Abstract
In the cementing industry, it is known that zonal isolation is dependent on a successful cement job. To achieve zonal isolation, effective mud removal is recommended (Crook et al. 2001). Efficient mud displacement can be achieved with the use of spacers and flushes before cement is placed. With an increasing need to successfully complete a well on the first try, accurately modeling the spacer rheology has become key.
This paper presents results from a comparison of two rheological models. The Bingham plastic and Generalized Herschel Bulkley (GHB) models examined in this work are both used to model rheologies of spacers. For most field operations, the Bingham plastic model is used to model rheologies; however, studies have shown that using this model can lead to over-predicting yield point. The GHB model is used to model non-Newtonian fluids by incorporating the possibility that the fluid might or might not have a yield stress and that the shear stress might be a nonlinear function of shear rate.
Spacers are used to separate one fluid from another. They are designed to be compatible with the mud being used in the well. This paper compares the performance of spacer and spacer/mud rheologies at different elevated temperatures (200, 300, and 350°F) with measurements from a Model 75 HP/HT viscometer.
Results have been modeled in a computational fluid-dynamics simulator to illustrate the effects of each rheological model used to describe the well-completions fluids. The simulator modeled displacement and intermixing of wellbore fluids downhole, and these are investigated in the annulus for the simulated case.
