Viscosity Reduction Of Hydraulic Fracturing Fluids Through Enzymatic Hydrolysis

Abstract

Abstract High viscosity formulations of guar are used as fracturing fluids to enhance oil and gas production. Following fracturing, these fluids are hydrolyzed and flushed out of the well to provide outflow for oil or gas. Enzymes offer an effective and environmentally benign method for hydrolyzing the guar to a low viscosity fluid. In this study, we used steady shear rheometry to elicit fundamental information on the capabilities and limitations of enzymes. The effect of commercial and new thermostable enzymes on polymer viscosity was investigated in terms of process variables such as temperature of hydrolysis, pH of solution and enzyme concentration. The commercial enzyme was most effective in degrading the guar at slightly acidic conditions and up to 60°C. Above 60°C, the extent of hydrolysis of guar solutions decreased. With increasing temperature, enzymatic activity increased but enzyme stability decreased and this balance was critical in determining the extent of viscosity reduction. Experiments using preheated enzyme also revealed lower viscosity reduction, suggesting that most of the hydrolysis occurs during the enzyme heat up, following which the enzymes deactivate rapidly. Similar experiments with the thermostable enzyme system demonstrated high levels of viscosity reduction at elevated temperatures (up to 85°C) and limited viscosity reduction at ambient conditions. This is suggestive of enhanced capability of this enzyme system at elevated temperatures compared to that of the commercial system. Experiments using purified enzymes from both enzyme systems also revealed that the largest reduction in viscosity of guar solutions occurs with endo-β-D mannanase, the enzyme cleaving the bonds between the mannose backbone units.