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The Arun Gas Field is located in the Special Province of Aceh in North Sumatra. The field straddles the Coastal Plain between the Barisan Mountains and the Strait of Malacca, 225 kilometers northeast of Medan. Condensate rich gas is found in reef and associated carbonates of Lower and Middle Miocene age which in places exceed 1000 feet in thickness. These carbonates occur near the base of a Tertiary sedimentary section having a thickness of over 10,000 feet. The carbonate rocks are underlain by a clastic sequence of variable thickness which in turn rests on economic basement of pre-Tertiary age. The reef carbonates occur on a large paleotopographic high trending in a general north-south direction. The gas accumulation is mainly stratigraphic, having been trapped in a porous reefoid facies which is overlapped by upper Baong (Middle and Upper Miocene) shales. Subsurface studies and early drilling results suggest an ultimate field size covering approximately 42,000 acres. The field was discovered by the Pertamina-Mobil Arun-A1 well drilled in late 1971, and since that time continuous appraisal drilling has seen the completion of four additional gas wells.