The large-scale(km)architecture of mass-transport complexes(MTC)and deposits offshore Borneo has been previously described using shaded relief maps of the seafloor and shallow subsurface(e.g. McGilvery et al,2004).These shallow examples are good analogues for subsurface mid-Miocene MTCs identified as largely transparent or chaotic seismic facies bounded by coherent layered facies and penetrated in offshore Sarawak/Sabah deep-water exploration wells.For the first time,using borehole image logs,the macro-scale architecture of the MTCs penetrated by five wells are analyzed.Detailed analysis of borehole image dips and lithofacies show drilled offshore Borneo MTCs comprise a mélange of stacked metre-to-decimeter scale slides,slumps,debris and grain flows that stack into techno stratigraphic units. Recognition and analysis of reservoir-scale architecture using borehole image logs is important for identifying potential sub-seismic reservoirs(thin-beds),high-grading zones for pressure samples and understanding reservoir emplacement processes.Observed changes in palaeoslope orientation reflect large basinal adjustments due to tectonics and large-scale mass-failures along the developing slope.Each onset of a new tectnostratigraphic regime results in a local reduction in sediment supply.The proportion of intra-MTC facies in each well illustrates the high degree of heterogeneity not generally reflected on the standard open-hole log suite.Intra-MTC heterogeneity may have a significant deleterious impact reservoir properties and reservoir productivity.The presence of MTC’s,generally a positive feature on the sea floor, may have an impact on sand fairways.
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