Flow of hydrophobically modified water-soluble polymers in porous media: controlled resistance factors vs. flow-induced gelation in the semidilute regime.
Résumé
The associative properties of hydrophobically modified water sol. polymers (HMWSPs) are attractive for improved oil recovery (IOR) because of both their enhanced thickening capability, compared with classical water-sol. polymers (for mobility-control applications), and their permeability-redn., or plugging, ability (for well-treatment applications). In previous works, we have studied the injectivity of HMWSP made of sulfonated polyacrylamide backbones and alkyl side chains in the dil. regime and have shown, in particular, that it was largely governed by adsorption. In this paper, we report new exptl. data on the injectivity of the same class of HMWSP solns. in the semidilute regime. From membrane filtration tests at imposed flow rate, we have first obsd. the formation of a filter cake made of HMWSP phys. gel, which remained largely permeable to polymers. Our observations are compatible with the creation of channels within the gel. This leads to a gel-filtration process, entailing modifications of the soln.'s viscosimetric properties, which can be explained by a rearrangement of the intra- and interchain hydrophobic bonds in the soln. The second part of our work consisted of injectivity tests in model granular packs. We have performed comparative expts. in porous media with variable permeabilities, but at the same shear rate in the pore throats. Results show that, above a crit. permeability kC, or a crit. pore-throat radius rCP, HMWSP injection led to stable resistance factors, with values close to the soln.'s viscosity, and that, at less than kC or rCP, the very high resistance factors obsd. suggest that flow-induced gelation of the HMWSP takes place. Furthermore, resistance factors measured over the core internal sections are compatible with an in-depth formation of the gel. These insights could be of use for designing HMWSP better suited to mobility-control operations and for tuning HMWSP-injection conditions for profile/conformance-control operations. [on SciFinder(R)]