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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 12 (1962), Pages 213-221

Improved Interpretation of Formation Productivity by Combined Use of Core Analysis and Electric Log Data

Raymond J. Granberry (1), Richard C. Wilshusen (1)

ABSTRACT

Reservoir properties, such as permeability, porosity, residual fluid saturations, and capillary pressure characteristics are obtained by direct measurement of core samples. Electric logging devices provide information for computing approximate values for the formation factor or porosity, formation water resistivity, and formation water saturation. In the past, these two formation evaluation tools have been used more or less independently of each other.

This paper presents a method of combining core analysis and electric log information to obtain more reliable interpretations of fluid productivity. The porosity and the immobile interstitial water saturation derived from core analysis may be used to compute a value which is called productive resistivity, or (Rp). Productive resistivity is defined to be the resistivity of a hydrocarbon-productive formation with an interstitial water saturation equal to or less than the immobile value. The deep investigation electric logging devices, such as the induction log, approach in measurement the true resistivity or (Rt), from which the formation water saturation can be calculated. If the true formation resistivity measured by the electric or induction log is less than the calculated productive resistivity, it may be concluded that or induction log is less than the calculated productive resistivity, it may be concluded that the actual water saturation is greater than the immobile interstitial water, and the formation interval may be either partially or wholly water-productive. On the other hand, if the measured resistivity equals or exceeds the productive resistivity calculated from core analysis, it may be concluded that the actual formation water saturation is no greater than the immobile interstitial water and the sand is probably wholly hydrocarbon-productive. A similar calculation may be made using a higher water saturation value taken from the transitional zone to determine a value called the minimum productive resistivity, or Rmp.


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