Preparation Of A Crosslinker And Study Of Its Synthesis Properties On Guar Gum Fracturing Fluid

The fracturing and reforming of oil and gas reservoirs is one of the main measures to increaseproduction and increase injection of oil and gas wells.The choice of fracturing fluid system directly affects the construction efficiency of fracturing.Guar gum fracturing fluid is a commonly used fracturing fluid system for the fracturing and reforming of oil and gas reservoirs.Its cross-linking time,viscoelasticity,temperature-resistance,shear-resistance,and sand-suspending properties directly affect the efficiency of fracturing operations,which are mainly regulated by crosslinking agent.In recent years,Henan University,through the surface modification technology in the reactive nano-silica surface supported boric acid,developed a series of nano-crosslinking agent with body structure:using nano-silica as a carrier,a boron-modified organosilicon compound as a modifier,a nano-crosslinking agent with a large size and a controllable structure was prepared,which significantly improves the crosslinking efficiency of guar gum fracturing fluids and temperature resistance,shear resistance and viscoelasticity.On the basis of previous research,a high-temperature-resistant and shear-resistant organic boron-titanium crosslinker?YJ-PT?was prepared by simultaneously modifying boron and titanium onto an organosilicon compound?KH550?containing a reactive functional group in this paper.Through the construction of the skeleton of the cross-linking agent,highly efficient organic titanium crosslinker?PAm-Ti?with large skeleton and multiple active sites was prepared.At the same time,the effect of hydrophobic nano-silica particles on the properties of guar gum fracturing fluid and polyacrylamide fracturing fluid were studied.The main research contents and results are as follows:1 An organic boron-titanium crosslinker?YJ-PT?with boron and titanium crosslinker properties was prepared by using an organic silicon compound?KH550?as a carrier and modifying boron and titanium on the surface simultaneously.The effect of reaction material ratio,reaction temperature and reaction time on the crosslinking time was investigated.The structure characteristics of organoboron-titanium crosslinker were investigated using laser particle size distribution analyzer and Fourier transform infrared spectroscopy.The results show that the molar ratio of boric acid to tetrabutyl titanate was 4:1,and the crosslinker prepared by reacting at 80°C for 3 h has better crosslinking effect.Boric acid and KH550 are bonded by N-B bonds,coordination bonds being formed between titanium and KH550,and the size distribution is about 20 to 30 nm.A comparative analysis of the temperature and shear resistance of organic boron-titanium crosslinking system,boric acid and organic boron systems?supplied by Sinopec?using a rotary rheometer.The results show that the organic boron-titanium crosslinking system exhibits better temperature resistance at the same amount of crosslinker.And the organic boron-titanium cross-linked system still maintains a viscosity of 150 mPa.s after being sheared at 170S^-1 for 30 min,exhibiting better shear resistance.However,the residual content of organic boron-titanium crosslinking system is slightly higher than that of boron-based crosslinking system.2 To reduce the residual content of titanium crosslinking system,we use pentaerythritol and 3-aminopropyltriethoxysilane?KH550?to construct the skeleton of crosslinking agent.By introducing titanium onto the organic skeleton,we obtain organic titanium crosslinker?denoted as PAm-Ti?with multiple active sites.The effect of reaction material ratio,reaction temperature,and reaction time on the crosslinking time was investigated.The FTIR was used to characterize the PAm-Ti.The FTIR spectra showed that coordination bonds were formed between titanium and condensates of pentaerythritol and KH550,indicating that Ti⁴⁺has successfully modified the surface of condensate.The rheological results showed that the crosslinking system of PAm-Ti exhibits better temperature resistance and viscoelasticity than that of the crosslinking system of TiCl₄ with the same amount of crosslinker.The results of SEM test also showed that the crosslinking system of PAm-Ti formed a more uniform and tighter membrane network structure,giving it better viscoelasticity and sand-suspending performance.Moreover,PAm-Ti could effectively reduce the concentration of guar gum by 16.7%,compared with borate and TiCl₄.The fracturing fluid made of the guar gum gel crosslinked with a low-concentration of PAm-Ti provides reduced residual amount and rock core damage rate as well.3 We introduced hydrophobic nano-silica into guar gum fracturing fluid and polyacrylamide fracturing fluid,exploring the effect of nano-silica on their performance.As a result,it was found that nano-silica acts like a crosslinker,significantly improving the pick-up performance of the guar gum fracturing fluid and the viscosity of the polyacrylamide fracturing fluid.Besides,nano-silica/polyacrylamide fracturing fluid system is almost no residue after gel-breaking,and its breaking fluid could reduce the oil-water interfacial tension,being conduce to return flow.