The use of high pH fluids, particularly borates, has been very prevalent at low to moderate temperatures in the industry and their use at high temperatures is also increasing. These non-metallic borates have been claimed to be less damaging to formations than metallic crosslinked gels. Breakers are commonly used in these aqueous fluids viscosified with guar, cellulose or their derivatives to degrade these fluids after the placement of proppant. Breakers are necessary to minimize permeability damage to proppant pack or formation face at temperatures where there is little thermal degradation of the polymers. The typical breakers that are used in fracturing fluids are enzyme breakers and oxidizers. Unfortunately, at temperatures below 150°F, persulfates, the typical oxidizing breakers, are not effective unless used in large concentrations or used with catalysts. On the other hand, conventional enzymes are not active in high pH systems (>8.5) typical of borates. It has been shown that enzymes break the gels much more efficiently in low to neutral pH fluids1 .
A new enzyme described in this paper is active in fluids in the pH range 5 to 11. The specially engineered enzyme, modified hemicellulase, is produced in a microbial fermentation process. The identified enzyme has been selected as the best from a collection of several engineered enzymes available. Data presented from the lab and field show enzyme activity at various pH, temperature, and salinity conditions. The enzyme remains active at mild temperatures and pH as high as 11.5. It breaks the gels of borate crosslinked guar and derivatives. The broken gel residue is comparable to residue obtained with application of conventional enzyme or oxidizing breakers.
In addition, application of this new enzyme improves the economy of well stimulation and completion at low temperatures (80°Fto 120°F).