Publications

The Eocene - Oligocene lacustrine syn-rift deposits in the South Sumatra Basin, known as the Lemat Formation, are considered a prolific regional source rock in the area, in which the hydrocarbon typically accumulates towards reservoir rocks of the Talangakar and Baturaja Formation. However, based on our study, there are sandstone intervals within the thick shale layers of the Lower Lemat Formation with the right petrophysical properties to become reservoir rocks and the potential to contain hydrocarbons.

This research was carried out by integrating wellbore data (wireline log, mud log & pressure log, core, biostratigraphy, and DST) and 2D seismic to obtain the of lithology, facies, sequence stratigraphy from well correlation and subsurface mapping. Furthermore, a static modelling of facies and petrophysical properties was conducted to get prospective hydrocarbon mapping for Eocene-Oligocene Lower Lemat Formation.

Based on the results of the 2D seismic analysis, this reservoir is trapped in the anticline structure which has been cut by reverse fault and acts as hydrocarbon trap within a three-way closure type. We found that the lacustrine syn rift deposits in the research area are composed of dark gray shale deposits with intercalations of fine-coarse sandstone with calcite cement which is thought to have potential as hydrocarbon reservoir. The interpretation of a lacustrine depositional environment is supported by the appearance of Oligocene green algae fossils with species Florschuetzia trilobata, Leiospheres, and Botryococcus algae, where the facies developed as subaqueous distributary channel, mouth bar and lacustrine shale. Based on the petrophysical analysis of the sandstone interval, we found that the shale volume has a range of 27.9 – 35.3 %; the effective porosity range is 8.6 – 14.1 %; the permeability range is 1.97 – 21.85 mD; and the water saturation range is 17.8 – 0.33 %. Through this research, it is hoped that future exploration activities may be focused on formations that are not well known as reservoirs.