Abstract

The Cagayan Valley Basin located on the Island of Luzon, Philippines, is a symmetrical structural trough with an areal extent of 20,000 square kilometers. It contains a predominantly marine clastic section of Oligocene to Pleistocene age rocks which have been rapidly deposited on a basement of pre-Oligocene, and older, volcanic and meta-sedimentary rocks. The total sedimentary section is variously estimated to range from 7,500 to 10,000 meters thick. Potential source and reservoir rocks are present in the stratigraphic sequence. Numerous oil and gas shows on the surface, and in several of the 16 wells drilled to date, are evidence that hydrocarbons have been generated in the basin. The possibilities for the entrapment of hydrocarbons in carbonate reefs is especially highlighted by the discovery of a small, subcommercial gas field in the southern part of the basin.

The current direct involvement of the Philippine Government in oil exploration, through the Philippine National Oil Company, is a recognition of the Cagayan Valley Basin’s potential as a future oil producing region. Geophysical and geological studies are presently being undertaken to identify and delineate Miocene carbonate reefs and other types of traps. Initial results of the seismic program show promising prospects.