Carbonate Rock Physics and Sequence Stratigraphy in Central Luconia, Malaysia: Towards an Integrated Acoustic Facies for Partially Dolomitized Platforms

Abstract

Reservoir characterisation from seismic data in carbonate rocks is challenging, in part because porosity, different pore types, and distinct pore architecture affect petro-acoustic properties. Diagenetic processes resulting in vuggy and moldic pores can have a stabilising effect on the rock framework and show higher seismic velocities compared to other pore types in carbonates with the same amount of total porosity. The influence of dolomitisation is less well constrained, as the changes in grain density, porosity, and pore type during cation exchange all affect the bulk modulus of the rock.

This study aims to establish an acoustic facies classification for a partly dolomitised, isolated carbonate platform of middle Miocene age in Central Luconia, Malaysia, which can be used for seismic inversion. Integrating rock physics with a sequence stratigraphic conceptual model based on a recent new core description will provide an enhanced understanding of the velocity – porosity transform, especially for dolo-lime and dolostones.

In the two available cores, occurrences of argillaceous limestone might represent flooding intervals, which form the basal layer of 6 sequences, each with a thickness of approximately 60 m. Argillaceous units are overlain by deposits representing platform aggradation and the development of a lagoon dominated by red algae and foraminifera, interpreted to represent a relative rise in sea level. These strata are in turn succeeded by coral-rich float- and rudstones, the product of coral debris shed into the lagoon during slow relative sea level rise to eventual stillstand, or fall.

Integration suggests a link between sequence stratigraphy and petro-acoustic properties. For example, red algae and foraminifera - dominated deposits during increasing relative sea level rise include velocities lower than predicted by the Wyllie time-average equation for their porosity (negative deviation). In contrast, coral - dominated facies deposited during decreasing relative sea level rise include higher velocities relative to Wyllie-predicted trends (positive deviation).

These patterns have the potential to aid reservoir characterisation of seismic units. This case study on a selectively dolomitised platform, influenced by relative sea level changes in a tectonically active setting attempts to pioneer a workflow that can be adapted and extended to comparable carbonate reservoirs.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018