Approximately 70% of all Indonesian oil production has come from the South and Central Sumatra Basins, with the Late Oligocene-Early Miocene sedimentary section accounting for 97% of this total. Over 4 billion barrels of oil have been produced from these two basins with the Central Sumatra Basin accounting for 3 billion barrels. Basic basin configuration was created by the Middle Mesozoic and Late Cretaceous orogeny when several deep fault controlled depressions were developed. A thick clastic section of Late Oligocene-Early Miocene sediment was deposited in these depressions and from this thick section the prolific oil accumulations of Central and South Sumatra were generated. However, oil which is now found in these two basins appears to have matured late in the history of the basins and the major entrapments of this oil are associated with late structuring. Essentially most of the Central and South Sumatra crude is trapped in struc-tures formed during the Plio-Pleistocene orogeny. Other trap which also developed are the paleotopographic traps where reservoir beds drape over or pinch out or onlap ancient topography. The two most critical factors for the generation of oil in Central and South Sumatra are tectonic evolution and depth of burial.
Authors : A.E. Harsa