Abstract: A current measurement circuit comprising a mutual inductance transformer 3, an integration circuit 2, and a dither circuit 1 which adds a square wave to the signal from the transformer 3 before the input of the integration circuit 2 in order that the integration circuit 2 provides a signal representing the measured current perturbed by a triangular dither signal.

Abstract: A gas meter installation comprises a gas meter and a regulator which are attached to a manifold. The manifold connects to a utility pipe for supplying gas and includes an orifice and various passageways for routing the gas from the utility pipe to the regulator, from the regulator to the meter, and from the meter to a house or other type of consumer. The manifold preferably has a shut-off valve integrated into the body of the manifold so that the manifold may be connected directly to the ground pipe without requiring a separate connection to a shut-off valve. The manifold greatly simplifies the installation by eliminating a number of pipes and fittings that were previously used to mount the shut-off valve, regulator, and meter together. The manifold also permits attachment and detachment of the meter or regulator independently of each other so that these components may be individually serviced or replaced.

Abstract: The invention relates to a method of determining the resistivity of a geological formation through which a metal-cased borehole passes, by means of at least three electrodes in contact with the casing and spaced apart in the longitudinal direction of the borehole. In order to eliminate the effect of any differences between the two sections of casing delimited by the electrodes, a circuit connected to the electrodes and forming a Wheatstone bridge is balanced, with said sections of casing constituting two of the resistances in said Wheatstone bridge circuit.

Abstract: The instruments of a pulsed nuclear magnetic resonance (NMR) device are included in a drill collar for evaluating earth formations. The resulting tool makes NMR measurements while the formation is being drilled.

Abstract: A method of logging an underground formation from within a borehole includes the steps of emitting an electromagnetic signal from a first location in a borehole, determining a time at which the signal is emitted, detecting a direct component of the signal which has passed from the first location to a second location without being reflected, determining a time at which the direct component arrives at the second location and determining the speed of the signal in the underground formation from the time at which the signal is emitted, the time of arrival of the direct component and the spacing of the first and second locations. The speed of the signal can be used for radar logging of the formation.

Abstract: An overbalance technique propagates a fracture in a formation to stimulate hydrocarbon production from a wellbore. A liquid column in the wellbore is driven into the formation by a gas generator to propagate the fracture. The gas generator can be compressed gas or propellant which is placed within the wellbore near or in the liquid column. Preferably the gas generator is placed in the wellbore above the production zone. The gas generator can be conveyed via tubing, wireline, or coiled tubing. Typically the liquid is brine, water or oil. The liquid can be a resin to consolidate a weak formation, sand and gel to prop a fracture, or acid to etch a fracture face. The overbalance technique has applications to cased and openhole wellbores. In cased wellbores, the technique can be performed as the casing is perforated or after the casing is perforated.

Abstract: There is provided a rheometer, comprising a cup for a fluid to be measured, a concentric rotor and stator arrangement, and a circuit for circulating the fluid which includes a pump for providing in pulsatile, non-laminar flow in the cup. By using the pump to provide both a turbulent and pulsating flow, particulate matter can be maintained in suspension and flow induced through the measuring system while any rheology effect the pumping system has on the fluid is introduced independently of rheology effects caused by the measuring system itself. Thus the pumping can be continued while the measurement is being made.

Abstract: Borehole tools are provided with at least one transmitter which generates acoustic waves at a plurality of azimuthal locations about the borehole, and at least one receiver which receives and measures a characteristic (e.g., velocity) of the acoustic waves at related azimuthal locations. The direction of minimum velocity around the borehole is considered the direction of maximum uniaxial stress in the formation. From the velocity as a function of azimuth information, determinations of formation properties, and logs of the same can be made. The azimuthal direction of minimum velocity around the borehole predicts the propagation direction of artifically induced hydrofractures. The velocity variation around the borehole at a particular depth of the borehole is taken as an indication of susceptibility to failure, with higher velocity variations indicative of a more poorly consolidated formation or a formation with a large uniaxial stress.

Abstract: A method of measuring flow velocities in flowing fluids includes injecting into the flow a non-radioactive tracer having a neutron capture cross section higher than that of the flowing fluids, for example a gadolinium compound, and measuring the neutron capture cross section in the fluid downstream of the injection point to detect the passage of the tracer and hence determine the time of flight. By making the tracer miscible with only one phase (typically the continuous phase) of a multi-phase fluid, it is possible to measure the flow velocity of that phase. The neutron capture cross section can be measured by irradiating with neutrons from a pulsed neutron generator and measuring capture .gamma. rays with a scintillation detector.

Abstract: Measurement-while-drilling apparatus includes a 14 MeV neutron accelerator, a near-spaced neutron detector which primarily senses source neutrons and whose output is proportional to source strength, one or more intermediately-spaced epithermal neutron detectors eccentered against the drill collar wall and primarily responsive to formation hydrogen concentration, and a third far-spaced radiation detector, either gamma ray or neutron, primarily responsive to formation density. The intermediately-spaced and far-spaced detector outputs, normalized by the near-spaced detector output, are combined to provide measurements of porosity, density and lithology and to detect gas. A thermal neutron detector and/or a gamma ray detector may also be provided at intermediate spacings to provide additional information of interest, such as standoff measurements and spectral analysis of formation composition. Tool outputs are related to the angular or azimuthal orientation of the measurement apparatus in the borehole.

Abstract: A method of determining a characteristic of an underground formation including the steps of irradiating the formation with high energy neutrons and detecting neutrons scattered by the formation having energies above epithermal to determine the nature of the formation matrix. Epithermal neutrons can also be detected to determine formation porosity. Apparatus includes a high energy neutron source, typically a D-T accelerator producing 14 MeV neutrons, and detectors such as .sup.4 He filled proportional counters for detecting neutrons having energies above epithermal and .sup.3 He filled proportional counters for detecting epithermal neutrons.

Abstract: A borehole logging tool such as a wireline logging tool or a logging-while drilling tool includes a tool body; a transmitting antenna located in the body; a pulser for causing the transmitting antenna to transmit an electromagnetic signal; a receiving antenna, located in the body, which includes an array of receiver elements disposed around the longitudinal axis of the tool body; and electronics for measuring the difference in signals detected by pairs of elements in the array. The receiver elements can be linear dipole elements and the electronics for analyzing the signals measures the difference in signals measured by pairs of elements so as to determine the direction of a reflecting structure from the tool.

Abstract: The invention concern a combination well logging device adapted to be moved inside a borehole to measure the properties of geological formations through which the borehole passes.The device according to the invention comprises a series of elongate logging sections mounted end to end, including a first section adapted to be maintained with a generatrix applied against the wall of the borehole, a second section comprising a body and a measurement pad adapted to be spaced radially from the body for application against said wall, a third section adapted to be kept space from said wall, and first and second hinges connecting the second section to the first and third sections respectively in order to allow respective angles of inclination between the second section and the first and third sections.

Abstract: A gamma ray or x-ray detector for borehole use includes a cadmium zinc telluride crystal having the general formula CD.sub.1-x Zn.sub.x Te, where x represents the zinc fraction of the material and preferably is within the range of 0.05.ltoreq.x.ltoreq.0.95. The noise edge and energy resolution characteristics of the detector may be improved by surface treating the crystal to reduce leakage current. The detector has particular application to bulk density and photoelectric absorption factor logging.

Abstract: A method of determining a physical parameter of geological formations having a borehole passing therethrough by using a sonde lowered down the borehole at the end of a cable and including a source of gamma radiation, a very near detector, a near detector, and a far detector, the method being characterized in that: for each energy window, a model is created characteristic of the response of each detector; a "low resolution" value of the looked-for parameter is determined which, when applied to the model, gives rise to a theoretical measurement that is substantially equal to the "low resolution" real measurement obtained by combining the measurements from all three detectors; the measurements from the two detectors nearest the source are combined to constitute a "high resolution" real measurement; and a "high resolution" value of the parameter is determined which, when applied to the model, gives rise to a theoretical value that is substantially equal to the "high resolution" real measurement, the determination

Abstract: A borehole logging tool includes a particle accelerator including a Cockcroft-Walton voltage multiplier that provides linear axial and radial fields. The Cockcroft-Walton voltage multiplier includes capacitors that are arranged radially relative to one another, such that a linear voltage increase occurs between the capacitors. The particle accelerator is made by placing conductive foils on an insulating sheet, connecting the foils as a Cockcroft-Walton voltage multiplier, and rolling the insulating sheet with the foils into a cylinder to form the radially arranged capacitors.

Abstract: A Cockcroft-Walton (CW) multiplying circuit is mounted to wrap around a cylindrical structure. A photomultiplier tube (PMT) has a photocathode which emits electrons and has dynodes connected to the CW multiplying circuit. The dynodes are biased to attract electrons from the photocathode. An electrical shield surrounds the PMT and the PMT nests within the shield. The cylindrical structure surrounds the shield and the shield nests within the cylindrical structure. The shield is a conductive material which electrically isolates the PMT from the CW multiplying circuit.

Abstract: A method of determining a depth correction for a logging tool that is moved, while suspended from a cable, along a well, the method being of the type in which a measurement of tool depth is performed at the surface at successive instants, the tool comprising at least two sensors suitable for measuring a characteristic of the well at each instant said two sensors being offset longitudinally in the displacement direction of the tool. The method comprises, at each of said instants:determining a first value for tool velocity by intrinsic measurement;determining a second value of the velocity by correlation between information received from the two sensors; andcombining the first and second velocity values to determine a depth correction to be applied to the surface depth measurement.

Abstract: Apparatus and methods for determining an indication of a nonlinear property of a formation traversed by a borehole are provided. An acoustic tool is used in a borehole to generate first and second signals of different frequencies. As a result of nonlinearities in the formation, the mixing of the first and second signals results in a third signal having a frequency equal to the difference of the frequencies of the first and second signals. The amplitude of the third signal is measured by a detector, and the indication of nonlinearity of the formation is determined according to a relationship which relates the measured amplitude at the measured frequency to the amplitudes of the first and second signals, the frequency of measurement, the velocity of the measured wave, the distance of the receiver from the source, and a function of the nonlinear and linear parameters of the formation.

Abstract: A method for determining the porosity of an underground formation includes the steps of irradiating the formation with neutrons, detecting and measuring gamma rays resulting from irradiation of the formation, discriminating between gamma rays from the formation and gamma rays from the tool, and using a measurement of the gamma rays from the tool to determine the formation porosity. A suitable logging tool includes a neutron source, a gamma ray detector, means for discriminating between gamma rays from the formation and gamma rays from the tool, and means for relating the gamma rays from the tool to the formation porosity.