Preparation Of A Highly Efficient Nano Crosslinker And Study Of Its Properties On Guar Gum Fracturing Fluid

The fracturing and reforming of oil and gas reservoirs is one of the main measure to increase oil and gas production.The choice of fracturing fluid system directly affects the construction efficiency of fracturing.The crosslinking agent can be used as an important component to construct the viscosity of fracturing fluid.It can regulate the crosslinking efficiency,delayed crosslinking time and breaking behavior et al.In recent years,task group has developed a series of nano-crosslinking agents with body structure based on nano-silica surface supported with boric acid that is prepared via surface modification technology.The cross-linked guar gum shows good delayed cross-linking performance,shear performance,viscoelastic properties,and breaking properties with the assistance of nano-crosslinking agent.On the basis of previous research,this paper utilizes the organosilane coupling agent containing reactive functional group(KH550)as the carrier to prepare water-dispersible and titanium functional nano-crosslinking agents which are surface modified by boric acid and transition metal titanium ions,respectively.At the same time,boric acid functional nano-crosslinking agent is prepared by using nano-silica as carrier and surface modified boron alkoxysilane as modifier.The main research contents and research results include the following aspects:1.The water-dispersible nano-crosslinker M-JL-1 was prepared by using the organosilane coupling agent KH550 containing amine as the carrier and boric acid as modifier.The fourier transform infrared spectroscopy(FT-IR),x-ray diffraction(XRD)and laser particle size distribution spectroscopy are used to characterize the water dispersible nano-crosslinker M-JL-1.The IR spectra showed that boron and KH550 are bound by N-B bond,and the XRD reveals that nano-crosslinking agent M-JL-1 is composed of many microcrystalline amorphous powder.The average particle size of M-JL-1 with the mass fraction of 1%,2%,3% and 4% is 10 nm,20 nm,30 nm and 35 nm,respectively.The results show that the delayed crosslinking time of crosslinked guar gum is about 15 min,which can effectively solve the rapid-crosslinking problem of boron cross-linking agent in practical application induced by large friction and high energy consumption.It is found that the M-JL-1 crosslinking system exhibits better resistance to shear resistance and viscoelasticity when the content of available boron is reduced by 88% compared with the boric acid crosslinking system in the M-JL-1 crosslinking system.This is because the M-JL-1 nano-crosslinking agent has a larger space size and easy to crosslink with the guar gum via inter-chain contacts,which improve its cross-linking efficiency,and form a much closer network structure.As confirmed by environmental scanning electron microscopy(ESEM),the guar gum gel crosslinked with the NPs exhibits a more compact network structure than the one crosslinked with borate.2.The boric acid functional crosslinked agent M-JL-2 is prepared by using nano-silica as carrier and boron-modified hydroxysiloxane as modifier.The effects of temperature,time,material ratio and reaction medium on the crosslinking time of nano-crosslinker are systematically studied.The structure-controllable M-JL-2 was characterized by FT-IR.The infrared spectra showed that the modifier was loaded onto nano-silica by the condensation of Si-OH.Moreover,the delayed crosslinking time of cross-linked guar gum was about 7 min,and the rheological tests of M-JL-2 cross-linked system were investigated.The results showed that when the content of available boron is reduced by about 98%,M-JL-2 cross-linked system has better resistance to shear resistance and viscoelastic properties than M-JL-1 crosslinking system and boric acid crosslinking system.The results of ESEM showed that the network structure of M-JL-2 cross-linked guar gum is more closer.3.The temperature of the oil and gas layer affects the performance of the fracturing fluid.The increase of the temperature leads to the rapid decline of the viscosity of the system,which limits its application in the high-temperature deep well.In this part,the titanium functional nano-crosslinker Ti-JL is prepared by using the organosilicon compound KH550 containing reactive functional groups.The average particle size is 2 nm.The effects of temperature,time,material ratio and reaction medium on the crosslinking time of nano-crosslinker are systematically studied.The results show that Ti-JL crosslinking system has good temperature resistance,that is,the viscosity of Ti-JL crosslinking system decreases slowly with the increase of temperature.The results of ESEM showed that the network structure of Ti-JL cross-linked guar gum is very compact with few gaps.4.In this paper,the nano-crosslinking agent M-JL-1,M-JL-2,Ti-JL is under the condition guar gum concentration of 0.3 wt%,the system pH of 9,the settling rate of 20-40 target ceramsite is less than 0.48 cm/min reported at home and abroad.When the concentration of guar gum solution is 0.3 wt%,the pH of the system is 9 and the amount of the breaker(ammonium persulfate)is 0.3 wt‰,the residue of M-JL-1,M-JL-2 and Ti-JL crosslinking system and the viscosity of the breaker are lower than SY/T 6376-2008 "fracturing fluid general technical conditions" requirements(residue content?600 mg/L and broken glue viscosity?5 mPa·s).They all show good breaking performance.