In water shut-off operations, the polymer solution and the crosslinker are currently mixed into surface facilities just before to be injected through the production or injection well and then inside the reservoir. Therefore, the crosslinking system is always subjected to shear stresses while « gelling » and the main question for the operator is the depth of penetration inside the reservoir of the « gelling » system. This paper reports a theoretical and experimental investigation of the process of crosslinking under shear. The model derived from our theoretical analysis predicts that the characteristics which governs penetration in porous media, i.e. viscosity and microgel size, can be easilly calculated from simple shear viscosity measurements. The proposed theory describes the crosslinking under shear as a four successive steps process. By taking into account the break-up of microgels by shear forces as soon as their size reaches a given value, this theory predicts that, under a constant shear rate flow, a solution of monodispersed microgels is obtained at the end of the final step. Using a scaling law approach, we derived a very simple equation linking final viscosity and microgel size to initial polymer characteristics as well as applied shear rate. The final shear stress is expected to be independent of shear rate but proportional to crosslink energy, thus providing a simple way to compare various available crosslinkers. New experimental data, obtained by using a low toxicity crosslinking system, i.e. a weakly hydrolyzed and sulfonated polyacrylamide together with zirconium lactate are reported. All the predictions of our model are in agreement with our own data, as well as with others found in the literature. In addition, new information on the physicochemistry of the acrylate-lactate-zirconium system is obtained. While increasing pH results only in a retardation of the crosslinking process without changing crosslink energy, both a retardation and a weakening of crosslinks is obtained by adding sodium lactate. Injectability experiments in porous media involving the injection of both the polymer and the crosslinker, mixed just at the entrance of the porous medium results in a strong plugging after a given time. On the contrary, the injection of preformed microgel solutions, does not show any plugging tendency, although giving higher mobility reduction in agreement with the proposed theory.

You can access this article if you purchase or spend a download.