Abstract: The apparatus includes an array of azimuthal current electrodes (Aaz.sub.i) that are circumferentially spaced apart from one another on a body together with two annular guard electrodes (A2) disposed on opposite sides of the array of azimuthal current electrodes (Aaz.sub.i). Measurement currents (Iaz.sub.i) are emitted by the current electrodes (Aaz.sub.i) and focusing currents are emitted by the guard electrodes (A2). Azimuthal monitor electrodes (Maz.sub.i) are associated with respective ones of the azimuthal current electrodes (Aaz.sub.i). Two annular monitor electrodes (M3, M4) are disposed on opposite sides of the array of azimuthal current electrodes (Aaz.sub.i). For focusing purposes, a servo-control system controls the emission of the currents so as to substantially cancel the potential difference detected between the short circuited monitor electrodes (M3, M4) and each of the azimuthal monitor electrodes (Maz.sub.i). In response to the measurement currents (Iaz.sub.i), output signals (Raz.sub.

Abstract: Low and high frequency flexural waves or their equivalents are generated with dipole or other source transducers. From measurements made at receiving transducers which are oriented at two orthogonal directions in a horizontal plane normal to the borehole axis, and via known processing techniques, the received signals are transformed into arrivals as a function of frequency such that the principal polarization directions and the magnitudes of the maximum and minimum wave velocities at those directions are determined at different frequencies. If the maximum velocity of the relatively low frequency flexural waves are in a first principal polarization direction, and the maximum velocity of the relatively high frequency flexural waves are in a second principal polarization direction which is substantially normal to the first principal direction, uniaxial stress in the formation is attributed to stress induced azimuthal anisotropy as opposed to an instrinsic anistropy in the formation.

Abstract: The apparatus includes an annular current electrode (Ao) mounted on a body and guard electrodes (A2, A'2) disposed on the body above and below the annular current electrode. A first measurement current (Io) is emitted by the central current electrode (Ao) and focusing currents are emitted by the guard electrodes (A2, A'2). A first output signal representative of the deep resistivity of the formations is generated in response to the first measurement current (Io). One of the guard electrodes (A2) includes two longitudinally spaced-apart portions, and an array of azimuthal current electrodes (Aazi.sub.i) that are circumferentially spaced-apart from one another is disposed between these two portions. Second measurement currents (Aaz.sub.i) emitted by the azimuthal current electrodes (Aaz.sub.i) are focused longitudinally by the currents emitted by the said two portions of the guard electrode (A2). Second output signals are generated in response to the second measurement current (Iaz.sub.

Abstract: A gamma-gamma sonde for use in determining the bulk density of an earth formation adjacent a borehole comprises a source of gamma radiation and three attenuation-type gamma ray detectors DN, DI and DF spaced apart from the source, respectively, at successively greater distances. The count rate of each detector is converted into an apparent formation density .rho. based on data derived from calibration of the sonde in calibration media having known uniform density, thereby to obtain apparent formation densities .rho..sub.F, .rho..sub.I and .rho..sub.N. The ratio(.rho..sub.F -.rho..sub.I) to (.rho..sub.F -.rho..sub.N)is substantially independent of mudcake density and provides an estimate of the mudcake thickness. The calibration data involving mudcakes of known density and thickness enable the use of the mudcake thickness estimate to determine the value of k in the algorithm.rho..sub.apparent =.rho..sub.F +k(.rho..sub.F -.rho..sub.N),from which formation density is determined.

Abstract: An NMR pulse sequence for use in a borehole logging tool includes a series of CPMG pulses according to:T.sub.r -90.degree..sub..+-.x -(t.sub.cp -180.degree..sub.y -t.sub.cp -echo.sub.j)where j is the index of CPMG echoes gathered, T.sub.r is wait time, t.sub.cp is the Carr-Purcell spacing. This pulse sequence is used to determine Bound Fluid Volume (BFV) which is subtracted from total porosity to yield Unbound Fluid Volume (UFV) of a formation surrounding the borehole. Measuring the BVF, the amount of rapidly relaxing fluid (less than 50 ms), is more efficient than measuring UFV (up to 2 secs), and is insensitive to motion of the logging tool.

Abstract: The disclosure invention is directed to a nuclear magnetic resonance measurement apparatus that can be utilized in a logging device which operates generally centrally in a borehole, and has a generally circumferential region of investigation, but which permits usage of relatively powerful permanent magnets, such as rare-earth magnets, that are not permeable to the RF magnetic field. This is achieved by employing side-by-side spaced apart elongated magnets, and an RF current loop in the region between the magnets. In a disclosed embodiment, the magnets are each in the shape of a segment of a cylinder, and the respective axes of elongation of the magnets are parallel. The magnets have respective casings with electrically conductive surfaces, and the RF current loop includes at least a portion of the conductive surfaces of the magnet casings.

Abstract: A borehole logging tool comprises a Nuclear Magnetic Resonance (NMR) tool and is pulsed according to a selected sequence. An interpretation is performed which involves a singular value decomposition and compression of data obtained by the tool. The compressed data is then subjected to a nonegative, linear least square fit to obtain a distribution function. The distribution function is used in determining bound fluid volume, unbound fluid volume, total porosity, spin-lattice relaxation time, spin-spin relaxation time, and mean relaxation time using only the pulse NMR tool.

Abstract: A method of analyzing the flow in an inclined well, which flow comprises both oil and water is described. For a depth at which at least one flow parameter measurement is available, and given the inclination and the diameter of the well at that depth, the measured value is used to establish a profile for the variation of the flow parameter. The profile of the flow parameter is established along an axis defined by the diameter of the well cross-section that lies in a vertical plane using a model that assumes a layer comprising a turbulent mixture of water and oil.

Abstract: A method and apparatus for perforating a formation surrounding a wellbore and initiating and propagating a fracture in that formation to stimulate hydrocarbon production from the wellbore. The technique uses a perforation and propellant loading device which perforates and fractures in a single operation to greatly increase the efficiency over current perforation techniques. Efficiency is increased by a number of factors including firing the perforating shaped charge through a gas zone, reducing the overall perforation damage to the formation, increasing operation speed, and increasing pressure in the area of the borehole surrounding the production zone before perforation and propagation are initiated. In accordance with the invention, the timing of the propellant ignition and charge detonation are critical to achieve the desired results.

Abstract: Methods are provided for processing spectral data detected by a gamma ray detector of a borehole tool in order to obtain quantitative determinations of formation and/or borehole properties. According to one invention aspect, spectral data are compressed using a principal components technique in order to find principal component coefficients. Those coefficients are supplied to an inverse filter which processes the data by inverting, deconvoluting, and filtering the data to provide determinations of formation properties such as formation density, Pe, and borehole parameters such as the mudcake thickness times the difference of the densities between the formation and mudcake. The principal components for which coefficients are found, as well as the inverse filter are generated from a calibration database. Prior information on noise and formation and/or borehole parameters are also utilized in forming the inverse filter.

Abstract: A form of the disclosure is directed to determining properties of formations surrounding an earth borehole having a standoff layer. A method is disclosed for determining the conductivity and permittivity of the standoff layer and the conductivity and permittivity of the formations adjacent the standoff layer. A further form of the disclosure is directed to an electromagnetic logging apparatus having transmitting and receiving antennas in RTTR, RRTTRR or TTRRTT arrangements.

Abstract: The invention relates to a logging method and apparatus using passive azimuthal electrodes. The apparatus includes an array of azimuthal electrodes (M'az.sub.i) that are circumferentially spaced apart from one another on a body together with two annular guard electrodes (A2) disposed on either side of the array of azimuthal electrodes (M'az.sub.i). The guard electrodes (A2) emit currents. Two annular monitor electrodes (M3, M4) are associated with the annular guard electrodes (A2). The potential difference (.DELTA.Vaz.sub.i) between the interconnected monitor electrodes (M3, M4) and each of the azimuthal electrodes (M'az.sub.i) are detected. In response to the detected potential differences, output signals (R'az.sub.i) representative of the resistivity of the formations in a plurality of directions around the axis of the borehole are generated.

Abstract: A borehole tool having adjacently located fluid injection/withdrawal apparatus and an electromagnetic measurement apparatus is provided. The electromagnetic measurement apparatus can be an imaging apparatus for helping set the tool in desired locations for permeability testing via fluid injection or withdrawal. In a second mode, during fluid injection or withdrawal, and if desired, before and/or after injection or withdrawal, a plurality of electromagnetic measurements (images) are made. Based on the electromagnetic and hydraulic measurements, and a model which interrelates the measurements, determinations are made as to various characteristics of the formation, including effective permeabilities. Related methods for utilizing the tool and for treating the data in an integrated fashion are also set forth.

Abstract: A new technique, called the sensitivity function technique, has been developed for modeling nuclear density tools. Specifically, sensitivity functions relate a change in formation properties to a change in detector response and are based on the first order perturbation expansion of the radiation transport equation. The sensitivity function is a quasi-linear model which works extremely well over a wide range of mudcake and formation conditions, as shown by extensive benchmark comparisons against actual tool measurements. The detector responses are calculated by a convolution of density sensitivity functions, calculated in a separate set of Monte Carlo computer runs, with the formation properties and is extremely fast. Because this technique is both fast and accurate, it represents a significant advance in the ability to model gamma-gamma density tools and will allow the use of fast forward modeling to improve the log interpretation process.

Abstract: The present invention offers methods and apparatus for low-frequency sonic borehole logging with tube waves using discrete frequency measurements. A source transducer emits sonic energy at a location in a borehole of at least one discrete frequency which induces propagation of tube waves in the borehole; sonic energy of the tube waves is received at multiple receiver locations in the borehole, the multiple receiver locations being spaced apart from one another and from the source transducer location; and at each said receiver location, the complex pressure response (amplitude and phase, or real and imaginary parts) of a receiver to the received sonic energy of the tube waves is detected relative to a phase reference.

Abstract: Methods for quantifying the oil and water fractions of a fluid stream. A first method broadly includes making optical density (OD) measurements of the fluid stream by detecting photons of a first predetermined energy where the oil and water absorption characteristics are substantially identical (e.g., 1710 nm wavelength), and determining the oil and water fractions f.sub.o and f.sub.w according to OD.perspectiveto.f.sub.w .alpha..sub.w l+f.sub.o .alpha..sub.o l where .alpha..sub.w and .alpha..sub.o are related to the absorption coefficients of the oil and water at the predetermined energy, l is the path width of the fluid stream, and f.sub.w +f.sub.o =1. A second method which eliminates scattering effects utilizes the photons at the first predetermined energy and further utilizes photons of a second predetermined energy which is sufficiently close to the first predetermined energy such that the oil fraction is a linear function of the OD over the energy range.

Abstract: A particle accelerator comprises 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: An apparatus for reducing or eliminating the effects of a quadrupole component of an acoustic signal received from a transversely mounted acoustic source in a drill collar of a logging while drilling tool. The apparatus includes a drill collar for supporting a drill bit, a transversely mounted transmitter situated in a first horizontal plane in the drill collar which transmits acoustic energy into an earth formation. The drill collar also houses at least one receiver mounted in a second horizontal plane in the drill collar at an angular displacement from the transmitter such that the effects of a quadrupole component of the acoustic energy detected by the receiver are rendered insignificant.

Abstract: A neutron generator, comprising:(i) an ion source comprising an anode and a thermionic cathode disposed in an ionizable gas environment (e.g. hydrogen isotope);(ii) means for heating the cathode so that the latter emits electrons which, when colliding with the gas atoms, generate ions;(iii) a target;(iv) an electrical gap to accelerate ions from the ion source towards the target upon impingement of the ions; and(v) control means for applying voltages to the anode, cathode and electrical gap.The cathode is of the dispenser type or volume type, and preferably comprises one block of material comprised of a substrate impregnated with an electron emitting material.

Abstract: Methods are provided for processing spectral data detected by a gamma ray detector of a borehole tool in order to obtain quantitative determinations of formation and/or borehole properties. According to one invention aspect, spectral data are compressed using a principal components technique in order to find principal component coefficients. Those coefficients are supplied to an inverse filter which processes the data by inverting, deconvoluting, and filtering the data to provide determinations of formation properties such as formation density, Pe, and borehole parameters such as the mudcake thickness times the difference of the densities between the formation and mudcake. The principal components for which coefficients are found, as well as the inverse filter are generated from a calibration database. Prior information on noise and formation and/or borehole parameters are also utilized in forming the inverse filter.