Publications

The Bengkulu Basin is a forearc basin situated to the western part of Sumatra with high tectonic activities due to being close to the subduction zone, which makes the study of hydrocarbon and exploration activities difficult because of the unstable tectonic conditions. The aim of the research is focused on identification of reservoir quality of sandstone in the Lemau Formation Middle-Late Miocene age, using the presence of ichnofossils, thin section, petrophysical properties of rocks and its implication value of porosity and permeability. The sandstones are dominated by the presence of four type ichnofacies with a bioturbation index 1 – 4. Ichnodiversity have tunnel and shaft shapes, class of ethology take places during resting, farming, escape and dwelling conditions. Sediment fillings occur in the trace fossils that affects the sorting grains, composition and the relation between grains. There are two conditions of sediment fillings as follows, (1) filled with finer grain sediment and heterogenic burrows compared to other layers around it, and (2) sediment fillings with coarser grain size and larger dimension found in several layers with medium-high energy. Thin sections analysis shows the porosity has a value of the interval of about 3,6 – 21,6% with permeability about 20 – 680 mD. The appearance ofglauconite and coral fauna shows the depositional environment occurred in a tidal process with tide and wave-dominated. The quality of reservoir will decrease in sandstone layer if the Thallasinoides distribution is found to be abundant and dominated with finer grain sediment that decreases the sandstone’s ability for hydrocarbon retention. But, the quality of reservoir will increase if the reservoir has a condition where the Ophiomorpha is filled with coarse grain and relatively large dimension that creates a bigger accommodation space, the movement and abundance of trace fossil is affected by the deposition energy. In addition, Skolithos and Chondrite are not significantly affected by the hydrocarbon reservoir. The parameters of current energy, grain size, burrow contents and burrow size need to be identified to be able to locate a good hydrocarbon reservoir.