Solubility models of CH4, CO2, and noble gases and their geological applications

Abstract

Solubility models for CH4, CO2, and noble gases are widely used in Earth Sciences, playing pivotal roles in the study of homogenization pressure of inclusions, paleoclimate variation, gas migration and accumulation, formation of helium-rich gas plays, and the volumetric ratio of gas to water in reservoirs. This paper reviews solubility models of CH4, CO2, and noble gases in pure water and aqueous NaCl solutions. Specifically, the models with high accuracy and wide applicability are introduced in detail: (1) CH4 solubility model in aqueous solutions within the range of 0–250 °C, 0.1–200 MPa, and 0–6.0 mol/kg NaCl; (2) CO2 solubility model in aqueous solutions within the range of 0–450 °C, 0.1–150 MPa, and 0–4.5 mol/kg NaCl; (3) Models for calculating the solubility and Henry's constant of atmospheric noble gases within 0–80 °C range; (4) Models for calculating the Henry's constant of noble gases in pure water; (5) Solubility models of noble gases in aqueous solutions within the range of 0–65 °C, 0.1 MPa, and 0–5.8 mol/kg NaCl. The paper also presents some calculated results obtained using these models. The solubility models of CH4 and CO2 are complex yet highly accurate, with a broad range of applications. In contrast, the solubility models of noble gases exhibit relatively lower accuracy and a narrower application range, necessitating corrections. In the noble gases-CO2-H2O system, low-density CO2 has little effect on the solubility of noble gases, whereas high-density CO2 significantly influences their solubilities. Currently, accurately evaluating the solubility of CH4, CO2, and noble gases in their mixtures proves challenging, warranting further research into solubility models for gas mixtures.