High pressure sorption of various hydrocarbons and carbon dioxide in Kimmeridge Blackstone and isolated kerogen

Abstract

We have measured adsorption and desorption of methane, ethane, propane, n-butane, iso-butane and carbon dioxide in Kimmeridge Blackstone at high pressures at temperatures of 60, 90 and 120 °C. Sorption of various light hydrocarbons and carbon dioxide in the isolated kerogen at 60 °C was also investigated. In our measurements, we used the gravimetric method. Physical and chemical properties of samples were measured to provide insight into sorption. Methane, ethane and carbon dioxide sorption was measured to 150 bar. Due to low vapor pressure of propane at 60 and 90 °C, the sorption was measured to 15 bar at 60 °C and 30 bar at 90 °C, respectively. At 120 °C, propane sorption was measured to 30 bar. Similarly, n-butane and iso-butane sorption was studied to 5, 9.5 and 15 bar at 60, 90 and 120 °C, respectively. Compared to sorption of these gases at moderate pressure in our recent work, high pressure sorption shows more pronounced hysteresis and non-monotonic excess sorption. In this work, we use the adsorbed layer density, estimated from grand canonical Monte Carlo (GCMC) simulations, and the liquid density to compute the absolute adsorption and examine the difference between the two. The results show that the absolute adsorption estimated with the two densities is significantly different in methane but similar in the other species. The butanes, n-butane and iso-butane, despite close bulk densities have very different adsorption. The adsorbed layer densities by GCMC simulations are different by about 10% which partly account for the adsorption difference. Other mechanisms may be at play due to different shape of the two molecules.