Located offshore South East Sumatera Indonesia, C-SY field is a structural trap with 4-ways dip closure and multiple reservoir targets with excellent rock properties, considered a marginal field and currently idle for 8 years. Challenges faced in reactivating C-SY field are high investments compare to other well service proposal and have limited reserves. The objective of this paper is to revive idle marginal offshore brownfield C-SY by increasing value of reserves and economics value. In order to do so, all prospects within C-SY area need to be assesed, including exploration prospects with high geological chance factor.

The evaluation process worked simultaneously by exploitation and exploration team. The exploitation team worked on re-estimate OOIP and reserves of existing reservoir by structural interpretation, reservoir characterization analysis using attributes, Decline Curve Analysis & Material Balance Analysis. While the exploration team worked on finding other reservoir prospects by doing prospect identification from 3D seismic analysis, structural play analysis, closure identification and migration pathway from kitchen to prospect area, calculate OOIP. Result from both teams were combined to estimate reservoir behavior and production forecast. The next step of evaluation was to create multiple cases of possibilities and calculate the economics to find the best and possible case with minimum calculated risk.

Collaboration between Exploitation and Exploration has lifted the value of C-SY idle marginal brown field, new structure has been found with promising reserves and initial production. Initial production C-SY field after the collaboration is 1,200 BOPD from previously 150 BOPD, while remaining reserves increase 3 times higher up to block expiration contract in 2038.

Developing marginal offshore mature asset is a risky business, especially considering high volatility in oil prices. Collaboration and technology are vital to escalate the economic value and achieve higher recovery factors. Application of the multidisciplinary methods was considered as an appropriate way to approach and manage a complex marginal mature field redevelopment.

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