The Quantitative Application of Radioactivity Logs
- Robert E. Bush (Lane-Wells Co.) | E.S. Mardock (Well Surveys Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- July 1951
- Document Type
- Journal Paper
- 191 - 198
- 1951. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
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The object of this paper is to report recent developments in thequantitative interpretation of radioactivity logs. The use of reference linesis described in the application of the new zero radioactivity reference linefor the determination of neutron derived porosities is discussed. Illustratedexamples are shown of logs from the reef limestone of the North Snyder Fieldand from the Lansing-Kansas City limestone of central Kansas.
A method of using an interrelation factor calculated from the neutron andgamma ray curves, called the neutron productivity number, for the estimation ofproductivity from sandstone formations is discussed. When used in a relativemanner the neutron productivity number has aided in predicting whether a givenzone will produce gas or liquid or whether it is too shaly to produce. Examplesof logs from wells in the Freites District, Venezuela, and in East Texas areshown to illustrate the application of the neutron productivity number.
The petroleum industry was introduced to some of the preliminary results ofinvestigations into the quantitative interpretation of radioactivity logs inOctober, 1949: It was stated at that time that the methods presented wereentirely relative because they involved the use of reference points obtainedfrom the radioactivity log, i.e., shale reference lines, dense zone referencelines, or a combination of both shale and dense zone reference lines. Theserelative methods offered many advantages to the industry in interpretingradioactivity logs in terms of porosity with particular application tolimestone and dolomite reservoirs. However, these relative methods did notoffer the wide range of applicability desired because the establishment ofreliable reference points from shale in some areas were difficult. It wasrecognized that a more reliable means of establishing reference lines wasvitally needed. Such a method is now available through the introduction of aninstrumental zero device. It is the purpose of this paper to discuss theapplication of this new zero reference to the quantitative interpretation ofradioactivity logs.
Previously all applications of quantitative interpretations of radioactivitylogs have been made in limestone reservoirs with little or no emphasis placedon sandstone reservoirs. A brief resume of investigations into the quantitativeinterpretation of radioactivity logs in sandstone reservoirs is presented here.This discussion deals primarily with the interrelation of the gamma ray andneutron curves and the response of the latter to the density of the fluidsfilling the pore space in relatively homogeneous sandstones of uniformporosity. The authors believe that the methods presented herein are onlyapplicable locally to specific fields and reservoirs, and that they probably donot offer a wide range of applicability.
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