Placement Using Viscosified Non-Newtonian Scale Inhibitor Slugs: The Effect of Shear Thinning

Abstract

Reservoir formations are often very heterogeneous and fluid flow is strongly determined by their permeability structure. Thus, when a scale inhibitor (SI) slug is injected into the formation in a squeeze treatment, fluid placement is an important issue. To design successful squeeze treatments, we wish to control where the fluid package is placed in the near-well reservoir formation. In recent work (Sorbie and Mackay 2005), we went "back to basics" on the issue of viscous SI slug placement. That is, we re-derived the analytical expressions that describe placement in linear and radial layered systems for unit mobility and viscous fluids. Although these equations are quite well known, we applied them in a novel manner to describe SI placement. We also demonstrated the implications of these equations on how we should analyze placement both in the laboratory and by numerical modeling before we apply a SI squeeze. An analysis of viscosified SI applications for linear and radial systems was presented both with and without crossflow between the reservoir layers.In this previous work, we assumed that the fluid being used to viscosify the SI slug was Newtonian (Sorbie and Mackay 2005). However, the question has been raised concerning what the effect would be if a non-Newtonian fluid was used instead. We mainly consider the effect of shear thinning, although our analysis is generally applicable if the non-Newtonian flow rate and effective viscosity function is known. We address the questions: Does the shear thinning behavior result in more placements into the higher or lower permeability layer (in addition to the effect of simple viscosification)? Can the shear thinning effect be used to design improved squeeze treatment? Review and Problem StatementLinear and Radial Models. The linear and radial layered systems considered in this work are shown schematically in Fig. 1. Here we will consider each of these in turn in the absence of crossflow between layers. For each of these cases, differential expressions are derived (which can be integrated numerically) and then used to show the level of diversion that occurs when viscous shearthinning fluid is injected into a layered system without crossflow.

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