Post-generative alteration effects on petroleum in the onshore Northwest Java Basin, Indonesia

Northwest Java Basin oils, largely derived from the fluvial-deltaic to nearshore marine Talangakar formation of Oligocene to Early Miocene, range from heavy oils to extremely light oils and retrograde condensates, with API gravities of a suite of oils ranging from about 17° to 53°. Heavy oils, with API gravities less than 22°, all of which are in shallow reservoirs, are biodegraded. Pristine oils concomitant with related derivative residual and retrograde condensate oil types indicate evaporative fractionation phenomena. Post-generative alteration processes are widespread in this highly faulted region. Pristane to phytane biomarker ratios of retrograde condensates and residual oils have been shown to be severely affected by evaporative fractionation. Principal component analysis (PCA) of isotope and biomarker data identified two oil families associated with source rocks of the Talangakar formation. One group is suggested to be derived from more marine influenced delta-front to prodelta depositional settings, while the second group is attributed to a higher plant-rich delta-plain to delta-front depositional environment. Correlation of these oil families with the varied depositional environments of the Talangakar formation has allowed a more refined approach to the identification of hydrocarbon migration pathways in the Northwest Java Basin. Multivariate statistical analysis is shown to be an effective tool in correlating high gravity condensate oil types.