Half Graben Series and Its Implications to Petroleum System in Barito Basin, Indonesia

Abstract

To date, Barito Basin is believed as series of horst graben formed by strike slip mechanism in the Paleogene time. N-S oblique subduction of Indo Australia beneath SE margin of Sundaland had formed NW-SE trending pull apart basin. Further study based on seismic section, aerogravity modeling, and well correlation shows that Barito Basin is more likely half graben rather than full graben series. Tectonic subsidence curve from well data reveals that no rapid subsidence observed as commonly found in strike slip induced basin. These evidence offers the possibility that lithospheric stretching mechanism might responsible for the basin formation process. Braided stream sandstone – conglomeratic sandstone of Eocene Lower Tanjung Formation are proven as the main reservoirs in the northern part of the basin (Tanjung Subbasin). The coarsening upward vertical stacking pattern of the sandstone represents the shift from underfilled to filled phase of synrift sequence. A section of well correlation from two fields shows that they are probably deposited in transfer zone setting. This facies is interpreted to be transported from NW to SE along elongated direction of the subbasin, and ends as shallow lacustrine setting in the center of the subbasin where the coaly source rocks exist, as indicated from oil geochemistry data. Barito basin itself is classified as foreland basin in the present day. The basin gradually deepens from west to east, and steepening abruptly close to Meratus. The area near Meratus, called Barito Fore Deep served as regional kitchen. The relatively gentle slope to the west makes the western part of the basin is favourable for oil migration, so that NW migration towards elongated direction in each subbasin would be dominant than to hinge margin direction. The proven petroleum system of the Tanjung Subbasin in the northern part of the Barito Basin could be applied as an analogue to hardly explore the other identified sub basins in the southern area.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015