A unified transient solid-liquid two-phase flow model for cuttings transport-modelling part

A unified transient model is presented for predictions of flow pattern transitions, pressure gradient, solid particle concentration in solid-liquid two-phase flow. The transient mechanistic model is based on the conservation of mass and momentum and coupled with flow pattern prediction methods. Changes of flow patterns are reflected by assigning certain terms to zeros in the general equations and changing the number of equations. Thus, the model can be automatically adjusted for flow patterns in transient simulation. A semi-implicit approach is used to solve the model. The velocities and pressures are solved implicitly based on the momentum conservation equations and the solids concentrations are updated explicitly based on the mass conservation equations. The model is validated by conducting a series of experimental tests on a full scale flow loop (0.2 x 0.11 x 25 m). The validation of the transient simulation includes the validation of the transient build-up stage and the validation of the cuttings volumetric concentration at fully developed stage. Results found that increase of the flow rate significantly reduces the build-up time, and effects of pipe rotation vary at different inclined angles. The effect of inclination angle on solids profile build-up is similar to the effects of well inclination angle on steady state cuttings concentration. Below 60 degrees, the build-up time increases significantly as the well inclination angle increases. When the well inclination angle goes to over 60 degrees, the effects of well inclination angle become insignificant.