Anatomy of a normal fault with shale smear
- Stanford Univ., Stanford, CA (United States)
- Ben-Gurion Univ., Beer-Sheva (Israel)
Some faults are fluid pathways but others are barriers. The latter type is well known in the oil and gas industry and attributed to granulation and shale smear. Fault zone granulation has been the focus of many recent studies, but shale smearing remains relatively obscure. We describe the geometry and structure of a normal fault with shale smear in a 1500m thick sedimentary sequence of Cambrian to Neogene age in a graben 10km west of Elat in southern Israel. The fault has a trace length of about 2km and is marked entirely by what remains of a formation made up of a 60m lower shale unit, 25m of middle carbonates, and 35m of upper shale. Both shale units have been stretched over a planar discontinuity defined by the footwall cut-off planes of the underlying sandstone and limestone units for 250m, the magnitude of the normal slip. Thus, the fault geometry and the position of the shale units reveal a smearing process by which the shale units reduce their thickness or nearly vanish by thinning perpendicular to the fault and stretching parallel to the fault. In a few exposures, the lower shale unit is reduced from 60m to a thickness less than 0.5m. The middle carbonates display boudinage and form discontinuous lenses along the fault. The impact of the intense continuous deformation, the discontinuous deformation by the faults, joints and veins of the shale and surrounding competent rocks, and mixing of the shale with adjacent permeable units, on the hydraulics of the fault zone and its sealing potential need to be carefully evaluated. This study improves the present knowledge about how fault zones may incorporate shales therein act as lateral seals for hydrocarbons, and when and how this sealing potential may be breached.
- OSTI ID:
- 6573629
- Report Number(s):
- CONF-960527-; CODEN: AABUD2
- Journal Information:
- AAPG Bulletin, Vol. 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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