An Integrated Approach for the Characterization of Shales and Other Unconventional Resource Materials

Production of oil and gas from unconventional source rocks (shales) has increased significantly in recent years, reflecting a shift in the focus of the oil and gas industry from conventional to unconventional oil/gas resources. An improved insight into the pore structure characteristics of these important porous materials will enable a better understanding and further optimization of the production behavior from such vast hydrocarbon resources. In particular, characterization of porosity and permeability of shales is the key to accurately estimating the initial oil and gas in place and fluid flow through these rocks. However, evaluating the pore structure of shales presents technical challenges due to the presence of a range of pores, from the nanometer to the micrometer size. Characterization of the entire range of pore sizes requires an all-inclusive study employing a variety of techniques. Such an integrated approach is followed in this work to understand the pore structure of Monterey shale samples as obtained from various characterization techniques: (i) mercury porosimetry, (ii) nitrogen adsorption experiments, (iii) high-resolution X-ray computed tomography (HRXCT), and (iv) focused ion beam scanning electron microscopy (FIB-SEM). These techniques are coupled with gas permeability measurements of the Monterey shale samples as well as spontaneous water air imbibition experiments. Calculated permeability values (via lattice Boltzmann flow simulations) based on the pore characterization data are in good agreement with the gas permeability measurements. Finally, the interpretation of the observed fluid flow dynamics during a spontaneous water air imbibition experiment, based on input from various characterization techniques, demonstrates the value of characterizing shale samples at a full range of pore scales.