Abstract: By taking the ratio of silicon to calcium pulsed neutron capture gamma radiations together with a formation capture cross section measurement, in formations (20) having low hydrogen index, a measurement indicator is provided for differentiating low porosity limestones from high porosity gas sands.

Abstract: Methods are disclosed herein for determining the point of entry of water cut into a cased well borehole. A well logging sonde is moved past a perforated interval in a cased well borehole. The borehole environment is irradiated with 14 MeV neutrons from a neutron source and measurement of movement of oxygen activated borehole fluid past two gamma ray detectors spaced from the neutron source is combined with the speed of movement of the logging sonde to derive a signal representative of the entry location and flow rate of the oxygen activated fluid. At least one borehole fluid sample is taken in the interval between the point of neutron irradiation and the detection of oxygen activation gamma rays to resolve any ambiguity in the total flow rate of borehole fluid in the interval.

Abstract: A method and apparatus (108) are disclosed for spectral gamma ray logging of a well borehole (106) to determine elemental concentrations of radioactive materials in subsurface earth formations (100) and in the borehole region. Anomalous radioactive deposition in the borehole region is identified and the effect thereof compensated for in the elemental concentration determinations.

Abstract: Statistical variations in simultaneous shallow and deep investigation nuclear borehole logs are reduced using digital moving average data processing while maintaining responsiveness to formation changes, by transitioning through a combination of long and short filtered data as a function of the statistical variation of the deep log data differences of the long and short derived averages. Borehole rugosity is also indicated as a function of the difference between the shallow and the deep log indexes of the differences between their respective narrow and wide derived averages.

Abstract: Uranium ore zones are quantitatively evaluated using the relative photoelectric absorption of naturally occurring gamma rays in two energy bands. One band experiences significant photoelectric absorption from uranium; the other does not. The ratio of the resultant measurements provides a quantitative indication of the uranium concentration.

Abstract: Compensation of photoelectric absorption measurements for borehole effects during nuclear logging of downhole earth formations is accomplished by detecting low energy gamma radiations entering two detectors in the logging tool along paths having substantially constant formation components but varying borehole components.

Abstract: Earth formations penetrated by a borehole are irradiated with pulses of fast neutrons. The epithermal neutrons resulting from moderation of the fast neutrons are detected in a plurality of time intervals to determine the porosity of the adjacent earth formations independently of lithology. Statistical results are improved by taking the ratio of the count rate during build-up of the epithermal neutron population to the count rate during die-away.

Abstract: An earth formation is irradiated with fast neutrons (18), and the formation porosity is determined by a dual-spaced fast/epithermal neutron measurement in which the fast neutron population is measured at a different source-detector spacing (20) than that used for measuring the epithermal neutron population (40).

Abstract: A method is disclosed for the simultaneous determination of borehole (11) and earth formation (20) thermal neutron decay time components. The method, which employs pulsed high energy neutron sources (21) and time gated detectors (23,24), furnishes several quality indicators, along with appropriate criteria for selecting which to use. The method also furnishes a new indicator for the borehole capture cross section.

Abstract: Earth formations penetrated by a borehole are irradiated with pulses of fast neutrons. The epithermal neutrons resulting from moderation of the fast neutrons are detected in a plurality of time intervals to determine the porosity of the adjacent earth formations independently of lithology. Borehole effects are taken into account by separately determining borehole and formation epithermal neutron decay constants.

Abstract: Earth formation porosity is determined entirely from fast neutron spectroscopy, preferably by taking the calibrated ratio of the counts in two different pulse height ranges of the observed spectrum. The determination may be made using a single detector.

Abstract: A multi-function compensated spectral natural gamma ray logging method provides for determining formation and borehole characteristics directly from naturally occurring formation radiation. The method, which measures formation lithology in open holes and mean casing thickness in cased wells, incorporates active compensation for differences in borehole conditions when calculating relative elemental formation abundancies or concentrations of potassium (K), uranium (U) and thorium (T).

Abstract: A method and apparatus for logging downhole earth formations which converts, for a given logging tool geometry, a measurement of the extent of energy degradation of the spectrum of gamma rays emitted from a source in the tool and Compton scattered by the formation back to the tool, into a measurement of the density of the formation.

Abstract: The disclosure relates to a well logging method which is capable of providing an indication of salinity and water fraction of the production fluid of a borehole. This indication of borehole parameters may be obtained through the use of a conventional gamma ray logging system that detects gamma rays produced by isotopes created from neutron activation of oxygen, sodium, and chlorine that may be present in the production fluid. A logging sonde is passed twice through a portion of interest in the borehole at two different logging speeds. The fluid velocity relative to the sonde may be determined using these two logging speeds and a displacement distance which reflects the time required for a detector associated with the sonde to reach fluid activated by neutrons produced by the sonde.

Abstract: Naturally occurring gamma radiations from earth formations in the vicinity of a well borehole are detected and spectrally separated into six energy regions or bands. Borehole compensation techniques are applied to the gamma ray spectra and the attenuation coefficient .eta. is determined as a result thereof. The attenuation coefficient is used along with predetermined borehole, casing and cement parameters to derive a measure of the density of the earth formations.

Abstract: A method for measuring the location, linear flow rate, and volume flow rate of undesired water flow behind well casing in a well includes irradiating borehole environs with high energy neutrons from a neutron source located in a well tool in the borehole. Gamma rays from the decay of an unstable isotope which comprises a portion of any undesired behind casing flow present are detected with gamma ray detectors located in the well logging tool. Count signals representative of the detected gamma rays from at least one of the detectors are separated into at least three energy dependent signals. A ratio signal corresponding to the ratio of at least two of the three energy dependent signals is generated and an indication of the linear flow rate of the undesired behind casing water flow in a preferred direction is determined from the count signals from the detectors and from the first predetermined relationship.

Abstract: This invention relates to a logging tool housing construction for use with gamma ray logging devices. The tool housing is constructed of materials designed for maximum transmission of low energy natural gamma ray energies (E=150-300 Kev). The housing material which encloses a gamma ray detector is a tubular, filament wound graphite composition and has a tubular metal sleeve for wear protection. The core and tubular metal sleeve are constructed and interconnected to meet mechanical and pressure requirements for oil well logging use.

Abstract: In the preferred and illustrated embodiment taught herein, method steps for monitoring of raw materials to be used in drilling mud are disclosed. The materials are monitored for radioactivity. Procedures for taking such measurements are disclosed, and the extent of gamma radioactivity in the raw materials used in drilling mud is determined. This is correlated to the increased radiation attributable to mud made from these materials and the effect the mud would have on gamma ray measuring logs. An alternate procedure for testing drilling mud, typically at the well site, is also disclosed. The method detects mud radioactivity from any additives including barite, potassium chloride, well cuttings or others. Excessive background levels due to mud gamma radioactivity in a well may very well mask the data obtained by various logging procedures dependent on gamma radiation. Procedures are also described for either rejecting mud which is too radioactive or correcting the log measurements for mud effects.

Abstract: Natural gamma radiation is detected by a scintillation detector in a well logging sonde and separated into at least six separate energy regions. The gamma ray counts in the higher four energy regions are used to derive borehole compensated elemental concentrations of potassium, uranium and thorium. The gamma ray counts lower two energy regions are used to identify formation lithology.

Abstract: This invention relates to an improved method for determining the oil saturation of subsurface earth formations in the vicinity of a well borehole. High energy neutrons irradiate the subsurface earth formations and gamma rays caused by inelastic scatter with the subsurface earth formation constituent materials are measured. For a chosen borehole depth, gamma ray logs are taken in different situations: first, with the formation fluid water and oil mixture in an undisturbed state; second, after flushing the formation with alcohol to displace the formation water and oil mixture; and, finally, after flushing the alcohol from the formation with water to obtain a measurement with no oil in the formation. The gamma ray measurements obtained are then used to determine the oil saturation without requiring knowledge of the porosity of the earth formation, borehole conditions or formation type.