Dual Induction-Laterolog: A New Tool For Resistivity Analysis
Authors: Tixier M.P. , Alger R.P. , Biggs W.P. , Carpenter B.N. 
Published: December 2007

Tixier, M.P., Member AIME, Schlumberger Well Surveying Corporation, Houston, Texas Alger, R.P., Member AIME, Schlumberger Well Surveying Corporation, Houston, Texas Biggs, W.P., Member AIME, Schlumberger Well Surveying Corporation, Houston, Texas Carpenter, B.N., Schlumberger Well Surveying Corporation, Ridgefield, Connecticut
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Abstract
The recently introduced dual induction-laterolog device provides the simultaneous recording of three resistivity measurements and an SP curve. Two of the resistivity measurements are obtained from induction devices of different depths of investigation, and the third from a shallow-investigation laterolog. Use of a logarithmic scale to record the resistivity curves permits visual estimation of the Rxo/Rt ratio and the degree of invasion, 2) gives improved resolution in formations of low resistivity, and 3) eliminates troublesome offscale traces and scale changes. This manner of presentation is most amenable to graphical methods of interpretation. To obtain true formation resistivity in case of deep invasion it is necessary to account for the effect of the invasion parameters. The total number of parameters in the problem can be reduced to four; these can be uniquely determined with no less than four independent measurements. One interpretation method for fresh muds, when invasion is appreciable, provides a complete solution of the problem when a Proximity Log is available along with the Dual Induction-Laterolog. Another interpretation method, also for fresh muds, depends on the use of the three focused resistivity measurements of the Dual Induction-Laterolog in conjunction with a good value of the formation factor, independently derived, for example, from a porosity log. In this simplified interpretation procedure, the first step is to compute tentative values of Rt, Rxo, and Di with the assumption of a step-contact invasion profile. If the existing invasion pattern does not match the equivalent step-contact profile, the value of Sw can be improved through a special technique involving a ratio of saturations computed in two different ways. The interpretation procedures are readily handled by both manual and machine computations. Various examples illustrate the logs and the use of the interpretation techniques.
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