Research On The Migration Law Of Proppant Carried By Supercritical CO₂ In Horizontal Annulus

As a new type of waterless fracturing technology,supercritical CO₂ fracturing is expected to become a new technology for unconventional oil and gas efficient development.Transport of proppant to the fracture is an important link of supercritical CO₂ fracturing technology,especially in the long horizontal well fracturing process,the success or failure of the horizontal annulus carrying proppant directly affects the success or failure of the fracturing operation.It is well known that supercritical CO₂ has lower viscosity and density than water,and its sand carrying capacity is lower than water,so it will affect its proppant carrying efficiency in horizontal annulus.In order to further clarify the migration law of proppant carried by supercritical CO₂ in horizontal annulus and provide theoretical basis for improving the capacity of carrying proppant with supercritical CO₂,the proppant migration law in horizontal annulus during supercritical CO₂ fracturing is systematically studied in this paper.A wellbore device for carrying proppant with supercritical CO₂ is designed,based on the similarity theory and the characteristics of fluid high pressure closed flow.High-speed photography is used to observe the proppant migration characteristics and laws in high-pressure windows.Experimental study on the parameter effect of the proppant axial migration velocity,the equilibrium height of sand bed is carried out to reveal the proppant migration patterns and proppant migration law.Experimental results show that the phase change of CO₂ can be clearly observed by high-speed photography,and the proppant is carried out in the particle collecting device,which proves the feasibility of the experiment and the experimental device;the migration process of sand bed particles in supercritical CO₂ can be divided into one layer,two layers and three layers;the axial migration velocity of proppant and the equilibrium height of sand bed change with the parameters obviously.Numerical simulation is carried out to study the migration law of proppant carried by the supercritical CO₂ in horizontal annulus,using Euler-Euler model and Realizable model.The parameter effect of the equilibrium height of sand bed,the length of sand bed and the concentration of proppant in horizontal is studied.By comparing and analyzing the results of calculation and experiment,the experimental results are close to the numerical simulation results,and the error is small,the the sand bed dynamic formation law and proppant migration law are revealed.Numerical results show that sand bed particles exhibit a three-layer phase migration pattern on the annulus section,namely suspension layer,jump layer and static layer;the velocity distribution of proppant migration in eccentric annulus is not uniform;the variation of equilibrium height of sand bed,length of sand bed and proppant concentration in annulus with parameters is obvious.The numerical simulation and experimental results complement and verify each other,which reveal the characteristics and laws of proppant migration in horizontal annulus,which provide a theoretical basis for parameters design of carrying proppant in annulus during supercritical CO₂ jet fracturing process.