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ABSTRACT: Tide-dominated deltas of Northwest Borneo: stratigraphic model and reservoir implications

Lambiase, Joseph J.1, Abdul Razak Damit2, Michael D. Simmons2, and John K. Warren1
(1) Universiti Brunei Darussalam, Tungku Link, Brunei
(2) University of Aberdeen, Aberdeen, Scotland

A stratigraphic model for Neogene tide-dominated deltas in NW Borneo derived from the facies distribution on modern deltas and outcrop stratigraphy indicates that stratigraphic architecture is controlled by the interaction of tectonically-driven subsidence, a high rate of sediment supply and basin hydrodynamics. The result is a largely aggradational, sandy intertidal succession on the delta plain and muddy delta front deposits. Individual delta lobes are separated by highstand mudstones and also are stacked aggradationally.

A single 2 m thick intertidal succession fines upward from thick-bedded, clean tidal channel sandstones at the seaward edge of the delta plain through thin-bedded, mud-draped tidal flat sandstones to tidal flat mudstones near the high tide line. However, the aggradational stacking generates tidal flat and tidal channel sandstone successions, with subordinate thin mudstones, wave-dominated storm and shoreline sandstones and rapid vertical facies changes, that are up to 60 m thick. These successions are proven petroleum reservoirs, notably in the Champion complex.

Channel switching occurs frequently on the delta plain because the limited intertidal accommodation space fills quickly and hydrodynamics prevent sand from reaching the delta front, thus minimizing progradation. This produces rapid lateral facies changes within the sandstone successions as well as laterally discontinuous sand bodies. The rapid facies changes and discontinuous sands result in heterogeneous reservoirs because porosity and permeability vary considerably in the tidal flat and tidal channel sandstones. Outcrop analogues suggest that storage capacity is significantly greater in the tidal flat sandstones while production is much easier from the tidal channel sandstones.

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