Poroelastic and Adsorptive Properties of Activated Carbon Available to Purchase

The characterization of petrophysical and geomechanical properties of source rocks presents inherent challenges due to lithology heterogeneity, lamination, distribution of organic matter, and presence of fractures. Organic-rich shales also present some distinctive features that make hydrocarbon production and CO₂ geological storage unique in these rocks. The objective of this paper is to quantify and model the deformational behavior of carbon-based compounds due to changes of stress and pressure that happen simultaneously with gas adsorption and desorption processes. We designed an experimental procedure that consists of: (1) compaction of organic-rich grains/powder under oedometric conditions, (2) measurement of poromechanical properties in the absence of adsorption effects using helium in a triaxial cell through independent changes of confining pressure and pore pressure, (3) measurement of the adsorption strain, and stress for methane (CH₄). An adsorptive-poromechanical model permits explaining the experimental data, discriminating between the strain/stress caused by poroelastic response from the adsorption-induced strain/stress, and measuring the poroelastic-sorption properties of the organic-rich compound. We applied this procedure to activated carbon and measured skeletal volumetric modulus ranging from 11.8 to 16.6 GPa and skeletal adsorption stress of ~100 MPa for CH4 at 7 MPa of adsorbate pressure. The proposed procedure and model are useful to explain and predict the unique properties of carbon-based adsorbents which can be extended to kerogen, a critical component in source rocks.

Reserves estimation and gas flow rate prediction are more challenging for organic-rich rocks than for conventional gas reservoirs. These challenges are not only limited to characterization of petrophysical and geomechanical properties (i.e., lithology heterogeneity, lamination, total organic content and, the presence of fractures) but also to capturing the physics that governs these processes. Gas adsorption heavily affects the estimation of the original gas in place (Moore et al., 2012). Organic-rich surfaces can adsorb various gas molecules (N₂, CH₄ and CO₂ among others) increasing vastly the storage capacity in organic-rich rocks (Busch and Gensterblum, 2011).