Abstract: A method for measuring properties of earth formations surrounding a borehole and, particularly, properties of the invaded zone of the formations. A short pulse of electrical energy is applied at a transmitter location, and signals are induced at a plurality of receiver locations. The polarities of the initial portions of the signals detected at the receiver locations are used in determining properties of the formation invaded zone, particularly its thickness and its conductivity as compared to the virgin formations.

Abstract: Method and apparatus for distinguishing oil from fresh water in situ in a subsurface geological formation are proposed which utilize the anomalous response of a neutron porosity tool to some oils. Apparent porosity derived from a neutron porosity investigation tool which measures spatial neutron flux distribution is compared to the porosity derived from a second investigating tool whose response is not or at least is less sensitive to the hydrogen density of the formation fluid than is the neutron porosity tool. Where a real difference is evident, oil rather than fresh water is indicated.

Abstract: The disclosure is directed to an improved method and apparatus for subsurface electromagnetic logging in a borehole wherein means are provided to detect transverse magnetic mode components and to either correct for these spurious components in the processing of the received signals or to generate suitable cancelling signals.

Abstract: A technique is described for producing an image log of an investigation of the wall of a borehole with a high resolution tool. The tool employs sensors for measuring a characteristic such as the conductivity of the wall at locations which circumferentially overlap. An accurate tool depth measuring device is employed to modify the measured characteristic so that the measurement can be displayed as a linear function of depth without visually detectable artifacts. Various signal processing and image enhancing techniques are described to produce an image log on which the characteristic can be seen as a variable intensity image in which small scale variations of the measured characteristic remain discernable and significant features visually stand out from the log.

Abstract: Diffraction tomography systems and methods are disclosed for the reconstruction of physical properties of two and three-dimensional objects from information collected in one or more diffraction tomographic procedures. A diffraction tomographic system is comprised of a continuous or pulsed source of wave energy, a detecting system for the measurement of the amplitude and/or phase of the scattered field resulting from the wave energy interacting with a two or three-dimensional object, a processing and filtering system for processing and filtering the measured signals according to a filtered backpropagation technique thereby generating arrays which are used to reconstruct the object properties, and a graphics display system for displaying obtained reconstructions. Specific embodiments include ultrasound transmission computed tomography; well-to-well electromagnetic and sonic tomography; subsurface electromagnetic or seismic exploration; and X-ray transmission tomography.

Abstract: A well logging apparatus and method is disclosed which can be used as a wireline logging device or technique, and is also suitable for being employed in a logging-while-drilling device. Electromagnetic energy having primarily a transverse magnetic mode component is guided along a tubular conductor in a borehole, and measurements of the transverse magnetic mode component can be used to obtain the conductivity and/or dielectric constant of formations surrounding the borehole.

Abstract: A method and apparatus for measuring an earth formation characteristic from inside a borehole penetrating earth formations is described. A tool carrying a sonic transmitter and an array of receivers is moved along the borehole and waveform signals from the receiver array are generated from repetetive operations of the transmitter. Sub-arrays of particularly related waveform signals relevant to a selected depth interval that is less in length than the aperture of the array are identified. Each sub-array of signals is then converted to a domain of signals composed of values of a coherence as a function of a range of values of a characteristic such as slowness. The converted signals are then combined so as to provide combined coherence values as a function of different values of the characteristic. One or several peaks of the combined coherence values are detected and determine the value of the characteristic for the selected depth interval. Similar processing is continued for other depth intervals.

Abstract: The disclosure is directed to an apparatus and method for subsurface electromagnetic logging in a borehole wherein means are provided to detect transverse magnetic mode components and to either correct for these spurious components in the processing of the received signals or to generate suitable cancelling signals.

Abstract: Pressure sensing diaphragms comprise a cylindrical or spherical crystalline member in which an internal cylindrical or spherical chamber is provided. In the internally loaded embodiments, a fluid is introduced into the chamber and the pressure exerted by the fluid causes generally tensile stress in the region of the diaphragm generally about the chamber. In the externally loaded embodiments, the diaphragm is immersed within the fluid and the pressure exerted by the fluid causes generally compressive stress in the region of the diaphragm generally about the chamber. For each of the embodiments, the stresses arising cause certain mechanical and electrical properties of the crystalline material to change. The change in these properties is detected by observing the frequency behavior of one or more oscillators whose frequencies of operation are controlled by respective surface acoustic wave devices provided in the regions of elastic deformation.

Abstract: Pressure sensing diaphragms comprise a cylindrical or spherical crystalline member in which an internal cylindrical or spherical chamber is provided. In the internally loaded embodiments, a fluid is introduced into the chamber and the pressure exerted by the fluid causes generally tensile stress in the region of the diaphragm generally about the chamber. In the externally loaded embodiments, the diaphragm is immersed within the fluid and the pressure exerted by the fluid causes generally compressive stress in the region of the diaphragm generally about the chamber. For each of the embodiments, the stresses arising cause certain mechanical and electrical properties of the crystalline material to change. The change in these properties is detected by observing the frequency behavior of one or more oscillators whose frequencies of operation are controlled by respective surface acoustic wave devices provided in the regions of elastic deformation.

Abstract: The disclosed invention is suited for use in conjunction with a borehole logging device wherein transmitting and receiving antenna coils are wound on insulating media around the axis of a support means that includes an elongated electrically conductive pipe. In accordance with the invention there is provided a shield for shielding each coil of the device, the shield being adapted to reduce spurious electromagnetic field components (especially transverse magnetic components) while not substantially interfering with the desirable transverse electric components. The shield for each coil comprises a hollow closed-end cylinder mounted on the pipe and surrounding the coil, the cylinder being formed of an electrically conductive material and having a series of equally spaced slots therein. Each slot extends radially outward from the support means along a plane which passes substantially through the axis of the pipe so as to pass through the ends and sides of the cylinder.

Abstract: Pressure sensing diaphragms comprise a cylindrical or spherical crystalline member in which an internal cylindrical or spherical chamber is provided. In the internally loaded embodiments, a fluid is introduced into the chamber and the pressure exerted by the fluid causes generally tensile stress in the region of the diaphragm generally about the chamber. In the externally loaded embodiments, the diaphragm is immersed within the fluid and the pressure exerted by the fluid causes generally compressive stress in the region of the diaphragm generally about the chamber. For each of the embodiments, the stresses arising cause certain mechanical and electrical properties of the crystalline material to change. The change in these properties is detected by observing the frequency behavior of one or more oscillators whose frequencies of operation are controlled by respective surface acoustic wave devices provided in the regions of elastic deformation.

Abstract: A seismic exploration method is disclosed for filtering the signals produced by a detector placed at different depths in a well in response to an emission of acoustic waves from a source on the surface: the signals comprising downgoing wave components and upgoing wave components.The filtering consists in sampling from among the N signals to be processed a group of n signals s.sub.1 . . . s.sub.n detected at respective levels x.sub.1 . . . x.sub.n, in determining the propagation time t.sub.k of the acoustic waves from the level x.sub.1 to each level x.sub.k, in both advancing and delaying the signals s.sub.k by the time t.sub.k in relation to s.sub.1, in adjusting the signals for the effects of the acoustic impedance of the formation, in combining s.sub.1 and the signals s.sub.k thus shifted and adjusted to obtain a sum z.sub.1 ', in calculating a sum y.sub.1 ' of s.sub.1 and of the thus delayed and adjusted signals s.sub.k, and in generating a signal u.sub.1.sup.

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: Methods and apparatuses for electrically investigating a borehole are described. Tool mounted pads are provided, each with a plurality of small measure electrodes from which individually measurable survey currents are injected toward the wall of the borehole. The measure electrodes are arranged in an array in which the measure electrodes are so placed at intervals along at least a circumferential direction (about the borehole axis) as to inject survey currents into the borehole wall segments which overlap with each other to a predetermined extent as the tool is moved along the borehole. The measure electrodes are made small to enable a detailed electrical investigation over a circumferentially contiguous segment of the borehole so as to obtain indications of the stratigraphy of the formation near the borehole wall as well as fractures and their orientations.

Abstract: Earth formations surrounding a well borehole are analyzed by obtaining a series of capture gamma ray spectra representative of the interaction of thermal neutrons with various chemical elements in the formation surrounding a borehole. The capture gamma ray spectra are used to determine spectral elemental yields quantitatively indicative of the relative abundance of various chemical elements present in the formation. These yields are recorded as a function of depth in said borehole to produce a plurality of traces. The relative sensitivities of the logging tool to a number of the formation components, such as sandstone and limestone, are predetermined either from tool responses in the borehole plus core measurements or from tool responses in a laboratory formation plus the known makeup of the laboratory formation.

Abstract: A gain stabilization loop for a gamma ray spectroscopy technique uses count rates from a pair of contiguous windows positioned on either side of at least one or more peaks of the detected spectrum. These count rates are combined to generate an error signal which minimizes the statistical errors. The stabilization loop modifies the response of the measurement apparatus so as to cancel the error signal.

Abstract: Method and apparatus for investigating earth formations according to the present invention include positioning an opening of a fluid reservoir in contact with the surface of an earth formation to be investigated and injecting the fluid at high pressures through the opening into the formation to cause a transient electrokinetic potential to form in the formation. The transient streaming potentials generated are detected by appropriate electrodes, and the outputs of the electrodes, representative of the generated potentials, are then processed to determine a characteristic response time of these streaming potentials. Thereafter, from a knowledge of the characteristic response time of the detected streaming potentials a measurement of the permeability of the formation is derived.

Abstract: A method for determining porosity or other formation characteristic of a sub-surface geological formation traversed by a borehole is claimed. A neutron logging tool is passed through the borehole while irradiating the formation with neutrons. The neutron logging tool includes a neutron source and first and second detectors spaced from the source by different distances. Neutrons exiting the formation are detected with the neutron detectors and count rate signals are generated. In response to these signals, an indication of porosity, substantially independent of error due to tool standoff from said borehole wall, is produced. In addition, values of tool standoff are also generated. These standoff values are then filtered by a filter to reduce statistical variations and are used to generate improved indications of porosity.

Abstract: Method and apparatus for determining the hydrogen and carbon densities of oil in situ in a subsurface geological formation are proposed which utilize the response of a neutron porosity tool to some oils. Apparent porosity derived from a neutron porosity investigation tool, which measures spatial neutron flux distribution, is compared to the porosity derived from a second investigating tool whose response is not or at least is less sensitive, say, to the hydrogen density of the formation fluid than is the neutron porosity tool. The magnitude of the difference is indicative of the hydrogen and carbon densities of the oil.