# Research on Nanoparticle-Enhanced Cooling Technology for Oil-Based Drilling Fluids
## 1 Introduction  
With the increasing global demand for energy and advancements in oil drilling technology, deep oil and gas exploration has emerged as a significant development trend within the drilling industry [1; 2]. High temperatures at the bottom of the well have become a distinctive feature of deep drilling operations, with downhole temperatures typically exceeding 150 \({}^{\circ}\)C and, in some ultra-deep wells, even reaching 200 \({}^{\circ}\)C or more [3]. The high-temperature environment induces substantial changes in the physicochemical properties of drilling fluids, such as dispersion and agglomeration, leading to a dramatic decline in key properties like rheology and filtration loss [4; 5; 6]. These changes may adversely affect the normal progression of operations. In addition, real drilling data indicate that high temperatures also compromise the stability and lifespan of drilling tools, further escalatingoperational risks and costs [7; 8; 9]. During the drilling process, continuous friction between the drill bit and the rock generates a significant amount of heat [10; 11]. If this heat is not dissipated in a timely and effective manner, the temperature of the drill bit will rapidly increase, which will lead to the shortening of its service life and may even cause serious downhole accidents [12]. Consequently, effective control of downhole temperatures to ensure the efficiency and longevity of the drill bit has become a critical challenge to be addressed in drilling technology [13]. Currently, the reduction of drilling fluids' inlet temperature is one of the most common and convenient cooling methods [14; 15]. This is accomplished through the use of surface cooling equipment, which includes technical approaches such as natural cooling, mixed cryogenic media cooling, and forced cooling [16; 17]. In these systems, a combination of heat exchangers and cooling media is employed, where the drilling fluid is cooled by exchanging heat with the external environment through large metal pipes [18]. Commonly used cooling media include water, air, or other suitable fluids that lower the temperature of the drilling fluids by removing their heat through heat exchange [19; 20]. The cooled drilling fluids are then re-injected into the wellbore through a circulation system to lower the bottomhole temperature. However, despite the alleviation of high-temperature issues to some extent, significant limitations persist. For one thing, surface cooling equipment is both expensive and energy-intensive. On the other hand, the greater the depth of the wellbore, the less effective these cooling methods become, making it very difficult to significantly reduce bottomhole temperatures. These limitations make it difficult for conventional surface cooling technologies to fully satisfy the demands for temperature control requirements of deep shale gas. Consequently, the development of more efficient drilling fluid cooling technology has become the focus of current research. In recent years, significant progress has been made in the research on the application of nanomaterials in drilling fluids, largely due to their unique physicochemical properties [21; 22]. Nanomaterials, characterized by high particle strength, high specific surface area, and high surface energy, have been shown to optimize the rheological properties, filtration loss, wall-building properties, and blocking capabilities of drilling fluids while also significantly enhancing their heat capacity properties [23; 24; 25; 26; 27; 28]. It has been demonstrated in the literature that the incorporation of nanoparticles into drilling fluids can improve thermal conductivity. For instance, it was shown by [PERSON] et al. that the addition of CuO and ZnO nanofluids to water-based drilling fluids resulted in an increase in thermal conductivity by up to 52.96% [29]. [PERSON] et al.