低温β-甘露聚糖酶的酶学性质及破胶性能

Enzymatic Properties and Gel Breaking Performance of Low-temperatureβ-Mannanase

页岩油气藏开发过程中返排液的破胶及低温油藏压裂液的破胶是目前页岩油气藏及致密油气藏开发过程中面临的一个难题。由于化学破胶剂使用时需要较高的温度,难以满足低温条件下彻底破胶的要求。为此,针对低温酶破胶剂,采用高通量筛选方法,从油田压裂返排水和魔芋地的混合样品中筛选出高效低温β-甘露聚糖酶产生菌,并对所产低温β-甘露聚糖酶的酶学性质及破胶性能进行了研究。结果表明,在筛选到的40个产酶菌株中,菌株O5鉴定为施氏假单胞菌,其产生β-甘露聚糖酶(ME-O5)的最适温度为50℃,在5~20℃时酶活力仍能保持约60%以上,低温活性突出,在中温区域的热稳定性良好;最适pH=7.0,具有一定的pH适应性和较宽的pH耐受范围。ME-O5在5和20℃下均能将瓜尔胶溶液的粘度降低至5 mPa·s以下,降粘率>99%,降粘效果显著。在10、20和50℃下,压裂液经ME-O5破胶处理3 h后,破胶液的表观粘度<5 mPa·s,表面张力<28 mN/m,界面张力<2 mN/m,残渣量<600 mg/L,均达到或优于我国石油天然气行业标准SY/T 6376-2008的要求,在油田压裂低温破胶方面具有良好的应用前景。

The gel breaking of flowback fluid and low temperature oil fracturing fluid is a difficult problem currently faced in the development of shale and tight oil and gas reservoirs.Due to the high temperature required for the use of chemical gel breaker,it is difficult to meet the requirements of completely gel breaking under low temperature conditions.To this end,a high-throughput screening methodis used to screen out highefficiency low-temperatureβ-mannanase-producing bacteriafrom the mixed samples of oilfield fracturing flowback fluid and konjac land.The enzymatic properties and gel-breaking performance of this lowtemperatureβ-mannanase are studied.The results show that,among the 40 screened strains,strain O5 is identified as Pseudomonasstutzeri.The optimum temperature forβ-mannanase ME-O5(ME-O5)is 50℃,and its enzyme activity could still maintain more than 60%at 5~20℃.The low temperature activity is outstanding,and the thermal stability is good in the middle temperature region.The optimum pH for ME-O5 is 7.0,with a certain pH adaptability and a wide pH tolerance range.At both 5 and 20℃,ME-O5 reduces the viscosity of guar gum to less than 5 mPa·s,the viscosity reduction rate is more than 99%,and the effect of viscosity reduction is remarkable.At 10,20 and 50℃,after the fracturing fluid is treated by gel breaking for 3 h with ME-O5,the apparent viscosity of the gel breaking fluid is less than 5 mPa·s,the surface tension is less than 28 m N/m,the interfacial tension is less than 2 m N/m,and the amount of residue is less than 600 mg/L.The results meet or exceed the requirements of Oil and Gas Industry Standard SY/T 6376-2008.It shows a good application prospect inlow temperature gel breaking of oil field fracturing.