| Not only has hydraulic fracturing technology of oil and gas wells been the effective methods of reforming formation, but also has improved production of oil and gas wells and increased injecting quantity of injection wells. During the fracturing execution, the fracturing fluid has capacity of carrying proppant, transferring pressure and creating the new fissure in formation. However effect of hydraulic fracturing has an influence on failure or success of fracturing execution and increase of production after fracturing execution. The carring capacity of strong, small damage to the reservoir, low use cost fracturing fluid system is one of the important direction of oilfield chemical research.Crosslinked polyvinyl alcohol can be effective enough to have a viscosity of the gel is the basic requirement of its fracturing fluid system. In this paper, borax and various organic ligands for esterification, synthesis of the crosslinking agent can be used polyvinyl alcohol fracturing fluid. The fracturing fluid crosslinking time and temperature resistance as the basis for evaluation,the best ratio and optimal synthesis conditions for optimizing the use of synthetic single-factor method. Optimal synthetic ligand ratio of organic boron complex cross-linker solution is:The dosage of borax is18%, three kinds of ligands of sodium gluconate, glycerine, triethanolamine, overall16%of the dosage, the mass ratio of these ligands is1"20:15; The amount of NaOH is1.5%. The optimum reaction conditions are: reaction temperature is80℃, reaction time is4～5h. The FTIR characterization of organic boron BOP shows that esterification reaction occurred and the product obtained is the desired product.With polyvinyl alcohol as thickener, organic boron BOP as crosslingker, and adding pH adjusting agent found the fracturing fluid basic formulation that suiting for the stratum temperature of50℃and70℃. Respectively, the formula is respectively:2.0%polyvinyl alcohol+1.0%crosslingker+0.2%pH regulator and2.0%polyvinyl alcohol+1.0%crosslingker+0.28%pH regulator. Reference to water-based fracturing fluid performance evaluation SY/T5107-2005, the comprehensive performances of polyvinyl alcohol fracturing fluid system under70℃were estimated. The result showed that:the polyvinyl alcohol fracturing fluid system mainly elasticity is given priority to in0.01～10Hz. It has good capability of carrying sand. The viscosity of fracturing fluid is56mPa· s under90℃. It has good temperature resistance. It has good heat resistance shear resistance at170s-1.and viscosity is50mPa.s when temperature is70℃. It has good performances of sand-carrying.60to80mesh quartz sand in polyvinyl alcohol sedimentation rate of fracturing fluid is0.038cm/min. Compared with gum fracturing fluid, the polyvinyl alcohol fracturing fluid has small filtration coefficient, easy to break, and gel breaking thoroughly, small gel breaking liquid surface tension, low residue, the core permeability damage matrix. With polyvinyl alcohol fracturing fluid gel breaking experiment, the study found that the fracturing fluid system not only can use the conventional ammonium persulfate as breaker, but also can adjust system pH value to about5could be breaken from gel to water.Regeneration of polyvinyl alcohol fracturing fluid for laboratory experiments, the results showed that with the increase of regeneration frequency, the viscoelastic property of PVA fracturing fluid can drop; Initial fracturing fluid viscosity decreased, the resistance of shear and prop-carrying capacity decreased. Supplement with a small amount of thickening agent, polyvinyl alcohol, fracturing fluid to improve the regeneration system of performance in2. |
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