Study On Preparation Technology Of Polyethylene Glycol Modified Guar And Its Application In Fracturing Fluid

Due to its special polysaccharide structure,guar gum has good water solubility,cross-linking and thickening ability.It has applications in oilfield,papermaking and pharmaceutical fields,especially in the hydraulic fracturing static rock breaking technology as a thickener widely used in oil and gas.However,guar gum has a series of shortcomings as a thickener.By chemically modifying guar gum to obtain guar gum derivatives with excellent physical and chemical properties is a hot research topic at domestic and abroad.In this paper,toluene-4-sulfonyl chloride was used to activate tetraethylene glycol,then tetraethylene glycol guar?PEG₄GG?was synthesized with guar gum by nucleophilicly substituted.Next the reaction conditions were optimized,the molecular structure of synthetic product was characterized by SEM,CHNS Element Analyzer,XPS,¹H NMR and TG.The rheological properties of PEG₄ GG under different conditions?temperature,concentration,Ca2+ salt content?and the performance evaluation of polyethylene glycol-200 guar fracturing fluid system were studied.The main research results were as follows:?1?In the synthesis process of PEG₄ GG,the product aqueous solution viscosity and water insoluble content were used as performance indexes,the reaction conditions were optimized by orthogonal experiment and single factor analysis.The optimized synthesis conditions were: guar gum 3.0g,activated tetraethylene glycol 4.95 g,Na OH 0.50 g,temperature 55?,reaction time 5h and H2 O 3.5g.?2?The molecular structure of PEG₄ GG was characterized by SEM,CHNS elemental analysis,XPS,¹H NMR and TG.There was no obvious change in the morphology and particle size distribution of PEG₄ GG compared with guar gum.The element content of S and C increased,O element decreased which was consistent with the PEG₄ GG structure.PEG₄ substitution degree in PEG₄ GG was 0.75.PEG₄ GG is more complex because of the introduction of branching,which makes the thermal stability better.The comprehensive performance test results show the properties of PEG₄ GG has improved significantly in water insoluble content,dissolution rate and p H adaptation range.?3?The rheological properties of two kinds of tetraethylene glycol guar?SPEG₄GG,D-PEG₄GG?showed that the S-PEG₄ GG and D-PEG₄ GG solutions were pseudoplastic fluids.When the concentration increased,the consistency coefficient K increased,the viscosity increasing-ability was increased,the viscosity coefficient n was decreased,and the shear thinning characteristic was more obvious.When the salt?Ca2+?content was less than 0.8%?Wt.%?,the S-PEG₄ GG and D-PEG₄ GG solutions showed an anti-polyelectrolyte characteristics of the solution;the viscosity of S-PEG₄ GG and D-PEG₄ GG solution increased first and then decreased with the increase of temperature,and the viscosity of the solution was the highest at 50°C.?4?The polyethylene glycol-200 guar fracturing fluid system was studied,it has good compatibility with the formation water,the different concentration ratios would not precipitate after being placed at 20? and 70? for 4h.It could be cross-linked with borax,which could be obviously hanged.Polyethylene glycol-200 guar fracturing fluid cross-links to form jelly resulted in a 4.5% reduction in volume expansion density,which was favorable for the return flow.It has better temperature and shear resistance,and the viscosity was higher than 120 m Pa·s after high-speed shearing for 120 mins.Polyethylene glycol-200 guar fracturing fluid system has better fluid loss resistance,and the fluid loss resistance was improved by more than 20% compared with guar fracturing fluid.