SEDIMENTOLOGY OF MALLAWA CLASTICS AND ITS IMPLICATION TO HYDROCARBON OCCURRENCES IN WESTERN PART OF WEST ARM SULAWESI

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21 – 22 November 2006

SEDIMENTOLOGY OF MALLAWA CLASTICS AND ITS IMPLICATION TO HYDROCARBON OCCURRENCES
IN WESTERN PART OF WEST ARM SULAWESI

Johnson Achmad Paju¹ ,Yudi Satria Purnama¹ ,Bayu Nugroho¹ ,Andang Bachtiar² , & Fatma Peera³

¹GDA Consultant
²Exploration Think Tank Indonesia
³Geology Postgraduate Program, ITB

ABSTRACT

A Paleogene clastic sediment package of Mallawa Formation has been recognized by several previous researcher in southern part of West Arm of Sulawesi. It’s unconformably overlying Flysch deposit of Balangbaru and Marada Formation and overlied by Tonasa Limestone and a thick volcanic sequence series of Camba Formation. Mallawa Formation also interfingering with volcanic sequence of Langi Formation to the east. The Mallawa distribution has N – S trend with covered area 4448 km² and from the regional cross section the thickness can reach 400 m. Several previous study and paper has indicated a Paleogene Basin which covered where Mallawa Formation deposited.

To figure out some opportunities of Mallawa Formation, several fieldworks has been done by author especially with Mallawa Sediment outcrops which have objectives to arrange a better tectonic setting and sedimentary response processes understanding of southern part of West Arm Sulawesi especially about sedimentology, stratigraphic correlation, lateral distribution and also hydrocarbon potential of Eo­Oligocene deposit of Mallawa Formation.

Sedimentology observation in 5 Mallawa outcrops (Watangmallawa, Gattareng, Padanglampe, Doi-doi and Siloro) result a widespread depositional environment. Mallawa location type outcrops in Watangmallawa consist of medium – fine sandstone, mudstone and coal interbedded with up to 40 m vertical thickness. The Location Type of Mallawa Formation in Watangmallawa unconformably overlied by Tonasa Limestone. The marine influx dominated such as shoreface bar complex also observed in three other location Padanglampe, Doi-doi and Gattareng with various lateral dimension. Meanwhile, observation in Siloro outcrop dominated by tidal – meandering/floodplain – braided sequences.

Hypothetically, Mallawa Formation has a complete petroleum system components. The type II and III of source rock can be provided by intraformational Mallawa shale and coal and reservoirs by its fluvio­deltaic clean sandstone facies, mean while the seal developed by younger tight limestone facies of Tonasa Formation.

It believed that Eo-Oligocene fluvio-deltaic Lower Toraja sediment which situated to the north of West Arm of Sulawesi is equivalent with Mallawa Formation to the south. To predict the hydrocarbon potential, some of geochemical parameter like Maturity and Hydrocarbon Index that adopted from Lower Toraja could be applied to Mallawa and build-up some model and probable reserves estimation.

An integration research should be establish to get further information about the potential yield of Mallawa source rock and maturation model, reservoirs quality and distribution, and also the multiple volcanics event which can affected the reservoirs quality and the geophysical subsurface data.