The Quantitative Aspects of Electric Log Interpretation

While intensive research continues to promote a more complete understandingof the potential and resistivity measurements that comprise the electric log, it is believed that consideration should also be given to translating thesenumerous and often widely separated findings into a coordinated and readablebody of fundamental facts designed specifically for the petroleum engineer andgeologist. Although provision is made through publication for a ready exchangeof new theoretical concepts, it is also desirable to provide reviews andappraisals of the more established techniques and methods from the operatingstandpoint so that an economic and practical application may be realizedconcurrently with the theoretical progress. With these basic premises as aguide the author reviews the present state of electric log interpretation. The paper is directed not so much to the logging or research specialist asto the petroleum engineer and geologist to whom the electric log is only one ofthe many tools which he employs. Frequently, these persons do not have the timeto follow in detail the many specialized contributions that appear and, as aconsequence, are not in a position to place these contributions in properrelation to each other, or to the art as a whole. The paper reviews the basic steps in making quantitative determinations fromthe electric log of the amount of oil or gas present in subsurface formationsand also discusses the degree of reliability of these determinations undervarious conditions. The paper also indicates the trend of future developmentsin electric logging systems and methods of interpretation. Introduction The electric log has been used about 20 years as a means for studying theformations penetrated by a well bore. The first half of this period ischaracterized by the development of suitable logging techniques and equipment.Although progress in this direction is continuing at a satisfactory rate, thelast ten years are characterized more by an increasing interest in methods ofelectric log interpretation. During this period, a large number of fundamentalpapers have been published, expounding various logging techniques andparticular phases of the interpretation problem. Many of these papers representimportant contributions, and a few are classic. T.P. 3280