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ABSTRACT: Criteria for Successful Exploration for Miocene Reef Production in the Philippines

Marlan W. Downey

An abundance of modern geologic, geophysical, and geochemical data has been provided to interested members of the petroleum industry by the Philippine government, in cooperation with the World Bank. These data have been analyzed to assess whether more, and larger, Miocene reef fields should be expected in the Philippines.
In the past decade, exploration by Cities Service (OXY), Amoco, Alcorn, and others has resulted in the discovery of several small Miocene reef and Miocene sandstone oil fields in offshore Palawan. Phillips/Shell also made a significant gas discovery of about 750 bcf in a Palawan Miocene reef that is currently uneconomic to develop given the water depth (1090 ft) and distance from users.

Miocene reefs are commonly buried within Miocene clastics, and, where these impinging clastics are porous, they allow pathways for hydrocarbons to leak from the Miocene reefs. Drape closure is an important positive factor in assessing seal risk for Philippine Miocene reefs.

Source rocks to charge middle and upper Miocene reefs are typically restricted to lower Miocene horizons. Geothermal gradients are modest in much of the Philippine offshore, and only select areas provide sufficient burial to mature and expel significant hydrocarbons.

It is predicted by the author that additional, larger, and highly profitable Miocene reef fields will be found by future explorers in areas where Miocene reefs have drape closure top seals and are adjacent to deeply buried Miocene source rocks.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990