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Sediment Supply Systems of the Champion "Delta" of NW Borneo: Implications for the Distribution and Reservoir Quality of Associated Deepwater Sandstones

Lambiase, Joseph¹; Cullen, Andrew²
¹Petroleum Geoscience Program, Chulalongkorn University, Bangkok, Thailand.
²Chesapeake Energy, Oklahoma City, OK.

Middle Miocene to Pliocene sedimentation on the NW Borneo margin has long been interpreted as the product of one relatively large deltaic system, the Champion Delta. However, several lines of evidence indicate that the Champion system was not a simple, large delta; its drainage basin was too small, several structurally active sub-basins, each with its own stratigraphic succession, comprised the area covered by the "delta" and structurally-generated topography segregated the Champion shallow marine strata into thick, wave-dominant and tide-dominant successions. Seismic stratigraphic and fluvial outcrop observations indicate that multiple modest-sized rivers comprise the Champion system, of which the Padas and Limbang appear to be the largest, longest-lived and most important with respect to sediment supply. The mineralogy and texture of the sand delivered to the shelf edge by these rivers was diverse owing to contrasting bedrock lithologies in the different catchment areas; reservoir quality of the resulting deepwater sands is expected to be comparably diverse.

Structurally-evolving topography continually modified the number and location of rivers reaching the paleo-shoreline. Growth faults, rapidly subsiding synclines, inversion anticlines and shale ridges trapped sand on the shelf resulting in a variable sand supply to the shelf edge. Because of the Champion system's multiple sources and frequently-changing sediment supply, the spatial and temporal distribution of its deepwater sand accumulations are not only expected to be less related to sea level fluctuations than those sourced from a single, large shelf edge delta, but should also be smaller in size with a more scattered geographic and stratigraphic distribution. The complex sediment supply pathways and variable provenance of the Champion system appear to explain some of the stratigraphic and geographic variability that occurs in the reservoirs of the deepwater Gumusut and Kikeh fields, despite their geographic proximity.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012