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 is used to derive the single phase hydrodynamic properties of the core. A CO 2 drainage experiment is conducted in the water-saturated core and imaged with a medical X-ray CT scanner. Medical CT enables CO 2 saturation quantification with increasing CO 2 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 CO 2 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.
Highlights• We introduce a new and automatic method for correcting CT beam hardening artefact • The method is implemented in an open source code running in ImageJ and it is suitable for expert and non-expert alike.• The method has been tested on homogeneous and heterogeneous rock samples with cylindrical and near-cylindrical shapes • We show how our method improves porosity and permeability measurements.
Progressive cementation and sealing of fault-localized fractures impact crustal mass transport and the recovery of fault strength following slip events. We use discrete fracture network (DFN) models to examine how fracture sealing during end-member cementation mechanisms (i.e., reaction- versus transported-limited cementation) influences the partitioning of fluid flow through time. DfnWorks was used to generate randomized fracture networks parameterized with fracture orientation data compiled from field studies. Single-phase flow simulations were performed for each network over a series of timesteps, and network parameters were modified to reflect progressive fracture sealing consistent with either reaction- or transport-limited crystal growth. Results show that when fracture cementation is reaction-limited, fluid flow becomes progressively channelized into a smaller number of fractures with larger apertures. When fracture cementation is transport-limited, fluid flow experiences progressive dechannelization, becoming more homogeneously distributed throughout the fracture network. These behaviors are observed regardless of the DFN parameterization, suggesting that the effect is an intrinsic component of all fracture networks subjected to the end-member cementation mechanisms. These results have first-order implications for the spatial distribution of fluid flow in fractured rocks and recovery of permeability and strength during fault/fracture healing in the immediate aftermath of fault slip.
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