Associative Polymer Compatibility with Surfactants: Advantages Vs. Standard Polymer in Bulk and under Flow Conditions
Authors: Miralles Vincent , Marlière Claire , Morgand Claire , Rome Virginie , Morvan Mikel , Courtaud Tiphaine 
Published: November 2020

Abstract
The purpose of surfactant-polymer (SP) formulation design is to concurrently achieve ultra-low interfacial tension and good mobility ratio. To this respect, associative polymers were found to be particularly interesting since their use could simultaneously solve demixing issues that can be observed in bulk when mixing surfactants with standard partially hydrolyzed poly-acrylamide (HPAM) polymers, and enhance the mobility ratio when injected in confined and under flow conditions.
Varying the brine salinity and the polymer chemistry (either HPAM or associative polymer) with the same surfactant system led to the definition of four SP compatibility cases, on the basis of phase diagrams. First the focus was specifically directed to bulk and kinetic studies based on viscosity, cryo-TEM and turbidity versus time measurements. Then, monophasic injections were performed in a coreflood rig with a 3D outcrop rock with the designed formulations. The mobility reduction entailed by the injected solutions was measured by monitoring the pressure drop along the core.
With the HPAM polymer, an increase in salinity leads to a clear degradation of the SP compatibility or even to a demixing behavior after a couple of days, due to depletion interactions. Interestingly, when the same surfactant system is mixed with the associative polymer, the demixing behavior vanishes due to a synergetic interaction between the surfactant and the associative polymer, hence changing the overall physical structure of the SP system and leading to a crystal clear formulation.
Regarding monophasic injections in coreflood, as expected the compatible SP formulations designed at low salinity led to excellent in-depth transport properties with both polymers. While demixing at high salinity, the SP formulation involving HPAM showed good transport properties since the mobility reduction stabilizes at a value close to the relative viscosity of the solution. More interestingly, the mobility reduction for the SP formulation integrating the associative polymer also reaches a plateau but with a value almost five times higher than its relative viscosity. These results highlight that the use of an associative polymer instead of a conventional HPAM in a SP formulation can present the double advantage of vanishing depletion interactions in bulk, hence improving the formulation's solubility, and enhancing the developed mobility reduction in a coreflood experiment.
It has been proven that associative polymers can bring a solution to SP compatibility issues by vanishing depletion interactions and hence improving the formulation's solubility. Depending on the surfactant formulation involved, the addition of an associative polymer can drastically enhance the developed mobility reduction while decreasing the polymer concentration compared to the use of a conventional HPAM polymer. This dosage reduction is also an element of economic advantage in favor of associative polymers.