Publications

Shallower reservoirs in Western Indonesia are essentially depleted where deeper target such as Paleogene syn-rift lacustrine deposits are believed as auspicious solutions, despite of being exceptionally risky and still moderately understood in terms of their quality, extent and connectivity. For purposes of understanding and reducing risk on syn-rift targets, a modern analog study was undertaken in Lake Singkarak (Sihombing, 2017), and the resultant observations (facies associations, dimensions and morphology) utilized in Jatibarang Subbasin. Sidewall core, 710ft core, mud-logs, logging suites from 22 wells, palyno-biostratigraphy, petrographic data were integrated with 850km2 of 3D-seismic and 36km of 2D-seismic lines to assess the nature of the deep Paleogene stratigraphic section by defining the gross depositional systems and the facies associations (architectural elements) of the syn-rift lacustrine system. Three depositional systems are established in the Jatibarang Subbasin, which are: (1) Confined Braided Fluvial System (BFS) that varies from alluvial fan to braided river, and (2) Fan Delta System (FDS), all proven reservoirs, but each with their own unique complexities and production risks. First, BFS Alluvial Fans are found as pebbly-breccia-sandstone, fan dimensions of 1-2km in width. These fans transform distally into pebbly-conglomerate-sandstone deposited by Braided Rivers with a wider distribution of facies. BFS deposits are found to have moderate porosity-permeability (10-100 mD, 1022% porosity). Secondly, FDS are deposits of 5-10ft pebbly-sandstone, intercalating with shallow lacustrine siltstone and shelf coarse-grain deposition, some deposits show slump structures, show high range of porosity-permeability (1-1000 mD, 3-25% porosity). BFS form major axial drainage and appear to be transporting more mature sediment, with elements more broadly distributed and stacked in hydraulic communication. In contrast, FDS generate sedimentologically immature to submature deposits which have been transported in by episodic discharge resulting in smaller, isolated deposits.