--> Exploring Stratigraphic And Subtle Combination Traps Using Pore Pressure Data In South Sumatra Basin, Indonesia

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Exploring Stratigraphic And Subtle Combination Traps Using Pore Pressure Data In South Sumatra Basin, Indonesia

Abstract

Limited number of remaining four-way and three-way structural closures in the matured South Sumatra Basin (SSB) has led to the initiation of stratigraphic-based exploration campaign. Baturaja Carbonates so far has contributed as one of the main producing reservoir interval in the region with total EUR of more than 1.5 BBOE. Interestingly, numerous major discoveries in this area were found under non-structural set-up associated with stratigraphic pinch-out and lateral facies change. These include Kaji-Semoga field from North Palembang Sub-basin and Pian-Jene complex from South Palembang Sub-basin with cumulative production of 170 and 61 MMBOE respectively. In this paper, we applied pore pressure-based technique to improve the interpretation of carbonates facies model and to address issues related with limited seismic coverage and off-set wells.

Pressure-depth plot from 240 pressure data points (RFT, MDT, and DST) in Baturaja Formation were generated in order to observed regional reservoir pressure trend variation. A range of 50-100 psi differential pressure was observed which indicates the presence of pressure cells associated with lateral and vertical reservoir compartments. This was followed by integrating shale-based pore pressure prediction, aquifer hydraulic head and seal capacity estimation. The result shows that in some area, systematic overpressure variation among pressure cells can be observed, confirming the presence of hydrocarbon-water contact that gently tilted toward basin regional dip. More importantly, the application of these approaches, combined with sequence stratigraphy study, has enabled to the identification of four key stratigraphic facies architectures; (1) Laterally extensive, good reservoir quality and regionally connected limestone, (2) Isolated, good to medium reservoir quality and locally connected limestone, (3) Moderately extensive, good to medium reservoir quality, locally connected with clastics from deeper basinal area, and (4) Sparsely distributed, poor reservoir quality with fair to good laterally-sealing rocks. The former three facies types resemble the variation of Baturaja reservoirs in term of quality and spatial distribution over Early Miocene carbonate platform, while the latter is linked with lithologic baffles and potential lateral sealing facies. The produced pore pressure-based GDE map was then incorporated into basin-scale petroleum system modeling. The migration and charge model indicates that porosity pinch-out often act as lateral sealing mechanism which can altering migration direction as well as creating migration shadows. This study suggest that stratigraphic and subtle combination trap formation is a direct proxy of overpressure-controlled secondary migration, basin structural evolution as well as lateral and temporal carbonate facies changes. Moreover, the effects of seal geometry and trap-fill mechanism on its response to the prediction of potential stratigraphic traps is explained.

This study allows the development of new exploration play fairway for future exploration portfolio decision related with stratigraphic and subtle combination traps.