We examine the role of preshearing on the flow properties of polymer solutions containing essentially an acrylamide-based copolymer obtained from an emulsified polymer emulsion inverted by a surfactant. The polymer solutions were presheared using three methods: (1) a Buddeberg disperser, (2) an Ultra-Turrax disperser, and (3) pressure-driven flow through a capillary. Shearing the polymer solution was done under fast flow to induce high stretching of the polymer chains and thus promote the break-up of the longest ones (i.e., decrease in relaxation time and shear-thinning level). The unsheared and presheared polymer solutions were forced through sand packs to compare their corresponding flow resistances. We observed that the reduction in the viscosity and screen factor of the presheared polymer solutions is path independent regardless of the shearing device. We found a critical Weissenberg number (Wic ∼ 13) above which the viscosity of the polymer solutions started to decrease. The resistance factor for the polymer solutions presheared with the Ultra-Turrax disperser at an energy input of 31.3 and 290.7 MJ/m3 was nearly 3 and 7 times, respectively, lower than for the unsheared polymer solution, while the viscosity decreased only by 27 and 48%, respectively. The sand-pack experiments were successfully interpreted using a numerical model taking into account time-dependent retention. The model showed that the flow of the presheared polymer solutions through the sand packs was enhanced mainly due to the breaking of the longest polymer chains, which results in smaller mechanical entrapment. This preshearing of the water-soluble polymers can be used in multiple industrial applications, including chemical enhanced oil recovery and optimization of polymer processing.@en

Synthetic high molecular weight polymers have been utilized for enhanced oil recovery applications. Improving their injectivity remains an important issue for field applications. Large entangled polymer chains can clog pore throats, leading to injectivity decline. We investigated an emulsion polymer system and have developed a series of processing techniques to condition an acrylamide-based copolymer inverse emulsion system at a salinity of 50,000 ppm TDS before injection into porous media. The investigated polymer solution contained 4,000 ppm active emulsion polymer and 2,400 ppm inverter surfactant. The un-conditioned polymer system and test conditions were chosen to clearly demonstrate the impact of processing techniques on the injectivity behavior. The polymer solution was sheared with two agitators, a disperser and Ultra-Turrax, at different intensities and with a pressure-driven flow into a thin capillary to reduce the size of the largest polymer chains and disentangle the polymer chains while maintaining its viscosifying power. The injectivity of such differently sheared solutions was evaluated by performing filtration tests using a 1-micron membrane and sand-pack flooding tests. Our experiments have established a master curve showing viscosity and screen factor dependences on accumulated energy during pre-shearing, regardless of the mode of shearing. The un-sheared polymer solution had an unfavorable behavior in filtration test and sand-pack flooding experiment. After pre-shearing, the filtration behavior of polymer solution and the injectivity in sand-packs improved significantly. Polymer solutions sheared with a disperser at an energy input of 15 MJ/m3 improved the injectivity gradient (e.g. the ratio of the resistance factor over 30 pore volumes injected) from 3.7 to 1.6, while the viscosifying power was reduced by only 2%. To reach the same injectivity improvement with Ultra-Turrax, an energy input of 31 MJ/m3 were required, which reduced the viscosity by 11%. Shearing the solution using a capillary at an energy input of 50 MJ/m3, did not reduce the injectivity gradient while viscosity was reduced by 19%. This indicates that the injectivity performance is shear-origin dependent and the resulting polymer structure, when sheared through contractions, has a different alignment as compared to shearing with the agitators, the disperser and Ultra-Turrax.@en