Publications

The North Tanjung Block is located in the northeastern end of the Barito Basin. The area is bounded by the Sunda Shelf basement complex to the west, the Adang Flexure and Kasale Massif ridges to the north. and the Meratus Mountains to the east. It is open to the south into the main Barito Basin. Sedimentation in the basin was completed in a single transgressive-regressive cycle typical of the combined East Kalimantan mega-basin. The basal Eocene units show interruptions and variations which recent studies suggest could be the basis of further sub-basin divisions.Extensive exploration has been conducted over the area since PerminTracer signed the block in 1993 as a standard PSC. and the effort has been rewarded with some encouraging results. The first test wells were drilled in the Beraspapan Sub-basin, Patas-1, drilled to a T.D. of 3548 ft, encountered minor oil and gas shows, while Ngurit-1, drilled 4 km to the east to a total depth of 3270 ft in the pre-Tertiary, struck gas in several sands within the Lower Tanjung Formation. These results improve chances for success in nearby similar prospects. A third well, Muya-1, was drilled to 2142 ft in the eastern part of the block on trend with the major Tanjung oil field, a 1938 discovery by BPM/Shell. The prospect, drilled on the basis of surface geology, was a postulated subthrust anticline of Tanjung field size and shape, and lies above lightly metamorphosed and intruded pre-Tertiary sediments.Several reservoir quality sands with good oil saturation failed to produce, as the formation temperature was below the pour point of the high wax Muya oil.The exploration rationale in the North Tanjung Block is to look for early formed structures which are intact after subsequent episodes of structuring, and which are reasonably filled with oil. There appears to have been long range migration of oil, wet gas and dry gas from the adjacent South Kutei Basin to the north into the Ngurit feature. Long range migration from the Kutei Basin is suggested by geochemical evidence from both outcrops and drilling data. The Muya oil may have undergone medium to long range migration from the Barito Deep to the south, but geochemical evidence suggests a local source in Lower Tanjung Formation coals which lie beneath the structure, and in the syncline to the southeast.