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Nano-Scale Pore Characterization of the Eagle Ford Shale, Texas


The Eagle Ford Shale, composed of very fine grains with relatively high interparticle porosity but low matrix permeability, shows various types of pores that are disseminated unevenly throughout the matrix and strongly related to the organic matter. This particular porosity distribution is commonly found in other mudrocks (e.g., Vaca Muerta) and implies certain flow characteristics that differ from rocks with higher permeabilities. In this work, 150 preserved rock samples of the upper and lower Eagle Ford Shale members in both oil and oil-condensate maturation windows are investigated at micro- and nanometer scales. We selected high-resolution FE-SEM images to show various pore types, pore geometries, porosity distribution, and the relationship between porosity and mineral and organic matter. In addition, matrix permeability and pore compressibility at reservoir effective stresses are investigated. Results indicate that organic matter intraparticle and mineral interparticle pores are the most abundant pore types in the Eagle Ford Shale. Moreover, microfractures observed at nano-scale are interpreted as artifacts of the sample preparation procedure prior to SEM imaging study. Given the lack of natural microfractures in the matrix, our hypothesis is that fluid flow through the matrix nanopore network might be greater than expected without the assistance of natural microfractures.