Publications

Naturally fractured reservoirs have attracted an increased interest of exploration and production in recent years. Fractured “Basement reservoirs provide a challenging environment to properly characterize. The term basement however, defines not just a single homogenous rock type, but a complex interplay of lithologies often genetically very different in origin. Hydrocarbon production from Pre-Tertiary rock is exceptional in Southeast Asia, gas fields in fractures basement are known in Indonesia. Indonesia provides a wide variety of basement reservoir lithologies that range from felsic intrusives to carbonate metasediments. Indonesian basement units are comprised of andesites, granites (granodiorites through monzonites), basaltic dikes, marbles, limestones, quartzites, conglomerates, and phyllites. Granites are dominated by SII intrusives and violent hydrothermal histories have overprinted many of the original “basement rock with eruptive histories dated at 51 mya. and 11 mya. respectively.Dayung Field is a gas reservoir lies on the western flank of the Central Palembang Sub-Basin (Corridor Block) of the South Sumatera Basin. The field was discovered in 1991 by the exploration well Dayung- 1. To date a total of 11 wells have been drilled. Lithologically, the Dayung Field is comprised of a Permian carbonate (Leko Formation) intruded by a Jurassic Granitic complex. Dayung host rock has been influenced by at least one hydrothermal event. This event is interpreted to be a violent event with the development of a quartz breccia pipe intruding the granite and leaching the host rock through dissolution of the feldspars. This process left a quartz breccia and sericitic zone of high porosity which could be interpreted as matrix but not in a conventional sense. The hydrothermal event at Dayung age dated at 17 mya. While the event is matrix specific (feldspar laths) it is focused along the tectonic features (faults) along which the original hydrothermal fluids traveled. Porosities in this “weathered zone can exceed 15%.Dayung is also interpreted to have a contact metamorphic halo adjacent to the Jurassic granite. This marble rhine contains marble with significant calcite filled veinlets. Most of these are from older events. Open calcite filled veinlets are present in the limestone and may be related to the 17 mya event. Laterally the marble grades to a limestone that can contain “patchy zones of porosity. Accordingly, the objective of this study is to give a better understanding of reservoir characterization in Basement complexity within the hydrothermal effect for hydrocarbon potential production in Dayung field.