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RESEARCH ARTICLE

An enhancement of the formation factor parameters ‘a’ and ‘m’

Walid M. Mabrouk 1 2 Khalid S. Soliman 1 Mohamed A. Tawfic 1
+ Author Affiliations
- Author Affiliations

1 Geophysics Department, Faculty of Science, Cairo University, Giza, Egypt.

2 Corresponding author. Email: walid_mabrouk@yahoo.com

Exploration Geophysics 43(2) 87-94 https://doi.org/10.1071/EG10015
Submitted: 7 May 2010  Accepted: 6 March 2012   Published: 23 April 2012

Abstract

The use of incorrect values of the formation constants a, tortuosity factor,and m, cementation exponent, in Archie’s water saturation equation, can result in the overlooking of potential producible zones. Usually, assumptions are made to approximate a and m where often m is 2, while a may be 0.81 or 1.0, depending on the type of lithology. When core is available, accepted laboratory practices exist to calculate a and m, however, these laboratory steps are generally not considered routine analysis and, in order to save time and money, may not be conducted.

Core analysis for a and m require saturating to 100% multiple plugs of varying porosity with water of known resistivity. The resistivity of each water saturated core is graphed on a log-log graph with porosity to determine a and m.

This work illustrates a simple method of calculating a and m that is dependent on sonic transit time and bulk density, and on knowing one cementation exponent value from core measurements.

The method is tested and applied on a large number of samples to ensure its ability to determine formation factor parameters a and m.

Key words: cementation exponent, formation factor parameters, formation resistivity factor, tortuosity.


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