Deepwater Sandakan Basin, Philippines: Results of Initial Exploration Drilling and Implications for Future Exploration and Development

Murray, Colin; Lunt, Peter
Mitra Energy Limited, Kuala Lumpur, Malaysia.

The first wells drilled in water depths greater than 1200 m in the Sandakan Basin have confirmed the presence of a working petroleum system, analogous with other circum-Borneo deep water basins. Previous drilling in the basin had focussed on the shallow water shelf section, with the most outboard wells having intersected a sand-poor upper slope section. In 2009 and 2010, three exploration wells were drilled to evaluate a gravity driven toe-thrust foldbelt play, with a fourth well targeting a stratigraphic play. The Dabakan-1 and Palendag-1 wells discovered significant net pay of gas in multiple stacked turbidite reservoirs, whilst the Babendil-1 well was a minor gas/condensate discovery. The Banduria-1 well tested stratigraphically-trapped channelized turbidites and had hydrocarbon shows.

These drilling results, plus 2D and 3D seismic data, have demonstrated the presence of good quality siliciclastic reservoirs, highly effective claystone seals as well as strongly sealing faults, and a prolific thermogenic gas charge. The source appears to be the same terrestrially-derived kerogen responsible for the giant fields in the Kutei, NW Sabah and Tarakan Basins. Like those basins, higher liquids content may occur in other deep water prospects in Sandakan.

Rates of sedimentation in the Late Miocene were extremely high, up to about 1,000 metres/Ma. Such a high rate of deposition has posed challenges in developing a stratigraphic model, understanding the structural history and both charge and pressure mechanisms for the basin. Post-well evaluation has included recalibration of seismic amplitude and AVO data, which has confirmed further prospectivity in the foldbelt and also highlighted additional plays in basin floor turbidites. Seismic and regional data indicates a major unconformity, below which there may be a reefal carbonate play with additional high impact potential.

This recent exploration drilling campaign has delivered not only significant exploration success, but also valuable understanding of regional geology in the least-known sector in the trend of prolific deepwater circum-Borneo play fairways.

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