Publications

Detailed sedimentologic, stratigraphic, and biostratigraphic analysis indicates that both regressive and transgressive deltaic successions comprise the continuous, nearly 400 m thick middle Miocene Balikpapan Formation succession that is exposed in the Grand Taman Sari Circuit outcrop. There are two major lithofacies associations: 1) a 115 m thick, fluvial-dominant regressive succession, and 2) an overlying 280 m thick transgressive shallow marine succession that becomes increasingly marine upward. The shallow marine succession is tide-dominant and includes progradational and retrogradational parasequences within a highly aggradational, retrogradational parasequence set. In the regressive succession, individual fluvial channel sandstones are up to 5 m thick and are occasionally stacked to a total thickness of 18 m and single crevasse splay sandstones up to 2 m thick. Fluvial channel and crevasse splay sands cannot be correlated across the outcrop because the width of fluvial channel is less than 300m. Conversely, back-filled distributary channel sandstones in the transgressive succession that are up to 20 m thick and single tidal bar sandstones up to 1.5 m thick are laterally continuous for at least the 600 m width of the outcrop. All the various sandstones have very good reservoir potential with respect to porosity and permeability but they have significantly different sand body geometries. The back-filled distributary sandstones are as wide as the distributary they filled and are relatively straight and shoreline-perpendicular shape while the narrower fluvial channel sandstones have the shape of a meandering channel. Crevasse splay sandstones are associated with fluvial channel sandstones and have a splay geometry, while the tidal bar sandstones are associated with back-filled distributaries and generally are perpendicular to the shoreline. The two types of channel sandstone can have similar thicknesses, but the thickness of back-filled distributary sandstones is not related to channel width, so width and reservoir volume can be highly variable and markedly different from fluvial channel sandstones within the same succession. It is difficult to distinguish the four types of sandstone in the subsurface because: 1) they can occur in very close vertical stratigraphic proximity (< 40 m in the Grand Taman Sari Circuit outcrop), and 2) they generate nearly identical well log signatures, both types of channel sand fine-upward over very similar stratigraphic thicknesses and the crevasse splay and tidal bar coarsen upward. Integrated sedimentologic and biostratigraphic analysis, may provide adequate resolution.