The paper reviews some of the neutron activation logging methods which have been used over the past few years. Due to the state of the art for activation logging instruments, these methods depend almost entirely on the half lives and radiation intensity of the activation products. The elements which are most conveniently identified in this manner include oxygen, silicon and aluminum. Field examples of the logs and/or measurements involved in each of these determinations are included in the paper. The application and relative value of each of these determinations, the discussion of limitations of the presently available field techniques, and possible solutions of the limiting problems are all discussed. The most likely solution of these problems is primarily related to the use of gamma spectral measurements to define the activation products. Field examples of test data that support the validity of these solutions are also presented. The method is shown to be a viable approach for determining lithologic components (through elemental assay) in well bores containing a wide range of conditions. While having certain limitations, the techniques described have the almost singular advantage of being direct measurements of the elemental constituents under investigation, while other methods described in the literature tend to be indirect or empirical approaches.

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