(706f) A Study of Condensation Phenomena in Shales and in Synthetic Model Materials

The presence of gas in Shale nanopores, caused by capillary condensation, strongly affects the estimation of the quantity of hydrocarbons in place. Capillary condensation also affects the mass transport in Shales due to the low mobility of the condensed hydrocarbon. The focus of this study is on the phase behavior of hydrocarbons when confined in nanopores, since the thermodynamic fluid behavior under confinement is known to be different from that of the bulk phase. In particular, we investigate low molecular weight (MW) alkanes relevant to shale gas production, and study capillary condensation, which is the vapor to liquid phase change that occurs in nanopores below the saturation pressure of the bulk fluid. We investigate, in particular, the impact on capillary condensation of the pore size, as well as of the pressure/temperature conditions of the bulk fluid in contact with the nanopore.
For the study, we have synthesized model porous media, specifically mesoporous silica disks with narrow pore size distributions, with varying average pore size <10 nm. We have selected ethane as a model low MW hydrocarbon component of shale gas. We utilize a high-pressure thermogravimetric microbalance to study adsorption and phase condensation of ethane in the silica nanopores. The experiments are complemented with models of the phase behavior, including the classical Kelvin Equation (KE), a reformulated KE model based on the Peng-Robinson Equation of State (EOS), as well as direct molecular simulations of ethane adsorption in the silica nanopores. Models and experiments are in satisfactory agreement with each other. The next stage of our work includes experimenting with the natural Shale materials to compare their behavior with that of the model analogs.