Proceedings, Indonesian Petroleum Association
Thirty-Sixth Annual Convention and Exhibition, May 2012
Tectonics, Stratigraphy and Geochemistry of the Makassar Straits: Recent Updates from Exploring Offshore West Sulawesi, Opportunities and Risks
Awang Harun Satyana*, Shinta Damayanti*, Cipi Armandita*
The western part of the Makassar Straits is a very prolific petroleum province proved by the numerous oil and gas fields of the LowerKutei-NorthMakassarBasin. These fields are found in the deltaic, shelfal and deep-water areas and are sourced and reservoired by a single petroleum system involving Miocene-Pliocene Mahakam deltaic sediments.
Its counterpart, the eastern part of the MakassarStraits or West Sulawesi Offshore, is very different from a petroleum geology perspective. The area has been under-explored and hence there is a lack of understanding. However, exploration activity in this area has been increasing significantly in the last five years. Several speculative seismic surveys have been acquired and working blocks have been established, operated by world-class operators. They have acquired detailed 2D-3D seismic data and other geophysical-geological data. Several expensive exploration wells have also now been drilled, mostly in the deep-water area.
The increase of exploration activity in West Sulawesi Offshore has enhanced our understanding but, it cannot instantly build a thorough knowledge of the petroleum geology of the area. There have been surprising results, both positive and negative, that were unexpected when compared with the prognoses for the wells drilled recently. It therefore appears that assessing the risk of both plays and prospects in this area is still difficult.
The Recent drilling results in West Sulawesi Offshore and South Makassar provide lessons in tectonics, stratigraphy and geochemistry for this area. For example the geotectonics of Western Sulawesi and the opening of the Makassar Straits affected Eocene source richness and sand or carbonate reservoir distribution. It has also been found that not every seismically low (deep) Eocene area is a source kitchen but it is has been proven that the Eocene is generating hydrocarbon in some areas, though the timing of hydrocarbon generation is critical for entrapped volumes. Also Neogene thin-skinned structures are now considered much more risky for source, reservoirs and hydrocarbon charging and sealing is another problem.
Integrated geologic-geophysical-geochemical (3G) evaluation, in accordance with post-drilling laboratory analyses, will improve the assessment of the opportunities and risks of exploring this challenging area.