| Fracturing is an important technology to improve the production of stored oil and gas resources by reforming high-temperature and low-permeability reservoirs.Fracturing fluid plays a major role in fracturing,and the temperature and shear resistance of fracturing fluid determines the success or failure of fracturing construction.Crosslinking agent is an important component of fracturing fluid and one of the decisive factors affecting the temperature and shear resistance of fracturing fluid system.The fracturing fluid obtained from the organoboron zirconium crosslinking agent has good temperature resistance and shear resistance.The study of the crosslinking characteristics of the organoboron zirconium crosslinking agent is of great significance for the temperature resistance and shear resistance of fracturing fluids.In this paper,a series of organic boron-zirconium crosslinking agents have been prepared by a one-pot method.H-C cross-linking agent,W-SN cross-linking agent,and A-B cross-linking agent were prepared from triphenylmethane triisocyanate and 2-amino-1,3-propanediol,melamine,tris(2-hydroxyethyl)isocyanate as ligands,sodium tetraborate and zirconium oxychloride as raw materials.The fracturing fluid corresponding to the three cross-linking agents was evaluated in the laboratory.The results are as follows:(1)The optimal conditions for preparing the H-C crosslinking agent were as follows:ligand PB is 2.5wt%,zirconium oxychloride and sodium tetraborates are7.5wt%,and 4wt%,the reaction temperature is 90?,p H value is 0.5,The reaction time is 4h.And H-C crosslinking agent has good stability.At the same time,the results showed that the optimal conditions for the formation of the gel were as follows:the cross-linking time is 25 minutes,and the cross-linking ratio is 100:2.0.The H-C crosslinking agent has good salt-resistance and stability which the anti-NaCl concentration of the gel is 6000mg/L,and the anti-(CaCl2+Mg Cl2)concentration is2500mg/L,respectively.(2)The optimum conditions for the synthesized A-B crosslinking agent were as follows:ligand 1wt%,zirconium oxychloride 5wt%,and sodium tetraborate 2.5wt%,p H value 0.5,reaction temperature 90?,reaction time 4h.And A-B crosslinking agent has good stability.The optimal conditions for the formation of the gel were as follows:the cross-linking time is 20 minutes,and the cross-linking ratio is 100:2.5.The A-B crosslinking agent has good salt-resistance and stability which the anti-NaCl concentration of the gel is 5000mg/L,and the anti-(CaCl2+Mg Cl2)concentration is2500mg/L,respectively.(3)The optimum conditions for the synthesized W-SN crosslinking agent were as follows:melamine ligand 1wt%,zirconium oxychloride 5wt%,sodium tetraborate2.5wt%,p H value 0.5,reaction temperature 90?,and reaction time 4h.And W-SN crosslinking agent has good stability.The optimal conditions for the formation of the gel were as follows:the cross-linking time is 25 minutes,and the cross-linking ratio is100:2.5.The W-SN crosslinking agent has good salt-resistance and stability which the anti-NaCl concentration of the gel is 6000mg/L,and the anti-(CaCl2+Mg Cl2)concentration is 2000mg/L,respectively.(4)The results show the viscosities of the fracturing fluids are all above 50m Pa.s when the three fracturing fluids systems are sheared at a shear rate of 170 s-1 at 100?for two hours.The viscoelastic properties of the three fracturing fluids show medium-strength gel when the shear stress is 0.1Pa,and the scanning frequency is 0.1-10Hz,at25°C.The breakers of the three fracturing fluids are all below 5.0m Pa.s when the ammonium persulfate is used as the breaker and the amount 0.06wt%.The gel breaker is also below 5.0m Pa.s by the Fenton method when the mass fractions of H2O2 and Fe S are 0.5wt%and 0.1wt%,respectively.Their residue content is below 600mg/L.The compatibility of the gel breaking fluid and formation water shows that the gel breaking fluid and compatible water are different Under different ratios(1:2,1:1,2:1),at 90?for 2 hours,no precipitation was observed.The sand-carrying settlement of each fracturing fluid system is 0.025mm.s-1,0.058mm.s-1 and 0.054mm.s-1,respectively.The above properties are consistent with the requirements of"oil and Gas Industry Standard SY/T6367-2008 General Conditions for Fracturing Fluid". |
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