Reservoir Heterogeneity in a Storm-flood Delta Succession, Acknowledging the Effects of Storm Processes: A Case Study from Field A, Balingian Province, off the Coast of Sarawak, offshore Malaysia

This study analyzes Oligocene to Lower Miocene reservoirs in Field A, Balingian Province, offshore Sarawak, Malaysia. By integrating regional studies, outcrops, and core data, it refines the understanding of sedimentological processes during the deposition of deltaic and shoreface successions, including seasonal storm-related deposits. Eleven sedimentary facies were identified in 268m of conventional core from five wells, grouped into facies associations that suggest the interaction of fluvial, wave, tide, and storm processes in an interconnected coastal depositional system. Two main reservoir depositional elements were identified: (i) a fluvial-dominated, tide- and wave-influenced delta, and (ii) a storm-flood delta front. The Oligocene to Lower Miocene reservoirs represent a long-term progradational succession with four depositional sequences: coastal tidal flats and creeks overlain by storm-related delta front deposits (Sequence 1), fluvial-dominated, tide-influenced mouthbar complex capped by storm-flood delta front deposits (Sequence 2), floodplain to marsh successions in a lower delta plain setting (Sequence 3), and distributary mouth bar complexes transitioning to sandy tidal flats (Sequence 4). Four rock types were identified using the flow zone indicator method. Understanding the linkage between depositional sequences, facies associations, and petrophysical rock types is essential for constructing detailed static geological models that capture heterogeneity in Field A.