X field was discovered in 2001 and started producing in 2003. The formation is limestone supported with large aquifer. Main challenge is that wells must be produced with critical rate limitation, if a well is produced too hard, water coning and water breakthrough can occur, then oil production will disappear, as happened in one of X's well. In 2011, several wells were becomes ceased-to-flow due to an increase in watercut value, then pumping units were installed on these wells. However, due to recurrent mechanical downhole problems which limit effective production days, a new initiative is required to overcome these issues. After thorough analysis, ESP was chosen as best-fit artificial lift considering its versatility in deviated wells and high deliverability. In 2017, pilot phase of ESP implementation started in X-D4 well, which gave 150 BOPD average oil gain. Learning from the success of X-D4, comprehensive production strategy using ESP is considered crucial for optimum recovery.

To support this strategy, an integrated optimization study with reservoir simulation model was used instead of analytical method to obtain more reliable production forecast. History matching was carried out from initial production data in 2003, a good match in liquid-oil-water-pressure data was successfully obtained, but poor match was occurred on gas production rate, this was ignored due to high uncertainty on gas measurements. The outcomes of simulation study were ESP well candidates, optimum production rate target and proper timing of ESP installation. The next step was the preparation of ESP which consists of the design and procurement of ESP. Following the ESP installation plan, it was also decided to increase power generation capacity at current surface facilities.

Currently, 7 out of 10 ESPs have been installed. Power plant upgrading and overhead line installation to support ESP have also been carried out. The average oil gain obtained was 700 BOPD with cumulative of 160 MBO (from 2017 – until 2018). This optimization case will contribute 1.5 MMBO additional reserve from "do nothing" case. Economic evaluation shows a very good viability with significant additional gross revenue.

This optimization project has succeeded in reducing oil deferment from ceased-to-flow wells and extending the field's life. Good collaboration between each part (subsurface and surface) in this project has succeeded in producing significant oil gains. Continuous monitoring is still needed to further match optimization forecast with actual conditions. Long-term plans, some improvements are still needed in the reservoir model, one of which is OOIP value, there is a possibility that the actual X OOIP is bigger than the one in the reservoir model.

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