Determining noble gas partitioning within a CO2–H2O system at elevated temperatures and pressures

Abstract

Quantifying the distribution of noble gases between phases is essential for using these inert trace gases to track the processes controlling multi-phase subsurface systems. Here we present experimental data that defines noble gas partitioning for two phase CO 2 -water systems. These are at the pressure and temperature range relevant for engineered systems used for anthropogenic carbon capture and geological storage (CCS) technologies, and CO 2 -rich natural gas reservoirs (CO 2 density range 169-656 kg/m 3 at 323-377 K and 89-134 bar). The new partitioning data are compared to predictions of noble gas partitioning determined in low-pressure, pure noble gas-water systems for all noble gases except neon and radon. At low CO 2 density there was no difference between measured noble gas partitioning and that predicted in pure noble gas-water systems. At high CO 2 density, however, partition coefficients express significant deviation from pure noble gas-water systems. At 656 kg/m 3 , these deviations are À35%, 74%, 113% and 319% for helium, argon, krypton and xenon, respectively. A second order polynomial fit to the data for each noble gas describes the deviation from the pure noble gas-water system as a function of CO 2 density. We argue that the difference between pure noble gas-water systems and the high density CO 2 -water system is due to an enhanced degree of molecular interactions occurring within the dense CO 2 phase due to the combined effect of inductive and dispersive forces acting on the noble gases. As the magnitude of these forces are related to the size and polarisability of each noble gas, xenon followed by krypton and argon become significantly more soluble within dense CO 2 . In the case of helium repulsive forces dominate and so it becomes less soluble as a function of CO 2 density.

Experimental determination of noble gases and SF6, as tracers of CO2 flow through porous sandstone

“…Since the calculated values for molecular diffusion are small, mechanical dispersion must be the dominant factor in curve shape. This suggests that there is a higher degree of dispersion with an increase in atomic size, which is confirmed by the modelling results in this study and previous work (Warr et al, 2015). …”

Turkish geothermal fields as natural analogues of CO 2 storage sites: Gas geochemistry and implications for CO 2 trapping mechanisms

“…It should also be noted that the quantitative estimates presented above are open to revision as they suffer from uncertainties associated with the fractionation and solubility factors which were experimentally determined for low pressure systems (Weiss, 1971(Weiss, , 1974Deines et al, 1974). Despite recent attempts to assess the solubility of He (and other noble gases) at high-pressure and high-temperature ranges (more relevant for carbon capture and storage, CCS, technologies) (Warr et al, 2015), the lack of information about the isotopic fractionation factors for highpressure systems restricts, at this stage, further constraints on this issue.…”

Optimizing Noble Gas–Water Interactions via Monte Carlo Simulations

“…When trace amounts of noble gases are present within a gas-water binary phase system, they exist as solute particles within both phases [1][2][3] . The exact ratio of noble gases in each phase, the partitioning, is dependent on environmental factors such as temperature and phase composition [2][3] .…”