Abstract: Analysis of Overpressure Zones at the Southern Margin of the Baram Delta Province and Their Implications to Hydrocarbon Expulsion, Migration, and Entrapment
Aristeo Mantaring, Fumiaki Matsuda, Masanori Okamoto
The Baram delta oil and gas province covers a major part of the onshore and offshore areas of northern Sarawak, Malaysia, and Brunei. Thick marine to deltaic sediments of late Eocene to Pleistocene age were rapidly deposited in the basin, resulting in widespread abnormal formation pressures. Overpressure zones are normally encountered within thick marine-deposited claystone intervals occurring below and/or just at the basal part of major oil and gas accumulations in the offshore areas of the Baram delta. Because of drilling hazards, the onset of overpressuring is regarded as an arbitrary economic limit for oil exploration.
In onshore Sarawak, the southern margin of the Baram delta province contains thick late Eocene to Miocene (Cycle l-V) sediments deposited and uplifted in the latest Pliocene. Abnormal pressure zones have been encountered in three different settings viz.: (1) undercompacted claystone predominant intervals, (2) uplifted reservoir sands with hydrocarbons, and (3) hydrodynamically pressured shallow sand intervals. A unique overpressure zone, which occurs below stacks of hydrostatic and permeable coastal-deltaic sands, has been observed.
The formation of these varied overpressure zones and the pressure regime in the area are studied in combination with the burial and structural development history of the southern margin of the Baram delta province. The implications to hydrocarbon expulsion, migration, entrapment, and retention are analyzed.
AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994