• Melnichenko, Yuri
• Pipich, Vitaliy
• Ruppert, Leslie
• Bahadur, Jitendra

Abstract

It is generally thought that most of the permeability in shale is controlled by organic matter contained in the matrix and a large portion of methane is sorbed onto the surface of pores within the organic material. However, the mineralogical composition of shale is quite variable which may affect how fluids move through a reservoir. We have used neutron scattering to study the effect of mineral matter on the accessibility of water and toluene to pores in Devonian Marcellus Shale samples. Three Marcellus Shale samples, representing quartz-rich, clay-rich, and carbonate-rich facies, were examined with the contrast matching technique of Melnichenko and others (2012). We used deuterated water (H2O/D2O) and toluene (C7H8/C7D8) mixtures as probe molecules to examine open and closed pores and wettability on the small-angle scattering diffractometer (KWS-1 – SANS ) and the very small-angle scattering diffractometer (KWS-3 – VSANS) instruments at the Jülich Centre for Neutron Science (Germany). The combination of the two instruments allowed for the measurement of pore radii at length scales of approximately 0.01 – >100 nm. Results show that the fractal dimension for the quartz-rich sample (Mar-1) is higher than for the clay-rich (Mar-2) and carbonate-rich (Mar-3) samples. Although the average pore radius is approximately the same in all three samples, the density of pores is highest in the clay-rich sample and lowest in the quartz-rich sample. We suggest that this is correlated to total carbon content as TOC is highest in Mar-2 (10.73 wt.%) and lowest in Mar-1 (6.69 wt.%). Contrast matching (CM) with H2O/D2O and Toluene/D-Toluene mixtures (Fig. 1) show that the accessibility of pores to water and toluene vary among the samples. In general, water accesses approximately 70–80% of the larger pores (>100 nm) in all three samples. As pore size decreases, the fraction of accessible pores decreases, but the quartz-rich sample exhibits lower pore volume accessibility than the clay- and carbonate-rich samples. At even smaller pore sizes (~<3 nm), in all samples, the fraction of accessible pores to water increases to approximately 70–80%. Accessibility to toluene very generally follows that of water, however, in the smallest pores (>~1 nm), accessibility to toluene decreases, with the clay-rich sample showing about 20% less accessible pores than in the quartz- and carbonate-rich samples. Results from this study show that mineralogy of producing intervals within a shale reservoir appear to effect accessibility of pores to water and the non-polar solvent toluene. Such differences in wettability may affect hydrocarbon storage and production and hydraulic fracturing characteristics. References: Melnichenko, Y.B.; He, L.; Sakurovs, R.; Kholodenko, A.L.; Blach, T.P.; Mastalerz, M.; Radlinski, A.P.; Cheng, G.; Mildner, D.F.R., 2012, Accessibility of pores in coal to methane and carbon dioxide: Fuel, v. 91, p. 200-208.

Topics

• density
• impedance spectroscopy
• pore
• mineral
• surface
• Carbon
• laser emission spectroscopy
• permeability
• porosity
• small-angle neutron scattering
• carbon content