| The high concentration of guanidine gum fracturing fluid in oil and gas field production currently leads to the increase of fracturing cost and a large number of insoluble residues after gel breaking,which has potential reservoir damage.In order to reduce the concentration of guanidine gum in fracturing fluid,firstly,modified guanidine gum is used to improve the water solubility of guanidine gum and increase the participation rate of guanidine gum.The second method is to research and develop efficient crosslinking agent,and improve the crosslinking efficiency of efficient crosslinking agents by optimizing their structures.The purpose of this paper is to provide a research basis for exploring an efficient and economical fracturing fluid system by synthesizing an efficient organic boron crosslinking agent suitable for low-concentration guar gum fracturing fluid system.In this paper,two different organoboron crosslinkers,BBS and BOA,were synthesized by using borax and boric acid as the main agents and hydroxyl alcohol and diethylenetriamine as the main ligands respectively.Taking the viscosity of gel formed by synthetic organoboron cross-linking agent and guar gum as an index,the main factors effecting the synthesis processes of two organoboron cross-linking agents,including the amount of reactants,reaction temperature and reaction time,were studied respectively,and the synthesis conditions and parameters of organoboron cross-linking agents BBS and BOA were optimized.Through determining the effects of p H of base solution,concentration of guanidine gum,crosslinking ratio and dosage of gel breaker on the properties of crosslinking agent,the application conditions of synthesized BBS and BOA organoboron crosslinking agent with low concentration guanidine gum were determined..The temperature resistance,shear resistance,sand carrying capacity and filtration performance of BBS or BOA cross-linked fracturing fluid with low concentration guanidine gum were evaluated,so as to evaluate their application potential.Main conclusions were as follows.（1）The synthesis conditions of the organoboron cross-linking agent BBS for borax system included the mass fractions of borax,glucose,ethylene glycol,triethanolamine and Na OH in the reactants were 25%～30%,14%～16%,19%～21%,25%and 1.1%～1.6%,respectively,the reaction temperature was 50°C,the reaction time was 4 h.Effects of reactants on the crosslinking properties of BBS were in the following order:glucose dosage>triethanolamine dosage>catalyst（sodium hydroxide）dosage>borax dosage.In the optimum conditions,the viscosity of gelatin crosslinked by BBS and 0.2%guanidine gum was>55 m Pa·s.（2）The synthesis conditions of the organoboron cross-linking agent BOA for boronic acidsystem included the mass fractions of diethylenetriamine,boric acid,ethylene glycol and n-butanol in the reactants were 22%～30%,14%～18%,38%and6.9%respectively,the esterification reaction temperature was 140℃,the esterification reaction time was 5 h,the complexation reaction temperature was 80℃and the complexation reaction time was 5 h.Effects of reactants on the crosslinking properties of BOA were in the following order:diethylenetriamine dosage>boric acid dosage>ethylene glycol dosage>n-butanol dosage.Under the optimum conditions,the viscosities of the gel crosslinked by BOA and 0.2%guanidine gum were all above 65m Pa·s.（3）The application conditions of BBS and BOA crosslinking with low concentration guanidine gum were as follows.The p H of guanidine gum base solution was about 10.With 0.18%guar gum concentration,the cross-linking mass ratio with BOA or BBS was 100∶0.5,and with 0.2%guar gum concentration,the cross-linking mass ratio with BOA or BBS was 100∶0.4.The dosage of gel breaker（ammonium persulfate,APS）was 0.08%when BOA and BBS were crosslinked with 0.18%guanidine gum,and was 0.1%when they were crosslinked with 0.2%guanidine gum.（4）Low-concentration guar gum fracturing fluid systems of organic boron cross-linking agents BOA or BBS had good gel breaking performance,and their gel breaking time and residue content are less than the industry standard requirements（≤720 min and≤600 mg/L respectively）.The filtration loss and filtration coefficient of low-concentration guar gum fracturing fluid crosslinked by them were both small,which meet the standards of fracturing fluid system(≤5.0×10-2m3/m2 and≤1.0×10-3m/min1/2,respectively).It had good sand carrying performance,temperature resistance and temperature resistance and shear resistance,and its viscosity exceeded 50 m Pa·s under the shear conditions of 60℃and 100 s-1,which meet the application requirements of 60℃reservoir for fracturing fluid viscosity.（5）The infrared spectra of organoboron crosslinking agents BOA and BBS contained amine,alcohol and other functional groups,and the characteristic peaks of C-O,C-N,N-H and O-H appeared at specific positions,indicating that the structure of the synthesized products basically conformed to the expected structure. |
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