Preparation And Performance Of A New Thermostable Enzyme Breaker For Application In Hydraulic Fracturing Fluids

Hydraulic fracture stimulation techniques create a conductive pathway into the reservoir from the well and have been developed as a preferred way to recover low permeability reservoirs. Generally, the fracturing fluid is first pumped into the well at a sufficient pressure to fracture the subterranean formation and the solid proppant maintains the increased exposure to the formation. Then the viscosity of the fracturing fluid must be subsequently broken in situ, so that the low viscosity fluid can be pumped out, after which oil or gas production can proceed. This study aimed to search for an efficient enzyme break of guar-based fracturing fluid for high temperature and low permeability reservoir.A new thermostable β-1,4-mannanase (DtMan) cloned from Dictyoglomus thermophilum showed the maximum activity towards hydroxypropyl guar (HPG) at 80℃, with a half-life of 46 h. DtMan exhibited good compatibility with alkaline conditions, keeping a viscosity reduction rate of 11.1 mPa·s·min-1 even at pH 10.0. Besides, DtMan retained more than 50% activity in the presence of various additives. More importantly, premature degradation could be alleviated significantly when using DtMan as breaker, because at 27℃ and 50℃ it displayed merely 3.7% and 18.5% activities compared to those at 80℃. In addition,0.48 mg DtMan could break 200 mL borax cross-linked fracturing fluid drastically at 80℃, with merely 18 mPa·s of the viscosity as measured after the broken fluid was cooled and only 161.4 mg·L-1 of the residue left. All these positive features demonstrate the potential of this mannanase as a new and promising enzyme breaker for application in enhanced recovery of petroleum oil.