Analysis of Critical Thermodynamic Parameters in Oil-Based Drilling Fluids: Implications for Wellbore Temperature Control

In the quest to exploit unconventional oil and gas resources within China's borders, rotary steering tools have been increasingly utilized to enhance the drilling speed and ensure the precision of the drilling trajectory. Nevertheless, the prevalent high temperatures within the well have been identified as a primary cause of failure in these rotary steering tools, thereby impeding the drilling process significantly. Consequently, the real-time prediction and meticulous control of the wellbore temperature have emerged as pivotal elements in the enhancement of drilling efficiency. A myriad of factors contribute to the wellbore temperature, among which the thermodynamic parameters of the drilling fluid play a vital role. In this context, a comprehensive analysis has been conducted on various oil-based drilling fluids, with a focus on controlling their fundamental properties, and the thermodynamic parameters have been meticulously measured. Subsequently, the sensitivity of these parameters to various factors has been scrutinized based on the experimental outcomes. The findings delineate that within a drilling fluid oil-water ratio range of 0.75 to 0.9, the impact of the sensitive factors on thermodynamic performance is ranked as follows: solid content > oil-water ratio > plastic viscosity > apparent viscosity. It is noted that a one percentage unit augmentation in solid content results in a 0.01284 kJ/(kgK) decrement in specific heat capacity, while the thermal conductivity experiences a 0.00528 W/(mK) increment. Conversely, when the oil-water ratio ranges from 0.9 to 1, the impact hierarchy of sensitive factors transforms to: oil-water ratio > solid content > plastic viscosity > apparent viscosity, with a one percentage unit increase in oil-water ratio leading to a 0.04121 kJ/(kgK) decrease in specific heat capacity and a 0.02669 W/(mK) reduction in thermal conductivity. The findings underscore that variations in the oil-water ratio yield disparate impacts on the thermodynamic performance of oil-based drilling fluids.