Density Logging with Gamma Rays

Abstract

Published in Petroleum Transactions, AIME, Volume 210, 1957, pages 289–294. Abstract An improved method of logging formation density has been developed in which the formation is bombarded with a collimated beam of gamma rays. By means of a scintillation detector and pulse height discriminator, the gamma-ray energy band is accepted and recorded which corresponds to deepest penetration into the formation. Laboratory tests on a field tool revealed no borehole diameter effect for smooth holes and no effect of formation chemistry, except insofar as chemistry affects density. In extensive field tests, the density log has exhibited satisfactory agreement with core measurements and has correlated accurately with other logs. Introduction This paper describes an improved method of logging formation density by means of back-scattered gamma rays to penetrate the formation together with energy discrimination to select only that energy (or frequency) range corresponding to deepest penetration into the formation. This method of density logging was developed at the La Habra laboratory of California Research Corp. Field instruments have been built and tested by McCullough Tool Co. and commercial service has begun in some areas. All of the data discussed here were obtained for the original field tool. The density log can be a valuable adjunct to existing logs because of its use in determining porosity quantitatively. It is useful also in connection with seismic and gravity surveys where formation density information is of interest.