Preparation Of Crosslinking Agent And Evaluation Of Its Performance In Guar Gum Fracturing Fluid

Hydraulic fracturing,as an important technology to improve the production of oil and gasreservoirs,has been paid close attention in the exploitation of unconventional oil and gas reservoirs.Crosslinking agent plays an important role in fracturing effect,as one of the most important additives in fracturing fluid.Crosslinkers with high performance?temperature resistance,suspended sand performance?,low damage and low cost have been the focus of research.Our research group modified boric acid to the surface of functional silic in the early stage,and prepared a high-efficient boron cross-linking agent,showing a good cross-linking effect.On the basis of previous studies,Water dispersible nano-crosslinking agent?W-NC?was prepared by using silica sol as matrix modified with borosilane on its surface.Using pentaerythritol,gamma-aminopropyl triethoxysilane,boric acid and ethyl titanate as raw materials,low harm boron crosslinking agent?PB?and excellent temperature resistance compound boron titanium crosslinking agent?PBT?were prepared by surface modification technology.The specific research content are as follows:?1?water-dispersive nano-crosslinking agent?W-NC?was prepared by surface modification ofsilica sol with the borosilane modifier.The influence of the reaction factors?reaction time,temperature,modifier dosage and pH?on the crosslinking properties of W-NC were investigated,and the results show the optimum preparations for preparation of W-NC with boron silane modifier:silica sol 0.6:10,reaction temperature 80?,pH of 12,reaction time 3 h.The morphology of W-NC was characterized by transmission electron microscopy.The rheological test results show the gel formed by crosslinking 542ppm W-NC and 0.3%guar gum maintained a high viscosity after the action of 170 S^-1 shear rate,and the crosslinking system had good viscoelastic properties.The deposition rate of ceramsite in the W-NC crosslinking system was 0.012 cm/min.After the W-NC cross-linking system was broken,the viscosity of the broken solution was low?3 mPa·s?and the content of solid residue was low?162 mg/L?.?2?Polyamine intermediates were prepared by reaction pentaerythritol with gamma-aminopropyltriethoxysilane,and then boric acid was modified on the surface of polyamine intermediates to prepare boron cross-linking agent?PB?with low damage.The influence of the reaction factors?reaction time,temperature,material ratio?on the effect of crosslinking were probed,and results show the optimum conditions for preparation of PB,boric acid:gamma-ammonia propyl triethoxy silane:pentaerythritol modify than for 5:5:1,reaction time 3 h,reaction temperature 80?.The structure of PB was characterized by infrared analysis and thermogravimetric analysis.The microstructure of PB crosslinked guar gum system was characterized by scanning electron microscope.The results show that compared with boric acid crosslinked system,PB crosslinked system has a more compact network structure,which is conducive to improving the ability of fracturing fluid to carry sand and create fractures.The results of rheological property test show that PB cross-linked system exhibits excellent rheological properties?temperature resistance,viscoelasticity?compared with boric acid cross-linked system.The guar gum?0.3%?gel crosslinked with 418 ppm PB,after 170 s^-1shear rate,maintains a viscosity of 90 mPa·s at 70?;and has good viscoelasticity.The guar gum?0.25%?gel crosslinked with 418 ppm PB after 170 s^-11 shear rate,shows a viscosity of 70 mPa·s at 70?,and has excellent viscoelasticity,with a reduced the amount of guar gum by 16.7%.After the PB crosslinked system was broken,the viscosity and residue content of the system were low,and the compatibility between the broken liquid and simulated water was good.The core damage test shows that the damage rate of PB system reservoir is 13.7%,which is less harmful than boric acid cross-linked system?24.1%?.?3?Boron cross-linking agents generally have the characteristics of shear resistance but poortemperature resistance.Titanium crosslinking agent has good temperature resistance,but low shear resistance.In this chapter,complex boro-titanium crosslinking agent?PBT?was prepared by modifying ethyl titanate and boric acid to the polyamine intermediate.The effects of different modification ratios of boric acid and ethyl titanate on the crosslinking performance were investigated.The modification ratio of boric acid and ethyl titanate was 1:4,and the crosslinking performance of the prepared PBT crosslinking agent was better.The infrared characterization of PBT shows that boron and titanium modified pentaerythritol effectively.The rheological test results show that the PBT system has better temperature and shear resistance than boric acid system and ethyl titanate system.418 ppm PBT crosslinked with 0.3%guar gum gel,after 170 s^-1 shear rate,shows a viscosity of 180 mPa·s at 70?.By Reducing 16.7%dosage of guar gum,0.25%guar gum gel crosslinked with 418 ppm PBT,after shearing action,has a viscosity of about 130 mPa·s at 70?,has excellent viscoelasticity,and effectively reduce the damage of fracturing fluid to reservoir.The microstructure of PBT crosslinked guar gum system was characterized by SEM,and the results show the PBT crosslinked system has a denser network structure,which was conducive to improving the ability of fracturing fluid to carry sand and create fractures.Sand suspension test results show that proppant has a relatively low settling rate?0.069cm/min?in the PBT crosslinking system.The viscosity and residue content of PBT break system are lower than the national standard.The result shows the gel breaking liquid has good compatibility with simulated water,and the damage to core is 17.4%.