Semberah field, located in East Kalimantan, has been explored since 1974 and developed in 1990. Peak production was reached in late 1998 at 180 MMscfd and 13,000 BOPD. Sharp production decline occurred since 2000 and the field rate dropped from 170 MMscfd to 25 MMscfd in 10 years. Several efforts have been made to sustain decline at economical rate by infill well drilling, horizontal well, and compression system optimization.

Until 2008 drilling is mainly focused in middle area of Semberah along crestal area containing large reservoir tanks with updip position thus favoring high additional reserve and avoiding water table. The well population in south area was very dense with average interval 300 meters. In contrast, to the north crestal areas which have more down dip structure are less developed. The challenge of developing north area is due to limited data from existing wells and the possibility of hitting water reservoir. In 2008, a study was conducted to assess the possibility of applying semi-grid based drilling campaign in north area. The method was based on the combination of deltaic reservoir, new geological understanding and statistical study from previous drilling result. As pilot project, one well was drilling in north area with distance over 800 meters from offset well.

The result was positive, the well encountered new reservoirs or pools with high gas deliverability. The semi-grid based drilling was then focused in north area with various distance 500 - 1000 meters. After 2 years, Semberah field rate increase from 25 MMscfd to 70 MMscfd. A cumulative of 18 BCF gas was produced until 2015 from new reservoirs. A methodology of optimizing well spacing in deltaic reservoir is studied and perfected. The most optimum well spacing to increase the possibility of getting new reservoirs in north area was 500 - 700 meters.

This paper describes the successful implementation of integrated development strategy, which proved to be an effective process to enhance production recovery of a mature asset.

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