The associative properties of Hydrophobically Modified Water Soluble Polymers (HMWSP) are known to be attractive for IOR, both because of their enhanced thickening capability as compared to classical water soluble polymers (for mobility control) and of their marked adsorptions on surfaces (for well treatments). In previous works, we have studied HMWSP injectivity in the dilute regime and shown, in particular, that adsorption played a major role in controlling injectivity. In this paper, we report new experimental data on the injectivity of HMWSP solutions in the semi-dilute regime.
From membrane filtration tests at imposed flow rate, we have firstly observed the formation of a filter-cake made of HMWSP physical gel, which remained largely permeable to polymers. This "gel-filtration" entailed modifications of the solution's viscosimetric properties, which can be explained by a rearrangement of the intra- and inter-chain hydrophobic bonds in the solution. The second part of our work consisted in injectivity tests in model granular packs. We have performed comparative experiments in porous media with variable permeabilities but at the same shear rate in the pore throats. Results show that, above a critical pore throat radius, rpC, HMWSP injection lead to stable resistance factors, with values close to the solution'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.