Abstract: A borehole logging tool for neutron lifetime logging of subterranean formations surrounding a borehole includes a pulsed source of fast neutrons and a radiation detector for measuring neutrons returning to the borehole from the irradiated formations surrounding the borehole. The radiation detector system comprises a neutron absorbing and gamma ray radiating material which is moved by an articulating arm into contact with the borehole wall and is azimuthally oriented so that such neutron absorbing and gamma ray radiating material is firmly pressed against the formation. A shielding material minimizes absorption of neutrons from the borehole fluid. A gamma ray detector located in the main body of the logging tool detects gamma rays from the radiating material as a measure of the epithermal or thermal lifetime characteristic of the formation adjacent the borehole.

Abstract: A borehole logging tool includes a pulsed source of fast neutrons and a neutron sensitive counter. A neutron filter encases the counter and has a thickness to permit the longest possible delay time following each burst of fast neutrons before epithermal neutrons from the irradiated formation are detected by the neutron counter while at the same time minimizing thermal neutron effects.

Abstract: A radioactive borehole logging tool employs an epithermal neutron detector having a neutron counter surrounded by an inner thermal neutron filter and an outer thermal neutron filter. Located between the inner and outer thermal neutron filters is a neutron moderating material for extending the lifetime of epithermal neutrons to enhance the counting rate of such epithermal neutrons by the neutron counter.

Abstract: A subsurface formation is irradiated with pulsed neutrons and both inelastic scattering and capture gamma-rays are measured in energy level bands characteristic of sulfur and iron. Differentials are determined between such inelastic scattering and capture gamma-rays for both the sulfur and the iron. The iron differential is then compensated by a select multiple of the sulfur differential. The ratio of the compensated iron differential and the sulfur differential is taken as a measure of the pyrite content of the formation.

Abstract: A subsurface formation is logged to provide a record of the natural gamma radiation of the thorium, uranium, and potassium trace elements in the formation. Both the clay and mica contents of an interval of interest are determined from the natural gamma-ray activities in such interval of interest, in a clean sandstone interval and in a mica-free shale interval.

Abstract: Thermal neutron capture logs obtained during a log-inject-log operation and utilized in the determination of the water saturation condition of a formation traversed by a borehole are corrected for neutron diffusion and borehole effects by a normalization factor relating the apparent and measured macroscopic absorption cross sections of the rock matrix in the formation.

Abstract: A borehole logging tool includes a steady-state source of fast neutrons and three thermal neutron flux detectors. First and second detectors measure the same thermal neutron flux parameter and the third detector measures a different thermal neutron flux measurement. A count rate meter is connected to each thermal neutron flux detector. A first ratio detector provides the ratio of the outputs of the two count rate meters conncted to the first and second detectors measuring the same thermal neutron flux parameter. A second ratio detector provides the ratio of the outputs of the two count rate meters connected to the third detector and one of the first or second detectors. By comparing the signals of the two ratio detectors, oil bearing zones and salt water bearing zones within the formation being logged can be distinguished and porosity can be determined.

Abstract: Method and apparatus for pulsed neutron logging employing detectors of different energy-dependent sensitivities to neutrons at energy levels less than the chemical binding energy of hydrogen in hydrogenous fluids found in subterranean formations. Fast neutrons from the pulsed neutron source enter the subterranean formation under investigation and are moderated therein to form populations of slow neutrons during a thermalization period occurring subsequent to the fast neutron burst and a thermal equilibrium diffusion period occurring subsequent to the thermalization period. The detectors are employed to obtain count rate measurements during at least one and preferably two time windows falling within the thermalization period and during a later time window occurring within the thermal equilibrium diffusion period.

Abstract: A borehole logging tool includes a steady-state source of fast neutrons, two thermal neutron detectors, and two gamma ray detectors. A count rate meter is connected to each neutron detector. A first ratio detector provides the ratio of the outputs of the two count rate meters connected to the two thermal neutron detectors. A second ratio detector provides the ratio of the outputs of the two count rate meters connected to the two gamma ray detectors. By comparing the signals of the two ratio detectors, oil bearing zones and salt water bearing zones within the formation being logged can be distinguished and porosity can be determined.

Abstract: A radioactivity well logging tool employs an epithermal neutron detector having a thermal neutron counter surrounded by a thermal neutron shield. Located between the counter and the shield is a neutron moderating material for slowing down epithermal neutrons penetrating the thermal neutron shield to enable their counting by the thermal neutron counter.

Abstract: A borehole logging tool includes a fast neutron source and at least two thermal neutron detectors spaced apart from the source. A count rate meter is connected to each thermal neutron detector. A ratio detector provides an indication of the porosity of the formation surrounding the borehole by determining the ratio of the outputs of the two count rate meters. A comparison unit provides a signal indicative of the macroscopic absorption cross section of the formation by comparing the indicated porosity with at least one of the count rate signals.

Abstract: A borehole logging tool includes a steady-state source of fast neutrons, two epithermal neutron detectors, and two thermal neutron detectors. A count rate meter is connected to each neutron detector. A first ratio detector provides an indication of the porosity of the formation surrounding the borehole by determining the ratio of the outputs of the two count rate meters connected to the two epithermal neutron detectors. A second ratio detector provides an indication of both porosity and macroscopic absorption cross section of the formation surrounding the borehole by determining the ratio of the outputs of the two count rate meters connected to the two thermal neutron detectors. By comparing the signals of the two ratio detectors, oil bearing zones and salt water bearing zones within the formation being logged can be distinguished and the amount of oil saturation can be determined.

Abstract: A borehole logging tool includes a source of fast neutrons and two thermal neutron detectors. A count rate meter is connected to each thermal neutron detector. A ratio detector provides a first signal indicative of the ratio of the count rates of the two thermal neutron detectors. A first comparator provides a signal indicative predominantly of the macroscopic absorption cross section of the formation by combining both such ratio signal and the count rate from one of the thermal neutron detectors. A second comparator provides a signal indicative predominantly of the porosity of the formation by combining both such ratio signal and such macroscopic absorption cross-section signal.