Characterizing petroleum charge systems in the tertiary of SE Asia

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Abstract
Most SE Asian Tertiary-aged petroleum has been derived from paralic (lower delta plain to prodelta, higher land plant dominated) source rocks, although the larger proportion of oil is from lacustrine (freshwater/brackish algal) sources. Because many SE Asian petroleum provinces have been largely explored without penetrating source rock, the source is inferred from the oil’s geochemistry. Prolific lacustrine sources develop mainly in rift lakes in the Palaeogene syn-rift megasequence common to many SE Asian basins, but floodplain lake sources are also important. Paralic source rocks include both coals and particularly coaly mudrocks developed within the Miocene post-rift megasequence with an oil-prone zone. Oil-prone source rocks are preferentially developed in the paralic realm between the lower coastal plain and lower estuary/delta front facies, perhaps involving a mangrove system. The stratigraphic position and kinetic expulsion behaviour of different source types, migration, seal timing and pressure-temperature-depth relationships converge to make younger plays, including carbonate buildups, more gas prone. The volumetric significance of biogenic gas is still poorly understood. Vertical migration is common in overpressured SE Asian basins; lateral migration is thus commonly restricted to distances of 20 km or less from the kitchen.

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