Lean gas injection in gas field is a good alternative to maintain reservoir pressure, minimize the condensate banking near wellbore and to mitigate the oversupply operation during low market. In this study, past gas cycling operation was examined to see the operability aspects and subsurface implications.

The Arun gas field was found in 1971. A 10,000 ft depth gas-condensate reservoir was found to have 503 ft thickness in average and 21,450 acres area with 7100 psig initial pressure and 352°F. Initial condensate-gasratio (CGR) was 50 bbl/MMSCF. The reservoir has 16.2% average porosity and initial water saturation (Swi) of 17%. Volumetric original gas in place is calculated to be 17 TSCF (excluded impurities). Baong shale underlain reefal carbonate of Arun reservoir is identified as the cap rock. Cumulative condensate production is 846 MMSTB. Approximately 5 TSCF (30% OGIP) had been recycled during 1977 – 1998.

Not many gas fields in the world with gas recycling had achieved 95% recovery factor. This paper will deliver the results of gas cycling, i.e. delay reservoir pressure decline, and maintain CGR and economic improvement of this field. Surface facilities and operation aspect will also be elaborated. Production and pressure data show that gas cycling indeed contribute to the improvement of field recovery factor and economics.

This paper should help the development of other new gas fields especially for carbonate gas reservoirs. The successful gas cycling in Arun field will encourage other gas field operators to implement the same methods.

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