Development studies of a heterogeneous carbonate reservoir in Abu Dhabi-United Arab Emirates based on 10 years of data from eight oil producers and one pilot water injection well concluded that mobility enhancement of the injected phase would be a key factor of effective pressure support and recovery. Development studies of different options concluded that miscible hydrocarbon gas injection would give the highest recovery and was adopted for implementation.

Variation of the reservoir fluid properties with presence of a gas cap at the crest was reported and the Minimum Miscibility Pressure (MMP) of the injected miscible hydrocarbon gas reported to be very close to the reservoir pressure. Simulation studies indicated that miscibility would not be sustained and gas percolation into the gas cap would always be there. The studies concluded that gas injection near the OWC would give better chance to benefit from gravity segregation of the percolated gas.

Five spot inverted pattern at the crest in the area below the gas cap and staggered line drive WAG down flank in the highly under-saturated oil were selected as the optimum development option that was implemented in Phase I development area. All the development wells were completed using long radius open horizontal hole completion technique for both the producers and injectors. Hydrocarbon associated gas was processed and injected in its rich composition.

Collected bottom hole samples after one year and half of injection indicated arrival of the miscible front into location of a newly drilled well offset to a gas injector suggesting successful miscibility. Project has been in progress achieving the target production plateau with some anomalies of high GOR. Surveillance plan was set to closely monitor front movement of both gas and water in key observation wells.

This paper presents a case history of an early miscible hydrocarbon gas injection project in a newly developed heterogeneous carbonate reservoir and observations after four years of production and injection.

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