Publications

Exploration in the West Natuna Basin (WNB) commenced in 1968 with the award of Block ‘A’ to AGIP and Block B to ConocoPhillips (COPI) which continues to operate Block B until the present day. The original Block ‘A’ included the areas known as Kakap Block and Block A, operated by Star Energy (Kakap) Ltd. and Premier Oil respectively. Large major inversion features were the main target for drilling in the early ‘70s, with disappointing results until the KG and KH discoveries in the late ‘80s, which were in relatively less deformed minor wrench related structures. This paper examines the overall effect of the tectonostratigraphic framework and structural history of the WNB and in particular, the temporal variation and magnitude of inversion, on the spatial distribution of known hydrocarbons. The integration of the regional mapping in North Kakap and the surrounding areas has provided an invaluable insight into the spatial and temporal relationship of all the essential play elements (source, reservoir, seal and trap) with regards to the deformational characteristics of this part of the basin and its remaining exploration potential. A clear structural distinction between Paleogene basement high (KRA play type), the Neogene minor wrench related- (KG and KH), and major inversion -structures (KF-Anoa) has been recognized. The classification of these trapping styles is essential to evaluate the requisite elements for hydrocarbon entrapment. The charging mechanism of these structures can be evaluated by analyzing the deformational characteristics affected by the extent and degree of inversion. The Anoa Deep discovery by Premier in 2012 has opened up potential for structures associated with major inversion and consequently within the deeper reservoir target, despite the fact that the principal reservoir in the basin (Upper Gabus and/or Arang) is absent by erosion over this structure. We conclude that field sizes and the controlling factors of the major inversion structures must be considered in more detail as a means of discovering the remaining potential of the basin.