Publications

A comprehensive stratigraphic and geochemical analysis of Cenozoic sequence outcrops and oil seeps were conducted in western Kendeng Zone fold thrust belt and foreland area in order to determine the potential for future exploration play concept. Analysis consisted of stratigraphic analysis of outcropped Miocene Kerek and Pelang Formations which comprise of detail-measured section, biostratigraphy, thin section, and depositional environment determination. In addition, geochemical analysis of oil seeps and rock from Miocene Kerek and Pelang Formation were also conducted in order to establish oil-source rock correlation, which include total organic carbon (TOC), Rock-Eval pyrolysis, and vitrinite reflectance analyses for rock samples and biomarker analysis for oil seeps. Approximately 1000m Miocene Kerek and Pelang Formation were deposited in the study area between N2-N20 (Early Miocene-Pliocene). Detail measured sections and biostratigraphic analysis revealed that Miocene Kerek and Pelang Formation were deposited in deep marine environment (lower fan sub-environment), which dominated by thick mudstone (approximately 20m-50m) and thin coarse to fine-grained sandstone (approximately 3m-7m). However, either proximal or medial fan sub-environment with thick sequence of good quality sandstone sealed by mudstone was not present in the Miocene Kerek and Pelang Formation. Furthermore, thin section analysis from the sandstone intervals of Miocene Kerek Formation show low porosity (<10%) and low permeability. These findings show that the potential of Miocene Kerek Formation to be a good reservoir is rather low. Geochemical analysis of Miocene Kerek and Pelang Formation shows that both formations have low potential to serve as source rock. Several samples taken from both formations show low organic content (TOC: 0.27-0.75 wt%) and low maturity (Ro: 0.21-0.31% and Tmax: 424-427). Biomarker analysis revealed that the oil seeps found in the area appear to originate from terrestrial source rock that was deposited under oxic-dysoxic condition as shown by pristine/phytane, pristane/nC17, phytane/nC18 and the other biomarker ratios. From this research, it can be concluded that Miocene Kerek and Pelang Formation have a potential to serve as a great seal rock, instead of potential source or reservoir rocks as previously suggested by many researchers. Furthermore, terrestrial biomarker signature of the oil seeps revealed that the active source rock is most likely syn-rift terrestrial deposits that still buried at the subsurface. These two important facts, integrated with the regional knowledge, lead to the idea of the future petroleum play concept of Kendeng Basin. Faulted anticline and inverted rift structure with Paleogene syn-rift terrestrial source rock and Miocene Kerek/Pelang seal as well as possible post rift shallow marine sandstone reservoir can be played in Kendeng Zone for future hydrocarbon exploration play concept.