Fluids identification in reservoirs that bear low or mixed formation water salinity poses a challenge for reservoir management in terms optimum well placement strategies and reservoir surveillance. The logging industry provides many technologies to help characterize in-situ fluids while drilling or during the production stage.

An integrated reservoir engineering team has established an integrated formation evaluation methodology to identify fluids encountered in the reservoir, while drilling or while monitoring saturation changes periodically in key observation wells. A number of new and re-entry wells were selected to measure fluid saturation while drilling via different saturation tools; namely, resistivity, nuclear magnetic resonance (NMR), formation pressure testing and fluid sampling, and advanced mud gas logging to complement each other. Carbon/oxygen (C/O), coupled with a flowmeter survey, were run in two observation wells, in both flowing and shut-in conditions, and showed positive results for enhacing the capability to monitor saturation.

Following a comprehensive evaluation of all acquired data and interpretation, the petrophysical model was calibrated using NMR and downhole fluid samplings. Results have enabled building fluid characterization criteria for low contrast salinity clastic rocks based on reservoir complexity and fluid uncertainty.

The optimized C/O acquisition helped with analyzing fluid saturations and building an intriguing process to address challenges related to different environmental conditions. This evolved methodology revealed a more consistent saturation mapping with the actual reservoir understanding while identifying the optimum completion and excellent wellbore conditions for such a method.

The established fluid identification process, while drilling, will help optimizing well placement and well completion to yield productive wells. The customized C/O log process will enhance reservoir surveillance and monitor saturation change to assess sweep efficiency and overall field performance.

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