Four-Dimensional Seismic Reservoir Monitoring Framework for Agbada Formation Waterflood Operations

This study develops an original four-dimensional (4D) seismic reservoir monitoring framework specifically adapted for waterflood operations in Agbada Formation reservoirs of the Niger Delta, addressing the challenge of extracting reliable production-related seismic signatures from the complex noise environment of repeated seismic surveys in this setting. Four-dimensional seismic monitoring of fluid movement during waterflood injection is a powerful reservoir management tool that improves sweep efficiency by identifying poorly drained reservoir volumes and fluid breakthrough pathways. Its application in the Niger Delta has been limited by the poor repeatability achievable with conventional marine seismic acquisition in shallow, geohazard-rich Niger Delta conditions. This study develops a comprehensive 4D monitoring framework that encompasses: acquisition design optimisation for maximum repeatability under Niger Delta shallow hazard conditions, processing workflows that minimise non-repeatable noise through source and receiver positioning corrections, time-lapse attribute normalisation procedures that account for time-variant near-surface effects, and petroseismic modelling that quantifies the expected seismic response to waterflood saturation and pressure changes in Agbada Formation sand properties. The framework is applied to a real 4D dataset from an onshore producing field comprising four seismic vintages spanning a 12-year production period. Findings reveal production-related time-lapse signatures of 4 to 12 percent amplitude change in the swept reservoir interval, correlated with water injection volumes, that were previously unresolved by standard 4D processing. Unswept reservoir volumes in the structural closure are identified from absence of expected time-lapse response, informing two infill well proposals. The study provides an original 4D monitoring methodology validated for Niger Delta conditions.

Keywords: 4D seismic, waterflood monitoring, Agbada Formation, time-lapse, Niger Delta.