Aquifer strength has a significant impact on recovery largely due to subsurface uncertainty in the aquifer connectivity and aquifer size. A wide range in recovery has been documented in the literature and has been similarly observed in gas reservoirs in the Columbus Basin (Trinidad) by comparing reservoirs with similar initial and platform pressures. Consequently, understanding aquifer systems can influence development strategies and economics. An example of this is in facilities design where stronger aquifers should have pipelines sized for large volumes of water post water breakthrough while the more volumetric fields should cater for lower pressures via compressors or eductors.

Uncertainties in aquifer support and gas-in-place estimates often introduce uncertainty in production forecasts. Dynamic data for some gas reservoirs reveal that aquifer pressure support strength varies between gas fields and also for individual reservoirs within some fields. This dynamic data includes the integration of surveillance data such as pressure transient derivative and saturation log time lapse data with material balance calculations. Typically the understanding of the geology of aquifers is limited to aquifer size, permeability, edge versus bottom water drive and high permeability streaks.

This paper collates a new combined dynamic and static analysis on a number of BP Trinidad and Tobago LLC mature reservoirs in the Columbus Basin that have been categorized from volumetric to strong aquifer behavior. This integrated view improves the overall understanding of how geology contributes to aquifer impact and helps to create integrated subsurface scenarios that characterize each aquifer system and enable better predictive capability in future developments.

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