Preparation And Rheological Characterization Of Xanthan-based Fracturing Fluid

In order to improve the performance of xanthan gum(XG)and broaden its application,water-soluble cross-linked xanthan gum(CXG)and hydrophobically-modified xanthan gum(HBXG)used as new thickeners were prepared from XG and modifier(epichlorohydrin or butyl glycidyl ether)under alkaline condition by ethanol solvent method.Rheological behaviors(shear thinning,thixotropy and viscoelasticity)and proppant carrying capacity of aqueous XG and CXG solutions were studied.The heat and shear resistance and gel-breaking performance of XG solutions were also investigated,obtaining a XG-based fracturing fluid system which shows good shear resistance performance under 180?.Furthermore,organic zirconium crosslinking agent was adopted to crosslink XG solution,and the rheological properties of XG gels and evolution of storage modulus of XG systems during the crosslinking and gel-breaking processes were investigated,establishing corresponding rheokinetics equations to describe the two processes.The detail works are as follows:1)Water-soluble cross-linked xanthan gum(CXG)used as new thickener was prepared from XG and epichlorohydrin by ethanol solvent method.The effects of technological conditions on the performance of CXG were determined,obtaining proper preparation condition of CXG.XG and CXG solutions behave shear thinning,and Jeffreys model can be used to describe the flow curves of the both solutions.Compared with XG solutions,CXG solutions exhibit higher viscoelasticity,much stronger network structure and better proppant carrying capacity.2)The effects of deoxidant,type of salt,amount of salt and modification on the heat and shear resistance of XG were evaluated,obtaining a XG-based fracturing fluid system which shows good shear resistance performance under 180?.The XG-based fracturing fluid system has good proppant carrying capacity after being sheared at 170s-1 and 180? for 90 minutes,suggesting the system can be applied for high temperature reservoir.3)The effects of temperature,amount of ammonium persulfate and amount of salt on the rheological properties of XG systems during gel-breaking processes were evaluated.Corresponding gel-breaking rheokinetics equation was established,which could characterize the gel-breaking processes of XG systems.4)The effects of concentration of XG and amount of crosslinker on the rheological properties of XG gels were investigated.At 30?,the apparent viscosity of XG solution(0.25%XG)and XG gel(0.25%XG + 0.3%crosslinker)was 20.47 and 205.6mPa·s,respectively.At 120?,the reserved viscosity of the XG gel after being sheared at 170s-1 for 90 minutes was 75.48 mPa·s,suggesting the XG gel have good shear stability at 120?.5)The effects of amount of crosslinker and amount of pH adjustor on the rheological properties of XG systems during crosslinking processes were evaluated.Corresponding crosslinking rheokinetics equation was established to describe the evolution of elasticity modulus with time in the gel process.Furthermore,the effects of temperature and amount of ammonium persulfate on the rheological properties of XG gel systems during gel-breaking process were evaluated.Corresponding gel-breaking rheokinetics equation was established,which could describe the evolution of elasticity modulus of XG gel systems in the gel-breaking process.