Publications

The Arun gas field was discovered in 1971 and came on stream in 1977. Hydrocarbon recovery is high, with approximately 14 TCF of dry gas has been produced to date. Late-stage field life has presented some significant development challenges. A necessary step should be a substantial increase in exploration activities while maintaining the existing production. This research aims to explore more potential in Seurula Formation as a future reservoir in Arun Field. The petrophysical calculation was performed to evaluate the petrophysical properties of the Seurula formation combined with mudlog data, drilling report and DST analysis. A comprehensive geological analysis was conducted from the well log and seismic interpretation with various outcrop data analogues around the Arun field. Sequence stratigraphic concepts were observed, and the differences between seismic, well log, and outcrop data were reconciled. Based on this study, the upper Seurula Formation consists of moderately dipping sand and shale units. The Upper Seurula sands occur within this formation and are correlated over a relatively small area. The Upper Seurula sequence is characterized by large-scale clinoforms that propagate to the North and indicate the rapid deltaic depositional of volcano-clastic sediments. There is a possibility that the Lower Seurula deposited in the delta front, showing the reservoir's highly laminated nature. Laminated reservoirs are characteristic of deposition on the distal edge of the sediment fairway. In seismic correlation, the Lower Seurula has discontinuity to shingled seismic reflection, indicating highly channelled, resulting in sinuous sand bodies. Wells which penetrate this interval encountered a frequent increase in mud gas and generally are a transition from normal to over-pressured section. The sediment provenance for reservoir sands of the Seurula Formation are potentially derived partly from the foreland and young rising Barisan Mountain. In X-1 well correlation, Lower Seurula can be divided vertically into several potential reservoirs separated by laminated shale. From the DST analysis of well X-1, a strong gas shows had been encountered within Seurula Formation overlying the Miocene Arun reservoir Carbonate, particularly in the northern area of the field. Some exploration wells are planned to be drilled in order to prove this play. This study can hint at the next exploration activity in North Sumatra Basin or the development strategy for the Arun field.