Abstract

The Barito Basin, located in southern Kalimantan, consists of approximately 5000 meters of Cretaceous and Tertiary clastics with subordinate carbonates deposited in a passive margin setting. Middle to Late Miocene compression set up the present basin architecture. The basin is structurally subdivided by the "Tanjung Line": to the North a highly deformed zone dominated by reverse faulted anticlines; to the South a virtually 'undistrubed' sedimentary package gently dipping into the axis of the asymmetrical basin trough.

The largest discovery in the basin to date is the Tanjung Field. The main productive sand is a basal transgressive unit, dated here as Lower Paleocene. About 800 MM bbls of oil (in place) have so far been discovered. The existing discoveries are restricted to the inverted area north of the "Tanjung Line". This study focused on the tectonically undisturbed southern part of the Barito Basin (South Barito Basin).

The sequence stratigraphic model for the Tanjung Formation presented in this paper shows an alternative to the conventional stratigraphy, incorporating older Paleogene and Cretaceous sediments in the Lower Tanjung Formation (previously assigned to the Lower Eocene).

The primary reservoir in the South Barito Basin is the basal transgressive sand of sequence-4 (63 Ma) which is equivalent to the Z860 sandstone in the Tanjung Field. The principal source rocks are coals and coaly claystone, containing Type III kerogens. Intraformational claystones associated with the maximum flooding surfaces of sequence-4 (Supersequence-2) act as the effective seal within the Tanjung Field and are also expected to provide the vertical seals in the study area.