Abstract: A method and apparatus are described for detecting the presence of an anomaly, such as the Groningen effect, whereby an error in a resistivity measurement of an earth formation layer is noted when such layer is located below a highly resistive bed. The resistivity is measured with a resistivity measuring sonde with the aid of a reference electrode located between the sonde and a conductive sheath around the cable from which the sonde is suspended in a borehole. A phase sensitive signal is measured and used to detect the presence of an error. In one embodiment, the out-of-phase potential of an electrode is recorded alongside a resistivity measurement as a function of depth. In another embodiment, the out-of-phase potential deviation from a normal value is determined and used to derive a corresponding in-phase potential deviation from which a measurement of the magnitude of the error in the resistivity measurement is made. Other embodiments are shown and described.

Abstract: An induction well logging apparatus and method is disclosed for determining dip and/or anisotropy parameters of formations surrounding a borehole. A transmitter is provided and includes a first transmitter coil having an axis which is substantially parallel to the borehole axis and a second transmitter coil having an axis which is substantially perpendicular to the borehole axis. A receiver is provided and includes first and second receiver coils having axes which are substantially mutually orthogonal. Each of the receiver coils is substantially perpendicular to the borehole axis. The transmitter and receiver are mounted in a mechanically passive manner on a support member adapted for movement through the borehole. The transmitter coils are energized in a manner which permits the separate detection at the receivers of the currents induced in the formations by each of the two transmitter coils.

Abstract: The invention is directed to induction logging apparatus and method for obtaining measurements dependent upon the vertical conductivity component of formations surrounding a borehole. The disclosed techniques can also be used to determine horizontal as well as vertical conductivity of the formations, and thereby achieve determination of formation anisotropy. A transmitter coil is provided with its axis substantially perpendicular to the borehole axis. A receiver coil is provided in spaced relation to the transmitter coil. The axis of the receiver coil is also substantially perpendicular to the borehole axis, and is preferably parallel to the axis of the transmitter coil. Means are provided for detecting signals induced in the receiver coil, these signals being a measure of the formation vertical conductivity. In a preferred embodiment of the invention, the detecting means is operative to detect both the resistive and reactive components of the signals induced in the receiver coils.

Abstract: A percussion technique is described with which an impulse is applied to an element to bounce it off the inner surface of a casing cemented in a borehole. The movement of the element is automatically measured to produce information from which the bond between the casing and cement behind the point of impact of the element can be evaluated. In accordance with one embodiment, the cement bond evaluation is automatically derived by comparing impact and rebound velocities of the element such as by generating a coefficient of restitution of the bouncing element. In another embodiment, the contact time of the element with the casing is measured to derive an indication of the quality of the cement bond.

Abstract: Methods and apparatuses for acoustically investigating a casing in a borehole to derive the quality of a cement bond behind the casing and casing thickness are described. The techniques employ an acoustic pulse source having a frequency spectrum selected to stimulate a selected radial segment of the casing into a thickness resonance. The selected frequency spectrum enhances the reverberations between the inner and outer walls of the casing which traps the thickness reverberations with significant amplitudes for a duration depending upon the amount of acoustic energy leaked into adjacent media. The acoustic pulse causes acoustic returns which are formed by the reflections from interfaces between media of different acoustic impedances and acoustic energy leaked into the bore of the casing from the acoustic thickness reverberations stimulated within the casing walls. The acoustic returns are detected to generate a reflection signal which is processed to determine casing thickness or to evaluate the cement bond.

Abstract: The determination of a "composite" parameter of the formation water in formations surrounding a borehole, for example the composite conductivity of the formation water, is used in the disclosure to obtain a relatively accurate determination of formation characteristics, such as water saturation. The determined values are meaningful even in shaly regions of the formations. In contrast to past approaches which attempted to determine the volume and distribution type of shale or clay present in the formations and then introduce appropriate factors which often involve substantial guesswork, the disclosed technique determines a composite water parameter, for example a composite water conductivity, which represents the conductivity of the bulk water in the formations, including both free water and bound water. Bound water trapped in shales is accounted for in this determination so unlike prior techniques, the shales can be considered as having a porosity.

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.

Abstract: A predetermined signal is removed from waveforms generated in an acoustic investigation of a borehole to enable the accurate detection of relatively weak formation signals. A plurality of waveforms are produced from different sonic receivers used in an acoustic investigation of an earth formation from inside casing set in a borehole. The waveforms include a casing signal which is representative of the acoustic casing wave which traveled from a transmitter through the casing to the receivers. The casing signal is removed by aligning the waveforms in accordance with the known travel times for the casing wave from the transmitter to the receivers and summing the waveforms to produce a casing signal emphasized waveform. A portion of the latter is then subtracted from the waveforms from which the casing signal is thus effectively filtered to facilitate detection and analysis of formation signals present in the waveforms.

Abstract: A method and apparatus are described for detecting an acoustic wave in a waveform produced from a sonic receiver in response to an acoustic investigation of a borehole. The maximum amplitude of the waveform is measured and a portion thereof utilized as a threshold for comparison with successively different combinations of initial portions of the waveform and the waveform location, where the threshold is exceeded, is identified as the location of the wave. A pattern comparison is made between waveform segments where the acoustic wave is initially located to provide a correction factor for a more accurate locating of the acoustic wave. A parameter of the wave, such as its interval travel time is measured with the acoustic wave locating techniques.

Abstract: At least four waveforms representative of sonic waves obtained from an acoustic investigation of a borehole with at least four sonic receivers are combined to automatically measure a parameter of a wave present in the waveforms. The waveforms are derived from sonic receivers which are selectively spaced from each other as well as the sonic transmitter whose sonic pulses caused the sonic waves. Several techniques are described to measure acoustic wave parameters such as the interval travel time of compressional and shear waves for open or cased boreholes. In accordance with one technique a multiple fold correlation process and apparatus are described to measure the acoustic wave parameter.

Abstract: The disclosure is directed to an apparatus and method for determining dielectric constant and/or conductivity of earth formations surrounding a borehole. Electromagnetic energy is generated at a first location in the borehole. The relative attenuation of the electromagnetic energy is detected at a second location in the borehole. The detection is preferably performed using a first or "close" differential receiver arrangement. The relative phase of the electromagnetic energy is detected at a third location in the borehole, the third location being spaced farther from the first location than is the second location; in other words, the second location is between the first and third locations. The relative phase shift of the electromagnetic energy is measured by a second or "far" differential receiver arrangement located at the third location in the borehole.

Abstract: A depth measurement system produces independent signals, each presumably corresponding to the same movement of a wireline if produced under ideal wireline measurement conditions. The system utilizes the signals to provide an accurate and repeatable signal under varying wireline measurement conditions and is particularly suitable for driving a recorder for depth recording and merging measurements from tools lowered in the borehole on different runs and to detect slippage between the wireline and a tangential wheel used to provide one of the signals. Slidably mounted measurement wheels insure tangential engagement of opposite sides of the wireline with equal pressure. Low-load signal generators each responsive to the rotation of the opposing wheels provide independent signals, each ideally corresponding to the movement of the wirline engaged between them. Magnetic marks written on the wireline are sensed and provide yet another independent signal.

Abstract: The disclosure is directed to an apparatus and method for determining the water-filled porosity of formations surrounding a borehole. Alternatively, where porosity is known from other logging information, the disclosed techniques can be utilized for determining the conductivity of the water in formations surrounding a borehole or for determining water saturation. The formations are assumed to comprise a matrix, which may be any subsurface solid material, and fluids contained in the matrix, such as in pore spaces or interstices therein. In accordance with one embodiment, means are provided for deriving a first quantity which is representative of the attenuation of microwave electromagnetic energy propagating between spaced locations in the borehole, the first quantity being, for example, the attenuation constant, .alpha..

Abstract: The disclosure is directed to an apparatus and method for determining the bound-water-filled porosity of formations surrounding a borehole. Bound-water-filled porosity is the fraction of the formation unit volume (matrix plus fluid) which is occupied by bound water, bound water being the portion of the total water which is adsorbed or bound to, or impermeably held by, the matrix. In one embodiment, means are provided for deriving a first quantity which is a measure of the attenuation of microwave electromagnetic energy passed through the formations of interest. This first quantity may be, for example, the attenuation constant determined for the microwave electromagnetic energy passing through the formations. Means are provided for generating a second quantity which is substantially proportional to the square of the first quantity. The second quantity is indicative of the bound-water-filled porosity of the formations.

Abstract: An apparatus and method for determining the amount of adsorbed fluid in formations surrounding a borehole. In accordance with the present invention, means are provided for deriving a first quantity which is a function of the dielectric constant of the formations as measured by passing electromagnetic energy of a first frequency through the formations. Means are also provided for deriving a second quantity which is a function of the dielectric constant of the formations as measured by passing electromagnetic energy of a second frequency through the formations. Finally, means are provided for determining the amount of adsorbed fluid in the formations as a function of the difference between the first and second quantities.

Abstract: A depth measurement system particularly suitable for automatically driving a recorder under varying wireline measurement conditions for repeatedly depth recording measurements from borehole tools produces different measurements at generally the same point on the wireline which would correspond if measurement conditions were ideal, but are subject to non-repeatable variations. Accordingly, these signals are automatically utilized to provide a repeatable signal. In one form, the signals correspond to magnetic marks and to incremental movement of the wireline, the latter produced by mechanically coupled devices subject to slippage, variations in circumference, etc. The incremental signals are counted and compared with the number expected for such intervals, a low count indicating slippage or the like and used to provide an appropriate alarm and/or an automatically slippage corrected signal particularly suitable for driving a recorder.

Abstract: Illustrative embodiments of the present invention include methods and apparatus for producing indications of the presence of hydrocarbons in subsurface earth formations. In one embodiment, two different pore volume indications are derived and comparably displayed. The first is primarily dependent upon the hydrogen content of the fluid in the pore space of the formation and may be derived from count rate ratios obtained between two epithermal neutron responsive detectors differently spaced from a neutron source. If thermal neutron or neutron captured gamma ray responsive detectors are used, compensation is provided for thermal neutron absorption effects. The second pore volume indication is produced directly from a measurement of the thermal neutron absorption characteristic of the formation and a value for the water component of the formation.

Abstract: An apparatus and method for determining the amount of adsorbed fluid in formations surrounding a borehole. In accordance with the present invention, means are provided for deriving a first quantity which is a function of the dielectric loss factor of the formations as measured by passing electromagnetic energy of a first frequency through the formations. Means are also provided for deriving a second quantity which is a function of the dielectric loss factor of the formations as measured by passing electromagnetic energy of a second frequency through the formations. Finally, means are provided for determining the amount of adsorbed fluid in the formations as a function of the difference between the first and second quantities.

Abstract: A method and apparatus for investigating earth formations surrounding a borehole by injecting microwave electromagnetic energy into the formations and then taking measurements which relate to the propagation of such energy in the formations. In the preferred form of the invention, the injected microwave energy establishes a lateral wave which travels in the formations adjacent the interface between the mudcake and the formations. Energy signals from the lateral wave are received at first and second receiving locations. The phase difference between signals received at the first and second receiving locations is measured. Also measured is the relative attenuation as between signals received at the two receiving locations. The loss-corrected dielectric constant associated with the formations surrounding the area between the first and second receiving locations is then obtained by judiciously combining the phase and attenuation measurements.

Abstract: A technique for determining the density of an earth formation with a logging sonde including a gamma ray source and two gamma ray detectors spaced at different distances from the source is disclosed. The count rate of the short-spaced detector is measured in two energy ranges covering back-scattered gamma rays which have undergone relatively low and high attenuations respectively. A first density correction is determined from the difference between the apparent density derived from the count rate of the long-spaced detector and the density derived from the count rate of the short-spaced detector in the energy range covering gamma rays with relatively low attenuation. A second density correction is determined from the difference between the densities derived from the two short-spaced detectors' count rates. These two density corrections are added to the apparent density to give the true formation density.