Interrelationship Between Facies Association, Diagenetic Alteration and Reservoir Properties Evolution in the Middle Miocene Carbonate Build Up, Central Luconia, Offshore Sarawak, Malaysia

Abstract

Carbonate build-ups are proven prolific hydrocarbon reservoirs located around the globe. In Southeast Asia, the carbonates are usually associated with grain-rich facies types. Understanding the carbonate reservoirs in terms of their internal characteristics, depositional environment, diagenesis and their impact on petrophysical properties are essential parts of successful exploration and production strategy. The present study provides a detailed work on carbonate reservoir facies, diagenetic history and reservoir quality including qualitative and quantitative analysis of thin sections of the Miocene carbonate platform, Central Luconia. The Central Luconia carbonates are subdivided into eight lithofacies based on specimens collected from five wells. Detailed lithofacies analysis and correlation of carbonate rocks from Well A and Well B allowed us to reconstruct the evolution of sedimentary environments and relative sea-level changes in a platform during the Early to Middle Miocene of Cycle IV and V. Five lithofacies are identified based on texture, sedimentary structure, grain composition, and fossil contents. These include (1) coated grain to packstone (av. O = 6%, av. Kh = 1 mD), (2) coral (m) lime grainstone (av. O = 14.7%, av. Kh = 6 mD), (3) oncolite lime grain to packstone (av. O = 10%, av. Kh = 4 mD), (4) skeletal lime packstone (av. O = 15%, av. Kh = 4.6 mD), and (5) coral (p) lime mud to packstone (av. O = 4%, av. Kh = 0.5 mD), respectively. Micritization, cementation, fractures, compaction, and dissolution are the dominant diagenetic parameters which are identified. The diagenetic features include dolomitization and dissolution (i.e., leaching) making Well A and Well B unique location to study facies distribution and its implication on reservoir potential. By integrating these parameters, facies 2, 3 and 4 are interpreted as a relatively good quality reservoir, whereas facies 1 and 5 are considered as poor reservoir quality. Among all the diagenetic features, dissolution phenomenon contributes to porosity enhancement and reservoir quality, whereas micritization, compaction and cementation have a negative impact on reservoir quality.