Abstract

The Paleogene "Syn-Rift" sequences in offshore Northwest Palawan consist mainly of marine deposits that filled rift depocenters. A mid-Oligocene unconformity in the South China Sea Basin separates the Syn-Rift from the widespread platform carbonates of the Nido Limestone.

The target of most exploration in NW Palawan are the buildups and folded fractured platform carbonates of the Nido Limestone, and the directly overlying turbidites of the lower Pagasa Formation. Very few play concepts have been developed for the Syn-Rift sequences due to poor seismic data quality and the scarcity of wells that have penetrated it. In outboard highs where most wells have been drilled, most of the Syn-Rift successions, except for the topmost few decameters, have low sandstone:mudrock ratios, giving a perceived lack of reservoir quality sands.

The presence of turbidite reservoirs in slope and basinal paleoenvironments are indicated by the turbidites found in Syn-Rift-equivalent units in onshore Central Palawan and new interpretation of 2D seismic data on the Syn-Rift sequences in offshore Palawan. Potential lowstand plays include basin floor fans, leveed channels, and incised valley fills. The basin floor fan may reach several km along dip sections and may be composed of more than one lobe. It is convex-up and shows bidirectional downlap. The leveed channel complex exhibits irregular and discontinuous reflections with occasional channel patterns almost 1 km wide. Incised valley fills are typically >2½ km wide. Exploration risks for Syn-rift plays include the lack of a local condensed section above basin floor fans to serve as seal and drilling a sand-poor fill in leveed channels and incised valleys.

The prospectivity of many of these deepwater plays is enhanced by their lateral proximity to inboard kitchen areas and favorable burial history. Despite water depths ranging from >1 to 2½ km, the Syn-Rift interval can potentially become significant exploration target and warrants more detailed evaluation.

Presented at: 2007 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2007