Total thickness of buildup 370 m.
16.2 % avg. porosity.
Early to middle Miocene.

Abstract ref. 604:
The Arun field is a giant gas-condensate field operated by Mobil and Pertamina with over 20,000 acres of closure at the top of the Arun reservoir.
A middle-shelf patch reef complex of early to middle Miocene age is the producing facies at the Arun field. About 1,100 ft of porous limestones, encased in shales, create a stratigraphic trap for overpressured hydrocarbons. Three main carbonate lithologies were encountered during the examination of over 4,300 ft of core: (1) a reef facies consisting of vuggy, coral encrusting, red-algal boundstones, (2) a near-reef facies consisting of foraminiferal, mixed-skeletal packstones with gravel-size coral fragments, and (3) an interreef lagoonal facies consisting of benthonic-foram packstones. Twenty-two species of corals have been identified from Arun reef facies; major reef-forming coals, listed in order of decreasing abundance, are Porites cf P. lutea, Cyphastrea microphthalma, Astreopora myriophthalma, Stylocoeniella guentheri, Porites solida, and Acropora ssp. The calcified tube around the siphon of the mollusk Kuphus is common in near-reef sediments. Two off-reef lithologies, interpreted as middle-shelf facies, were observed in cores: (1) benthonic-foram and planktonic-foram packstones on the gentle northwestern flank of the reef, and (2) dark-gray foram, mixed-skeletal packstones with intraclasts, on the steep eastern flank of the reef.
The Arun reef is comprised of limestones (with minor amounts of dolomite). No shale beds occur in the sequence, and all carbonate facies are in communication. A pervasive microporosity, occurring throughout the Arun Limestone, results from meteoric alteration of original carbonate mud to form a microrhombic porosity that accounts for about three-fourths of the field's total porosity. The remaining one-quarter is mainly vuggy porosity found in reef facies and, to a lesser extent, moldic porosity in lagoonal foram packstones where forams are preferentially dissolved.
