Study On The Viscoelastic System Of Surfactant Combination And Performance Of Its Clean Fracturing Fluid

Hydaulic fracturing technique is a necessary measure to increase oil and gas seepage capacity,improve oil and gas production capacity.While facturing fluid is an indispensable injectant and affects the results of the fracturing.Traditional fracturing fluids often cause fluid plugging and residue in reservoirs,which will reduce the conductivity of fractures,affect oil and gas production,even cause a permanent damage to reservoirs.By contrast,clean fracturing fluid automatically breaks and has the advantages of no residue and complete backflow,which makes up for the defects of traditional fracturing fluid and has important significance and application prospects in oil and gas development.Based on the hydrophobic effect and electrostatic interaction between molecules,the viscoelastic composite system CTAB/SDS was constructed.The optimum mass ratio and total concentration of the system were optimized by response surface methodology.The influence factors of viscoelasticity were evaluated by rheological method.The viscosity-temperature relationship of the preferred system was described by Arrhenius formula,and the temperature range that WLMs existed was given by calculating activation energy in segments.Dynamic light scattering and thermal analysis methods were used to elucidate the effect of temperature on phase transition process and aggregation transition.The mechanism of phase transition was revealed by freeze-etching transmission?FF-TEM?electron microscopy.Anionic-nonionic surfactant composite systems CTAB/NPEC-n?Nonylphenol polyoxyethylene ether carboxylate-n?containing 5,7 and 10 oxyethylene groups EO were constructed.According to the viscosity and phase behavior of CTAB/NPEC-n,the peak viscosity ratio of CTAB/NPEC-n was determined.The response of CTAB/NPEC-5 to total concentration,temperature,salt and shearing effect was investigated by rheological method,Cryo-TEM and FF-TEM.The interaction energy and charge distribution of CTAB/NPEC-n were calculated by Gaussian 09 quantum chemical calculation method,and the mechanism of the EO group in the rheological properties and aggregates morphology of each system was revealed.The applicability of the composite systems CTAB/SDS and CTAB/NPEC-5 were discussed.TSI was used to analyze the sand-carrying performance and stability of the clean fracturing fluid;the water gel-breaking and kerosene gel-breaking performance were evaluated.The results show that the CTAB/SDS clean fracturing fluid formula is:2.25%CTAB+0.75%SDS+1.0%Na Cl;the formation temperature of WLMs is 30°C-40°C;the formula was with strong and stable sand-carrying effect,good water gel-breaking and low formation damage,it is suitable for low-temperature oil and gas reservoirs.The ratio of peak viscosity of CTAB/NPEC-5 was determined to be?_CTAB=0.76,and CTAB/NPEC-7had two viscosity peaks,and the ratios were?_CTAB=0.3 and?_CTAB=0.4,respectively.The latter system is more likely to form a sticky system due to its"circle"configuration.The CTAB/NPEC-5 clean fracturing fluid formula is:95mmol/L CTAB+30mmol/L NPEC-5+171mmol/L Na Cl;the higher the formula concentration,the better the sand-carrying property;the water gel-breaking and kerosene gel-breaking are instantaneous and thorough;the shear resistance is strong;it is suitable for high-salt oil and gas reservoirs,and the salt-resistant concentration can be up to 2565mmol/L.