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Abstract: Carbonate Petroleum Systems in Myanmar

John M. Hurst, Philippe A. Lapointe, U. Kyaw Nyein, U. Maung Nyunt, U. San Lyann

Three Oligocene-Miocene carbonate depositional morphologies commonly occur: shoals, reefs, and isolated platforms.

Lenticular shoals (0-25 m thick, 1 km long) are stacked and intercalated with siliciclastic mudstones. Facies include trough/festoon cross-bedded benthic foram grainstones passing laterally and vertically into red-algal dominated graded-laminated beds, bioturbated silty calcareous mudstone, and siliciclastic sandy foram wackestone and packstone. The morphology and facies are hydrodynamically controlled. Pinnacle reefs (1-2 km2) dominated by red-algae, branching corals, and large mollusks occur on structure or aligned within shelf mudstones. The latter location reflects low sedimentation rates and hydrodynamic control. Isolated platforms (up to 150 km2) are environmental mosaics of marginal patch reefs and shoals, interior lagoons, and islands plus marginal slopes Facies are similar to shoals and reefs except there are more muddy fabrics and less high-energy facies. They develop on tilted fault blocks or eroded submerged arcs in the offshore Gulf of Martaban, distal to the ancestral Irrawaddy delta.

Isolated platforms form the most homogenous reservoir at the regional migration foci. Yadana (gas) is the largest field. Platform failure relates to charge entry prior to sealing. Shoal reservoirs are heterogeneous, but have reservoir volume for giant fields. Their identification/prediction is difficult and the fill amount/migration focus risky. The Htantabin gas-condensate field is the only shoal field known, and it probably drains immediately surrounding organic rich mudstones. Reefs on structure occur downdip from platforms and not at the regional migration foci. The dissected nature of the basement cover drain (below most reefs) produces local migration shadows. Several reefs have shows (gas) but not fields.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994