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Scientific Investigations Report 2011–5005

Connectivity Equation and Shaly-Sand Correction for Electrical Resistivity

By Myung W. Lee

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Estimating the amount of conductive and nonconductive constituents in the pore space of sediments by using electrical resistivity logs generally loses accuracy where clays are present in the reservoir. Many different methods and clay models have been proposed to account for the conductivity of clay (termed the shaly-sand correction). In this study, the connectivity equation (CE), which is a new approach to model non-Archie rocks, is used to correct for the clay effect and is compared with results using the Waxman and Smits method. The CE presented here requires no parameters other than an adjustable constant, which can be derived from the resistivity of water-saturated sediments. The new approach was applied to estimate water saturation of laboratory data and to estimate gas hydrate saturations at the Mount Elbert well on the Alaska North Slope. Although not as accurate as the Waxman and Smits method to estimate water saturations for the laboratory measurements, gas hydrate saturations estimated at the Mount Elbert well using the proposed CE are comparable to estimates from the Waxman and Smits method. Considering its simplicity, it has high potential to be used to account for the clay effect on electrical resistivity measurement in other systems.

 

First posted January 28, 2011

For additional information contact:

U.S. Geological Survey
Central Energy Resources Science Center
Box 25046, MS-939
Denver Federal Center
Denver, CO 80225-0046

http://energy.cr.usgs.gov/

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Suggested citation:

Lee, Myung W., 2011, Connection equation and shaly-sand correction for electrical resistivity: U.S. Geological Survey Scientific Investigations Report 2011–5005, 9 p.



Contents

Abstract

Introduction

Theory

Archie Equation

Waxman and Smits Equation

Connectivity Equation

Connectivity Equation and Shaly-Sand Correction

Proposed Connectivity Method

Analysis of Formation Resistivity

Laboratory Data

Well Log Analysis

Considerations for the Application of Connectivity Equation

Archie Parameters and Connectivity Exponent

Saturation Differences

Original and Proposed Connectivity Methods

Conclusions

References Cited


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