A unique two-detector Neutron tool has been developed and introduced commercially in the United States. More than 600 open-hole logs and 150 cased-hole logs have since been recorded. This new tool records a Compensated Neutron Log (CNL) for which the effects of hole conditions (mud cake and rough borehole walls) have been minimized and are generally small. Since the CNL may be run in combination with other logging tools, rig time is saved and wellsite interpretation becomes easier. Recorded with the Density log, the CNL delineates gas-bearing intervals in sand-shale sequences. A simple crossplot method delineates shaly gas zones on which gas effect is less apparent. The new Neutron log investigates more deeply into the formation than the Density. This complicates the computation of porosity in gas-bearing zones, but makes gas zones easier to find. For instance, in most low-porosity gas zones, the porosity is given directly by the Density whereas the CNL shows an appreciable gas effect. The CNL has a greater shale effect than the epithermal neutron tools such as the SNP. Studies, made in numerous wells where both types of Neutron logs were recorded, show that the CNL can be used in determination of both bulk-volume fraction of shale and porosity. A study of CNL responses in different lithologies has been made. The results show greater matrix effect on the CNL than on other Neutron tools. Porosity derived from the CNL-Density is potentially more accurate than that derived from previous Neutron-Density by computations.

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