Tectonic Controls on Reservoir Quality and Distribution Based on Modern Sedimentological Study in Thrust Fold Belt System of Lariang Basin, West Sulawesi, Indonesia

Bachtiar, Andang ¹; Purnama, Yudi Satria ¹; Suandhi, Purnama Ary ²; Krisyunianto, Andi ²; Simanjuntak, Kristian ²; Baroes, Febrio ²
(1)Exploration Think Tank Indonesia, Jakarta, Indonesia. (2) GDA Consulting, Jakarta, Indonesia.

Lariang Basin covers onshore and offshore areas of West Sulawesi Province, Indonesia. The basin started as an extensional basin on the edge of Sundaland during Eocene. Subsequently, it was experiencing several inversion events associated with volcanisms peaked on Middle Miocene. Finally it became thrust fold-belt system from Late Miocene until Recent due to compensating compressional effect of the Banggai-Sula docking to Sulawesi in the east of this area. Late Miocene - Pliocene reservoirs both in onshore and - especially - offshore have being targeted as hydrocarbon-bearing reservoirs after unsuccessful previous exploration efforts which mostly focusing on Eocene-Miocene reservoirs onshore. Modern sedimentological study on rivers, beach and deep seabed samples was conducted in the area in order to get analogues of reservoir characters based on the assumption that the thrust-folding and faulting are active until present day. Hence, the present is the key to the near past.

Stream sediment samplings and corings were carried out in Karama, Lumu and Budong Budong Rivers as well as on western beach and offshore deepwater of 2500 meter depth (seabed sampling). Interpretation and quantification of modern environment are also based on SAR image delineation in onshore area and multibeam bathymetry and backscatter data of offshore deepwater area. Stream sediment and core samples are analyzed for granulometry, petrology, biostratigraphy, heavy minerals and XRD.

The shift of present-day structural trend from onshore to offshore, i.e. from NNE-SSW to N-S seems to have controlled the locus and trends of respective Miocene to Pleistocene reservoirs. Although there is also a signal of long distance provenance of the reservoir grain components, the majority of thrust-fold belt system reservoirs are shown to be sourced locally from local thrust highs. Systematic pattern of grain size and sorting index variations also suggests controls of thrust faulting on the sediment quality. Hence, the quality of the Late Miocene - Pliocene sediments in the subsurface of offshore area is predicted to be controlled by the lithology exposed under water in the adjacent thrust highs during corresponding time of deposition.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.