Direct simulations of bedrock core and cuttings transport phenomena in reverse circulation drilling

Polar drilling is essential for obtaining ice and bedrock samples, providing critical insights into climate and geological history. The reverse circulation drilling method, utilizing a dual-wall drill pipe, presents a stable and efficient strategy. Nonetheless, the intricate dynamics involving drilling fluids, rock cuttings and cores necessitate sophisticated modeling to elucidate the underlying mechanism and optimize drilling efficiency. To address this, we developed a multiphase flow model that accounts for non-Newtonian fluid behavior, turbulence, particle dynamics, and fluid–structure interactions, enabling a thorough assessment of various operational parameters. The model's temporal–spatial sensitivity was evaluated, and its accuracy was confirmed by comparison with three different sets of experimental data. A detailed parametric investigation was then conducted to systematically assess the effects of various parameters, including the non-Newtonian behavior and inlet velocity of the drilling fluid, the rate of penetration, and the dimensions of the cuttings and core. The simulation results indicate that the non-Newtonian behavior of the drilling fluid has an non-negligible effect on the transport efficiency of both cuttings and core. An increase in the fluid inlet velocity leads to faster transport, albeit at the cost of higher pump pressure. The rate of penetration has a minor influence on the core transportation but largely affects the cutting transportation. More interestingly, larger cuttings demonstrate enhanced transport efficiency, attributed to a more uniform velocity distribution. Furthermore, the core diameter plays a pivotal role in transport efficiency by significantly altering the fluid dynamics, whereas the core length has a negligible effect. These results may have direct applications for optimizing polar drilling operations, potentially leading to enhanced drilling efficiency, reduced drilling costs, and informing future drilling technology advancements.