Abstract

Hydrocarbon generation and migration pathways were evaluated for the deep-water North Aceh Offshore Basin based on sequence stratigraphy, seismic interpretation, source-rock geochemistry and thermal modeling combined with migration pathway mapping. This evaluation provided a tool to reduce the risks associated with stratigraphic prospecting in deep water operational areas.

The best source-rock is the transgressive marine Bampo mudstone (P21 to N4), which is primarily gas-prone with Type III or II/III kerogen and occasionally light-oil/condensate-prone. The source-rock shows facies-change from a dark-colored, clastic clayey rock (source rich) deposited in the basin-center to a grayish, calcareous rock deposited in a slope setting. Better preservation of algal content explains higher source-rock potential at the basinward sites.

The marine Bampo represents a regional seal that controlled hydrocarbon migration with the underlying sandy carrier beds. Faults occasionally provide vertical migration pathways. A structural map of P22 SB is used to depict migration pathways.

We calibrated the parameters used in the thermal modeling against the Lho Sukon Deep. Gas released from the Lho Sukon Deep charged the giant Arun gas field. The Bampo source-rock is mature in the North Lho Sukon Deep and has generated significant volumes of gas with some liquid hydrocarbons since the Pliocene. Primary controls of the source-rock maturity are the heat flow history (heat flow increased during the Oligocene early syn-rift and the Miocene late syn-rift phases), sea bottom temperature history (bathymetry-related), and variations in the thickness of the overlying sediment (Upper Miocene to Pleistocene).

The migration pathway map defined three migration fairways from the North Lho Sukon Deep to its peripheries. Regional distributions of the existing gas discoveries and of significant gas shows match the migration fairways. Trapping mechanism and closure size are the main elements to evaluate in prospecting in this deep-water region because based on simple volumetrics calculations the charge potential from the North Lho Sukon Deep is significant enough to charge the defined traps.