Publications

The geochemical characterization of gas seepages offshore Timor-Tanimbar provides new insights of the petroleum geology of this area. The gas samples were obtained from seabed coring. Hydrocarbon composition and specific carbon isotopes content were obtained using Gas Chromatography Isotope Ratio Mass Spectrometry (GC-IRMS) method. The results show that biogenic gases, with ?13C1 ranging from -50 � to -100.5 � and ratio of molecular compositions (C1/(C2+C3)) ranging from 469 to 46700, dominate the eastern part of offshore Timor-Tanimbar. The western offshore area of Timor-Tanimbar is dominated by mixed biogenic-thermogenic gases, with ?13C1 ranging from -69 � to -96 � and ratio of molecular compositions (C1/(C2+C3)) ranging from 4.12 to 286.95. Pure Thermogenic gases, showing ?13C1 ranging from -31 � to -33.1 � and ratio of molecular compositions (C1/(C2+C3)) ranging from 12.03 to 20.59, are also identified in this area. We interpret the main factor controlling those gas characteristics to be the thrust-fold belt zone, formed by the collision between the Sunda and the Australian Plates, used as pathway during hydrocarbon migration. The sources of the biogenic gases are possibly found in the organic-rich, thermogenically immature, shale dominated Wangarlu Formation (Upper Cretaceous). The thermogenic gases may be sourced from the Plover Formation (Jurassic) or the Echuca Shoals Formation (Lower Cretaceous), both shale-dominated and organic rich, and expected mature for thermogenic activation.