A New Technique for the Measurement of the Formation Factors and Resistivity Indices of Porous Media
- F. Morgan (Gulf Research and Development Co.) | M.R.J. Wyllie (Gulf Research and Development Co.) | P.F. Fulton (Gulf Research and Development Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1951
- Document Type
- Journal Paper
- 15 - 16
- 1951. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
- 5.5.2 Core Analysis, 5.6.2 Core Analysis, 1.6.9 Coring, Fishing, 4.2.3 Materials and Corrosion
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The importance of formation factor, F, not only in electric logging but as afundamental rock parameter has recently been stressed. The desirability ofinvestigating the range of variation of the resistivity index exponent, n, inthe relationship I = Sw-n, where I is the resistivity index and Sw the watersaturation as a fraction of the void volume of a porous medium, has also beenurged. The magnitude and variation of n with saturation and rock texture is asubject not only of theoretical interest but also one of prime importance inthe interpretation of electric logs.
A simple technique has recently been developed which enables both F and n tobe measured with high accuracy and which may also find acceptance as aconvenient method for the determination of irreducible saturation attainment inthe restored state method of core analysis.
Experience has taught that reproducible measurements of F are possible onlyif the resistance measuring electrodes are so arranged with respect to a planeface on a porous medium that they are able to make electrical contact withsubstantially all entry pores in that plane. In practice this may be achievedby using a platinized-platinum gauze electrode backed by some absorbentmaterial (such as felt) which has been saturated with a fluid identical withthat used to saturate the porous medium. Application of pressure to theelectrode and absorbent material then forces the gauze against the plane faceof the porous medium and simultaneously squeezes saline solution through themeshes of the gauze. By this means the electrode is in continuous aqueouscontact with all pores and satisfactory and reproducible low resistance contactwith the porous medium is achieved.
Clearly this method, although satisfactory for measurements of F, cannot beapplied to the making of continuous resistance measurements on a porous mediumwhile capillary pressure desaturation is being carried out. However, acceptingthe principle that for satisfactory results electrical contact must be madebetween a measuring electrode and all pores adjacent to that electrode, methodsof bringing electrodes into intimate contact with the surfaces of porous mediawere investigated.
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