Preparation And Property Of Low Viscosity Fracturing Fluid And Hydrophobically Associating Polymer For Low Viscosity Fracturing Fluid

Due to the special molecular structure of hydrophobically associating polymer,it can be compounded with surfactants under some conditions to form the hydrophobically associating polymer fracturing fluid.The fracturing fluid with high viscosity has the excellent high temperature and shear resistances as the special molecular structure.There are two parts of this work: one is to prepare the hydrophobically associating polymer by introducing a two non-ionic hydrophobic monomer with amphiphilic properties,and the other is to screen the surfactant with which the hydrophobically associating polymer can be compounded to form the low viscosity fracturing fluid system.The traditional hydrophobic monomer was usually cationic or anionic type,and the non ionic type was less used as the poor water solubility of non ionic.It may take several weeks for the complete dissolution of nonionic hydrophobically associating copolymer in aqueous solution.In this study,a new tetrabasic copolymer hydrophobic associating copolymer HPAF was obtained by using nonionic hydrophobic monomer with two amphiphilic properties EDP-10,hydrophilic monomer acrylamide(AM)and acrylic acid(AA)as main monomers,and 2-Acrylanmido-2-methylpro panesulfonic acid(AMPS)as functional salt monomer with solution polymerization method.The effects of reaction conditions on the properties of HPAF products were analyzed by single factor experiments.The structure of HPAF was characterized and verified,and the solubility,thickening properties and rheological properties of the solution were also tested.The low viscosity fracturing fluid was prepared by using polymer HPAF as thickening agent and the screened NST60 as crosslinking agent.The influence factor was discussed to determine the composition.The rheological properties,sand suspension and gel-breaking properties were all discussed.The results show that:(1)The optimal preparing conditions were determined to be as follows: the addition of EDP-10 1.2wt%,a complex initiation system which contains ammonium persulfate/ascorbic acid/water-soluble azo,the dosage of initiation system 0.024wt%,trigger temperature 2 ?,the dosage of urea 3wt%,the concentration of the monomers 28wt% and the reaction time 6h.The Fourier transform infrared(FTIR)results show that the characteristics of functional groups such as hydroxyl,carbonyl,ether,amide and sulfonic groups have their own peaks as expected.The thermogravimetric analysis shows the good thermal stability of the polymer which was consisted with the FTIR results.The X-ray diffraction(XRD)demonstrated the amorphous structure of HPAF which was corresponded to the molecular structure design requirements.The rheological results show the good thixotropy,viscoelasticity,and also the good temperature and shearing resistance due to the introduction of non-ionic hydrophobic monomer EDP-10.The intermolecular and intramolecular of HPAF polymer in aqueous solution could form a strong network structure due to the introduction of EDP-10.(2)The low viscosity fracturing fluid was prepared by using the polymer HPAF and crosslinking agent NST60.The crosslinking agent NST60 has a wide usage range of concentration,and the construction difficulty was reduced adequately.The concentration of HPAF was 0.3%-0.5%.Two gel-breaking methods were provided: using VC gel-breaker when the temperature was high and VC/ SAT70 compound gel-breaker when the temperature was low.The breaking speed was fast and the viscosity of the gel is low.The low viscosity fracturing system has excellent temperature and shear resistance.The static sand suspension was good.In the specified time,the settling velocity is slow and the properties were good.The intermolecular and intrarmolecular association existed in the formation of hydrophobic associated polymer gel system.Compared to the ordinary fracturing thickening agent type,its properties are dominant.After gel breaking,the gel breaking liquid was transparent,low viscosity,and the gel breaking formation temperature could be reached quickly.The interfacial tension of the gel breaking liquid was low,which was good for folwback,and provided some convenience for on-site production.(3)The low viscosity fracturing fluid system was also carried out in the XX well,and mixed water fracturing method was adopted.During the test,pre slick water ftracturing fluid was mainly made up of 0.2% HPAF.Besides,the late sand-carrying fracturing fluid consisted of 0.25% HPAF and 0.12% NST60,and the highest sand-carrying fluid ratio could be reach 40%.The filed test results of the low viscosity fracturing fluid system show that sand carrying field effect is good,and the medicaments are low which reduce the cost effectively.