Defining in-fill drilling locations seems a simple task in natural depletion reservoirs while in special fields like those under miscible gas injection operation is challenging. The aim of this paper is to scrutinize the production and injection of existing wells and derive some extra rules to optimize the new well placement in miscible gas injection fields.

DGN is an undersaturated light oil field situated in south west of Iran. The field has been producing since 2003 and miscible gas injection started in 2009. After 5 years of miscible gas injection, unexpected and different types of breakthrough happened in some producing wells which made defining new well locations a challenging task. Gas injection has sweeping role as well as pressure maintenance, and based on studied reservoir heterogeneity the latter one was recognized as a dominant factor. After reviewing all available studies and static and dynamic models as well as real field production and welltesting data, some rules were extracted to narrow the window to some specific regions. Therefore, a new gas injection well was spotted on the anticline of the reservoir even close to other injection wells and five new locations were decided. Afterward, they were put into dynamic model and their production was compared. At the end, those wells with better performance were given higher priority and sent for drilling.

Considering recovery factor of the reservoir, it indicates that new gas injection well can have better performance on the crest of the reservoir even in the vicinity of the other injectors, and oil producing wells should be in symmetrical pattern, down-dip and farthest from injection wells.

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