Techniques of Electric Log Interpretation

Abstract

The generally used techniques of electric log interpretation are reviewed and discussed, including the determination offormation water resistivity from the SP curve,true resistivity values from log data,water saturation from electric logs, andformation porosity from resistivity data. Particular emphasis is placed on the assumptions made in log interpretation. It is hoped that efforts will be stimulated which, in the future, will make it possible to reduce the number of assumptions necessary for log interpretation. Introduction Petroleum engineering and geology can be said to be based upon both facts and assumptions. So too, are the various techniques of electric log interpretation. For the last few years, some assumptions which have been made in developing log interpretation methods have been repeated so often that they are now accepted by many persons as facts. In reviewing the principles of resistivity and potential curve interpretations, many of the assumptions (and how they affect the results of interpretation) will be considered. Because this is a review, the purpose of this paper is not to present new methods of interpretation. However, the reader of this review should be stimulated to consider whether he should accept these assumptions as they are made now or whether he would prefer to explore possible ways to reduce the number of assumptions required for log interpretation. Assumptions To emphasize the assumptions used in most interpretations of electric logs, they will be tabulated here and then referred to as each technique of interpretation is discussed. No particular emphasis is inferred by the order of tabulation.