Core Laboratories has completed a sequence stratigraphic and regional geochemical study of the Tarakan Basin. Consistent problems have plagued operators in the Tarakan Basin, namely poor sequence and seismic control, extensive reworking of sediments, poor stratigraphic controls, lack of closures, young migration and lack of competent seals. The main aim of the study was to erect a usable sequence stratigraphic and chronostratigraphic framework for the Tarakan Basin, to constrain the extensive geochemical database within this framework and to identify the functioning of petroleum systems in the Tarakan Basin.
The study was focused on fourteen (14) key stratigraphic control wells in the Tarakan, Muaras and Berau sub-basins of the Tarakan Basin and on circa 2,000 km of regional seismic lines which were made available for appraisal and limited reinterpretation. The geochemical component focused on thirteen (13) key wells, plus oil/extract data from an additional one well and five (5) oil/gas fields.
Biostratigraphy
- Detailed re-interpretation and new analysis were confined to the fourteen (14) key wells. Data from an additional six (6) wells were also reconsidered in the context of the evolving chronostratigraphic framework. These additional data proved especially useful for seismic correlations and paleoenvironmental mapping.
- Additional information on “peripheral” wells was obtained from a number of reports made available by the client companies and these are referred to, where necessary, in the text. Despite the fact that paleoenvironmental and biostratigraphic information was not as complete or as thorough in these “peripheral” wells with no re-interpretation carried out, this additional information proved useful in compiling the paleoenvironmental maps.
Seismic
- The seismic database consisted of approximately 2,000 line km of multifold subsurface coverage seismic, well synthetics, well velocity time-depth tables and two-way-time converted logs. The lines were selected in a sparse grid to aid in the well correlation of biostratigraphic events, sequence boundaries and sequences, rather than be used in basin seismic stratigraphy study of paleoenvironments away from well control. At its most dense (rarely), the seismic grid was in the order of five (5) km but generally was twenty (20) km or greater.
Geochemistry
- A detailed review of a pre-existing comprehensive database on potential source rocks throughout the stratigraphic record was performed for thirteen (13) key wells. Measured and modeled maturity data from these wells (plus hypothetical wells in undrilled depocentres) were interpreted to evaluate the thermal history of the Tarakan sub-basins. Oils/extracts data from the key wells, plus reservoired oils from one additional well and four (4) oil fields, were also considered with a view to understanding the oil-source rock relationships active throughout the entire Tarakan Basin.