Structural Interpretation and Seismic Facies Analysis of the Sandakan Sub-basin, Sulu Sea, Philippines

Futalan, Krestabelle M.; Mitchell, Andy; Amos, Kathryn; Backe, Guillaume
Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.

The Sandakan Sub-basin is located in the SW part of the Sulu Sea between the islands of Borneo and Sulu. The sedimentary fill is associated with a long-lived delta system which deposited sediments into the Sub-basin from the Middle Miocene onwards. The Sub-basin comprises two distinct structural provinces in the study area. Planar and listric normal growth faults related to margin-parallel extension occur in the delta top. These are linked to fault propagation folds compatible with margin-normal compression in the delta toe. This structural framework is typical of a delta deepwater fold and thrust belt system (DDWTFB). Similar systems are observed in Tertiary deltas around Borneo, such as the Baram Delta System.

This study also presents a gross seismic facies mapping analysis focused on the Pliocene to Middle Miocene rocks of the Togopi, Ganduman and Sebahat Formations, and is based on the interpretation of seismic reflection patterns together with gamma-ray logs, biostratigraphy and cuttings descriptions from four wells. This approach provides a description of the depositional sequences in the Sandakan Sub-basin and a framework for correlating seismic and well data.

The structural interpretation of the seismic data gives information about the timing of deformation in the Sandakan Sub-basin and related structural traps. The seismic facies mapping reveals the changes in depositional environments due to the evolution of the Sub-basin through time. The Sandakan Sub-basin shifted from an actively prograding fluvio-deltaic system during the Late to Middle Miocene, into a shelfal marine environment during the Pliocene. The results of this investigation improve our understanding of the sub-basin's prospectivity, specifically the quality and distribution of source, seal and reservoir rocks.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012