The Bottom Hole Temperature Observation and Control with Optimized Drilling Parameters in HPHT Shale Gas Drilling

Abstract High-temperature challenges in deep shale gas drilling in the Sichuan Basin are a significant issue, and high temperature failed the MWD module in the rotary steering system and caused significant change in the properties of drilling fluids. This research is to depict the circulation temperature profile in the lateral drilling and reduce the rapid temperature increase rate with optimization drilling operation parameters. The results were compared with the logging data of bottom hole temperature. Under the drilling engineering parameters mentioned above, the BHT can reach up to 145.66°C (at a lateral section length of 2230m) and may even exceed the static bottom hole temperature of 141°C. A decrease in drilling fluid density from 2.3 g/cm3 to 1.9 g/cm3, a change in drill string configuration from 139.7mm + 127mm composite drill pipe to 139.7mm drill pipe, a reduction in pump rate from 35 L/s to 28 L/s, and a decrease in drill pipe rotation speed from 120 rpm to 80 rpm—the BHCT can drop by 20-27°C. By optimizing drilling parameters, it is possible to control the bottom hole circulation temperature within the normal operational range of rotary steering system, thus extending the tool's lifespan. When other identical drilling parameters are met, medium flow rate, low rotational speed, and low-density drilling fluids are beneficial for reducing bottom hole circulation temperature during drilling. During actual drilling, after circulation cooling, if the original drilling parameters remain unchanged, the bottom hole circulation temperature will return to its original predicted temperature trend line after drilling an additional 150m. Higher specific heat capacity by increasing the specific heat capacity of the drilling fluid can significantly lower the bottom hole circulation temperature. This research explores the heat transfer theoretically in the long lateral shale gas drilling. It combines the simulation with the measured data together, the results show the transient bottom hole temperature versus time or depth are pseudo-linear, observed interruption of drilling could lower the bottom hole temperature shortly and resumed drilling brings the bottom hole temperature to normal trend abruptly.