Nano Modified Boron Crosslinking Agent And Its Application In Fracturing Fluid

Due to the shortage of conventional resources,the exploitation of unconventional resources is expected to change the oil and gas market all over the world.Hydraulic fracturing is usually used to form artificial fractures in oil and gas reservoirs to improve fluid fluidity and production.Hydraulic fracturing technology is an effective way to increase production and injection.It is the most widely used production technology in the oil and gas industry at present.It injects fracturing fluid under high pressure,uses the viscosity of fracturing fluid to squeeze the formation out of fractures through the wellbore and generate fracture network,so as to increase the conductivity of oil and gas.But water-based fracturing fluid has poor stability and low viscosity at high temperature.Nano materials can play the role of unclear point and skeleton in the cross-linking system or intertwine with guar gum macromolecular chain to significantly enhance the network structure and the temperature resistance of fracturing fluid.In this paper,hydroxylated carbon nanotubes OH-MWCNTs and nano silica are selected as nano materials to modify organic boron crosslinking agent to improve the temperature resistance of fracturing fluid.Six different organic boron crosslinking agents were prepared with borax and boric acid as inorganic boron and polyols and amines as organic ligands.By investigating the influence of temperature resistance and p H of the fracturing fluid system,B5 D prepared with borax,glycerol,ethylene glycol and polyethylene polyamine was finally selected for the next step of nano modification.Hydroxylated carbon nanotubes and nano silica were modified with silane coupling agent KH550 to obtain C-KH550 and Si-KH550.The effective modification of nano materials was detected by infrared analysis.The modified nano materials modified B5 D prepared by borax,glycerol,ethylene glycol and polyethylene polyamine to obtain nano organic boron crosslinkers B5D1 and B5D2 for fracturing fluid.Used hydroxypropylguanidine gum as thickener,B5D1 and B5D2 fracturing fluid systems were prepared and their crosslinking effect was evaluated.The effects of crosslinking ratio and p H value on the performance of fracturing fluid system,as well as the temperature resistance,shear resistance,sand suspension and gel breaking of fracturing fluid system were investigated,and the preparation conditions of B5 D,B5D1 and B5D2 were optimized.The results show that the mass ratio of organic boron B5 D formula is borax: ethylene glycol: glycerol: polyethylenepolyamine = 38:62:46:73.The best crosslinking performance can be obtained by reacting B5 D with C-KH550 at 100 ℃ for 4 hours.And the optimum service conditions are p H=7.5 and crosslinking ratio 100:0.2.B5D2 with the best performance can be obtained by reacting B5 D with Si-KH550 at 100 ℃ for 5 hours.And the optimum service conditions are p H=7.0 and crosslinking ratio 100:0.2.At 90 ℃ and170 s-1,after constant temperature shear for 30 min,the viscosity of B5 D crosslinking system is 85.36 m Pa·s,that of B5D1 crosslinking system is 103.8 m Pa·s,and that of B5D2 crosslinking system is 225.8 m Pa·s.The viscosity and residue content of fracturing fluid after gel breaking meet the industrial standards.The crosslinking performance is significantly improved after the crosslinking agent is connected with nano materials,and the temperature resistance of B5D2 fracturing fluid system is better than that of B5D1.