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Peciko field is an offshore gas field located in Mahakam delta, East Kalimantan. This field consists of dominated mouth bars sands in Main zone and channels sand in Shallow zone. Gas bearing reservoirs of Main zone had been produced since 1999 and recently Shallow gas reservoirs are contributing significantly on field production. Main contributors of Shallow gas reservoirs are MF4 and Y-channel reservoir. To have better production forecast and a good quality of production historical matching in dynamic simulation, residual gas saturation (Sgr) is needed. Since no core data available in this reservoir, an estimation Sgr derived from cased-hole Pulsed-Neutron Logs (PNL) was performed. PNL is recorded to monitor the fluid changes after production. The primary product measurement of PNL called as Sigma (Σ). PNL represents the interactions between neutron and formation, responds the amount of hydrogen in the formation, hence the saturation in the formation can be estimated. Quantitative interpretation to derive Sgr from sigma logs can be performed only in optimal condition where there is a sufficient contrast between sigma gas and water. Due to limited condition (low salinity and borehole architecture complexity), the standard formula of Sgr derived from Sigma could not be applied. So, an alternative approach must be developed. Count rate neutron ratio (near to far detectors) in PNL was assumed similar to standard neutron porosity in open-hole. This log is less dependent to salinity compared to sigma log, so it could provide more contrast signature if there is any changes in saturation. This approach is based on analogy that the change of hydrogen index corresponds to change of water saturation. The neutron porosity from cased-hole and open-hole log was compared by overlaying one another and the discrepancy interpreted as saturation changes. Therefore Sgr value can be estimated from this neutron ratio.