Publications

The East Natuna Basin, separated from the West Neptune Basin by Natuna Arch, is a relatively under explored petroleum province in the Natuna Sea, Indonesia. Exploration in the early 1970's focused mostly on the North East Natuna Basin and the Paus-Ranai Ridge and many of the wells encountered gas with high CO2 contamination. The South Sokang block which lies between the Natuna Arch and the Paus-Ranai Ridge was considered non-prospective as the majority of the area was thought to be a basement high, part of the Natuna Arch. Between 2007-2011 Lundin Indonesia in-filled the sparse regional seismic coverage with new acquisition and purchase of 5874 kms of 2D seismic data. Seismic stacking velocities indicated no significant velocity contrast across the major unconformity which would be expected if this was the top basement reflector as had previously been interpreted. Images from the regional satellite gravity data indicate a significant gravity low to the west of the Sokang Sub-Basin at the perceived basement high. This suggests that an older Paleogene basin may lie beneath the major unconformity. Regional tectonic studies indicate that at the end of the Cretaceous continental growth on the eastern margin of the Natuna Arch was occurring through continental fragment accretion related to subduction processes. Palinspastic reconstruction based on a new seismic interpretation suggests that the Sokang Sub-Basin is deforming within mainly a “Strike-Slip” regime. The Sokang Fault zone is closely related to the boundary between the Luconia Micro Continent Block and the Indochina East Malaya Continent Block. The dextral strike-slip nature of this plate boundary allows for the repetition of transtensional basin opening events and transpressional inversion and erosion events. The interpretation of an earlier Paleogene basin beneath the Miocene basin is consistent with this strike-slip model. By analogue with the West Natuna Basin, the major unconformity is re-interpreted as the Early Miocene unconformity and the section previously called "basement" is interpreted as Paleogene syn- and post-rift deposits, based on their seismic character which is similar to the Eocene/Oligocene sediments in the West Natuna area. Therefore two different Tertiary petroleum systems are interpreted to exist in the Sokang Sub-Basin, a Neogene petroleum system related to the East Natuna Basin geology, and a Paleogene petroleum system related to the West Natuna Basin geology. This new interpretation opens up a new play in the South Sokang block. Recent seismic interpretation has identified a number of leads in both the Paleogene and Neogene plays and a 3D seismic survey will be acquired in 2013 to firm up a potential drilling target.