Gas & Petrochemical: Borehole Flow

Computational Investigation of Liquid–Solid Two-Phase Flow in a Borehole: Implications for Gas and Petrochemical Engineering

The interaction between flowing fluids and the surrounding formation within a borehole constitutes a fundamental concern in upstream hydrocarbon operations, where drilling provides the principal access to subsurface reservoirs. This study examines that interaction through a computational fluid dynamics (CFD) simulation of liquid–solid two-phase flow in a vertical wellbore, conducted in ANSYS Fluent. The objective is to characterise the mechanism by which soil grains detach from the borehole wall and become entrained in the fluid stream, a process of direct relevance to wellbore stability and solids production in oil and gas wells.

An Eulerian multiphase formulation is employed, with water designated as the primary (continuous) phase and soil grains as the secondary (dispersed) phase. This approach is appropriate for particle-laden flows in which the volume fraction of the dispersed phase exceeds approximately ten percent, as is characteristic of the slurry-type regimes encountered in drilling and in petrochemical particulate processing. Turbulence is represented using the standard k–ε model with standard wall functions and a dispersed turbulence multiphase treatment, while the computational domain is reduced to a representative cylindrical sector to limit computational cost. Water enters the central region of the well at 1.6 m·s⁻¹ together with soil particles at 1 m·s⁻¹, and the unsteady, pressure-based solver resolves the evolving flow field and phase distribution.

The results, presented as contours of phase volume fraction and velocity, indicate that a portion of the soil grains is liberated from the borehole wall and joins the fluid stream, while some fluid simultaneously penetrates the formation. This behaviour demonstrates that the shear stress generated at the fluid–solid interface exceeds the cohesive adhesion between soil grains — the governing condition for the onset of solids detachment.

The findings carry several implications for gas and petrochemical engineering. First, the identification of the threshold at which interfacial shear overcomes grain cohesion provides a physical basis for predicting sand and solids production, a phenomenon responsible for erosion of downhole and surface equipment and for wellbore plugging. Second, the same fluid–formation interaction underlies wellbore stability: controlled flow preserves wall integrity, whereas excessive scouring promotes hole enlargement and instability. Third, the computed volume-fraction and velocity fields inform the assessment of drilling-fluid carrying capacity and cuttings transport, both central to effective hole cleaning. Collectively, the study offers quantitative insight into the conditions under which a formation begins to fail under imposed flow, thereby contributing to the design of safer wells and to improved strategies for solids control during drilling and completion.