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ABSTRACT: Turbidite deposition in a muddy bypass system on the upper slope, offshore Brunei

Meckel, L.D.1, Abdullah Ibrahim2, and Shane M. Pelechaty3
(1) Shell International Exploration & Production, Rijswijk, Netherlands
(2) Brunei Shell Petroleum, Seria, Brunei 
(3) Petroleum Development Oman, Muscat, Oman

The Mio-Pliocene upper continental slope of Brunei was characterised by thrust-related shale diapirism, and transpressional tectonics. The relatively slow kinematics of these movements created a 'stepped' (and locally ponded) slope profile with limited accommodation space. This dynamic slope topography localised turbidite deposition to depositional lows. However, the likelihood of muddy turbidity flows in this setting, poses a significant risk to reservoir development within these minibasins.

Calibrated seismic facies analysis of 3D seismic suggests, however, that sand-prone turbidite units (represented as convergent, baselapping, highly reflective (Cbh) packages) are probably preserved in the paleo-minibasins. These packages typically link updip to chaotic seismic facies representing the ancient turbidite feeder systems. More continuous reflectors above and below these packages are interpreted as hemipelagic slope drapes.

Syn-depositional ridge growth preferentially locate Cbh facies in structural lows but many of these reservoirs also drape the flanks of bordering highs due to continued growth of the diapirs following deposition. Stacked reservoirs are present in several of the minibasins due to selective focusing of turbidite flows into them, and the episodic growth of the intervening ridges.

The Cbh packages reveal a variety of internal seismic configurations related to reservoir architecture. Cbh facies illustrate more continuous internal seismic events representative of sheet sand development, as well as highly discontinuous internal events typical of loosely and highly amalgamated channel sands.

The Brunei slope is similar to other settings, such as the Niger slope in Nigeria, and illustrates a typical shale-based system characterised by healed-slope turbidite deposition.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia