Epithermal neutron lifetime logging in partially saturated formations and large-diameter holes

A prototype logging tool which measures hydrogen content using epithermal neutron lifetime was operated in air-filled holes through partially saturated formations at the US Department of Energy´s Nevada test site. Data from model formations of known hydrogen content show that the tool can be calibrated to provide volume fraction of water in partially saturated formations. Such calibrations were obtained for air-filled holes 12 inches in diameter and 8 feet in diameter, which are typical hole sizes at the nuclear weapons test site. Data from the calibration models also allowed determination of the effects on the measurement caused by tool standoff from the wall of the hole. An 8-foot diameter hole was logged for 1000 feet through a partially saturated silica formation. Comparison to the standard, steady-state neutron log, in this hole showed good agreement in calculated water volume. Water volume percentages were generally in the range 10-20%, although values as high as about 30% were encountered for one extended interval