Study On The Flowing Law Of Supercritical Carbon Dioxide In The Fracture

In recent years,China’s dependence on foreign oil and gas energy has been increasing,which has seriously affected energy security.In this context,the development of unconventional oil and gas energy has become an urgent task.Supercritical carbon dioxide fracturing is a new type of fracturing technology,which has many advantages in developing oil and gas energy,such as fast back drainage,low cost and reservoir protection.However,in the process of fracturing,the physical properties of carbon dioxide are sensitive to the changes of temperature and pressure.While the changes of flow state and thermal physical parameters seriously affect the fracturing effect.Therefore,studying the heat and mass transfer law of supercritical carbon dioxide in cracks,determining the temperature field and pressure field in cracks,and then determining the density field and viscosity field provides a basis for the study of the flow law of supercritical carbon dioxide proppant in cracks.Firstly,the physical models of carbon dioxide are optimized,and the changes of physical properties with temperature and pressure are analyzed.Which provides a theoretical basis for the later analysis of heat and mass transfer process model of carbon dioxide in porous media.Meanwhile,the influence factors of supercritical carbon dioxide heat transfer process in the crack are analyzed by numerical simulation method.Through screening the convection heat transfer correlation in the horizontal tube,the heat transfer correlation suitable for the actual crack is summarized.Secondly,the theory of gas permeation and diffusion in porous media is optimized by comparison,and Binomial Dust Model is established.Through verification,the model can be used to calculate the permeation and diffusion process of gas in porous media.On this basis,Binomial Dust Model are modified to obtain the permeation and diffusion model suitable for carbon dioxide in porous media.Finally,a three-dimensional porous medium crack model is established,and the temperature,density,viscosity distribution,surface heat transfer and resistance characteristics of carbon dioxide flow in the crack are obtained.At the same time,the effects of engineering parameters such as injection temperature and displacement,and formation parameters such as porosity and fracture height on the temperature and density of carbon dioxide in fractures are analyzed.The results show that increasing injection displacement can reduce the temperature of carbon dioxide on the upper wall and increase its density,but it is opposite on the lower wall;With the increase of injection temperature,the temperature of carbon dioxide on the lower wall increases steadily,and the density decreases,but it has little effect on the upper wall;with the increase of formation porosity,the temperature difference between the upper wall and the lower wall increases,and the density difference increases.Finally,it is found that the crack height has little effect on the temperature and density distribution of supercritical carbon dioxide in the crack while maintaining the same inlet velocity.In this paper,the heat transfer criterion equation and osmotic diffusion equation suitable for supercritical carbon dioxide in narrow cracks are obtained by combining theoretical analysis and numerical simulation.The density and viscosity distribution law of supercritical carbon dioxide in three-dimensional cracks is obtained by simulation calculation.According the result,the possible distribution law of proppant in cracks is analyzed.It provides a theoretical basis for the development of supercritical carbon dioxide fracturing technology.