As shown in the previous chapters, determining the porosity and true resistivity of a zone is the first step in converting the raw log data into estimated quantities of oil, gas, and water in a formation. These estimated quantities are used to evaluate a zone and to determine whether a well completion attempt is warranted. This chapter covers some of the different methods from which these estimates are derived. The methods discussed are: Archie water saturations (Sw and Sxo) and the ratio method, quick-look technique, bulk volume water (BVW), and saturation crossplots (Pickett plots and Hingle plots). Determination of log-derived permeability (Ke) and shaly sand analysis are also discussed.

As important as this log-derived information is, however, it should not be applied without the inclusion of other data. This statement is, perhaps, obvious to the reader, but it can’t be overemphasized. A geologist should always consider every item of relevant data, such as drill stem tests, sample shows, mud-log analysis, nearby production, etc., before making a decision to set pipe.

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