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Shale Smear Geometries and Implications for Fault Seal: An Outcrop Study from Mt Messenger, New Zealand
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fifth International Conference on Fault and Top Seals, Sep 2019, Volume 2019, p.1 - 5
Abstract
Summary
Faults in reservoirs can act as both conduits and barriers to fluid flow. Fault seal arises due to a number of mechanisms including, juxtaposition of permeable and impermeable lithologies, fault cementation, and the production of low permeability fault rock by deformation of host beds. This presentation focuses on the production of low permeability fault rock by shale smear. The aim of this investigation was to gain a representative sample of the smearing behaviours of siltstone beds within the Mount Messenger Formation, a poorly lithified unit with a maximum burial depth of 1.5 km. Siltstone beds appear to be incorporated into fault zones by two end-member mechanisms; smearing and meso-scale synthetic faulting. Thin sections of these smears show that they are often deformed by brittle micro-faulting which is generally sub-parallel to the fault zone. Similarly, meso-scale faulting is most often characterized by multiple synthetic slip surfaces that displace the host beds across the fault zone. We suggest that shearing and incorporation of siltstone beds into fault zones is primarily a brittle process. This distinction is important for fault seal as it is more likely to produce variable silt source bed thicknesses within fault zones.
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