Permeability estimation is a crucial part of the shale mudrock characterization because it affects the production rate, the pace of recovery and the technically recoverable hydrocarbons. Shale permeability typically falls in the low range of tens of micro-Darcy down to nano-Darcy. Accurate measurement of permeability is a challenging task because the measurement errors are more likely to occur in the low permeability range. This paper presents a common and accurate experimental method for permeability measurement of shale mudrocks known as the canister desorption test. We describe the experiment procedure and present the governing partial differential equation (PDE). The impact of linear and nonlinear adsorption isotherms and the corresponding analytical and numerical solutions are discussed. A workflow for the estimation of permeability and the gas adsorption parameter is presented. The workflow is used to measure the shale matrix permeability and the adsorption parameter for an organic-rich sample from the Marcellus formation. The measurements are in good agreement with an independent study on the Marcellus organic-rich core samples. The results show that the measurement of the adsorption parameter is as important as the permeability measurement in the organic-rich shales. In addition, given that the measurements of permeability and adsorption parameter are performed at a small scale and the gas properties are approximated by average values, it is recommended to perform multiple experiments at different pressures to constrain the uncertainty of the permeability and adsorption measurements. The limitations of the proposed workflow are discussed.
- Canister desorption experiment
- Linear and nonlinear adsorption isotherms
- Shale permeability measurement