Optimal production of enzymatic guar gel breaker by Bacillus sp. M1-4 and its potential in hydraulic fracturing

Recent developments in the petroleum industry have established a need for the in situ hydrolysis of galactomannans (guar gum) and utilisation of enzymes for guar gel breaking (known as EGGB), such as cleavage activity at low temperature, substrate specificity and environmental acceptability. The medium composition for EGGB production was optimised using response surface methodology. The optimised medium contained (g/L): guar gum 4.08, peptone 11.74, NaNO3 5.22, K2HPO4 2.0, MgSO4.7H2O 1.0 and CaCl2 0.05, and achieved a yield of 239 IU/ml of β-mannanase in EGGB, which exhibited a significant stability over a wide range of temperature (below 60°C), pH (neutral) and chemicals (cations, EDTA, bactericide and cross-linker agent). Full maintain of permeability of the formation core was accomplished by addition of EGGB in physical simulation experiment. Based on the results of medium composition optimisation, enzyme assays and physical simulation experiment, the enzymatic guar gel breaker presented a great prospect in the hydraulic fracturing. [Received: August 14, 2014; Accepted: September 22, 2015]