| Since the industrialization, a large number of greenhouse gases, especially carbon dioxide emissions cause global climate change, the international community calls on the reduction of carbon dioxide emissions and to develop relevant policies. China, as the world's first carbon-emitting country, the development of carbon dioxide emission reduction technology is without delay. Carbon capture and storage (CCS) technology is internationally recognized as an effective emission reduction measure, including saline aquifers. Due to its wide distribution and huge storage capacity, this method is of great attention. Related research at aboard mostly focus on marine saltwater layer and rarely talk about terrestrial saline aquifer. And geographical characteristics of our country show huge potential of saline aquifer storage in continental sedimentary basins. Therefore, combined with this kind of geographical characteristics, related studies of carbon dioxide under the conditions of terrestrial saline aquifer storage is of great significance.Capillary capture is one of the most important mechanism of continental saline aquifers geological storage of carbon dioxide. The capillary forces is induced by interfacial tension (IFT) of CO2-fomation water in the pore size. This work focused on the capillary storage mechanism, aimed to secure long-term storage for research purposes, and established axisymmetric drop shape analysis-pendant drop method measuring experimental system to measure the IFT of CO2-brine system under a simulation of the actual storage conditions. Experimental conditions corresponded to the actual formation of 1000-2000 m depth, thus the temperatures ranged from 300-353 K, pressures ranged from 3-12 MPa, and considered the salinity differences of actual formation water, six salinities within 0-117 g/L ranges was chosen. This work gained 1254 data point as a whole.This paper shows that, within the experimental conditions, the lowest interfacial tension is 23 mN/m or so, never appear plummeted to a value of 0, this demonstrates the feasibility of sequestration. By analyzing the temperature, pressure and salinity influence upon the interfacial tension, it can be found that, as the pressure increases the interfacial tension decreases, and with increasing temperature and salinity the interfacial tension increases. As the pressure increases to a certain extent, the interfacial tension will reach a pseudo-plateau. At a given temperature, CO2-pure water/brine system of different salinities reach plateau at the same pressure, at different temperatures the plateau pressures are also different. The plateau IFT values slightly increase with the increasing temperature and salinity, and pressures take no impact on that.This study also showed that the linearly relationship between the interfacial tension increment and molarity concentration of brine. IFT variation with the function of density difference are also discussed in this paper. It is shown that there is a threshold of density difference value, when the density difference is higher than the value of the threshold, small changes in the density difference will cause a substantial change in IFT, and when the density difference is less than this value, IFT variation is relatively stable.Based on the deformation Parachor model and conclusions obtained herein, an empirical formula was established to describe the relationship between IFT values and pressure, temperature and molarity of brine. The empirical formula was built on Parachor physical model, and when the temperature, pressure and salinity was given, the empirical formula could be applied to calculate the corresponding IFT of CO2-brine system. |
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