INDONESIA - Madura.

Following earlier disappointment in the East Java Sea, substantial gas reserves have been established in the Madura Strait and oil production by Mobil (now ExxonMobil) began in late 1994. A significant oil discovery in a Tertiary reefal prospect was made in 1994 in the region's onshore.

East Kalimantan, on the island of Borneo, has two main petroleum producing regions: the Tarakan Basin, associated with Tarakan island and primarily an oil play in Tertiary clastics, is a very old group of oilfields whose cumulative production appears to have exceeded the calculated volumes of the producing reservoirs, which has suggested communication with other sources of oil; and the Kutei Basin in the Mahakam Delta, where oil has been produced since the late 19th century. Gas production in these regions is a more recent activity, with the fields being a major source of supply for the LNG trains at Bontang.

Oil and gas in the Kutei Basin are produced from Tertiary deltaic sands in multi-reservoir fields. Fields occur both onshore and offshore and recent exploration has shown that much of the pre-Mahakam Delta area is underlain by gas deposits, with Total having had impressive gas finds there. Papua: The main plays in this frontier province discovered so far are in West Irian region now called Papua. They include the Tertiary pinnacle reef play located on the western Vogelkop peninsula, and the offshore Roabiba discovery made by Occidental Petroleum (Oxy). The area has been a major oil producer in the past.

In 1995 a giant gas field, Wiriagar Deep, was found by Atlantic Richfield (Arco - now part of BP). The gas lies in a Pre-Tertiary formation. Now BP says the field contains more than 18 TCF of gas, of which a large portion will be recoverable, and is hoping to find additional gas reserves in the region. The field lies in the west of Papua.

In 1994, KUFPEC of Kuwait made a major oil discovery in a Pre-Tertiary formation on the island of Ceram, in the west of Papua. The company's wildcat resulted in a 6,800 b/d flow of oil, which was the highest of any oil exploration rate in Indonesia during the previous two years.

In March 1996, Santa Fe Salawati announced the discovery of gas in its Papua block of Salawati. Its SW0-1 wildcat tested 12.5 MCF/d of gas and over 3,500 b/d of oil. But the oil reservoir is said to be small.

Exploration is in its infancy in the difficult mountainous region in the east of Papua. So far there has been no evidence that the Mesozoic oil play of the adjacent Papua New Guinea extends west into Papua. However, a deep wildcat drilled beneath a small Tertiary reef field in Papua was reported in 1994 to have found large quantities of gas in sandstones. The Natuna Sea, in the South China Sea, is a large shelfal area extending as a northern salient between East and West Malaysia. It contains a number of islands. The western Natuna Sea has a small number of oil and gas fields in Tertiary clastics which are part of the south-easterly extension of the Malay Basin.

The eastern Natuna Sea contains a Tertiary limestone play with reefal limestones built up on a carbonate shelf sealed by shales. One of the world's largest gas fields was discovered there in 1973 by Agip. This is to be developed by ExxonMobil, in the most expensive gas project in the world. Moveable gas in this field, called L, is estimated at 210 TCF. But 71% of this is unwanted CO2, a greenhouse gas associated with global warming. ExxonMobil will be developing the field for a giant LNG project, with the CO2 to be reinjected into the same carbonate reservoir but beyond the limits of the producing structure.