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Petroleum systems are controlled by the evolution of sedimentary basins and the provenance of their sedimentary fills. As the result of a favourable combination of these factors Sumatra is rich in petroleum resources. The discovery and exploitation of commercial accumulations of oil and gas has so far been restricted to the backarc region of Sumatra, NE of the Barisan Range and the active volcanic arc, where three major sedimentary basins, the North, Central and South Sumatra Basins are distinguished. Exploration in the Sibolga, Mentawai and Bengkulu basins along the western margin of Sumatra in the forearc region has, so far, not been as successful. Commercial success has also eluded companies which have explored basins or sub-basins, such as the Ombilin Basin, which occur within the Barisan Range.
Plate-tectonic mechanisms and the resultant crustal thicknesses control this distribution of the Sumatran petroleum resources. To the east of the Barisan Range, beneath the backarc basins, the crust has been stretched and thinned and thus has a high geothermal gradient, suitable for the generation of hydrocarbons. In the forearc region, to the west of the Barisan Range, the lithosphere is thicker due to the subduction of the Indian Ocean Plate beneath the Sunda Craton in Sumatra. This effective doubling of lithospheric thickness has resulted in lowering of the geothermal gradient, so that sediments in the forearc basinal setting have a lower thermal maturity. Also, clastic sediments in forearc basins, due to their volcanic and metamorphic provenance, tend to be poor in quartz, and
