Borehole Measurement and Significance of Mass-transport Deposits Offshore Borneo: Pores to Mega-structures, the Good, the Bad and the Ugly

Bal, Adriaan; Hardikar, Nikhil; Kyi, Ko Ko

doi:10.3997/2214-4609.20132109

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“…3D resistivity tensor logs are particularly useful over zones where shale bedding is poorly developed or borehole conditions too poor for optimal image log acquisition. Past work shows that these need to be identified for optimal decision making, because they tend to have low productivity and are difficult to sample successfully or seal for pressure tests (Bal et al 2014).…”

Section: Iptc-17984-msmentioning

confidence: 99%

The Macro-Scale Architecture of Mass-Transport Complexes Offshore Borneo, South China Sea

Bal

Gaafar

2014

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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. . 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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Section: Iptc-17984-msmentioning

confidence: 99%