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ABSTRACT: Seal Evaluation of the Talang Akar Formation (Offshore Northwest Java) Using Geochemical and Petrophysical Methods

NOBLE, RON A., Arco Exploration and Production Technology, Plano, TX, JOHN G. KALDI and CHRISTOPHER D. ATKINSON, Atlantic Richfield Indonesia, Inc., Jakarta, Indonesia

An integrated approach to seal evaluation has been developed using petrophysical and geochemical rock properties. Mercury injection capillary pressure (MICP) measurements were used to determine the maximum heights of hydrocarbon column that could be supported by various sealing lithologies. Geochemical techniques were used to measure the concentration and composition of hydrocarbons within the seal (Rock-Eval pyrolysis and thermal extraction-gas chromatography). A case study from the Talang Alcar Formation in the Ardjuna basin of offshore northwest Java, Indonesia, shows a strong inverse relationship between seal capacity and the concentration of free (non-indigenous) hydrocarbons within the seal. Using MICP data, the poorest seals in the study area were found to be delta plain shales This facies association consistently contains the highest nonindigenous oil saturation, as shown by the high ratio of the Rock-Eval S1 peak to total organic carbon (S1/TOC above 100 mgHC/gC). The composition of the oils within the seal is similar to oil in the underlying sandstone reservoirs. In reservoirs that are capped by delta plain shales, the maximum seal capacity has been exceeded, since oil impregnation of the seal has occurred. The best sealing lithology is a transgressive shelf carbonate (argillaceous dolomite). This facies shows low TOC values and low S1/TOC ratios (no oil impregnation), indicating that hydrocarbon columns in excess of the sealing capacity are not present. Integration of petrophysical and geochemical methods provides a means of evaluating the maximum possible height of hydrocarbon column as well as testing whether or not this maximum has been attained in any particular reservoir/seal couplet.


AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)