Gas injection is the most widely applied process in enhanced oil recovery (EOR) for light oils. Most of the oil production in the Middle East comes from carbonate reservoirs, the majority of which are highly fractured. Gas injection in fractured reservoirs has been used less than conventional single porosity reservoirs. Three natural phenomena of gas channeling, viscous fingering and gravity over ride jeopardize the final oil recovery in gas injection projects. In fractured reservoir due to higher vertical permeability, and strictly higher rock heterogeneity, these phenomena are more probable and this fact will challenge the feasibility of gas injection projects in fractured reservoirs.
In this work, miscible/immiscible gas injection was studied in a fractured reservoir through compositional simulation. The oil field under study is a fractured oil reservoir located in west of Iran. A homogenous DPSP (Dual Porosity-Single Permeability) synthetic model was generated which investigates the effect of molecular diffusion, displacement velocity, gas/oil fracture capillary pressure, slug size and injection pressure of injectant on final oil recovery of gas injection process. Minimum miscibility pressure (MMP) and Minimum miscibility enrichment (MME) of gas injection was determined using slim tube through compositional simulator.
Three possible scenarios – natural depletion, miscible gas injection and immiscible gas injection were compared. Results indicated that miscible injection yields better recoveries than the other, so miscible gas injection in this reservoir can be a potentially good scenario.