The Significance of Particle Shape in Formation Resistivity Factor-Porosity Relationships

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Abstract
Results of laboratory tests are presented to show that the value of "m", in the Archie expression is determined by the shapes of the particles in the system. The value of m, "the shape factor", is constant for a system of particles of a given shape for a range of values. Applying this concept, one can predict relationships for mixtures of particles with different shapes, and these predicted relationships are useful in electric log interpretation. It is suggested that an equation of the form can be used to describe the properties of natural formations containing varying amounts of sand and clay. From this work and values of "a" and "m" reported in the literature, it appears that in many cases rocks in the same geological horizon have a common primary porosity but contain varying amounts of a particular clay. It is concluded that the equation can be applied to a rock-water system only when values of "a" and "m" have been established for the particular system. Introduction: The petroleum literature contains many reports of the results obtained by determining formation resistivity factor and porosity of rock samples from oil fields all over the world.

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