The Use of Electrode Spacing in Well Logging
- Richard H. Zinszer (Union Oil Co.)
- Document ID
- Society of Petroleum Engineers
- Transactions of the AIME
- Publication Date
- December 1943
- Document Type
- Journal Paper
- 164 - 174
- 1943. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 1.11 Drilling Fluids and Materials, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 5.6.1 Open hole/cased hole log analysis, 4.3.4 Scale, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 1.6.9 Coring, Fishing, 2.4.3 Sand/Solids Control
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Application of electric logs has been used in correlation of subsurfacestructure to determine the size and shape of the oil reservoir.
Such a knowledge is hardly complete until saturation and productivity aredetermined for the various horizons. It is difficult to use electric logssuccessfully for this purpose because of the many factors that influence thecurves. In this work an effort was made to establish an empirical correlationbetween formation resistivity for a series of electric-log curves and watersaturation and oil productivity of sand. Electric logs were obtained byrecording with 10 different electrode spacings through the same interval of awell. In the analysis of these curves all factors except two, a dependent andindependent variable, were held constant. The interval studied had been coredand a large number of samples were analyzed in the core laboratory in order tocompare the values of permeability and saturation with the measured values offormation resistivity.
Results of this analysis indicate: (I) the depth to which mud filtrateenters a sand body, (2) a correlation between permeability and sand resistivityfor shallow penetration depths, and (3) that the water saturation for an oilsand can be determined from the measured sand resistivity after making suitablecorrections for sand thickness. The procedure in the last method depends on acorrection for thickness factor and a theoretical curve. The accuracy of thetheoretical curve is now being tested in the laboratory.
In an effort to place the analysis of electric logs on a quantitative basis,there is need for a better understanding of the many factors that influence anelectric-log curve. These factors may be large differences in sand thickness,permeability of the sand, salinity of the interstitial water, mud resistivity,formation temperature, and other sources. A number of examples were presentedby Archie, which treat the effect of sand thickness on measuredresistivity.
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