INTERFACE LOCATION IN EMPTY
STEEL-CASED BOREHOLES WITH NUCLEAR LOGS
Hugh E. Hall, Jr.
Physics Department,
Sam Houston State University,
Huntsville, Texas
The true depth of an interface between a water saturated sand and an air filled sand and the apparent depth on a log are often different. This work presents experimental results of using neutron-neutron logs and gamma-gamma logs for depth interface location between such formations. Measurements were made inside a two inch i.d. air filled steel pipe passing through the formations. Differences between the true depth and the apparent log depth are in the centimeter range. Depth differences in the neutron-neutron system depend heavily on the hydrogen concentration difference in the two media on each side of the interface. In a finite (other that zero) spaced neutron-neutron system, the apparent interface depth depends on whether the source is above the detector or the detector is above the source.
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