Abstract: An apparatus for measuring the resistivity of earth formations penetrated by a wellbore having a conductive conduit. The apparatus includes an elongated sonde mandrel, a plurality of electrodes positioned at axially spaced apart locations along the mandrel, the electrodes being electrically insulated from the mandrel and from each other, the electrodes adapted to electrically contact the conduit and positioned collinearly so that the electrodes contact the conduit when the mandrel is radially displaced towards the wall of the conduit. Some electrodes are for injecting electrical current into the conduit, other electrodes are for measuring voltage drop along the conduit at axially spaced apart locations. The mandrel includes selectively extensible locking arms for urging the mandrel into contact with the conduit. The arms are radially positioned opposite to the electrodes.

Abstract: A method of correcting receiver signals in an induction well logging instrument for skin effect. The method includes determining a magnitude of signals induced in an induction receiver at each one of a plurality of different frequencies, determining a relationship of the magnitudes with respect to frequency, and determining a skin effect corrected conductivity by determining a value of the relationship which would obtain when the frequency is equal to zero. In a preferred embodiment, the step of determining the relationship includes calculating a best fit curve of the magnitudes with respect to the frequency, calculating the first derivative of the best fit curve with respect to the frequency, and calculating a correction for the signals at a selected frequency according to the relationship of the first derivative with respect to the frequency. The correction is applied to the signal at the selected frequency to calculate a skin effect corrected signal.

Abstract: A method of measuring the density of an earth formation penetrated by a wellbore. The method includes irradiating the earth formation with gamma rays from a source, detecting Compton scattered gamma rays at a plurality of locations spaced apart from the source along the wellbore, calculating an apparent density of the formation from the detected gamma counting rate at each of the locations, calculating differences in apparent density between pairs of the apparent densities, calculating a correction for the apparent density from a distal one of the locations by scaling the differences in apparent density according to an empirical relationship, and calculating the density by combining the correction with the apparent density from the distal one of the locations.

Abstract: A liner for a shaped charge formed from a mixture of powdered tungsten and powdered metal binder. The liner is formed by compression of the mixture into a substantially conically shaped solid body. In a preferred embodiment of the invention, the mixture comprises a range of approximately 70 to 90 percent by weight of tungsten and 30 to 10 percent of the powdered metal binder. In a specific embodiment of the invention, graphite powder is intermixed with the powdered metal binder and tungsten to act as a lubricant. The powdered metal binder preferably comprises a malleable, ductile metal such as lead, bismuth, tin, zinc, silver, antimony, cobalt, nickel or uranium.

Abstract: A method for detecting alteration of earth formations penetrated by a wellbore. The method includes determining a first arrival velocity of dipole acoustic energy propagated through the earth formations. A first frequency dependent velocity of the dipole acoustic energy is then determined. A first dispersion characteristic is determined from the difference between the first arrival and frequency dependent velocities. The method includes determining a frequency dependent velocity and a first arrival velocity for synthesized waveforms for an unaltered formation. The synthesis uses the first arrival velocity of the dipole acoustic energy as a shear velocity. A second dispersion characteristic, related to a difference between the frequency dependent velocity and the first arrival velocity of the synthesized waveforms is determined. The alteration is detected by finding a difference between the first dispersion characteristic and the second dispersion characteristic.

Abstract: A method for logging a subterranean formation from within a well that has been cased and cemented is disclosed. An acoustic signal is transmitted into the formation from a pulse-echo transducer placed within the wellbore and the first casing echo and the first formation echo are detected. The amplitude and the arrival times of these two echoes, combined with some known information about the wellbore, the casing, and the cement enable several parameters to be calculated. These parameters in turn may be used to image the formation around the well.

Abstract: A method for using geometrical data to determine characteristics of a wellbore penetrating a subterranean formation is disclosed. The method involves converting data obtained form acoustic well logging into cartesian coordinates and solving a general quadratic equation by a least squares fit to an elliptical or circular model. More specific information, such as tensor strain and formation compaction along the wellbore may then be obtained from the geometrical data.

Abstract: A method of determining an amount of dissolved gas in a fluid sample is disclosed. The method includes hydraulically confining and expanding the sample while measuring pressure and volume. A first volume and pressure are determined at which the rate of change in pressure with respect to volume deviates from a linear relationship. A second volume and pressure at which continued expansion of the fluid causes substantially no change in pressure is determined. The first pressure and volume are extrapolated by the linear relationship to intersect an extrapolation from the second volume and pressure at no change in pressure, thereby determining a bubble point comprising a bubble point pressure and a bubble point volume. A third pressure corresponding to measured pressure of the fluid sample at the bubble point volume is determined.

Abstract: A method of determining volumetric flow rates of gas and liquid in a highly inclined conduit. The method includes measuring the velocity the gas, measuring the velocity of the liquid, calculating a fractional amount of the cross-sectional area of the conduit occupied by the gas and occupied by the liquid, and calculating the volumetric flow rates from the measurements of velocity and from the calculated fractional amounts of the cross-sectional area of the conduit occupied by the gas and by the liquid. In a preferred embodiment, the gas velocity is measured by cross-correlating measurements of two spaced apart temperature sensors after momentarily heating the gas. In the preferred embodiment, the liquid velocity is measured by a spinner flowmeter.

Abstract: An apparatus for imaging the thermal properties of fluids in a wellbore. The apparatus includes a tool mandrel adapted to traverse the wellbore. The apparatus includes temperature sensors positioned at spaced apart locations along radially extendible arms attached to the mandrel. A temperature measuring circuit connected to each one of the sensors. The apparatus includes a circuit for applying a momentary current pulse to each of the temperature sensors, for momentarily raising their temperatures. Momentary increases in the sensor temperatures are provided so that the thermal transient response of the fluid in contact with each sensor can be determined. The invention includes a method of determining the flow regime of the fluid flowing in the wellbore. The method includes the steps of measuring the temperature of fluids in the wellbore at spaced apart locations within the cross-sectional area of the wellbore, using a tool having temperature sensors positioned at spaced apart locations.

Abstract: A method for determining orientation of an instrument with respect to earth's gravity. The method includes measuring components of earth's gravity along mutually orthogonal axes. One of the axes is substantially parallel to an axis of the instrument. Tilt of the instrument along two orthogonal axes is measured. One of the tilt axes is substantially parallel to the instrument axis. The instrument is rotated about its axis, and biases of the sensors used to measure the components of earth's gravity perpendicular to the instrument axis are calculated by averaging measurements made by these sensors during rotation. The ratio of gains of these sensors is determined from the range of amplitudes of the output of these sensors during rotation. A roll angle is determined from the bias corrected measurements of components of the earth's gravity perpendicular to the axis. The tilt measurement with respect to the two orthogonal axes is then calibrated by using the calculated roll angle.

Abstract: The present invention is a method of processing digitized signal samples generated by a free running analog-to-digital converter and sampled at a first sample rate. The method includes the steps of convolving the digitized signal samples with a single-stage digital filter and generating a series of resampled signal samples having a second sample rate no greater than the first sample rate. The resampled signal samples are synchronized with a predetermined time reference during the step of generating the series of resampled signal samples.The present invention is also an apparatus for recording seismic surveys.

Abstract: An apparatus for calibrating phase response of a receiver in an induction well logging instrument. The apparatus includes a source of alternating current selectively coupled to a transmitter. A low-gain antenna is disposed proximal to the transmitter for generating voltage in response to a magnetic field generated by the alternating current in the transmitter. The instrument includes a receiver spaced apart from transmitter. A phase comparator is coupled at one input to the low-gain antenna and at its other input to the source of alternating current. The phase comparator generates a signal corresponding to phase difference between the voltage in the low-gain antenna, and the alternating current. A sample and hold circuit is coupled to phase comparator for retaining the most recent signal from the phase comparator. A time-delay circuit is coupled to the source of alternating current and to the sample and hold circuit.

Abstract: A method of correcting compressional velocity well log measurements for the effects of gas in the pore space of earth formations. The method includes the steps of determining a relationship between measurements of shear velocity and a ratio of measurements of compressional velocity with respect to shear velocity for the earth formations for when the earth formations are substantially liquid-filled. A first boundary of the relationship is determined for when the earth formations are substantially composed of shale, a second boundary is determined for when the earth formations are substantially devoid of shale. A cutoff is determined by adjusting an ordinate intercept value of the relationship to substantially include shear velocity and compressional velocity measurements corresponding to the earth formation having gas in the pore space. The cutoff is set to substantially exclude shear and compressional velocity measurements corresponding to the earth formations being substantially liquid-filled.

Abstract: A method of determining porosity of an earth formation penetrated by a wellbore including irradiating the earth formation with bursts of neutrons from a source in the wellbore and counting epithermal neutrons at a first detector axially spaced from the source to be primarily responsive to output of the source. Counting neutrons is divided into buildup periods contemporaneous with the bursts and decay periods between bursts. Neutrons are counted at a second detector during buildup and decay, the second detector axially spaced from the source and radially displaced towards the wellbore to be responsive to epithermal neutrons from the formation and relatively insensitive to lithology. Neutrons are counted at a third detector during burst and decay, the third detector axially spaced from the source and radially displaced towards the wellbore to be primarily responsive to epithermal neutrons from the formation, but the response is partially affected by said lithology.

Abstract: A method of preserving frequency components in digitally sampled signals exceeding a maximum frequency related to a predetermined digital sample interval. The signals correspond to a plurality of sensors positioned at spaced apart locations, and the signals from each of the plurality of sensors are digitally sampled at the predetermined digital sample interval. The method includes the steps of determining time adjustment values corresponding to each sensor which provide amplitude correspondence between each of the signals generated by each of the sensors in response to different propagation times of energy from an energy source to each of the sensors; adjusting a time of acquisition of each digital sample from each of the sensors by applying the corresponding time adjustment value to generate time-adjusted samples; and combining all the time adjusted samples into a combined output signal having a sampling time interval smaller than the predetermined digital sample interval.

Abstract: A method of extracting a phase and amplitude modulation signal impressed on a carrier is disclosed. The method includes generating the carrier at a frequency which is a multiple of the bandwidth of the modulation signal. The multiple equals 4N+1, where N is an integer. The modulation signal is impressed on the carrier, generating a phase and amplitude modulated carrier, The modulated carrier is digitally sampled at a frequency of four times the bandwidth the modulation signal. The digital sampling is initiated substantially contemporaneous with initiation of generating the carrier. A 90-degree phase shift is applied to the digitally sampled carrier to generate a quadrature component of the digitally sampled carrier.

Abstract: A method of determining the volume of a fluid sample withdrawn from an earth formation penetrated by a wellbore is disclosed. The method includes the step of positioning a formation testing tool adjacent to the earth formation. The tool includes a probe which can be selectively placed in hydraulic communication with the formation and excluded from hydraulic communication with the wellbore. The probe can be in hydraulic communication with a pressure transducer. The tool includes a sample chamber selectively placed in hydraulic communication with the probe. The chamber includes means for measuring the volume of the chamber and means for selectively controlling the volume of the chamber.

Abstract: A method of reducing bias error in nuclear magneic resonance (NMR) spin-echo signals. The method includes filtering the signals using a filter having a bandwidth inversely related to the length of time from the initiation of the measurement of the NMR signals. In a preferred embodiment, the NMR spin-echo signal measurements are filtered using a moving average filter having an averaging span which increases with respect to the time elapsed from initiation of the spin-echo measurement sequence.

Abstract: An apparatus for measuring resistivity of an earth formation. The apparatus includes at least one source of measuring current. The source includes a delta-sigma modulator and a serial bit source coupled to the modulator. The serial bit source represents the magnitude of the measuring current at spaced apart time intervals. The apparatus includes a sensor responsive to formation current resulting from interaction of the measure current with the earth formation. The sensor is coupled to a sigma-delta modulator. The modulator is coupled to a digital mixer and a digital filter. The output of the digital filter corresponds to the magnitude of the measure current detected by the sensor sampled at spaced apart time intervals. In a preferred embodiment, the apparatus includes a plurality of current sources each having a different frequency. The sigma-delta modulator is coupled to a plurality of mixers each for demodulating one of the different source frequencies.