Reservoir monitoring requires an accurate assessment of hydrocarbon saturation. As oil fields mature, reducing uncertainty in this parameter can yield major economic benefits in field development and reservoir management.

Recent advancements in resistivity tool design and enhancements in pulsed neutron and NMR tools have expanded the scope of petrophysics in reservoir monitoring projects. Optimal utilization of these technologies requires an understanding of the uncertainties that are associated with these measurements in different types of environments.

A new application has been developed that uses numerical analysis to compute the range of uncertainties inherent in petrophysical analysis. These uncertainties are then used as guidelines to optimize data acquisition.

This methodology defines petrophysical uncertainties on a foot-by-foot basis; consequently decisions are based on prior knowledge of the uncertainty of two of the most important petrophysical parameters, water saturation and porosity.

Several wells have been used in this paper to demonstrate the utility of this application and how this analysis is used to design cost-effective logging programs. Even though this technique can be used with any logging measurements, the focus of this paper will be on resistivity and pulsed neutron devices which are widely used in reservoir monitoring. The examples will show how quantifying uncertainties of key petrophysical parameters reduces reservoir management risk.

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