A Comparison of SATORI and HB Effective-Medium Conductivity Models

Charles R. Berg: ResDip Systems

Abstract: Two effective-medium shaly sand models are compared, one based on SATORI (symmetrical anisotropic theory of resistivity interpretation) theory (de Kuijper et al., 1996) and one based on HB (Hanai-Bruggeman) theory (Berg, 1995). The basic HB equation has lower incoherence (better accuracy) when compared to its SATORI counterpart on the Group II experimental samples from Waxman and Smits (1968) in spite of having only two free variables to SATORI's three. The HB saturation equation (Berg, 1995), when applied as published with no changes, appears to be slightly less accurate than SATORI on the Group III (Hofman et al., 1995) data set. However, when clay-water effects are taken into account, as they are in SATORI, the HB saturation model is more accurate than SATORI. Furthermore, the addition of another free variable to the HB saturation model to equal the number of free variables in SATORI resulted in saturation calculations that were much more accurate than SATORI.

A Novel Array Laterolog Method

Yong-Hua Chen and Weng Cho Chew: Center for Computational Electromagnetics, Department of Electrical and Computer Engineering, University of Illinois Geng Ji Zhang: Department of Petroleum Exploration, University of Petroleum, Dongying, Shandong, China

Abstract: The dual laterolog tool has been used widely and traditionally to investigate the resistivity profile of formations. In this paper, we point out some weaknesses of the traditional method and introduce a new tool design-the Array Laterolog tool. The finite element method is used to simulate the apparent resistivity curves for both the dual laterolog and Array Laterolog tools for various formation models. Numerical results show the Array Laterolog tool has both higher vertical resolution and more flexible radial investigation than the dual laterolog tool. With its unique new electrode configuration, the Array Laterolog tool can theoretically measure an unlimited number of shallow apparent resistivity curves. While having approximately the same high vertical resolution as the deep Array Laterolog (ALD) measurement, each of these curves has a different investigation depth. These shallow Array Laterolog (ALS) curves, combined with the ALD curve, can provide a full formation radial resistivity profile.

Nonlinear Response of Gamma Ray Logging Systems in the Copper Mountain Uranium Deposits

Robert E. Enwall: Saudi Arabian Oil Co., Dhahran, Saudi Arabia

Abstract: Quantitative calibration of total-count gamma ray logging systems assumes that a linear relationship exists between log response and uranium concentration. Analysis of logging results obtained in the Copper Mountain uranium deposits, located in north-central Wyoming, indicates the log response varies nonlinearly with uranium concentration as measured by core assays. This relationship is attributed to differential gamma attenuation effects that vary nonlinearly with the thickness of mineralized zones. Application of linear K-factors, derived by conventional calibration procedures, in field logging environments characterized by very thin mineralized zones can result in conditionally biased uranium grades and lead to serious overestimation of reserves. Biased results can be precluded by employing logging tools with filtered detectors or by applying in-situ site-specific calibration based on a nonlinear relationship between log response and uranium concentration.

Borehole-Diameter and Mud-Weight Corrections for a Gamma-Gamma Density Tool

Gordon L. Moake: Halliburton Energy Services

Abstract: Curvature mismatches between the diameter of gamma-gamma density tools and borehole walls cause small errors in density measurements. Consequently, a correction for variations in borehole diameter and mud weight must be made. A mathematical form of the correction is devised and applied to a commercial tool.