Evaluation of drilling fluid removal by cement slurry from horizontal wells with the use of an accurate mathematical model

Abstract

Prediction of optimal conditions for the displacement of drilling fluid by cement slurry from the annulus has become increasingly important for completion of horizontal wells. This paper presents a mathematical model to describe the displacement of drilling fluid by cement slurry from horizontal annulus taking into account the effects of different parameters: i.e., fluid properties (drilling fluid and cement slurry or spacer fluid), hole geometry and displacement rate. The equation-of-motion and the equation-of-continuity were used to describe the fluid flow in the annulus and the power-law relation was used to model the thixotropic nature of the fluids. The model was applied to a range of displacement conditions (densities, viscosities, displacement rates, hole geometries and cementing lenghts). Parameters that were found to strongly affect the displacement efficiency are the rheology of drilling fluid and displacement rate. The results suggest that optimal or near-optimal conditions are possible to obtain, and provide a basis for designing efficient cement job for horizontal wellbores. The computed results have shown a general agreement with results presented by previous investigators.