マハカムデルタ地域の石油探鉱における石油システム概念の歴史と機能

抄録

The Tertiary Mahakam Delta Province, East Kalimantan, Indonesia, has produced significant oil and gas in amount to more than 3 billion barrels of oil equivalent from the late 19th Century to the end of the 20th Century. The origin of the oil and gas is widely believed to be non-marine. Pre-PSC activities of oil and gas exploration began in the onshore area of the Samarinda anticlinolium, and resulted in the discoveries of the Sanga-Sanga oil fields. The oil fields produced mostly waxy, heavy to medium oil. The activities produced 33 millions barrels of oil to 1940. PSC activities commenced in late 1960's, and are essential to the oil and gas production in the area including onshore and offshore Mahakam Delta Province. The PSC exploration was initiated with a geological imagination that folding structures similar to those onshore should have been extended off the Mahakam delta, too. The activities in the PSC exploration in early 1970's resulted in the beginning of oil production in 1972 and gas in 1982. Exploration concept established in 1970's also resulted in the discovery of Sisi-Nubi and Peciko gas fields more off the delta. The exploration concept consisted of an idea of non-marine origin of oil and gas, and of corridor function of reverse faults for the oil and gas migration.
Exploration opportunity on the shallow-water areas was saturated in the middle of 1990's, which corresponded the peak of oil production in Indonesia. The exploration targets shifted to deepwater areas. The shift needed a new concept to establish a reasonable mechanism of oil and gas charge to the anticlinal traps in the deepwater areas. An idea for this need is significant supply of coal and coaly mud from the delta to the deepwater areas in periods of lowstand.