Tectonic structure and petroleum potential of Tayabas Bay southeast Luzon, Philippines

Tayabas Bay is one of four offshore Philippine areas where the Australian Geological Survey Organization and the Philippine Department of Energy conducted a cooperative marine seismic, gravity, magnetic, bathymetry and geochemical survey. The project acquired new seismic data and reprocessed the 1983 World Bank seismic sections which were all integrated with previous oil company data. In the absence of wells drilled offshore, interpretation of offshore seismic data was complemented by onshore well log information and stratigraphy of the Bondoc Peninsula. Geochemistry data, both offshore and onshore, were analyzed to confirm the presence of mature source rocks and hydrocarbon migration. A new seismic interpretation has revealed the structure of this tectonically active geologically complex area. A major structural feature interpreted in offshore Tayabas Bay was a N-NW-trending strike-slip fault which is believed to be a northern splay of the Sibuyan Sea Fault. The authors named this fault the Tayabas Bay Fault and due to its association with the Philippine Fault System the movement is assumed to be left-lateral. The present study suggested the presence of a prolific source rock in the Middle Miocene Vigo Formation and/or the Late Oligocene to Early Miocene Panaon Limestone. Oil and gas generation have been and are occurring in the Bondoc Sub-basin. Two groups of reservoirs were identified, the shelf carbonates beneath the Middle Miocene shales on the Marinduque Platform and the early Middle Miocene carbonates and basin-floor clastics near the base of the Vigo Formation. Carbonate reservoirs an believed to be present in traps formed when the Late Oligocene to Early Miocene carbonate reefs and shelf deposits of the Panaon Limestone were buried by the Middle Miocene shales. A later set of traps was formed and possibly superimposed by the intense deformation associated with the Philippine Fault System which has continued from the Late Pliocene up to the present. Evaluation for hydrocarbon reserves of several possible traps identified three significant leads, namely the Yuni Lead in the south, the Mulanay in the central area and the Mabio in the North. (C) 1997 Published by Elsevier Science Ltd.