Subcore scale fluid flow behavior in a sandstone with cataclastic deformation bands

Romano, Carla R. and Zahasky, Christopher and Garing, Charlotte and Minto, James M. and Benson, Sally M. and Shipton, Zoe K. and Lunn, Rebecca J. (2020) Subcore scale fluid flow behavior in a sandstone with cataclastic deformation bands. Water Resources Research, 56 (4). e2019WR026715. ISSN 1944-7973 (https://doi.org/10.1029/2019WR026715)

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Abstract

Accurate determination of petrophysical and multiphase flow properties in sandstones is necessary for reservoir characterization, for instance for carbon dioxide and hydrogen storage in geological formations or for enhanced oil recovery. Several studies have examined the effect of heterogeneities, such as fractures, bedding planes and laminae, on core-scale fluid flow. However, the influence of deformation bands that commonly occur in high porosity sandstones, is poorly understood. In this study, we consider a core sample of Navajo sandstone characterized by diagonally oriented deformation bands and two laminae perpendicular to the core axis, as determined from micro X-ray computed tomography (micro-CT). Positron emission tomography (PET) is used to derive the single phase hydrodynamic properties of the core. A CO2 drainage experiment is conducted in the water-saturated core and imaged with a medical X-ray CT scanner. Medical CT enables CO2 saturation quantification with increasing CO2 injection rate. Experimental results and the accompanying numerical simulations indicate that both the laminae and the deformation bands act as capillary barriers, with the laminae forming weaker capillary barriers than the deformation bands. The deformation bands have lower permeability and porosity due to grain crushing, and a very high capillary entry pressure that inhibits CO2 migration across the bands. At the reservoir scale, deformation bands form conjugate sets and are often present in thick anastomosing clusters that define lozenge-shaped compartments. These findings have important consequences for subsurface fluid flow. For example, the presence of deformation bands may reduce the storage capacity and injectivity in carbon storage reservoirs.

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