Controlling Gelation Time and Microgel Size for Water Shutoff

Abstract

Abstract Injecting stable preformed microgels as relative permeability modifiers to reduce water production is an attractive new procedure to minimize the risk of formation plugging and consequently of inefficiency of in-depth treatments. This paper describes the mains results of theoretical and experimental investigations carried out to know how to control both size and conformation of microgels formed under constant shear flow. Since gelation kinetics strongly depends on crosslinker chemistry, Zr K-edge XANES and EXAFS studies of zirconium speciation were performed under the complex conditions of polymer gelling for water shutoff. The results show that crosslinking species may be dimers, tetramers and associations of tetramers depending on pH and Zr concentration in presence of lactate. In polymer gels, Zr monomers were observed. The generalisation of our crosslinking-under-shear theory described in this paper provides simple power laws. The microgels formed in diffusion regime are isotropic and their size decreases significantly as shear rate increases, while when formed in correction regime, they are anisotropic and their size decreases negligibly with shear rate. All experimental data are in agreement with this theory so that conclusions can be derived to optimize microgel preparation as a function of their role in the aimed application, either relative permeability modifiers for water shutoff or viscosity enhancers for polymer flooding.