only weakly sensitive. The results provide theoretical support for wellbore temperature prediction and fracturing parameter optimization.