Effects Of Supercritical Carbon Dioxide On Mechanical Parameters Of Shale

Demand for natural gas in China is increasing.It is of great significance to efficiently develop shale gas to ease the contradiction between energy supply and demand,in order to adjust energy structure.Due to the low porosity and low permeability of shale reservoirs and the easily-expanded clays,the use of supercritical CO₂ fracturing has great applications in shale reservoirs.At present,due to little understanding of the influence of supercritical CO₂ on the mechanical parameters of shale,and it is necessary to study the mechanism of shale fracture by supercritical CO₂.In this paper,the corresponding test device is designed,and the system configuration and test method of the device are given.The supercritical CO₂ immersion test of shale in Sichuan Wufeng formation under different saturation pressures/temperatures was carried out.The uniaxial compression test and acoustic emission test of shale before and after saturation were performed.Combining XRD Test and SEM Test to analyze the influence of supercritical CO₂ on mechanical parameters of Shale The main conclusions obtained are as follows:Supercritical CO₂ weakens the strength and elastic modulus of shale,and its strength and elastic modulus decrease with increasing saturation pressure/temperature,but its decreasing trend gradually become slow;Supercritical CO₂ has limited effect on shale Poisson's ratio.After the supercritical CO₂ treatment,the acoustic emission events of shale increase,and the energy and cumulative energy show an increasing trend with the increase of saturation pressure/temperature.XRD test and SEM test show that the supercritical CO₂ changes the proportion of mineral components and the microscopic pore structure of the shale,which reduces the mechanical parameters of the shale.