Indonesia's Tarakan basin draws attention

Indonesia's Tarakan basin, where exploration dates to 1897, is enjoying more drilling after the testing earlier this year of its first deepwater discovery.

By OGJ editors
HOUSTON, June 14 -- Indonesia's Tarakan basin, where exploration dates to 1897, is enjoying more drilling after the testing earlier this year of its first deepwater discovery.

GeoPetro Resources Co., San Francisco, said its Seberaba-1 wildcat on the onshore 900,000-acre Bengara-II Block is drilling below 2,000 m and has encountered oil shows in drill cuttings. Below 2,400 m it is programmed to test the Meliat sandstone, Tabalar limestone, and Tempilan and Sujau sandstone formations, all of Tertiary age.

Seberaba-1, projected 4,000 m, is 40 miles southwest of Aster field, a 2004 discovery by Eni SPA on the Bukat Block. The Bukat and Ambalat blocks are in Northeast Kalimantan off Borneo near an area of boundary dispute between Indonesia and Malaysia.

The Aster discovery well was not tested, but Aster-2 and 3 confirmed the presence of hydrocarbons and the basin's potential. The Aster-4 appraisal well flowed 5,000 b/d of 28° gravity oil earlier this year (OGJ Online, May 14, 2007). Interests in Aster are Eni 66.25% and Anadarko Petroleum Corp. 33.75%.

Eni, operator with 100% interest, tested the Tulip-1 discovery in 800 m of water 10 miles north of Aster. Eni said Tulip "revealed significant oil and gas deposits." It gave no details and did not say whether it tested the well.

"The Tempilan and Sujau formations that will be tested at Seberaba-1 are of a very similar, look-alike geology to the recent and nearby Tulip oil discovery and to the Aster field," GeoPetro Resources said.

Eni will submit a development plan for Aster, begin appraising Tulip, and assess the potential for their joint development.

Tempilan and Sujau outcrop west of the Bengara-II block, "where each exhibits both organic rich shales conducive to hydrocarbon generation, and porous sandstones ideal as reservoirs," the company said. Seismic indicates that the wells will penetrate the formations in a fault closed rollover, which should serve as an effective trap.

GeoPetro owns 12% of Continental-GeoPetro (Bengara-II) Ltd., which holds the Bengara-II production sharing contract.

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