Injectivity of hydrophobically modified water soluble polymers for IOR: controlled resistance factors vs. flow-induced gelation.
Résumé
The associative properties of Hydrophobically Modified Water Sol. Polymers (HMWSP) are known to be attractive for IOR, both because of their enhanced thickening capability as compared to classical water sol. polymers (for mobility control) and of their marked adsorptions on surfaces (for well treatments). In previous works, we have studied HMWSP injectivity in the dil. regime and shown, in particular, that adsorption played a major role in controlling injectivity. In this paper, we report new exptl. data on the injectivity of HMWSP solns. in the semi-dil. regime. From membrane filtration tests at imposed flow rate, we have firstly obsd. the formation of a filter-cake made of HMWSP phys. gel, which remained largely permeable to polymers. This "gel-filtration" entailed modifications of the soln.'s viscosimetric properties, which can be explained by a rearrangement of the intra- and inter-chain hydrophobic bonds in the soln. The second part of our work consisted in 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. pore throat radius, rpC, HMWSP injection lead to stable resistance factors, with values close to the soln.'s viscosity, and that, below rpC, gelation occurs during injection. Furthermore, resistance factors measured on the cores internal sections evidence for in-depth gel formation. These insights could represent a new step towards the tuning of HMWSP injection conditions to the application targeted: mobility control or profile/conformance control. [on SciFinder(R)]