Platform Evolution and Sequence Stratigraphy of Natuna L-Structure, South China Sea, Indonesia

Kurt W. Rudolph, Patrick J. Lehmann

By integrating seismic, well-log, and core data into a sequence framework, we are able to recognize seven complete depositional sequences in the Miocene age Terumbu Formation carbonates of the Natuna Platform (L-Structure). Each sequence consists of a lowstand systems tract, a transgressive systems tract and condensed section (seismic downlap surface), and a highstand systems tract.

Terumbu carbonates display a downward shift of reservoir facies in the lowstand systems tract, deepen upward (retrograde) in the transgressive systems tract, and shoal upward (prograde) in the highstand systems tract. At each sequence boundary, there is erosional truncation of the platform margin and upper slope and exposure of the platform crest.

The highest porosity occurs in grain-prone shoal water carbonates of the late highstand systems tract on the platform crest. Porosity also occurs downdip from the platform crest in the onlapping lowstand systems tract. Sequence stratigraphy, seismic facies, and seismic modeling analysis are used to map and predict reservoir distribution on the Natuna Platform.

Increased subsidence from the Miocene onward caused the retreat of the Natuna Platform. Retreat occurred in an asymmetric fashion with more retreat on the west, or low-productivity, side of the platform. Platform retreat occurred incrementally, during deposition of transgressive systems tracts and the condensed sections. The large eustatic sea level rise in the early Pliocene, combined with continued rapid subsidence, drowned the platform and ended carbonate production.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.