Miscible gas injection in near critical oil or volatile oil reservoir improves the recovery due to interfacial tension effects and better microscopic displacement efficiency compared to immiscible water injection. In a graded undersaturated gas-oil fluid system, all fluids are initially first contact miscible with neighboring fluids throughout the reservoir if full- pressure maintenance is supported by injection process.

Smorbukk south is characterized as a compositionally graded gas condensate and volatile oil reservoir which lies near the critical region in the phase diagram. Compositional graded reservoir systems exhibit significant variation in the minimum miscible pressure (MMP). MMP variations with depth pose a challenge in selecting reservoir recovery technique to maximize the ultimate recovery.

This paper deals with different scenarios of miscible flooding and compares the results with immiscible flooding for a 3-D homogeneous reservoir system. Here, MMP, determined by different injection gases, can develop far below the saturation pressure. If the injectant is CO2 or sufficiently enriched with intermediate components, the condensing and vaporizing (C/V) mechanism was developed throughout the reservoir. Dipping effects and placement of injector -producer were studied here and was found that updip formation gives highest recovery. Various injection schemes (i.e. Separator Gas and CO2) were studied in miscible flooding scenarios. The results of gas alternating gas (GAG) were compared with the water alternating gas (WAG) method and GAG was found to be the best alternative.

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