Reassessing Aquifer Contribution in Over-Pressured Gas Reservoir for Maximum Recovery

Abstract

Aquifer support in gas reservoirs is often regarded as detrimental to ultimate recovery due to early water encroachment, reduced gas relative permeability, increased water handling, and premature abandonment pressures. This study challenges that generalised assumption by evaluating the conditions under which aquifer influx can positively contribute to gas recovery. The objective is to quantify the impact of aquifer support on pressure maintenance and recovery efficiency in over-pressured gas reservoirs with favourable geological architecture. A high-resolution 3D dynamic reservoir simulation model was developed for an over-pressured, clean, channelized gas reservoir characterised by a large gas column and optimized well placement, with strategic well perforations offset from the fluid contact. Results reveal that, under these specific conditions, aquifer support enhances gas recovery by sustaining the reservoir pressure, maintaining efficient gas drainage without inducing early water production. The clean, channel-dominated architecture limits water bypass and coning, allowing aquifer energy to act primarily as pressure support rather than as a displacement mechanism. Sensitivity analysis shows that increasing effective aquifer length within the uncertainty range further improves recovery and delays abandonment pressure, contrary to traditional expectations for gas reservoirs. These findings highlight the importance of case-specific evaluation of aquifer behaviour in gas reservoir management and demonstrate that aquifer influence is not universally detrimental. Finally, for over-pressured gas reservoirs in fairly homogeneous depositional settings without intercalations to portend water fingering and by-pass, and with large gas column including optimized perforation strategies, aquifer support is not a detriment but a valuable drive mechanism. The study provides a revised framework for gas reservoir management in the Niger Delta and analogous settings by prioritizing reservoir-specific context than generalised assumptions.