Exploratory drilling in Manila Bay appears to have proven the presence of quality carbonate reservoirs in an area that was thought to be devoid of any carbonate development.
A group led by Cophil Exploration Corp., Manila, is preparing to test at least two zones at its second well in Manila Bay in the southwestern portion of the Central Luzon Valley basin. Cophil, the operator of Geophysical Survey and Exploration Contract No. 72, in June 1995 drilled a rank wildcat, Manila Bay-1/1A/1AST.
After drilling into an Upper Miocene-Pliocene limestone section with persistently good gas shows, the well drilled into an overpressured, water saturated sandstone section that brought about severe hole problems resulting in the well's premature termination at 7,430 ft.
After its setbacks in the first well, Cophil spudded an offset well, Manila Bay Redrill, about 500 m east of the previous location on Mar. 3, 1996. As expected, the redrill well encountered the same Upper Miocene-Pliocene limestone section from 6,630-7,360 ft and recorded similar gas shows composed mainly of C1 to C3.
Two sets of cores taken show a fractured character of the limestone reservoir. Preliminary indications from the observed gas shows and wireline logs suggest at least two discrete major intervals to be potentially gas-bearing. Continued drilling resulted in the well encountering another thick limestone section at 9,844-11,126 ft. Intermittent drilling breaks indicated several porous horizons within this limestone interval.
Gas, liquids indications
A significant gas peak composed of C1 to C3 was recorded upon penetrating the top of the limestone. Wireline logs that were run over the interval indicate that this limestone could also be gas bearing.
Past the limestone at 11,126 ft, the well encountered a clastic sequence of claystone and sandstones. Gas shows of C1, C2, C3, iC4, and nC4 were recorded at 11,540-565 ft, and liquid hydrocarbon shows were observed on the cuttings. Mud losses and a small diameter hole size (6 in.) hampered further drilling, and the operator decided to TD the well at 11,565 ft.
Wireline logs were being run at mid-May, and at least two testing zones in the Upper Miocene-Pliocene limestone had already been decided. It is expected that after the final logs have been run, additional test zones will be determined.
In an area considered as a frontier environment for exploration, the Manila Bay Redrill can already be considered as a geological success. The drilling results should usher in a new concept in rethinking the hydrocarbon potential of the Central Luzon Valley basin, Cophil said.
Furthermore, the success of the Manila Bay Project should add vigor to exploration efforts in the Philippines.
Geological details of the Manila Bay Redrill will be contained in a paper to be presented by E.F. Durkee & Associates Inc., Manila, at the AAPG convention in San Diego May 18-23.
Present interests are Cophil and the Coplex Group each 27.5%, Oriental Petroleum & Mineral Corp. 25%, and Pacrim Energy NL 20%. British Gas Exploration & Development Inc. has an option to take a 25% working interest in the project.
Copyright 1996 Oil & Gas Journal. All Rights Reserved.
