The Offshore Mahakam Delta of East Kalimantan: A New High Resolution Perspective

Harry H. Roberts, Johan Sydow

Ancestral Miocene deposits of the Mahakam delta (East Kalimantan) contain known hydrocarbon reserves of over 3 bbl of oil and 25 tcf of gas. Most reserves have been found in shallow deltaic reservoirs. Consequently, most research has been focused on the modern delta's subaerial to shallow water depositional environments. A general concern is that most shallow-water reserves have been found, and that new exploration models need to be developed. In response, VICO, TOTAL, and UNOCAL sponsored a research project with emphasis on the Mahakam delta's shelf and slope sedimentary architecture.

Over 2100 km of high resolution seismic (Geo-Pulse boomer and 15 inc³ water gun) and side-scan sonar data were acquired (spring 1993) from the outer delta platform (~25 m water depth) to a depth of 1000 m. Initial results indicate that: (1) lowstand delta locations switch laterally through time, (2) shelf-edge deltas are present within different stratigraphic intervals along the entire shelf margin, (3) faulting thickens shelf-edge delta facies and contributes large blocks of sediment to deep water, (4) biohermal buildups (Halimeda) are important components of both modern and Late Pleistocene delta-building cycles, (5) mounded seismic facies and infilled slump scars occur on the upper slope and, (6) a gullied slope below ~500 m suggests sediment transport to the deep Makass r Strait. This Holocene-Pleistocene deltaic complex is an excellent example of the interplay between terrigenous clastic and carbonate sedimentary systems modified by tidal scour and modulated by high frequency sea level changes.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995