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The AAPG/Datapages Combined Publications Database

Southeast Asia Petroleum Exploration Society (SEAPEX)

Abstract


Proceedings of the South East Asia Petroleum Exploration Society Volume III, 1976
Pages 8-38

Petroleum Geology of Young Regressive Sequences

Richard E. Chapman

Abstract

Young regressive sequences with abnormally-pressured shales are mechanically unstable while the pressures are abnormal, and so suffer an early deformation that is revealed by growth structures.

The abnormal pressures are a consequence of under-compaction, so fluid migration is retarded. This exposes more of the original pore fluids to higher temperatures and much higher pressures for a longer time. Since the mechanical instability is contemporaneous with the retarded compaction, the structural consequences precede or are contemporaneous with the migration of the bulk of the fluids. Growth structures exist before the bulk of the fluid migrates, and they exist down the migration path: they are, therefore, potential traps.

Petroleum accumulation in structural traps in regressive sequences in Southeast Asia is not usually the consequence of orogeny of the sedimentary basin itself, but rather the consequence of orogeny in neighbouring areas outside the sedimentary basin. Orogeny outside the sedimentary basin creates the mountains that generate the sediment that accumulates as a regressive seqeunce, and the structures are a consequence of instability in this seqeunce.


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