Molecular Simulation Of Thickening CO₂ Of Erucic Acid Amide Propyl Dimethylamine And Numerical Simulation Of Fracture Characteristics

China’s coalbed methane reserves rank the third in the world,which is basically equivalent to the onshore conventional natural gas reserves and relatively rich.The exploitation of coalbed methane can reduce the gas accident rate,reduce the emission of greenhouse gas,and also produce huge economic benefits as a clean energy,and contribute to the effective supply of energy.Coalbed methane exploitation is faced with the problems of low permeability,small scale and high proportion of low-producing Wells.Through hydraulic fracturing,fracture channels are formed in the reservoir to improve its permeability.Hydraulic fracturing mainly uses active water fracturing fluid,but the viscosity of active water fracturing fluid is low.There are problems such as high construction displacement,large filtration loss and difficult control of longitudinal crack extension.Therefore,it is necessary to develop fracturing fluids with moderate viscosity and low damage to coal seam.CO₂ responsive surfactants have adjustable rheological properties and are easy to break glue,thus causing little damage to reservoir.Meanwhile,as an intelligent fracturing fluid,CO₂ responsive surfactants have a good application prospect in coalbed methane exploitation.In this paper,the microscopic mechanism of erucic amide propyl dimethylamine CO₂ responsive surfactant was studied by means of total atomic dynamics method.The aggregation state of erucic acid amide propyl dimethylamine in solution after protonation under the action of CO₂ was analyzed.The microcosmic properties of protonated surfactant solution were systematically analyzed by using three important parameters:mean azimuth shift,radial distribution function and relative concentration.The results show that protonated surfactants have better solubility and dispersion properties.It is more likely to be wound to form micelles under the action of electric charge and thus has a thickening effect.The viscosity of erucic acid amide propyl dimethylamine CO₂ solution at different shear rates.And through molecular simulation,it can be intuitively observed that the shear effect makes micelles more dispersed in solution.Secondly,using finite element numerical simulation of fracture propagation.The adaptability and propagation law of erucic acid amide propyl dimethylamine used as fracturing fluid for coal seam fracturing in a block of North China are evaluated based on reservoir reconstruction effect.The simulation results show that when the fracturing fluid viscosity is 45-60 mPa·s and the displacement is 4-6 m3/min,the purpose of constructing long joints required by engineering construction can be achieved.The increase of Young’s modulus leads to the rapid narrowing of crack width,which is conducive to the formation of long cracks.With the decrease of Poisson’s ratio,the width of fracture gradually increases,but the change of fracture length is not sensitive under different Poisson’s ratio.The fracture length increases with the increase of horizontal stress difference.Molecular dynamics simulation reveals the microscopic action mechanism of erucic amide propyl dimethylamine CO₂ responsive fracturing fluid.The influence of the fracturing fluid viscosity,displacement and mechanical properties of coal seam on the propagation of coal seam fracture is clarified.It provides a theoretical basis and guidance scheme for the development and application of CO₂response fracturing fluid.