Interfacial tension of carbon dioxide - water under conditions of CO2 geological storage and enhanced geothermal systems: A molecular dynamics study on the effect of temperature. (1st April 2023)

• Record Type: Journal Article
• Authors: Shiga, Masashige; Morishita, Tetsuya; Sorai, Masao
• Is Part Of: Fuel. Volume 337(2023)
• Publication Date: 2023-04-01
• Subjects: CO2 geological storage -- CO2 utilization -- Geothermal systems -- Interfacial tension -- CO2-water interface -- Molecular dynamics simulations; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2022.127219
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: Interfacial tension (IFT) of CO2 -water at 573 K is about 80% lower than that at 313 K. The IFT increases with temperature near the critical point of CO2 . Surface excess molar entropy computed from the Gibbs-Duhem relation and the MD data. Stability of CO2 adsorbed on the water surface evaluated by PMF. More ordered adsorption layer of CO2 ; relevant to the increase in the IFT. Abstract: In recent years, CO2 injection into geological formations under a wide range of temperature conditions, including super-hot geothermal reservoirs, has attracted much attention (i.e., higher than 500 K). Despite the importance, however, no study has been reported on the interfacial tension (IFT) of CO2 - water systems at temperatures higher than 478 K. In this study, we performed molecular dynamics (MD) simulations to estimate the CO2 - water IFT from 278 to 573 K at 8 to 50 MPa. Our results show the IFT at 10 MPa and 573 K is approximately 80% lower than that at a typical reservoir condition for CO2 geological storage. This indicates that the effect of the capillary pressure on the flow of CO2 and water in the geological formation is expected to be significantly reduced in such a super-hot geothermal reservoir. We discuss a possible mechanism for the IFT variation against temperature, including the maxima around 373 K at 8 to 12 MPa, which is reproduced and tackled by MD simulations for the first time. On the basis of the Gibbs-Duhem relation, the temperature dependence is directly related to the interfacial excess molar entropy. Our analyses show (1) the IFT increase is attributed to the substantial variation of the entropy and density of the bulk CO2 phase near the critical point, and (2) this variation is characterized by the distinct behavior of the molecular ordering and the mobility of CO2 at the interface, consistent with the close relationship between the disorder in molecular arrangement and configurational entropy.