Pressure-dependent Compressibility Research Articles

Pressure-dependent compressibility of K2X(CO3)2 (X = Ca, Mg) under high pressure

The high-pressure phase transition behaviors and pressure-dependent compressibility are investigated on K2X(CO3)2 using first-principles calculation from ambient pressure to 30 GPa. The reversible structural phase transitions of K2X(CO3)2 are determined based on enthalpy difference and cell volume collapses. The pressure point of structural phase transitions of K2Ca(CO3)2 is obtained at around 3.3 GPa and 10.3 GPa, while that is found at about 6.2 GPa and 22.6 GPa for K2Mg(CO3)2. Compared with the high axial rigidity of C-O bonds in [CO3] groups, the Ca+ and Mg+ coordination polyhedron show much more compressible. The displacement behavior of the Ca+ and Mg+ coordination polyhedron occurs simultaneously with the rotation behavior of [CO3] groups during compression, and reverses induced by the structural phase transition.

Convective carbon dioxide dissolution in a closed porous medium at high-pressure real-gas conditions

We combine modeling and measurements to investigate the dynamics of convective carbon dioxide (CO2) dissolution in a pressure-volume-temperature cell, extending a recent study by Wen et al. (J. Fluid Mech., vol. 854, 2018, pp. 56–87) at low-pressure under ideal-gas conditions to high-pressure and real-gas conditions. Pressure-dependent compressibility and solubility are included to model the evolution of CO2 concentration in the gas phase and at the interface, respectively. Simple ordinary-differential-equation models are developed to capture the mean behavior of the convecting system at large Rayleigh number and are then verified by using both numerical simulations and laboratory experiments. The prefactor for the linear scaling of convective CO2 dissolution is evaluated – for the first time – by using pressure-decay experiments in bead packs at reservoir conditions. The results show that our models could quantitatively predict the process of the convective CO2 dissolution in pressure-decay experiments. Moreover, the results also reveal that for increasing gas pressure in closed systems, the negative feedback of the pressure drop – resulting from the dissolution of CO2 in the liquid – is weakened due to the decrease of the solubility constant at real-gas conditions. Our analysis provides a new direction for determination and validation of the convective dissolution flux of CO2 in porous media systems.