Enzymes breakers for viscosity enhancing polymers

A screening of enzymes as filtercake breakers was performed on several commercially available enzymes. Two enzymes, a thermostable amylase from Bacillus licheniformis and a cellulase from Trichoderma reesei, were found to be effective on the basis of activity tests in the presence of the most common biopolymers used in drill-in fluids such as starches and scleroglucan. Whereas the amylase can hydrolyze chemically modified starches, which are not its natural substrates, the cellulase is able to attack scleroglucan and even xanthan gum, both used as viscosity enhancers in drill-in fluids. The enzyme activities towards the polymeric substrates were controlled by viscosity, fragment mass distributions and time dependence hydrolysis tests. It was also found that both enzymes retain a good activity in concentrated brine solutions. When assayed as filtercake breakers on core flooding experiments, cellulase and amylase were able to reestablish efficiently the core performance. The permeability return was higher than 80% after the enzymatic treatment of the filtercake, reaching almost 100% after a mild formic acid washing to remove insoluble carbonate particles. In the case of a double treatment with both enzymes, the filtercake removal efficiency depended upon the order of the enzymes sequence, being the most effective when cellulase was used first.