Numerical Simulation Of Leakage And Diffusion In Buried CO₂ Pipeline

CCUS?Carbon Capture,Utilization and Storage?technology is an emerging technology that can reduce CO₂ potential on a large scale.The main purpose is to capture,use and store large amounts of CO₂ emitted by industry.Based on the background of the 360,000-ton/year CO₂ pipeline transportation conditions in Yanchang Oilfield,this paper studies the five factors of soil porosity,leakage hole diameter,pipeline transportation pressure,pipeline diameter,and buried depth to the leakage and diffusion of buried CO₂ pipeline pores Influence,analyzing the characteristics of CO₂ diffusion process in the soil,and finally give the specific warning range of the ground surface of the buried CO₂ pipeline during operation.Based on the jet dynamics,porous media,fluid mechanics and other related theories,constructe a three-dimensional buried CO₂ pipeline leakage and diffusion geometric model,and FLUENT software is used to simulate the diffusion of CO₂ in the soil after pipeline leakage under different factors.And the concentration of 5%CO₂ is set as the critical value of the dangerous concentration to determine the dangerous concentration range,and carry out the qualitative and quantitative analysis of CO₂ diffusion in soil.By studying the leakage process characteristics of buried supercritical/dense phase CO₂ pipelines,the diffusion distribution law of pressure field and concentration field was obtained after 800 seconds of simulated leakage diffusion.The results show that the soil porosity increased from 0.35 to0.65,the time for the diffusion of CO₂ to the surface was shortened by 28.13%,the radius of the dangerous circular area diffused to the surface was increased by 16.86%;the leak diameter of the pipeline increased from 8mm to 16mm,and the diffusion of CO₂ to the surface time is shortened by 60.38%,and the radius of the dangerous circular area spread to the surface is increased by 79.64%;The pipeline pressure increased from 9.5MPa to 13MPa,the diffusion time to the surface was shortened by only 7.21%,and the radius of the dangerous circular area on the surface was only increased by 3.25%;the diameter of the pipeline increased from 114mm to 273mm,and the diffusion time to the surface was all around 290s,The maximum difference is within 5%.The radius of the dangerous circular area spreading to the surface is about 1.875m;the maximum difference is within 5%;the buried depth of the pipeline is reduced from 2.0m to 1.2m,the time for the CO₂ to diffuse to the surface increases by 66.67%,and the dangerous circle spreading to the surface radius of the shaped area has increased by 23.91%.Therefore,the three factors of soil porosity,leakage pore diameter,and pipeline depth have a greater impact on the leakage and diffusion of small holes in buried CO₂ pipelines;however,pipeline transportation pressure and pipeline diameter have less influence on diffusion.Through the above simulation results,the analysis of the development of clouds in the process of CO₂ pipeline leakage and diffusion is revealed,and the influence of the concentration difference between the high-pressure stage and the stable diffusion stage of the jet is revealed.Aiming at the condition of small hole leakage in the extended buried supercritical/dense phase CO₂ pipeline,according to the simulation calculation results,the range of setting warning signs on the ground is given:the warning signs are set at the boundary of the dangerous concentration at 2m from the center line of the pipeline,and the distance between the warning signs is 10m-20m.