Abstract: The invention relates to an apparatus for detecting and measuring water production in oil and gas wells and in injection wells, involving a neutron source for activating oxygen atoms in any water produced or injected in the well, and a plurality of detectors, at least three (3) but preferably four (4), longitudinally spaced within the housing for detecting and counting gamma ray emissions resulting from the oxygen activation.

Abstract: A method for the determination of petrophysical characteristics of earth formation surrounding a borehole, comprising detecting gamma rays or neutrons representative of the formations and forming therefrom a set of detected data "U" which is then expressed as a function of the unknown characteristics "Y", and of a set of response data "S", representative of the conditions under which the detecting step is performed; and wherein "Y" is expressed as r=R Y, where "r" represents prior information independent from the detected data and obtained from other sources, and "R" indicates a set of relationships between at least part of the unknown characteristics. The detected data and response data are e.g. in the form of spectra, and the method may further include irradiating the formation with neutrons or gama rays.

Abstract: A method and an apparatus for correcting nuclear measurements performed in a borehole traversing earth formation, for the effect of said borehole, wherein the formation is irradiated with high energy neutrons source and the gamma rays resulting from the capture of neutrons with atoms of the formation and the borehole are detected and processed so as to generate two energy spectra representative of gamma rays coming from two respective zones radially spaced from the neutron source; from each spectrum is derived a response of atoms of a same element located at the respective zones, a first response being mainly representative of the borehole and a second response being mainly representative of the formation; from a predetermined relationship between the responses and from calibration a corrective factor for borehole effects is obtained.

Abstract: A nuclear spectroscopy method for pulse height analysis of an electrical signal emitted by a radiation detector and including nuclear events, such as pulses, whose amplitude is a measure of the energy of the gamma rays collected by said radiation detector, wherein (1) said signal is continuously converted to digital samples, at a given rate, and (2) each of the digital samples is processed so as to form a digital image of each detected pulse. The energy of each pulse is calculated by summing all sample values representative of this pulse and the sample just preceding the first sample representative of a pulse, as well as the sample just following the last sample representative of the same pulse.

Abstract: A method and an apparatus for determining the hydrocarbon saturation S.sub.o in an earth formation surrounding a borehole, and/or the hydrocarbon saturation C.sub.b in said borehole, comprising:irradiating the formation with a source of neutrons of sufficient energy to interact with atoms of the formation and the borehole, according to inelastic neutron reactions; detecting the resulting gamma rays at a near detector and a far detector; expressing the measured carbon (C) and oxygen (O) yields respectively as a first and second linear function of S.sub.o, S.sub.w the water saturation in the formation, C.sub.b and/or C.sub.o water saturation in the borehole; combining the respective carbon and oxygen yields (C.sup.n, O.sup.n) for the near detector, and the respective carbon and oxygen yields (C.sup.f, O.sup.f) for the far detector so as to form the differences C.sup.n -O.sup.n and C.sup.f -O.sup.f ; and solving for the unknowns S.sub.o and C.sub.b.Alternately, in case either S.sub.o or C.sub.

Abstract: Method and apparatus for identifying and determining the concentrations of subsurface formation elements next to a borehole, by detecting and counting the gamma rays resulting from the activation of Al atoms by neutrons emitted by a high energy source. The total count rates from Al are corrected for Si interference by (1) calculating the ratio of the count rates of gamma rays from Si activation to the count rates of the gamma rays resulting from the inelastic collisions of neutrons with Si atoms, thus providing a reference ratio independent of environmental parameters; (2) detecting and counting the gamma rays resulting from the Si inelastic collisions; (3) determining from the count rates of silicon inelastic gamma rays and from said ratio, the count rates of Si activation gamma rays; and (4) subtracting, from the total count rates of activation gamma rays, the count rates of Si activation gamma rays.

Abstract: A nuclear spectroscopic method and apparatus for determining hydrocarbon saturation or water saturation of a formation adjacent a well bore is disclosed. Near and far inelastic gamma ray spectra are detected in response to pulses of fast neutrons irradiating the formation and materials in the borehole. Near and far carbon/oxygen (C/O) ratios are extracted from each spectra using predetermined spectra of postulated elements. The near and far C/O ratios are combined to determine a representation of formation hydrocarbon saturation substantially corrected for borehole gamma rays produced by inelastic reaction of fast neutrons and hydrocarbons in the well bore. Shielding of near and far detectors is provided to make the near detector more sensitive to gamma rays emanating from borehole gamma rays and to make the far detector less sensitive to borehole gamma rays and more sensitive to formation gamma rays.

Abstract: In order to properly treat the tubing of an oil producing borehole, and prevent hazard to personnel at the oil production site, the contamination of tubing by the formation of scale or radioactive deposits on the inner wall thereof is determined by measurement of the low-level radiation emitted by the scale and calculation of the radiation level which would be detected in the vicinity of the outer wall of the tubing in the absence of contributions by the radioactivity of surrounding earth formations. This is accomplished by a logging tool and method which includes a sonde which includes a detector and is lowered in the tubing to detect and count the gamma rays emitted by the scale or radioactive deposits at different depths in the borehole tubing.

Abstract: Nuclear spectroscopy method and apparatus for the stabilization of an energy spectrum, made from a signal, emitted by a radiation detector, and containing nuclear events, represented by pulses, whose amplitude is a measure of the energy of the particles, such as gamma rays, collected by the detector, the spectrum including at least a first reference energy peak coming from an ancillary nuclear source, wherein the method comprises: detecting the radiation under analysis by two detectors between which is placed the ancillary source; establishing at least one coincident spectrum corresponding to pairs of events simultaneously detected in both detectors and originating from the ancillary source; and stabilizing the coincident spectrum by using one energy peak of said spectrum as said first reference energy peak.

Abstract: Logging method and tool string for identifying and determining the concentrations of subsurface formation elements next to a borehole, by (i) using a low energy neutron source (either a chemical source, e.g. a .sup.252 Cf, or a deuterium-deuterium electronic source), and (ii) detecting and counting the delayed gamma rays resulting from the activation by the neutrons of atoms of at least one element of interest (e.g. aluminum). Two gamma ray detectors may also be disposed on either side of the low energy neutron source, for detecting and counting the prompt gamma rays resulting from the capture of neutrons by atoms of elements, such as Si, Ca, Fe, S, H, or Cl, Gd, Ti, or K.The low energy neutron source is used for both the "activation" and the "capture" measurements. The tool string may also include a natural gamma ray tool for the determination of uranium, thorium and potassium, and for measuring the background to be subtracted from the gross Al activation measurement.

Abstract: A method for determining the compensated density of a subsurface geological formation wherein the effect of borehole rugosity is reduced or eliminated utilizes the differences in the vertical response functions of the detectors at different distances into the formation. The method eliminates the contribution of the "shallow" formation region, irrespective of whether its properties are varying slowly or rapidly, without degrading the resulting vertical resolution. Furthermore, the method for determining such a characteristic of a subsurface geological formation does not require any additional or new measurements to be made, thus logging data from older wells can easily be reevaluated.

Abstract: A crystal oscillator including a crystal element designed to oscillate at a given frequency when subjected to an exciting voltage, and mounted parallel to and on a base through at least a wad made of at least a thin wound wire. Advantageously, the wire is randomly wound and is electrically conductive. The wad is elongated and is disposed parallel to said crystal and to said base.

Abstract: A method for investigating a gravel pack located in the annulus between the tubing/screen and the casing of a borehole, comprising the steps of:moving a logging tool through the tubing/screen over the depth region of the gravel pack, said logging tool including a neutron source able to emit neutrons at such an energy that their interaction with a first set of atoms indicative of the gravel pack quality causes the production of gamma rays, and at least one gamma ray detector; andderiving a measurement of the number of gamma rays resulting from the interaction of said neutrons and said first set of atoms of the gravel pack material, and which are detected by said detector over a predetermined counting time interval.

Abstract: A borehole logging method for determining the porosity of a formation surrounding the borehole, comprising the steps of: irradiating the formation surrounding the borehole from a location within the borehole with a burst of neutrons, detecting at a near detector indications of the concentration of thermal neutrons following the burst of neutrons and generating near count rate signals as a function of time in response thereto, detecting at a far detector indications of the concentration of thermal neutrons following the burst of neutrons and generating far count rate signals as a function of time in response thereto, fitting a count rate model to the near count rate signals to determine a near impulse formation count rate amplitude, fitting a count rate model to said far count rate signals to determine a far impulse formation count rate amplitude, determining the ratio of the near and far count rate signals as a characteristic proportional to the porosity of the formation.

Abstract: The apparatus of the present invention relates to a down hole tool capable of extraction of valid samples and making pressure measurements useful in calculating formation permeability. The tool incorporates the features of a straddle packer to allow formation fluid specimens to be taken at large flow rates without depressing the pressure below the formation fluid bubble point. When used in combination with a pressure probe the tool is used to obtain meaningful permeability readings in a larger radius area than previously permitted with known designs. Additionally, the apparatus of the present invention allows flow control during the creation of the pressure pulse which enhances extraction of valid samples and the permeability determination.

Abstract: A nuclear spectroscopic method and apparatus for determining hydrocarbon saturation or water saturation of a formation adjacent a well bore is disclosed. Near and far inelastic gamma ray spectra are detected in response to pulses of fast neutrons irradiating the formation and materials in the borehole. Near and far carbon/oxygen (C/O) ratios are extracted from each spectra using predetermined spectra of postulated elements. The near and far C/O ratios are combined to determine a representation of formation hydrocarbon saturation substantially corrected for borehole gamma rays produced by inelastic reaction of fast neutrons and hydrocarbons in the well bore. Shielding of near and far detectors is provided to make the near detector more sensitive to gamma rays emanating from borehole gamma rays and to make the far detector less sensitive to borehole gamma rays and more sensitive to formation gamma rays.

Abstract: A novel neutron burst timing, detection, and calculation method and apparatus are disclosed for a Thermal Decay Time Logging System. A neutron bursting regime is provided which includes a short burst, long burst repetitive sequence. After a short delay from the short burst, a first series of time gates is provided for accumulating gamma ray counts. After a relatively longer delay from the long burst, a second series of time gates is provided for accumulating gamma ray counts. The thermal neutron decay time constant .tau. and the macroscopic capture cross-section .SIGMA. of the formation are determined through an iterative procedure by which the formation .tau. is estimated from the second series of time gates which have been stripped of borehole decay counts determined from the first series of time gates. Similarly, the borehole .tau. is estimated from the first series of time gates which have been stripped of formation decay counts determined from the second series of time gates.

Abstract: In the preferred embodiment of the well tool disclosed herein, a main body adapted to be suspended in a borehole includes a pivoted tool-decentralizing arm which is movable between a retracted position along the rear of the body and an extended position where the free end of the arm is biased into sliding engagement with a wall of a borehole for urging the forward face of the body into sliding engagement with the opposite borehole wall. A second body is pivotally coupled on the mid-point of the decentralizing arm for maintaining the second body in alignment with the longitudinal axis of the borehole as the free end of the decentralizing arm moves along the borehole wall. Caliper arms are pivotally mounted on each side of the second body for moving in unison between retracted positions and extended positions where the outward ends of the caliper arms are respectively engaged on opposite sides of the borehole.