Publications

Naturally fractured reservoirs have attracted an increased interest in recent years. Fractured “Basement reservoirs provide a challenging environment to properly characterize and model. The term basement however, defines not just a single homogenous rock type, but a complex interplay of lithologies often genetically very different in origin. Dayung Field is a fractured basement gas reservoir that 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 10 wells have been drilled. Lithologically, the Dayung Field is comprised of a Permian carbonate (Leko Formation) intruded by a Jurassic Granitic complex. Dayung has been influenced by multiple tectonic events and at least one hydrothermal event. The field is well connected through tectonic fractures and has tank like behavior. Several events and modified the metasediments and granites that comprise the reservoir. The hydrothermal event has been interpreted to be a violent event with the development of a quartz breccia pipe intruding 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. While the event is matrix specific (feldspar laths), it is focused along the tectonic features (faults) in which the original hydrothermal fluids traveled. Porosities in this “weathered (hydrothermally baked) zone can exceed 15%. Dayung is also interpreted to have a contact metamorphic halo adjacent to the Jurassic granite. This contains marble with significant calcite filled veinlets. Open tectonic fractures containing calcite crystals are present in the marble and limestone. These may be related to the 17 mya hydrothermal event. Laterally the marble grades to a limestone that can contain “patchy zones of primary porosity. The objective of this study is to provide a better understanding of reservoir characterization in a complex basementhydrocarbon charged reservoir affected by multiple intrusive events through a single deterministic model.