Investigating Gas Injection Pressure Maintenance Efficiency in Retrograde Condensate Reservoirs: A Compositional Simulation Study of OML 64, Delta State

Gas injection for pressure maintenance in retrograde condensate reservoirs is technically more complex than in oil reservoirs because the injected gas composition and injection pressure relative to the dew point determine whether miscibility is achieved and whether retrograde condensate dropout is reversed through revaporisation. This study investigates the efficiency of gas injection pressure maintenance strategies in retrograde condensate reservoirs through a compositional simulation study of OML 64, Delta State, South South Nigeria. A full-field compositional model incorporating 18 pseudo-components tuned to recombined wellstream PVT data was constructed in CMG GEM software and history matched against five years of production data from nine producing wells. Three injection strategies were evaluated: lean gas cycling, enriched gas injection with added propane to increase minimum miscibility pressure, and simultaneous water injection to maintain total reservoir pressure above the dew point. Condensate recovery factors at ten-year forecast periods differ substantially among strategies: enriched gas injection recovers 78 percent of total condensate in place, compared to 62 percent for lean gas cycling and 55 percent for water injection under identical injection capacity constraints. The higher cost of enriching the injection gas stream with purchased propane reduces the economic advantage of enriched gas injection at condensate prices below 55 USD per barrel stock tank condensate. A break-even analysis defines the economic threshold conditions under which each strategy is preferred. Keywords: gas injection, condensate recovery, compositional simulation, OML 64, Delta State.