A comparison of the moisture gauge and the neutron log in air-filled holes

The soil science, agriculture and construction industries measure the water content of a formation using a moisture gauge characterised by a neutron count rate which increases with increasing water content. The petroleum industry uses a neutron log, with a count rate which decreases with increasing water content: the two techniques have never been directly compared. In an air-filled hole, the neutron log is significantly more sensitive to water content than the moisture gauge below about 10 vol%, and the moisture gauge is significantly more sensitive between about 30 and 60 vol%. Effects of hole size, thermal neutron absorbers, sonde-wall gap, and density are similar for the two tools. (author)