Multi-Component Physical Sorption Investigation Of Gas Shales at the Core Level

Abstract

Abstract The purpose of this paper is to investigate multi-component sorption in gas shales at the core level in order to better understand the connectivity and flow mechanism in these tight rocks. Such data allow us to recognize the sensitivity of shale physical properties to the gas mixture saturating the pore space. To investigate multi-component gas sorption at the core level two experimental setups were constructed in house: a high precision volumetric gas adsorption apparatus and a dynamic breakthrough apparatus. The novelty in the volumetric apparatus lies in the thermodynamically closed system design in which simultaneous measurements of three fundamental rock properties at the core level are obtained including porosity, permeability and excess adsorption. Initial experiments using both apparatuses were conducted to measure the sorption properties of samples from the Haynesville and Barnett shale plays. Different gases were used to assess the preferential adsorption of each component in a gas mixture. Utilizing the volumetric apparatus, excess sorption measurements were carried out on three intact shale core samples with pure gases including N2, CH4, and CO2. Absolute sorption calculations confirmed the preferential sorption of CO2 in shales compared to other gases. The Barnett sample in particular adsorbed about four and a half times more CO2 than CH4. N2 and CH4 sorption were fitted with a Langmuir model where a monolayer sorption is assumed. The, CO2 sorption isotherm did not follow the standard Langmuir model and was fitted with an N-BET model where multilayer sorption is occurring. With these pure isotherm measurements, mixed gas sorption measurements were also carried out on shales for the first time, to quantify the recovery and selectivity of each component in a gas mixture. Results show a preferential adsorption of methane over nitrogen as indicated by an increasing selectivity coefficient. Dynamic breakthrough measurements were also carried out for the first time on shales. Measurements were conducted with methane on both core and powder-sized samples. Results indicate a methane capacity with powder that is 5 times higher in comparison to core level measurements. These experimental results shed light on the importance of carrying out adsorption measurements at the core level for accurate gas in place estimations.