Permeability of Utica Shale Fractured at Reservoir Conditions
Abstract
Knowledge of the permeability of fractured shale is important for understanding potential leakage through seals in oil and gas reservoirs, CO2 storage, or nuclear waste repositories as well as the potential production of hydrocarbon during hydraulic fracturing. In this study, we investigate the effect of confining pressure on shear fracture behavior of Utica shale (40% clay, 30% carbonate, 25% quartz + feldspar). We use a triaxial coreflood and x-ray tomography system to create fractures while simultaneously collecting permeability data, x-ray radiograph video and x-ray tomography all at reservoir stress conditions. The samples were fractured in a direct-shear configuration that allows measurement of the permeability across the length of the specimen. We compare the results of experiments conducted at 3.5 MPa and 22 MPa confining pressure (the latter approaches the approximate effective stress conditions of the Utica shale). These pressures span a transition from the formation of a highly permeable to a relatively impermeable fracture system. At low pressures, the Utica shale develops relatively simple fractures with well-resolved apertures (25-μm resolution tomography) and permeabilities from 15-900 mD (measured in terms of total flow across the 2.54 cm diameter specimen). At high pressure, the Utica shale develops a distributed fracture system, rather than failing along a primary fracture plane, and deforms with an outward appearance of ductility. At 22 MPa, the fractures were not resolvable but were evident as discrete continuities. At room conditions, these fractures opened and were easily resolved by tomography. The permeability at high-pressure was < 0.1 mD, 2-4 orders of magnitude less than the low-pressure fracture system. The results demonstrate the importance of the depth of fracture events in relation to the specific rock properties of the Utica shale specimens. The transition from permeable to low-permeability fracture systems reflects a transition from rock suitable for hydraulic fracturing and perhaps ineffective as a reservoir seal to a rock that could absorb deformation without developing permeability as desirable in a caprock and problematic in hydraulic fracturing.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMMR44A..01C
- Keywords:
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- 1847 Modeling;
- HYDROLOGYDE: 5104 Fracture and flow;
- PHYSICAL PROPERTIES OF ROCKSDE: 5112 Microstructure;
- PHYSICAL PROPERTIES OF ROCKSDE: 5114 Permeability and porosity;
- PHYSICAL PROPERTIES OF ROCKS