John B. Dunham1, T.J. Brown1, Rui Lin1, R.B. Redhead1, H.F. Schwing1, S.H. Shirley1
(1) Unocal Indonesia Company, Balikpapan, Indonesia
ABSTRACT: Transport and Concentration of Gas- and Oil-Prone Kerogens into Deep Water Sediments of the Kutei Basin, East Kalimantan, Indonesia
Geochemical work on numerous hydrocarbon and kerogen samples shows that terrestrial organic matter is the source for oil and gas accumulations discovered in the Deepwater Kutai Basin. Conventional core, sidewall core, and cuttings samples show that the organic matter consists of plant leaves, plant fragments and coal fragments. This material is clearly derived from terrestrial sources, and was originally deposited in deltaic and shallow-shelf environments. It was subsequently transported into the deep-water basin by turbidity currents. Specifically, terrestrial organic matter is concentrated in the upper fine-tails of turbidite deposits. The same turbidites that carry sand, also carry the terrestrial organic matter into the basin. The organic matter is not disseminated within the turbidite; rather, the kerogen becomes concentrated into laminae that can reach up to 15% TOC. Though the resin and plant fragments making up the oil-prone source material are often in the coarse to very-coarse sand-size range (1 to 2+ mm), the low density of this material leads to the particles having the hydraulic equivalent of silt-size quartz. As a result, the organic matter specifically concentrates in the silt and mud-rich fraction of the turbidite deposit. This method of deposition is in marked contrast to typical marine source rocks, which become enriched in organic matter during periods of exceptionally low terrigenous-clastic influx, as during times of condensed sequence deposition. In contrast, terrestrial oil-prone kerogen becomes concentrated in the deep-water Kutei basin during times of high clastic-influx from the shelf.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado