Publications

The Gabus Massive Sand and the Gabus Zone-3 are the two main reservoirs in the Belanak Field, South Natuna Sea Block B PSC, Indonesia. The Gabus Massive Sand reservoir, containing gas with a relatively thin oil rim, is situated about 250 above the Gabus Zone-3 reservoir. The Gabus Massive Sand is interpreted to have been deposited in a fluvial channel environment, along the margins of a lake in a fan delta situation. The reservoir is mainly composed of multi-storied channel sands as observed from logs and cores throughout the field. The sand net-to-gross ratio is very high and the reservoir is considered to be in fluid and pressure communication across the field. Early reservoir simulation studies indicated that using long horizontal wells placed close to the oil-water contact and to the base of the reservoir would maximize oil recovery.A feature of this reservoir is that due to different sand facies, porosity ranges are very similar throughout the field, but permeabilities are highly variable. The reservoir architecture was modeled incorporating a seismic inversion volume calibrated to VShale. However the spatial distribution of permeability remained uncertain. In order to minimize the risk of intersecting shale sections and low permeability reservoir while placing the horizontal wells, a drilling strategy was developed to drill the production wells to the underlying reservoir horizon first and use the data from these wells to refine the facies model within the Gabus Massive Sand reservoir.A total of ~17,000 ft (~5,180 m) horizontal section was then drilled from 6 wells containing almost 100% sand, 74% of which has high reservoir quality.