Research and Application of Drilling Fluid Cooling System for Dry Hot Rock

The drilling fluid cooling system is a key technology for reducing wellbore temperatures, improving the working environment of downhole equipment, and ensuring safe and efficient drilling in high-temperature wells. Based on the existing drilling fluid cooling system, this article designs and develops a closed drilling fluid cooling system according to the working environment and cooling requirements of the GH-02 dry hot rock trial production well in the Gonghe Basin, Qinghai Province. The system mainly includes a cascade cooling module, a convective heat exchange module, and a monitoring and control module. Based on the formation conditions and drilling design of the GH-02 well, a transient temperature prediction model for wellbore circulation is established to provide a basis for the design of the cooling system. Under the conditions of a drilling fluid displacement of 30 L/s and a bottomhole circulation temperature not exceeding 105 °C, the maximum allowable inlet temperature of the drilling fluid is 55.6 °C, and the outlet temperature of the drilling fluid is 69.2 °C. The heat exchange of the drilling fluid circulation is not less than 1785 kW. Considering the heat transfer efficiency and reserve coefficient, the heat transfer area of the spiral plate heat exchanger calculated using the average temperature difference method is not less than 75 m 2 . By applying this drilling fluid cooling system in the 3055 m~4013 m section of well GH-02, the inlet temperature is controlled at 45 °C~55 °C, and the measured bottomhole circulation temperature remains below 105 °C. After adopting the drilling fluid cooling system, the performance of the drilling fluid is stable during the drilling process, downhole tools such as the drill bits, screws, and MWD work normally, and the failure rate of the mud pump and logging instruments is significantly reduced. The drilling fluid cooling system effectively maintains the safe and efficient operation of the drilling system, which has been promoted and applied in shale oil wells in Dagang Oilfield.