ABSTRACT: Post-generative alteration effects on petroleum in the Northwest Java basin, Indonesia

Ellis, Leroy¹, Haposan Napitupulu², and Robert M Mitterer³
(1) Terra Nova Technologies, Dallas, TX 
(2) PERTAMINA EP, Jakarta, Indonesia
(3) University of Texas at Dallas, Richardson, TX

Northwest Java Basin oils, largely derived from the fluvial-deltaic to nearshore marine Talangakar Formation of Oligocene to Early Miocene age, 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 condensates oil types indicate evaporative fractionation phenomena. Post-generative alteration processes affecting crude oils are widespread in this highly geologically faulted region. Pristane to phytane biomarker ratios of retrograde condensates and residual oils have been shown to be severely affected by evaporative fractionation processes. Residual oils are further indicated by depletion in light ends, lower API gravity than original oils, and enhanced concentration of aromatic compounds.

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 depositional environments of the Talangakar Formation has allowed a more refined approach to the identification of hydrocarbon migration pathways in the Northwest Java Basin.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia