Non-Newtonian Flow: Well Drilling, Mud and Sand Separator

1. Description

This study simulates well drilling and cuttings (sludge) transport using ANSYS Fluent. The wellbore is modeled as a cylindrical annulus containing a rotating inner cylinder (100 rpm). A non-Newtonian drilling fluid (CMC) flows through the cavity, entraining and lifting solid mud particles. An Eulerian multiphase framework is adopted: the primary phase is the CMC base fluid and the secondary phase comprises drilling solids.

The Eulerian approach is suitable for high dispersed-phase loadings (>10%), slurry and liquid–solid transport, and deposition studies. Here, the base fluid volume fraction is 0.87 and the solids (drilling particles) volume fraction is 0.13. Viscosity behavior is non-Newtonian for the CMC phase (contrast to Newtonian fluids, whose shear stress varies linearly with strain rate).

2. Geometry & Mesh

The 3D domain consists of two eccentric coaxial cylinders, each 10 m long. The inner cylinder diameter is 0.128 m and the outer cylinder diameter is 0.444 m. Meshing is performed in ANSYS Meshing with an unstructured grid totaling 179,820 elements.

3. Simulation Setup

A pressure-based, transient (unsteady) solver is used. Gravity is included with a magnitude of −9.81 m/s². Because the well axis is inclined by 30° relative to gravity, the gravitational acceleration resolves to 4.9 m/s² in the xxx direction and 8.5 m/s² in the zzz direction. The inner cylinder’s rotation is prescribed at 100 rpm to promote solids lifting and separation within the annulus.

4. Results & Discussion

Post-processing yields 2D and 3D contours of pressure, CMC velocity, drilling-solids velocity, CMC volume fraction, drilling-solids volume fraction, and turbulent kinetic energy. These fields characterize the coupling between rotation-induced shear and buoyancy components, illustrating how the non-Newtonian carrier mobilizes and transports the cuttings while mitigating deposition within the inclined wellbore.