Quantifying the Impact of Drilling Fluid Rheology on Downhole Turbine Performance

Summary Turbine motors are widely used in drilling in deep and complex formations due to their compact structure, stable output, and adaptation to complex formations. However, its performance changes under high-viscosity and high-density drilling fluid conditions still lack in-depth research. Based on the 3D computational fluid dynamics (CFD) method, we establish a numerical model of the turbine motor and conduct simulation analysis under different drilling fluid viscosity, density, and rotational speed conditions. The results show that as the speed increases, the overall output torque of the turbine motor shows a downward trend; high-viscosity drilling fluid enhances viscous dissipation and weakens the pressure gradient of the blade channel, resulting in an intensified torque attenuation in the high-speed zone; hydraulic efficiency is single-peak distributed, and the peak value shifts to the low-speed zone with the increase of viscosity; the increase in the density of the drilling fluid can increase the torque in the low-speed zone, but it is manifested as nonlinear attenuation in the high-speed zone. Under the viscosity of 30 mPa·s, the torque attenuation rate of the turbine motor in the range of 200~1,000 rev/min is about 48.6%. The research results provide theoretical support for the structural optimization and working conditions of turbine motors under high rheological drilling fluid conditions.