Study On The Law Of Flow And Heat Transfer In Narrow Seam With Supercritical CO₂

Supercritical carbon dioxide fracturing technology has the advantages of low damage,easy backflow,and no swelling of clay.However,due to the small density and viscosity of carbon dioxide and its sensitivity to changes in temperature and pressure,the actual technology is still facing pressure in applications.Difficulties such as carrying sand inside the cracks.Therefore,on the basis of studying the heat transfer law of supercritical carbon dioxide in narrow gaps,the temperature field and pressure field in the fracture are determined,and the density field and viscosity field are determined,which is used to lay the propagating agent for the supercritical carbon dioxide in the narrow gap.The study provides the basis.Firstly,by comparing,preferably,the supercritical carbon dioxide physical property calculation model,the model includes the Liang-Biao Ouyang polynomial fitting auxiliary equation for calculating density,the Fenghour model for viscosity,the Span-Wagne equation for specific heat capacity,and the Vesovic model for thermal conductivity,which simplifies The calculation method improves the calculation accuracy.Secondly,based on the characteristics of the narrow-slot shape and the temperature and pressure of the formation under actual operating conditions,the heat transfer criterion equation of Dittus-Boelter type supercritical carbon dioxide level pipe is optimized,and the flow acceleration effect correction criterion,buoyancy force correction criterion,and heat are comprehensively considered.The physical property correction criterion uses the least squares method to correct the optimized heat transfer equation,and compares the corrected heat transfer equation with the numerical calculation value to verify the correctness of the method.Finally,the numerical calculations of the flow law in the narrow seams of supercritical carbon dioxide were conducted.The variation of temperature,pressure,density and viscosity with the fracturing time in the narrow gap was obtained.The injection displacement,injection temperature and injection were analyzed.The effect of pressure changes on the density and viscosity of supercritical carbon dioxide in the narrow gap.The influence of the density and viscosity on the settling velocity of the proppant was analyzed.The results show that the density of the propellant reaches a steady state as the injection displacement increases.As the viscosity decreases,the settling velocity of the proppant increases;as the injection temperature increases,the density and viscosity decrease and the proppant settling velocity increases;as the injection pressure increases,the density and viscosity increase,and the proppant settling velocity increases.Increase.In this paper,the theoretical analysis and numerical calculation method are used to obtain the change rule of temperature,pressure,density and viscosity of supercritical carbon dioxide in the narrow gap,which provides a basis for the development of supercritical carbon dioxide drilling and completion theory and technology.