Research On The Safety Of Casing Cement Ring Micro Gaps For Gas Storage

Gas storage catches more and more attention for its peak regulating function,which makes nature gas widely used as a kind of clean energy.For the complexity and variability of gas storage injection and output,annular pressure and gas channeling affected by the integrity of cement ring sealing become the main reason leading cementing stability of gas storage is higher than that of conventional cementing operation which leads production accidents.Based on the data of Xinjiang Hutubi this paper analyzed the effect of internal pressure on formation of micro cracks with its mechanism combining micro cracks prediction model and Jackson cracks experiment and got the minimum internal pressure change that causes micro cracks,determined the maximum test and operating pressure differences,at the same time the effect of temperature change and cement stone elastic modulus on the formation of micro gap was studied.Compared with the experimental results of Jackson model this prediction is confirmed right.The process of natural gas leaks through micro cracks is divided into two parts:underground leakage and ground diffusion.To analyze the process of underground leakage this paper adopted small hole leakage calculation model the influence of micro cracks size,running temperature and running pressure on gas leakage rate has been analyzed.The analysis shows that the change of micro gap,running pressure and running temperature will affect the leakage rate of natural gas,as the running temperature increases,the corresponding decrease shows a linear change.For the surface diffusion,using Fluent software to establish the geometric fluid leakage and diffusion model to simulate and analyze the time,micro crack size,wind speed and other factors impacting on natural gas leakage distance.The analysis shows that,for the time state,the horizontal diffusion distance increases with the increase of time,it shows accelerated increasing and decelerated increasing followed by a stable state,the risk of vertical diffusion distance with the change of time,showing slow increasing and then accelerated increasing followed by a stable state at last,the gas diffusion concentration increases first and then stabilizes as the time changes.The diffusion concentration and distance of natural gas increase with the increase of micro crack size.Dilatation of micro slits has an effect on the stability of diffusion,when the dilatation of micro slits bigger it’s harder to keep stable for the gas diffusion.For the wind speed,the horizontal diffusion distance increases with the increase of wind speed,the vertical diffusion distance will decrease as the wind speed increases,the concentration of natural gas decreases with the increase of wind speed.This paper analyzed the main factors which has significant influence on leakage distance in micro crack in the process of micro crack formation,gas underground leakage and surface diffusion,and indicated that pressure changes,temperature changes,modulus of elasticity,and wind speed affect mainly.Based on this research safety precautions has been proposed which do has positive meaning to ensure the safe operation of gas storage.