Predicting Fluid Flow Regime, Permeability, and Diffusivity in Mudrocks from Multiscale Pore Characterisation
Abstract
In geoenergy applications, mudrocks prevent fluids to leak from temporary (H2, CH4) or permanent (CO2, radioactive waste) storage/disposal sites and serve as a source and reservoir for unconventional oil and gas. Understanding transport properties integrated with dominant fluid flow mechanisms in mudrocks is essential to better predict the performance of mudrocks within these applications. In this study, small-angle neutron scattering (SANS) experiments were conducted on 71 samples from 13 different sets of mudrocks across the globe to capture the pore structure of nearly the full pore size spectrum (2nm-5μm). We develop fractal models to predict transport properties (permeability and diffusivity) based on the SANS-derived pore size distributions. The results indicate that transport phenomena in mudrocks are intrinsically pore size dependent. Depending on hydrostatic pore pressures, transition flow develops in micropores, slip flow in meso- and macropores, and continuum flow in larger macropores. Fluid flow regimes progress towards larger pore sizes during reservoir depletion or smaller pore sizes during fluid storage, so when pressure is decreased or increased, respectively. Capturing the heterogeneity of mudrocks by considering fractal dimension and tortuosity fractal dimension for defined pore size ranges, fractal models integrate apparent permeability with slip flow, Darcy permeability with continuum flow, and gas diffusivity with diffusion flow in the matrix. This new model of pore size dependent transport and integrated transport properties using fractal models yields a systematic approach that can also inform multiscale multi-physics models to better understand fluid flow and transport phenomena in mudrocks on the reservoir and basin scale.
Authors 8
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Amirsaman Rezaeyan corresponding
Affiliation as printed
Heriot-Watt University
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Forschungszentrum Jülich · Heinz Maier-Leibnitz Zentrum
Affiliation as printed
Forschungszentrum Jülich GmbH, (Jülich Centre for Neutron Science, JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ)
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Affiliation as printed
Heriot-Watt University
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Affiliation as printed
Imperial College London
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Timo Seemann Aachen
Affiliation as printed
RWTH Aachen University
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Affiliation as printed
Chemical Sciences Division, Oak Ridge National Laboratory
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Affiliation as printed
Australian Synchrotron
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Affiliation as printed
Heriot-Watt University, Lyell Centre
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