A new type of polyacrylamide flow-induced retention has been observed in core experiments simulating near-wellbore flow conditions. The retention is due to the bridging of pore throats by adsorbed macromolecules previously stretched under elongational flow. It occurs in low-to-medium permeability granular packs (up to k=1000 mD in our test conditions) and leads to progressive but severe plugging. The present paper shows that polymer placement in the reservoir surrounding the wellbore can be very different from what is predicted from stable values of polymer mobility. In heterogeneous reservoirs, polymer penetration in low-permeability layers is expected to be strongly reduced, thus allowing a deeper penetration into higher permeability zones. The polymer can thus improve reservoir conformance around the wellbore when injected directly through the entire opened interval. Near-wellbore polymer or gel treatments may thus not require zone isolation to be efficient.
Polyacrylamides are extensively used in the oilfield industry because of their low cost, good filterability and high viscosifying power. In polymer flooding applications, high-molecular-weight polyacrylamides are added at a low concentration (frequently below 1000 ppm) to injection brine in order to thicken and thus improve the sweep efficiency of the displacing fluid. In heterogeneous reservoirs, the role of the polymer is to provide a good mobility control to injection brine, thus avoiding water channeling through high-permeability streaks.