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Fault Seals: Smears, Holes and SGR
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 81st EAGE Conference and Exhibition 2019, Jun 2019, Volume 2019, p.1 - 5
Abstract
Column heights in faulted traps are thought to be controlled by juxtaposition of reservoirs against top seals and/or capillary effects of the fault-rocks themselves. In binary sand/shale sequences, fault rocks are often composed of discrete shale smears, quantified by the shale smear factor (SSF). Field observations supplemented by sandbox experiments show that smears tend to be continuous in cross-section from footwall to hanging wall at low values of SSF but become breached (forming holes) as displacement increases. The critical value of SSF at which breaching occurs depends on the strength/brittleness of the clay/shale layer and the confining stress at which fault displacement occurs. In this case the distribution of smears and holes may directly control column height in a way analogous to juxtaposition. However, the location of holes is not predictable and we address this variation using the probabilistic shale smear factor (PSSF). Convolution of stratigraphy with shale smear architecture introduces a spectrum of complexity. For multiple beds and probabilistic smear breaching, holes are more likely at lower SGR. However, these holes may themselves have limited seal capacity due to cataclasis and/or cementation.