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Banyu Urip is an onshore oil field located in Cepu Block, Central Java, Indonesia. It is currently producing from Oligocene-Miocene carbonate build up. The original oil column is about 1,000 ft thick and in communication with overlying Seravalian clastic section through the gas cap. The oil column also connected to the large aquifer beneath. The gas contains about 1.7% H2S and 45% CO2, the oil density is 32 degree API with solution gas oil ratio (GOR) at 375 scf/bbl. The reservoir has been characterized as multiple pore system, with large voids, fractures and touching vug-like facies were identified in image logs (Zeiza et al., 2016). In addition, well test results suggested the average permeability is 2 to 35 times higher than core-based permeability (Zeiza et al., 2016) Later data from development drilling and actual production shows that the permeability can go up to several Darcy due to the excess permeability features, emphasizing the existence of excess permeability features/zones (Ahdyar et al., 2019)

Banyu Urip began its production in 2009 through Early Producing Facility (EPF) from four producer wells at 20,000 BOPD through 5.5” tubing and 5” perforated liner. In 2013 – 2015, the development wells were drilled and completed with 5.5” tubing and 4.5” perforated liner, resulted in total 30 oil producers, 13 water injectors, and 2 gas injectors. In December 2015 the full scale Central Processing Facilities (CPF) was started with production ramping up to the POD target of 165,000 BOPD and with further optimization to above 220,000 BOPD in 2019. Initially the wells were producing at solution GOR and zero water cut (WC). In 2016, one of the producers started to show increasing GOR and by 2018 several wells were showing gas breakthrough. On the other hand, the water encroachment did not occur until 2019, about four years after the full field production start-up. By end of 2020, the field gas production has reached the maximum gas handling capacity limit of 130 MMcfd thus the oil production came off plateau. (Sulistyaningrum et al., 2022)

In 2021, oil production continued to decline due to increasing Gas-to-Oil Ratios (GOR) and aggressive gas coning in certain wells. This decline was partially offset by well intervention programs, including gas shut-off (GSO) using expandable casing patches, acid washes, and other methods. In 2022, extensive production optimization efforts were undertaken, focusing on low GOR wells, GSO, water shut-off (WSO), and converting oil producers to gas injectors, among other initiatives. By June 2023, nearly all low GOR wells had been fully opened to 100% choke.

To further counteract the decline, gas lift activation became the next key initiative. Initially planned for use only in high water cut wells, gas lift was expanded to accelerate and increase liquid production in moderate to high water cut wells as well. In 2024, a high-graded wellwork program was implemented, incorporating lessons learned from previous years. This program

included gas lift installations, additional perforations, GSO using expandable casing patches, and scale squeezes.

However, these optimization strategies will soon face limitations as the number of viable well candidates decreases. This has highlighted the need for alternative strategies to sustain production optimization in the future.