Abstract: The invention is a stationary radiation detection tool that provides an azimuthal indication of the location of subterranean radiation sources. In one embodiment, the tool has four gamma ray sondes, each of which receives gamma rays from a discrete sector of surrounding formation.

Abstract: A standoff compensation system is disclosed for use in an LWD system implementing gamma density and/or neutron porosity measurements. An acoustic transducer is provided to measure the standoff distance between the logging tool and the borehole wall. The present invention includes a downhole processor for determining a weighting factor for the density and/or porosity measurements based upon the measured standoff distance. The weighting factor can either be calculated by the downhole processor according to a predetermined weighting function, or can be retrieved from a pre-calculated look-up table in ROM. The processor then multiplies the weighting factor by the count data from the sensor to determine a weighted count value. The weighted count values are accumulated during an averaging period and normalized, so that a single normalized count value can be generated and either stored in downhole memory, used immediately, or transmitted by telemetry to the surface.

Abstract: A method and apparatus for verifying operation and achieving gain stabilization in a helium-3 proportional counter radiation detector utilized in nuclear logging operations. The detector includes a beta-minus particle source selected to provide a predetermined number of radiation counts for a specified time period to verify detector operation. The beta-minus source is further utilized to achieve detector gain stabilization by defining two energy windows on either side of the characteristic beta-minus energy peak. The difference in counts for the two energy windows is used to define an error signal which is applied to negative feedback loop in the detector electronics. The beta-minus source is preferably selected such that the type of source and activity is exempt from Nuclear Regulatory Commission licensing and safety requirements.

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: 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: Statistical variations in 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 differences of the long and short derived averages.

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: 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.

Abstract: A method of logging earth formations to ascertain relative elemental abundancies of potassium (K), uranium (U) and thorium (T) is disclosed. A natural gamma ray spectrum of an unknown borehole is compared with individual standard gamma ray spectra of potassium, uranium and thorium in at least four energy ranges or bands. Decay peaks of the three elements are encompassed by three of the energy bands and at least one other energy band is used to monitor the changes in shape of the unknown spectrum caused by borehole conditions differing from that of the standard or calibration boreholes. A function derived from the gamma ray count rates in the four bands is used to compensate the elemental abundancies of the three elements to be detected in the unknown spectrum for the effects of differing borehole conditions in the unknown borehole from the standard borehole conditions.

Abstract: A method is disclosed for simultaneous determination of borehole and formation thermal neutron decay time components. The methods employ pulsed high energy neutron sources and time gated dual spaced detectors. Exponential decay curves are assumed for each of the components and iterative least squares fitting employing rapid convergence techniques are utilized.

Abstract: Earth formations surrounding a well borehole are bombarded with high energy neutrons which react with chemical elements in the formation components, giving rise to gamma radiation. The gamma radiation is detected by two separate, spaced detectors from which well logs are obtained indicating a ratio of the relative presence of silicon to oxygen in the formations.

Abstract: A simultaneous pulsed neutron porosity and thermal neutron capture cross section logging system is provided in the present invention. A logging tool provided with a 14 MeV pulsed neutron source, an epithermal neutron detector, and a combination gamma ray and fast neutron detector is moved through a borehole. Repetitive bursts of neutrons irradiate the earth formations and, during the bursts, the fast neutron and epithermal neutron populations are sampled. During the interval between bursts the thermal neutron capture gamma ray population is sampled in two or more time intervals. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity .phi.. The capture gamma ray measurements are combined to provide a simultaneous determination of the thermal neutron capture cross section .SIGMA..

Abstract: An improved measurement of earth formation porosity is provided by the present invention using measurements of the energy spectrum of fast neutrons. A continuous source of fast neutrons is used to irradiate earth formations penetrated by a well borehole. Two neutron detectors, a fast neutron detector sensitive in the high energy range of the fast neutron energy spectrum, and an epithermal neutron detector, sensitive in the lower energy range of fast neutrons, are spaced at the same effective distance from the neutron source. Measurements of the neutron population at each detector are combined according to predetermined relationships to derive a measurement of earth formation porosity.

Abstract: An improved pulsed neutron porosity logging system is provided in the present invention. A logging tool provided with a 14 MEV pulsed neutron source, an epithermal neutron detector, and a fast neutron detector is moved through a borehole. Repetitive bursts of neutrons irradiate the earth formations and, during the bursts, the fast neutron population is sampled. During the interval between bursts the epithermal neutron population is sampled along with background gamma radiation due to lingering thermal neutrons. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity.

Abstract: An improved pulsed neutron porosity logging system is provided in the present invention. A logging tool provided with a 14 MEV pulsed neutron source, an epithermal neutron detector and an inelastic scattering gamma ray detector is moved through a borehole. The detection of inelastic gamma rays provides a measure of the fast neutron population in the vicinity of the detector. Repetitive bursts of neutrons irradiate the earth formation and, during the bursts, inelastic gamma rays representative of the fast neutron population is sampled. During the interval between bursts the epithermal neutron population is sampled along with background gamma radiation due to lingering thermal neutrons. The fast and epithermal neutron population measurements are combined to provide a measurement of formation porosity.

Abstract: Measurement of the distance from a gamma ray detector to a gamma ray source for locating of a channel of undesired behind casing water flow in a producing well is provided. A relationship is given for the count rate ratio at a detector in two distinct energy regions of the gamma ray spectrum as a function of the distance from the gamma ray source. When counts of characteristic gamma rays due to the decay of radioactive nitrogen 16 produced by the activation of elemental oxygen nuclei comprising the molecular structure of undesired water flow are made then the distance R to such flow may be determined by means of the above relationship. This may then be interpreted in terms of the volume flow rate V of the undesired water flow.

Abstract: Background corrected inelastic neutron scattering gamma ray counts for selected energy regions of the gamma ray spectrum corresponding to calcium and silicon are compared with thermal neutron capture gamma ray counts for selected energy regions of the gamma ray spectrum. These data are functionally related to chlorine presence and are used to derive an estimate of the salinity of earth formations. The inelastic scattering and thermal neutron capture gamma ray data are separated from each other by the use of a pulse neutron source and time gating techniques.

Abstract: A system for logging earth formations traversed by a borehole wherein a high energy pulsed neutron source (14 MeV) repetitively irradiates earth formations. Two time gates operated after each neutron pulse are provided for detecting count rates from which the decay time and the macroscopic capture cross-section .SIGMA. can be determined. Background gate means are also provided to eliminate the effects of background and detector radiation. In the detection system, output pulses whose voltage level is proportional to the energy detected are produced. A cut-off voltage level is set at approximately 0.8 MeV, which is above the energy of gamma rays produced following neutron capture by the element Boron and below the energy of most gamma rays produced following capture by all other significant formation elements. By comparison of the count rates (obtained by summing these voltage pulses) in a Boron containing formation with macroscopic capture cross-section .SIGMA.

Abstract: An illustrative embodiment of the invention includes methods for linearizing the gain of borehole gamma ray energy measurement apparatus. A known energy peak (or peaks) which is prominent in the gamma ray energy spectra of borehole measurements is monitored and any drift in its apparent location in the energy spectrum is used to generate an error voltage. The error voltage is applied in an inverse feedback manner to control the gain of system amplifiers to cancel the drift.