ABSTRACT

The Dual Spacing Neutron Log, known also as the Compensated Neutron Log, or simply CNL, has been run commercially in Eastern Venezuela and on Lake Maracaibo. Prior to the introduction of the CNL, the Sidewall Neutron Porosity Log (SNP)was extensively used throughout Venezuela for formation evaluation purposes in shaly sands and to differentiate gas from oil reservoirs. In both cases the SNP was generally run with the Formation Density Log as a companion log. The new CNL can now be recorded in combination with the Density Log, thus making it possible to obtain, in a single run into the borehole, depth-matched porosity measurements which can be used to detect and evaluate clean and shaly oil- and gas-bearing reservoirs. The presence of mud cake and rough borehole walls affect the CNL to a much smaller degree than the SNP; its ability to investigate deeper into the formation makes it more sensitive for gas detection. Whereas the SNP tool was designed for use only in open hole, the CNL can be run in open or cased hole and gives in both cases comparable porosity readings. The Compensated Neutron Log has been eminently successful since its introduction into Venezuela. Qualitative as well as quantitative results will be presented of experience gained during the first year of use of the tool there. The examples presented will show several of the more important features of the tool.

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