Effects Of Temperature And Pressure On Residual Water In CO₂ Geological Storage And Its Mechanism

CO₂-water-rock interaction plays a vital role in CO₂ geological storage.CO₂geological storage is achieved by several different storage mechanisms:structure and formation storage,capillary residual storage,dissolution and storage,and mineral storage.Among them,capillary residual storage is a storage mechanism that improves CO₂ storage efficiency by injecting CO₂ to replace pore water and reduce water in the pore space of the reservoir.However,residual water formed during drainage is detrimental to CO₂ storage.Therefore,it is necessary to explore the formation mechanism of residual water in the CO₂-water-rock system so as to reduce the residual water in the pores of the rock as much as possible."Temperature and pressure"as a significant difference between reservoirs at different depths will play a crucial role in the formation of residual water in the CO₂-water-rock system,but its effect on residual water and its effect The mechanism has not yet been revealed.Therefore,it is of great significance to carry out research on the influence of temperature and pressure on residual water and its mechanism of action.In this study,three sets of temperature?40?,50?and 60??and three sets of pressure?8MPa,10MPa and 12MPa?were combined.The displacement experiments of CO₂-water-rock system were carried out,and the following Experimental results:In this study,the drainage process is divided into three stages:in the first stage,the water in the saturated core flows out from the outlet end of the core holder and falls into the gas-liquid separator;in the second stage,the drainage flow rate decreases sharply,and The residual water saturation can no longer be reduced;the amount of water in the core pores of the third stage?ie,the residual water can no longer be reduced?remains constant and no longer decreases.The mechanism of the influence of temperature and pressure on residual water saturation was determined by analyzing the experimental results.The analysis shows that in a certain temperature and pressure range,the residual water saturation can not be reduced in the drainage process with the increase of pressure,and increase with the increase of temperature.The interfacial tension is positively correlated with the residual water saturation;as the pressure increases,the interfacial tension decreases;and the interfacial tension increases with increasing temperature.Under the experimental conditions of this study,for P-T hybrid systems,the effect of temperature on interfacial tension is greater than the effect of pressure on it.In addition,the residual water saturation decreases as the viscosity of CO₂ increases,decreases as the density of CO₂ increases,and increases as the difference in density of deionized water and CO₂ increases.Finally,this study concluded that high-pressure and low-temperature reservoirs have better gas storage effects and can achieve higher CO₂ storage efficiency.At the same time,changes in pressure and temperature also affect the viscosity and density of CO₂:when CO₂ is in a high viscosity and high density state,residual water saturation can also be reduced.In addition,the preference for low salinity reservoirs?ie,when the viscosity and density of the formation water is low?can also achieve good CO₂ storage.