Robert C. Ransom
What are Archie’s Basic Relationships
What is Meant by the Plot of Rt versus Swtϕt
Parallel Resistivity Equations Used in Resistivity Interpretation
What is the Formation Resistivity Factor
Table of Retrievable Contents:
SYMBOLS DEFINED
a Historically, the coefficient of the Formation Resistivity Factor. In this paper, the coefficient of Rw . Usually equal to 1.0 in clean rocks, and different from 1.0 in the presence of any conductive influence other than formation water. Often lower than 1.0. When incorporated in comprehensive Rwe relationships, the numerator in the Formation Resistivity Factor must always be 1.0.
m The porosity exponent in the Formation Resistivity Factor. Related to the shape and dimensions of electrolyte-filled paths.
n The saturation exponent found in Archie's water saturation equation. Related to the electrical interference caused by the presence of hydrocarbon in electrolyte-filled paths. A form of m after hydrocarbon has displaced water.
ϕt Total porosity fraction consisting of the sum of effective and noneffective porosity fractions.
ϕe That part of the total porosity fraction that is hydrodynamically effective and can be occupied by hydrocarbon.
ϕne Is the noneffective porosity in clay shale and is directly related to the fraction of clay shale present. A porosity volume that has not been penetrated by hydrocarbon. Water saturation in the noneffective pore space is 1.0 and resistivity is represented by Rwb .
Ft The Formation Resistivity Factor of the rock, where the conductive water volume fraction always is Swtϕt , where Swt ≤ 1.0. In this paper, the numerator always is equal to 1.0.
Rw Formation water resistivity. Interstitial-water resistivity.
Rwa The apparent resistivity of formation water found by dividing Rt by Ft , where Swt = 1.0.
Rwb The apparent resistivity of water bound in clay shales.
Rwe A calculated value for the equivalent or pseudo water resistivity when secondary conductive influences are present. In this paper, the product of coefficient a and Rw as it is incorporated in the equation for the calculation of Rwe .
Rwz Is the Rwa value determined from a zone known to be or believed to be completely filled with water or nearly saturated with water. Hydrocarbon saturation is zero or near zero. Rwz is a graphical equivalent to Rwe and a special condition of Rwa .
R0 The true resistivity of the uninvaded rock when water saturation is 1.0. The water or pseudo water can have the resistivity value Rwe . Sometimes calculated, sometimes read directly from the deep resistivity curve, sometimes derived from the deep resistivity curve. R0 is a special condition of Rt .
Rt The true resistivity of the uninvaded rock, whether or not it contains hydrocarbon. Sometimes read directly from the deep resistivity curve, sometimes derived from the deep resistivity curve, sometimes calculated. R0 is a special condition of Rt .
Swe Water saturation as a fraction of the effective porosity ϕe .
Swt Water saturation as a fraction of the total porosity ϕt .
Swtϕt The total conductive water volume fraction where Swt ≤ 1.0. A fraction of one unit of formation volume.
A CLARIFYING CONCEPT OF ARCHIE'S RESISTIVITY RELATIONSHIPS AND PARAMETERS.
A MODEL AND DISCUSSION
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