3D Seismic study of a shale expulsion syncline at the base of the Champion delta, offshore Brunei and its implications for the early structural evolution of large delta systems
Van Rensbergen, P.; Morley, C.K. (2000). 3D Seismic study of a shale expulsion syncline at the base of the Champion delta, offshore Brunei and its implications for the early structural evolution of large delta systems. Mar. Pet. Geol. 17(8): 861-872. dx.doi.org/10.1016/S0264-8172(00)00026-X
In: Marine and Petroleum Geology. Elsevier: Guildford. ISSN 0264-8172; e-ISSN 1873-4073, meer
An example of a Late Miocene expulsion rollover syncline related to mobile shale is described from 3D seismic data offshore Brunei. Prodelta shales accumulated in the subsiding syncline were altered after deep burial by overpressure increase and hydraulic fracturing. Consequently seismic facies was modified from a continuous divergent reflection pattern to a low-amplitude, disrupted to chaotic seismic facies bounded by a high-amplitude event that cross-cuts original stratification. Without the resolution provided by 3D data, the high-amplitude event would be mistaken for early growth faults and the subdued country-rock reflections for mobile shale, typical features at the base of large deltas. This study shows the existence of expulsion rollovers related to mobile shale, which have not been described before, and demonstrates that not all bright reflections at chaotic-coherent facies boundaries are actually fault planes. It also suggests that expulsion synclines, even during early phases of delta development may be compaction-related features rather than ones that drive the shale mass out of the area of progradation.
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