Abstract: A gravel pack evaluation tool comprised of a low energy radiation source and multiple directionally-collimated radiation detectors to analyze small, azimuthal segments of a gravel pack. Methods of use are also provided. Collimators and radiation shielding used in conjunction with multiple detector arrays allow an azimuthal segmented view of a gravel pack, particularly at certain defined depths into a gravel pack. Radioactive tracers may be used in conjunction with these tools to produce enhanced images of gravel packs and formations.

Abstract: Logging apparatus and methods for detecting first signals indicative of the absolute concentrations of the first category of elements in the rock matrix, for irradiating the formation with a pulse of high energy neutrons and for detecting a second signal indicative of the relative concentrations of a second category of elements in a rock matrix. The absolute and relative concentrations of a plurality of elements are determined, and this information is used to transform at least one of the relative concentrations into an absolute concentration. One of the measured absolute concentrations is for aluminum, from which correlations are used to determine the absolute concentrations of other, non-measured elements. A tool system for measuring the absolute aluminum concentration includes a californium-252 source and a gamma ray detector having a plurality of windows from which the aluminum count rate can be compensated for interference by manganese activation.

Abstract: A method and apparatus for determining the contents of a borehole traversing a subterranean formation is provided. In the method, a well-logging sonde is used to bombard the contents of a borehole and the formation with fast neutrons. An early capture spectrum signal is generated to reflect the composition of the formation and the contents of the borehole. A late capture spectrum signal is generated to reflect the composition of the formation. The early capture spectrum signal is compared with the late capture spectrum signal to derive an output signal representative of the spectral composition of the contents of the borehole.Additionally provided are improved methods and apparatus for determining the contents of a subterranean formation. An inelastic spectrum signal is generated to reflect the detailed combined composition of the formation and contents of the borehole.

Abstract: The composition of a geological formation traversed by a borehole is investigated by measuring an energy spectrum of the radiation within the borehole. The measured spectrum is thereafter analyzed by comparing it with a composite spectrum, made up of standard spectra of constituents postulated to comprise the formation-borehole system. As a result of such analysis, the proportions of the postulated constituents in the formation are determined. Where the measured spectrum is subject to degradation due to changes in the resolution of the detector, a filtering arrangement effects modification of the standard spectra in a manner which provides for a more accurate determination of the constituents of the borehole-formation system.

Abstract: In the illustrative embodiments of the invention disclosed, the composition of an earth formation is investigated by repetitively irradiating the formation with bursts of fast neutrons and generating an energy spectrum of the gamma rays resulting from the inelastic scattering of such neutrons by nuclei of the formation. The inelastic scattering gamma ray spectrum is analyzed by comparing it with a composite spectrum, made up of standard spectra of constituents postulated to comprise the formation, to determine the proportions in the formation of the postulated constituents. A background energy spectrum is generated from gamma rays detected during periods between neutron bursts and is utilized to provide one or more standard background spectra for use in the analysis of the inelastic scattering gamma ray spectra. The standard background spectrum or spectra are preferably updated on a repetitive basis to reflect the current background component in the detected inelastic scattering gamma ray spectrum.

Abstract: Method and apparatus, for use in the detection of inelastic neutron scattering gamma ray spectroscopy, effect data acquisition efficiency enhancement by operating a neutron generator such that a resulting output burst of fast neutrons is maintained for as long as practicably possible until a gamma ray is detected. Upon the detection of a gamma ray the generator burst output is terminated. Pulsing of the generator may be accomplished either by controlling the burst period relative to the burst interval to achieve a constant duty cycle for the operation of the generator or by maintaining the burst period constant and controlling the burst interval such that the resulting mean burst interval corresponds to a burst time interval which reduces contributions to the detected radiation of radiation occasioned by other than the fast neutrons.

Abstract: The composition of an earth formation is investigated by repetitively irradiating the formation with bursts of fast neutrons and generating an inelastic energy spectrum from gamma ray counts detected during first time intervals which are contemporaneous with the bursts. A second energy spectrum is generated from gamma ray counts detected during second time intervals which immediately follow respective first time intervals. Gamma ray counts comprising the second spectrum are thereafter subtracted from the gamma ray counts comprising the inelastic spectrum to provide an inelastic energy spectrum with reduced background.