Continuum model for the numerical simulation of the sedimentation process of two immiscible non-Newtonian suspensions confined in an annulus

The sedimentation process in a single suspension was broadly studied in many previous works. In the annular region of oil wells, the presence of the drilling fluid is common, which contains solid particles acting as a weighting agent. Additionally, there is a second confined fluid, known as a washer, that has the function of avoiding contamination of cement paste by the drilling fluid. The washer is heavier than the drilling fluid and may also have solid particles in its composition. The batch sedimentation of two immiscible suspensions is yet now well known. Here we employed a continuum model for the sedimentation in one suspension, which was previously validated with experiments and was able to obtain the solids concentration profile over time. We extended the model to the case with two immiscible fluids. The domain was discretized using the finite volume method. The problem was evaluated at a real well scale. The results showed that the presence of the second fluid may significantly alter the sedimentation process of the light suspension and depend on the fluid base type, as well as the difference in the suspensions’ properties. Formation of sediment may be observed above the interface between the suspensions, depending on the heavy suspension rheology and solids concentration. The rheological parameters had a key role in the process. Also, we studied the cases with different temperature conditions, as the model may account for the temperature effect locally in the rheological behavior of the suspensions.