(499a) Establishing Analytical Adsorption Methods for Pore Characteristic Evaluations in Gas Shales

Authors: 
Rupp, E. C., National Energy Technology Laboratory
Wilcox, J., Stanford University

The advent of hydraulic fracturing, when combined with vertical and horizontal drilling, has allowed for increased production of natural gas and liquids from tight shale formations. The rapid ascent of shale sourced gas has created a need for analytical evaluation of shale, in order to determine permeability and gas-in-place. The majority of the work has focused on permeability and flow properties, as this relates directly to hydraulic fracturing effectiveness and production rates. Researchers have also focused on the adsorption properties of shale, in order to evaluate potential gas-in-place and understand how gas transports from micropores to macropores to fractures. The literature, to this point, has been unfocused, and pointed towards evaluating as many shale samples from the broadest perspective as possible. However, analytical adsorption approaches appropriate for investigating homogenous samples, such as activated carbon or zeolitic material, has limitations when applied to highly heterogeneous samples. Shale, which has high variability at all scales, from the formation level to the microscopic level, is a particularly difficult challenge.

This work focuses on creating a standard analytical method for the evaluation of gas shale, focused on low-pressure adsorption techniques. The outgas temperature will be evaluated to determine effects on adsorption isotherms, with emphasis on potential changes in pore volume. The samples will be evaluated with 3 probe gases (N2 at 77 K, Ar at 87 K and CO2 at 273 K). Isotherms will be evaluated with DFT techniques to determine pore size distribution, while using information from Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), elemental analysis and total and inorganic carbon contents to support the gas adsorption observations. The thorough analytical approach presented in this work will present a method that researchers can use to properly evaluate pore characteristics of shale gas, which can be used to support research in flow models and gas-in-place estimates.

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