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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.

Synthetic polymers, in the emulsified form, have been utilized for enhanced oil recovery applications by using saline make-up water. However, there are concerns that have been raised about their injectivity. The large entangled polymer chains can clog the pore throats, giving a tendency to cause injectivity reduction. In this study, processing techniques were used to condition an acrylamide-based copolymer inverse emulsion system at a salinity of 50,000 ppm TDS before being injected into porous media. The investigated polymer solution contained 4,000 ppm active emulsion-polymer and 2,400 ppm surfactant, providing a zero-shear rate viscosity of 13 mPas. Shearing with two agitators, a disperser and Ultra-Turrax, at different intensities and pressure-driven flow into a thin capillary reduces the size of the largest polymer and disentangles the polymer chains while maintaining its viscosifying power as much as possible. Subsequently, the filtration ratios (퐹푅) with optimum between 1–1.2 were determined by performing filtration tests in a 1-micron polycarbonate membrane to evaluate the plugging behavior. This was followed by sand-pack flooding tests of differently sheared solutions in order to investigate the impact of pre-conditioning on injectivity. Bulk experiments enabled the establishment of master curves showing viscosity and screen factor dependences on accumulated energy during pre-shearing, regardless of shear origin. The injected unsheared polymer solution has an 퐹푅 of 1.6 and an injectivity gradient, e.g. ratio of resistance factor over 10 pore volumes, of 2.4. All injected pre-conditioned solutions have an 퐹푅 in the optimal range between 1 to 1.2. By imposing 15 MJ/m3, the disperser-sheared solution improves the injectivity by decreasing the injectivity gradient to 1.3, while the viscosifying power is reduced by 2% and the screen factor by 30%. To reach the same injectivity gradient of 1.3 with Ultra-Turrax, 31 MJ/m3 were imposed, which reduces the viscosity and screen factor by 11% and 44% respectively. The sheared solution into a capillary imposes 50 MJ/m3, giving an injectivity gradient of 2.7. Both viscosity and screen factor are reduced by 19% and 53% respectively. 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. In conclusion, the rheological dependencies of sheared polymer solutions form a master curve dependent of accumulated energy during shearing with different shearing devices. Further, the proven beneficial impact of pre-conditioning with agitators before injection enables a better utilization of polymer flooding operations by reducing the risk of pore plugging.

Few structures of viral serine proteases, those encoded by the Sindbis and Semliki Forest viruses, hepatitis C virus (HCV) and cytomegalovirus, have been reported. In the life cycle of HCV a crucial role is played by a chymotrypsin-like serine protease encoded at the N–terminus of the viral NS3 protein, the solution structure of which we present here complexed with a covalently bound reversible inhibitor. Unexpectedly, the residue in the P2 position of the inhibitor induces an effective stabilization of the catalytic His–Asp hydrogen bond, by shielding that region of the protease from the solvent. This interaction appears crucial in the activation of the enzyme catalytic machinery and represents an unprecedented observation for this family of enzymes. Our data suggest that natural substrates of this serine protease could contribute to the enzyme activation by a similar induced-fit mechanism. The high degree of similarity at the His–Asp catalytic site region between HCV NS3 and other viral serine proteases suggests that this behaviour could be a more general feature for this category of viral enzymes.

New methodology was developed toward the synthesis of 8-de-ethyl-8-vinylchlorophyll-a 1. Such 8-de-ethyl-8-vinyl derivatives of the green plant pigment chlorophyll-a 2 have been proposed to be inte...