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The Sanga-Sanga region, Indonesia has several mature fields which have many wells without open-hole logs. The goal is to determine if these wells can be reactivated or improved performance. A pulsed neutron log was used to identify the remaining hydrocarbon potential by zone. Recompletion resulted in peak oil production of 700 BOPD with lower water cut.

The production data in the target well hinted at water encroachment or potential commingled production. The target well had cumulative oil production of 388 MBO through 1987 with subsequent deterioration to 12 BOPD on sucker rod pump today. Correlation with nearby wells shows the deeper sand has produced a cumulative of 65 MBO, with latest production of 36 BOPD and 51% WC. It was not clear whether the high-water cut is due to oil depletion in one or both sands.

The pulsed neutron logs with carbon oxygen ratio (C/O) and sigma measurements were acquired to determine the current oil saturation over each zone to design the recompletion strategy. C/O provides saturation independent of formation water resistivity whereas sigma is used for reservoir characterization (shale volume and porosity) due to unavailable open hole data. The C/O is the main source for saturation computation due to the low formation water salinity (3,000 – 3,500 ppm) of the reservoir. The target interval is correlated to a nearby offset well with open hole logs to constraint the porosity and shale volume calculation for saturation computation.

The pulsed neutron calculated 40-50% oil saturation and the well was successfully recompleted, with initial production up to 700 BOPD and stable production near 100 BOPD with a low water cut. Good well correlation is critical to ensure that the porosity is reliable and identify any water zones for reference to reduce uncertainty in the C/O based oil saturation.

This case study supports that old wells without open hole data can be reactivated by integration of historical well completion and production data and cased hole pulsed neutron data which is correlated to offset wells.