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Recognition of the importance of sedimentary deposits derived from mass transport complexes (MTCs) has increased significantly as offshore energy industry exploitation and development activities extend into deeper water. This understanding is in part due to improved seismic data. It certainly is the case in the foundation zone, defined in this study as the upper 100 m below the seafloor. The purpose of this study is to assess the physical characteristics of MTCs within the foundation zone and relate these characteristics to installation performance of jetted conductors and design considerations for suction anchor piles. The evaluation of physical characteristics of these features is based on a review of published scientific literature and results of geotechnical soil borings. Three case studies, involving either jetted conductors or suction anchor piles, are evaluated to understand the potential condition that may be encountered while penetrating MTCs in the foundation zone. The important conclusions that emerge from this review of previous data and the examination of three case studies are threefold. First, MTCs appear to be more consolidated, when compared to unfailed, conformable deposits. Second, the identification and characterization of MTCs is vital to assess the performance of jetted conductors and suction anchor piles. Third, presence of MTCs should be considered in the design, in order to minimize costly operational delays.
Gas hydrates are a major component in the organic carbon cycle. Their stability is controlled by temperature, pressure, water chemistry, and gas composition. The bottom‐simulating reflector (BSR) is the primary seismic indicator of the base of hydrate stability in continental margins. Here we use seismic, well log, and core data from the convergent margin offshore NW Borneo to demonstrate that the BSR does not always represent the base of hydrate stability and can instead approximate the boundary between structure I hydrates above and structure II hydrates below. At this location, gas hydrate saturation below the BSR is higher than above and a process of chemical fractionation of the migrating free gas is responsible for the structure I‐II transition. This research shows that in geological settings dominated by thermogenic gas migration, the hydrate stability zone may extend much deeper than suggested by the BSR.
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