Hydrocarbon identification in mature fields located in Mahakam area is very challenging due to thin and multi layers of reservoir geometry, wide range of water salinity in deltaic environment, depletion and water-rise phenomena in highly producing zones. There are numerous possible gas reservoirs which were dubious and not included in perforation targets due to poor quality sand or risk of water production which could jeopardize the entire well potential. These possible gas reservoirs need to be re-evaluated in order to add perforation targets portfolio in maintaining field production when less new wells drilled.

An integrated methodology has been continuously developed and calibrated to reduce uncertainty, hence elevate confidence level of fluid interpretation by combining the existing and recently developed techniques in Mahakam fields. The existing techniques are (1) Conventional Qualitative interpretation, (2) True-Wet Resistivity separation, and (3) Gas-Oil Volumes from simultaneous solution. The new developed techniques are (4) Swirr-SWT comparison, (5) Water Saturation Array Gradient with salinity, (6) AutoFluid resistivity specific cut-off, (7) Dual logs sliding average analysis, (8) Neutron Count Rate, (9) RT-GR cut-off, and (10) Gas Chromatograph dynamic baseline.

In collaboration between petrophysicist, development geologist & reservoir engineering, this new integrated fluid interpretation methodology has been applied to re-evaluate more than 11,000 possible gas reservoirs in Mahakam fields. This effort has revealed around 32% of them as hydrocarbon potential reservoirs with total thickness of 4,195 meters. Those reservoirs are then convincingly re-interpreted as gas bearing reservoirs and included as additional perforation candidates. Some of those reservoirs have been perforated and giving additional gain in maintaining gas production of Mahakam fields.

By capitalizing the existing data, with no additional data acquisition, hence no additional cost, this integrated fluid interpretation methodology, could be implemented in other fields outside Mahakam to find hidden potentials which not identified yet.

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