Semut Field is a small brown field located in Central Sumatra basin produced since 1966 and waterflooded since 2009. Semut Field production has already depleted at 1/10 from its peak production and produced with high water cut. Earlier production strategy had been targeted at waterflooded thick and good permeability (~1 Darcy) reservoir and produced comingle. Deep dive and comprehensive analysis on G&G and rock properties on sand basis will be the answer to reveal any hidden opportunity on mature reservoir to increase oil production in Semut Field.

The approach to increase oil production is done by using and analyzing new data from Carbon-Oxygen (CO) logs and new infill well in 2021 to map the unrevealed potential of remaining by-passed oil. This field opportunity is hidden in lower permeability thin sand (<300 mD) with limited distribution that was previously overlooked in wide scale stratigraphic analysis. Comprehensive analysis of high-resolution stratigraphy also could figure out some thin sand that separated from the main sand lobes in each formation. More analysis on historical production and completion of old wells that have thin sand opportunity should be done to find out the earlier sand performance.

High-resolution stratigraphy approach analysis by layer sand is proven for revealing hidden opportunity in Semut Field. The remaining oil was found stored in a thin sand layer with perm ~200 mD which is lower than the average overall sand formation permeability. There are two main recommendations to unlock the opportunity at Semut Field based on the analysis result. First, completion strategy by selecting and precising perforation depth is critical since the separation between sand layer could only be between 2-3 ft shale. Second, production strategy by producing single or commingle with other sand that have similar PI and reservoir pressure. This approach gives outstanding results with oil gain 1,600 BOPD and oil cumulative 28 MBO within 1 month production, it is doubling Semut Field production.

This effective approach could be an alternative strategy to be applied in other Mature waterflood field or Primary field. This is a good case of how workovers on old wells can increase oil production in cheap way and dramatically extended good economic life.

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