Collision Tectonics and Hydrocarbon Exploration Targets in the Philippines

Emmanuel G. Ramos

Manila Observatory

Noe Caagusan

PetroEnergy Corp.

In a tectonically active area like the Philippines, the location and features of hydrocarbon deposits are largely influenced by the geologic events in the recent 30 or so million years. Thus, hydrocarbon exploration should be guided by the knowledge about how the archipelago had been deforming since the mid-Tertiary Period. We posit the concept that tectonic collision has been the major geological environment in the Philippines in the late Cenozoic.

The indentation of Benham Rise along the East Luzon Trough governs the recent deformation in northern Philippines. The sequence of historical seismicity and faulting, the geometry of the Benioff Zone, and the discontinuous and deformed outline of the trench all suggest that collision along this trench has commenced and controls the geometry of potential hydrocarbon fields. This convergence has led to the northwestward migration of the Northern Sierra Madre and Cordillera arcs and the ensuing internal deformation of the sedimentary basins which host hydrocarbons.

In central Philippines, collision of Palawan into the arc has led to the time-space sequence of folding and creation of back-arc basins. This deformation caused the south-easterly shift in the deformation front that can be traced from Panay in Miocene to the present day deformation in southern Bohol. Using this sequence of island-forming events, the geography of the Visayas also becomes tractable. The timing and evolving geometry of post-Eocene folding and orogenies in central Philippines as defined by this sequence can serve as a powerful tool in identifying targets for exploration.

Geological conditions in Mindanao are also affected by tectonic collision. Collisional deformation in western Mindanao led to the disappearance of the trench and the shift in the locus of subduction. The same can be said of the conditions that have affected Palawan since the Paleocene, where potential source areas and reservoirs are migrating and deforming in response to the convergence of micro-continental elements into the island arc.