Scale inhibitor placement: Back to basics - Theory and examples

Downhole scale inhibitor (SI) squeeze treatments are a common feature of the scale control plans of many oil operators. However, reservoir formations are large, heterogeneous rock bodies in which fluid flow is strongly determined by the permeability structure. Thus, when a slug of scale inhibitor is injected into the formation, fluid placement is an important issue. To design successful squeeze treatments, it is necessary to know where the injected fluid goes or, even better, we would like to control where the fluid package is placed in the near-well reservoir formation. In this paper, we go "back to basics", in that we re-derive the analytical expression that describe placement in linear and radial layered systems for unit mobility and viscous fluids. In itself, this is not new since these equations are well known. However, we apply them in a novel manner to describe scale inhibitor placement. We also demonstrate the implications of these equations on how we should analyse placement both in the laboratory and by numerical modelling before we apply a scale inhibitor squeeze. We present an analysis of viscosified SI applications for linear and radial systems both with and without crossflow between the reservoir layers. Visualisation experimental results are also presented of simple and viscosified slug placement in layered bead packs with crossflow between layers. It is shown that these agree very well with the numerical predictions. Additional calculations on near well placement in radial systems are also presented showing how the theory carries over into real field near-well, heterogeneous systems. Some novel ideas are presented on the application of viscosified scale inhibitor treatments.