PROMINENT “S” GAS FIELD DISCOVERY IN CENTRAL SULAWESI
D. Hasanusi, R. Abimanyu, E. Artono, Anies Baasir
The “S” gas field is located within the JOB – PSC area of the eastern arm of Central Sulawesi. This structure is the first “giant” gas field discovered in a frontier petroleum exploration province of the Sulawesi Island of eastern Indonesia. The first petroleum exploration in the Tomori PSC area had been carried out by Union Texas Petroleum, under a PSC contract from 1980-1997. In 1997, following the relinquishment of the original “T” PSC area, a small portion of the previous working area referred to as the block was awarded to Union Texas Petroleum under a JOB type of contract. The established entity name is JOB Pertamina – Union Texas Tomori Inc.(UTTI).
In 1998 ARCO took over Union Texas Petroleum, including their Indonesian assets such as Senoro-Toili. In 1999, JOB Pertamina–Arco drilled the Senoro-1 well and discovered gas. In 2001 and 2002 following the acquisition of Arco’s interest by PT. Medco Energi Internatiuonal, JOB Pertamina–Medco Tomori drilled two appraisal wells S-2 and S-3, which proved that the “S” structure is a giant gas field with a total estimated reserve of 3.7 TCF gas and 65 MM Barrels condensate.
Three principal play types are present in the “T” area, consisting of Miocene carbonate reef buildups, wrench-fault anticlines and thrust-sheet anticlinal structures. There are two potential hydrocarbon source rock sequences recognized in the “T” area: Jurassic marine shales and Miocene marine shales and coals. However, geochemical analyses to date indicate that oil seeps and all of the oils and gas tested from the Tomori wells are most likely related genetically to shales and coals within the Early to Middle Miocene “T” Formation. Hydrocarbon generation commenced during the Early-Middle Pliocene due to burial of the source rocks by rapidly-deposited Pliocene sediments and loading by thrust sheets. Some remigration of hydrocarbons has also probably occurred due to regional basin tilting caused by uplifting of the fold belt during the Pleistocene. Potential reservoirs are provided by Miocene carbonates of the “T” Formation and the “M” Formation, including the “MA” Member reefal facies limestones, which contain excellent porosity and permeability. Bathyal shales of the Pliocene “K” Formation, at the base of the post-tectonic sediments of the Sulawesi Group provide an effective regional seal for the Miocene carbonate reservoirs.
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