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Impacts of Mineralogical Variation on CO2 Behavior in Small Pores from Producing Intervals of the Marcellus Shale: Results from Neutron Scattering
journal contribution
posted on 2020-02-25, 21:47 authored by Leslie F. Ruppert, Aaron M. Jubb, Thomas F. Headen, Tristan G.A. Youngs, Bryan BandliThe Near and InterMediate
Range Order Diffractometer (NIMROD) was
used to examine the potential impact of shale mineralogy on CO2 behavior within micropores. Two samples with varying mineral
compositions were obtained from producing intervals in the dry gas
window in the Middle Devonian Marcellus Shale. One of the samples
contained relatively high amounts of quartz and clay and low carbonate,
the other contained relatively equal amounts of quartz, carbonate,
and clay. The samples were probed with CO2 at subcritical
pressures (20–50 bar) and temperature (22 °C) and characterized
over a neutron scattering vector (Q) range of 0.02
< Q < 50 Å–1. This Q range provides information from the atomistic length-scale
up to pore radii of 10 nm. Mineralogy variations between the samples
did not affect scattering ratios over the entire Q range accessible with the NIMROD. Q values for
the minimum scattering ratios of both samples at similar pressures
are remarkably similar, particularly for Q < ∼0.09
Å–1, and maximum scattering ratios are similar
in both samples suggesting that mineral pores are so uncommon in the
pore sizes examined that they cannot be resolved due to the overwhelming
amounts of organic pores in these samples. Overall, these findings
suggest that mineralogical variations have little effect on CO2 behavior within organic matter-hosted shale micropores at
high thermal maturities and they lend support to the assertion that
CO2 cannot be stored in the vast surface areas of micropores
in organic material in shale formations. In addition, CO2 enhanced oil recovery (EOR) is unlikely to displace petroleum from
some of the smaller mesopores (2.5 to ∼3.5 nm) and all of the
micropores because they are effectively closed to CO2.