Abstract: Appraisal of Present Petroleum-Exploration Activities in Philippines

Ernesto P. Sonido

The oil crisis of the 1970s brought about the need for utilization of indigenous energy resources and, consequently, a renewed search for fossil fuels. Oil discoveries in carbonate reefs in Indonesia, United States, and Canada changed the primary target trends from structural sandstone to carbonate reefs. Improvements in equipment, data gathering, processing, and interpretation of geophysical data, particularly in digital multiple seismic reflection with CDP stacking, led to the discoveries of difficult to locate targets, such as the carbonate reefs.

Through the promulgation of Philippine Presidential Decree No. 87, the Service Contract System was established in addition to the older concession system. Several incentives were added by Presidential Decree No. 529 which allowed a relaxation of custom tariffs and granted duties which spurred interest in oil exploration.

During the 19th century, exploration efforts were concentrated mainly on geologic techniques. From the 1950s to the early 1960s geophysical techniques such as reconnaissance land- and marine-gravity, analog land seismic reflection, airborne and land magnetic surveys, and photogeologic and subsurface geologic methods were adopted. During this period, the first gas discovery well, Ipil I, in the Cagayan Valley basin and high gravity paraffin oils in Cebu were discovered. In the late 1960s, more sophisticated seismic reflection equipment and CDP stacking with high-resolution gravity methods were employed both in onshore and offshore exploration areas. From 1971 to the present, improved energy sources, shooting array, recorders, processes including spot correlation techniques, and three-d mensional array have been employed in exploration onshore and offshore in the Philippines.

From 1896 to the end of December 1969, 240 wells, with a total 634,402 ft were drilled. From 1970 to 1973, 33 holes with a total footage of 172,578 ft were drilled under the concession system and from 1973 to the end of December 1976, 24 holes with a total footage of 215, 834 ft were drilled under the new service contract system. Under the service contract system, 119,743 sq km have been granted to 21 contract holders. Of the total area granted, 9,668 sq km are onshore and 110,075 sq km are offshore.

Presently, offshore drilling is concentrated west of Palawan where Nido 1 (carbonate target) and Sampaguita 1 (structural sandstone target in the Reed Bank)--the oil and gas discovery wells--are located. During 1977, other wells, such as the South Nido in the Nido complex and the Cadlao well, also hit oil- and gas-bearing reefs in greater quantities than previously found. Although drilling was undertaken in the Cagayan basin, the Bicol shelf, the Iloilo basin, the Visayan Sea basin, and the Southwest Sulor basin, there were no significant discoveries. Development of the Palawan oil fields and further exploration in other sedimentary basins are being carried out.

AAPG Search and Discovery Article #90962©1978 AAPG 2nd Circum-Pacific Energy and Minerals Resource Conference, Honolulu, Hawaii