Rethinking Reservoir Characterization: The Complex Reality of Rock Types and Facies - Evidence from Malaysia Basins

Reservoir characterization in complex depositional environments requires integration of geological and petrophysical data to understand reservoir quality distribution. Traditional approaches often treat sedimentary facies and facies associations, and petrophysical rock types as directly linked, if interpreted depositional environments correspond to arithmetically derived fluids flow units. However, this deterministic approach may inadequately capture reservoir heterogeneity, particularly in mixed energy depositional systems where energy processes and variation significantly affect sedimentary rocks fabric and facies distribution.

Rock typing methodologies using Flow Zone Indicator (FZI, Amaefule & Altunbay, 1993 ) provide quantitative characterization of reservoir quality through porosity-permeability relationships, while facies associations interpreted from cores offer qualitative understanding of depositional processes and sedimentary fabric. The relationship between these datasets is crucial for optimizing reservoir characterization, static and dynamic models and ultimately field development strategies. However, to our knowledge, limited studies have described the probabilistic nature of this relationship in complex depositional environments.

This study integrates FZI rock typing (Amaefule & Altunbay, 1993 ) with facies associations from conventional cores of multiple fields in the Malay and Sarawak basins, offshore Malaysia. The depositional environments span from fluvial to marine transition, tide-dominated delta, and shallow marine settings.