Abstract
This study investigates the geological controls on the seismic responses of gas-saturated sandstone reservoirs in offshore Australia. The targeted reservoirs belong to the Middle Jurassic Plover Formation, which comprises interbedded sandstone, mudstone, and coal deposited in a fluvial–deltaic environment. These reservoirs display significant and poorly understood variations in seismic amplitude responses, observed on stack sections both between proximal wells and across different reservoir intervals. Such inconsistencies introduce high uncertainty in lithology and fluid prediction. Amplitude Variation with Offset (AVO) analysis conducted on both synthetic and real seismic gathers reveals distinct AVO classes (I to IV) within the reservoirs. Rock physics analysis, supported by petrographic evidence and seismic inversion, demonstrates that these seismic expressions are primarily controlled by three key geological factors: (1) Variable lithology and thickness, particularly the occurrence of volcanic and siltstone interbeds acting as seals above certain reservoirs, which can shift the amplitude response from hard to soft; (2) Diagenetic alteration, including quartz cementation and chemical compaction, which stiffen the rock framework and modify AVO behavior; and (3) Depositional texture and grain-contact types, which vary laterally due to compartmentalizing faults. This study establishes a comprehensive interpretation framework where amplitude behavior serves as a diagnostic indicator of reservoir quality and connectivity. The proposed workflow and findings provide a valuable analog for de-risking amplitude-supported hydrocarbon prospects in similar fluvial–deltaic systems affected by diagenetic overprinting and structural complexity.