Construction And Performance Evaluation Of An Aromatic Acid Supramolecular Clean Fracturing Fluid System

The thickening agent used in the conventional clean fracturing fluid has many problems,such as complicated synthesis and low yield,the large dosage and high cost in middle-high temperature reservoirs,which limit its large-scale application in oil industry.However,due to the simple synthesis,low dosage,good thickening ability,and controllable viscosity,the supramolecular systems constructed by non-covalent bonds can well solve these problems and possess extensive application prospects.Firstly,the cationic surfactant N-erucamidopropyl-N,N-dimethylamine(EA)and aromatic acids were used to construct the active supramolecular systems.The types of cationic surfactants,aromatic acids and their molar ratios were optimized by comparing the appearances and rheological properties of different systems.Then,the transmission electron microscopy(Cryo-TEM),dynamic light scattering(DLS)and surface tension measurements were conducted to reveal the micro-thickening mechanism.Subsequently,the effects of pH and temperature on the rheological behaviors of the optimized supramolecular systems were studied by rheological method.The microscopic mechanisms of pH-responsive and temperature alterant for the viscoelasticity of the systems were developed through the nuclear magnetic resonance spectroscopy(¹H NMR)and optical micro-rheology.Thus,a suitable supramolecular system as the host agent in clean fracturing fluid was selected.Ultimately,the formula of supramolecular clean fracturing fluid was decided by investigating the optimum concentration,influence of inorganic salt and corrosion capacity.In this case,the applied performances of this formula were systematically studied through temperature and shear resistance,viscoelasticity,proppant-carrying ability,gel breaking property,and core damage tests.The results show that o-EAPA,m-EAPA and p-EAPA active supramolecular systems,constructed by EA and phthalic acid(PA)at a molar ratio of 2:1,have extremely high zero-shear viscosity and elasticity at 25?and pH 6.17.The active supramolecular systems exhibit excellent thickening ability due to the formation of‘gemini-like'surfactant structure and tight arrangement of molecules.In addition,the viscoelasticity of three supramolecular systems has a pH-sensitive reversible regulation performance since the ionization of of PA and reversible protonation of EA,and 6.17 is determined as the optimum pH value.Temperature regulation has different effects on the viscoelasticity of supramolecular systems.Among them,the wormlike micelles are converted into low-viscosity vesicles at high temperatures in o-EAPA system,while the p-EAPA system still has good thickening ability at high temperatures due to the poor solubility of terephthalate.Thus,p-EAPA is selected as the host agent for clean fracturing fluid.Ultimately,the supramolecular clean fracturing fluid with a formulation of 2%EA+0.391%p-PA can maintain 38 m Pa·s after 100 min under continuous shearing at 170 s^-1and 90?,which exhibits an excellent temperature and shear resistance,shear recovery and proppant-carrying ability.Besides,kerosene and ethanol can both quickly,completely break the gel,and the core damage rate of the breaking fluid is only 8.01%.Therefore,the supramolecular clean fracturing fluid has many advantages like simple construction method,low dosage and efficient performance.It has a desirable application prospect as an ideal low-cost clean fracturing fluid in middle-high temperature formations.