High-Temperature Stable Specific Enzyme for Guar Polymer Based Fracturing Fluid Degradation

Hydraulic fracturing, commonly referred to as fracking, is a widely used technology to enhance the productivity of low-perm reservoirs and the aqueous-based fracturing fluids use guar as the rheology builder. Residual polymer layer over the fractured surface results in a reduced matrix to fracture permeability, causing reduced well productivity. This research aims to develop a specialized mannanase enzyme and evaluate its efficiency in degrading linear and cross-linked guar polymer gel as a function of time, temperature, and breaker concentration, to enhance the effectiveness of the fracturing process and yielding higher production. The study begins with developing high-temperature stable mannanase using "protein engineering" tools to minimize denaturation at high temperatures and the underlying formation chemistry, followed by optimization of polymer, crosslinker, and breaker concentration through the measurement of rheological properties at moderate to high temperature. Initial studies were conducted using HT-HP filter press and filter papers as porous media for visual inspection of polymer cake dissolution efficiency. Final conclusions were drawn from the simulated coreflooding studies, wherein the injection and production return permeabilities were investigated on post-fracture and enzyme-treated cores, where the breaker was mixed with the frac fluid applied once the frac fluid is in place. The thermal stability of the enzyme breaker vis-à-vis viscosity reduction and degradation pattern of linear and cross-linked gel observed from the break test showed that the enzyme is stable up to 250 °F and can reduce viscosity by more than 1800 cp (99% breaking ability).