| Abstract |
The invention relates to an apparatus for investigating the porosity of a subsurface formation surrounding a borehole. The apparatus comprises a tool body and a neutron source is located in the tool body operable to repetitively irradiate the borehole and earth formation with discrete bursts of high energy neutrons~ Near and far detectors are provided for detecting then, populations of epithermal neutrons resulting from irradiation ot he borehole and formation with high energy neutrons. Counter.~ are connected to the near and far detectors for generating count signals indicative of the magnitudes of the detected epithermal .. neutron populaltions at the near and far detectors. Decay C detecting means with deriving means is provided in the said tool body, for detecting the decay of epithermal neutron population.. Porosity deriving means is connected to the said counters and the c said deriving means for providing a measurement signal. representative of the porosity of the fo~mation surrounding borehole. |