Squeeze cementing: Invasion of a yield stress suspension into a pore

Abstract

Squeeze cementing is a process of fundamental importance in oil & well operations, in which cement slurry is injected under pressure into void spaces in defective sections of a wellbore, The aim is to isolate the borehole from adjacent geological zones and repair defects in the existing cement sheath, e.g. cracks, debonding and micro-annuli. Although cement slurries are often considered a homogeneous fluid, on the scales of relevance the multiphase nature of the cement slurry becomes relevant. In this context, we propose a model in which the cement slurry is considered as a viscoplastic suspension, in which both rheological and particle migration effects can be investigated. This allows us to explore different stoppage mechanisms, that combine bulk yield stress effects, enhancement by the solids fraction and modification by particle migration. Our approach is a continuum model based on the suspension balance model. We use this to model slurry penetration in long ducts, driven by a constant pressure difference. As well as a starting point for a more complex process model, our model provides insight into how shear induced migration combines with yield stress effects to produce non-monotone solids distributions adjacent to plug regions.