Professional Evaluation of Gas Reinjection Schemes for Reservoir Pressure Maintenance and Condensate Recovery in the Agip-Operated Obiafu-Obrikom Field, Rivers State

Gas reinjection for simultaneous pressure maintenance and condensate recovery enhancement is an established but technically demanding strategy in gas condensate fields, requiring careful management of fluid phase behaviour and injection well capacity. This study professionally evaluates gas reinjection scheme options for the Obiafu-Obrikom gas condensate field operated by Nigerian Agip Oil Company in Rivers State. Full-field compositional reservoir simulation was performed using CMG GEM software to evaluate three reinjection strategies: crestal injection through existing gas injectors, peripheral injection to maximise condensate banking displacement, and miscible displacement injection at pressures above the dew point. PVT characterisation was refined using a 24-component equation of state model tuned to measured recombination sample data from four representative wells. Simulation results over a twenty-year forecast period indicate that miscible injection above the dew point pressure recovers 13.4 percent additional condensate compared to the base case of primary depletion, while crestal injection achieves only 6.7 percent incremental recovery due to gravity override under high-permeability reservoir conditions. The economic attractiveness of each scheme is evaluated at condensate prices of 60 to 90 USD per barrel. Operational considerations including compression requirements, injection well workovers, and produced gas recycling infrastructure are detailed. The study recommends a phased programme beginning with peripheral injection and transitioning to miscible injection as compression capacity is expanded. Keywords: gas reinjection, condensate recovery, Obiafu-Obrikom, reservoir simulation, Rivers State.