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Regional Depositional Environment Model of Muara Enim Formation and Its Significant Implication for CBM Prospect in South Sumatra Basin, Indonesia

Muksin, Nanang¹; Yusmen, Dedi¹; Waren, Riedo²; Werdaya, Andromeda A.²; Djuhaeni, Djuhaeni³
¹New and Renewable Energy, Pertamina, Jakarta, Indonesia.
²CBM Exploration, BP, Jakarta, Indonesia.
³Geological Engineering, Institut Teknologi Bandung, Bandung, Indonesia.

Two main coal horizons exist within the South Sumatra basin, the Oligocene Talang Akar (TAF) and the Miocene Muara Enim (MEF) formations. Typically coals are recognized thin toward the east as they pinch out against the Sunda landmass. The Main Coal Bed Methane (CBM) targets are the MEF coals which are known to have good coal thickness and favourable depth for CBM. The important considerations for CBM play is coal presence and coal lateral distributions so that the objective of this study is concern for indentifies coal prone area by using depositional environment model.

This study is based on analyses from some seismic and wells data and integrated sedimentology & structural geology features. In general, attempted to use sequence stratigraphic approach and sedimentological observations based on sediment packages, log character and cuttings description. MEF can be divided into two depositional packages: Lower and Upper MEF. The Lower part of MEF interval appears uniform in thickness while the upper part of MEF interval shows thicker interval in the synclinal area.

Study area is dominated by faulted anticlinal features trending NW - SE. Pre-existing structure seems to influence the deposition of the lower Muara Enim interval, while the syn-orogenic structure and post depositional structure controlled the present day distribution of the upper Muara Enim interval. In some areas, post depositional tectonic event has exposed Muara Enim formation to the surface.

MEF were predominantly deposited on tide dominated coastal with overall regression cycle. Present day environment probably serve as a good analog for MEF coal deposition. A depositional environment model was proposed for two MEF packages with three identified subenvironments, there are tidal mud flat, tidal mixed flat and tidal sand flat. Generally coals developed in tidal mud flat and tidal mixed flat subenvironment.


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