Abstract: Sparsely spatially-sampled seismic time-scale trace gathers may be aliased for certain spatial and temporal frequencies. Aliasing may be avoided by application of a spatial interpolation scheme that uses the phase difference between the f-k phase spectra of the odd and the even traces to generate an interpolation operator in the f-k domain. The operator is multiplied point-by-point with the f-k transform of the original recorded trace gather. The resulting complex product is inverse transformed to the t-x domain whereupon the interpolated traces are interleaved between the original recorded traces to unwrap the aliased events.

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 using a compressional-wave source to produce converted shear waves which are subjected to Alford 4-component rotation to align the observation coordinates with the natural coordinates of the principal anisotropic axes of a birefringent formation. The static time shift between the fast and the slow shear wavefields due to shear-wave splitting is determined so that they can be synchronized thereby to isotropize the birefringent formation. From those data, fracture-plane orientation can be determined. Based on those data, the direction of a deviated bore hole is aligned perpendicular to the fracture plane strike. For a deep-seated target formation, shallower layers are isotropized prior to rotation and synchronization of the converted shear wavefields originating from that deeper formation.

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: A firing head for actuating an explosive charge in a perforating gun. A firing pin is positioned within the firing head housing to actuate a booster charge leading to the perforating gun. The firing pin can be actuated by mechanical techniques, by controlling the differential pressure between the housing pressure and the well pressure, and by controlling the absolute fluid pressure inside the housing. A release pin initially secures the firing pin, and the release pin can be mechanically actuated. The release pin is also releasably engaged with a differential piston that communicates with the well pressure through a port in the firing head housing. Increases in the housing fluid pressure moves the piston and attached release pin to release the firing pin into contact with the booster charge. Alternatively, the port can be plugged to permit absolute pressure actuation of the firing pin.

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: This invention provides a method for performing three dimensional seismic surveys. In one configuration, receiver lines containing equally spaced receiver stations run in one direction while the source station lines run orthogonal to the receiver station lines. The receiver stations and/or the source stations are offset to obtain a desired spatial sampling (number of bins) or multiplicity of the common mid points. In an alternate configuration, the receiver line spacing is offset by a fraction of the source station spacing and/or the source line spacing is offset by a fraction of the receiver station spacing to obtain the desired spatial sampling. These configurations provide higher spatial sampling (smaller bins) compared to the conventional geometries. The smaller bins may be combined to obtain folds (multiplicity) which is sufficient to provide desired seismic imaging while preserving the benefits provided by the higher spatial sampling by the method of the present invention.

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 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 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: In the presence of an anisotropic near-surface earth layer, orthogonally oriented microspreads are provided from which shear-wave velocity vectors V.sub.si.theta. and V.sub.s.theta. may be determined. The respective velocities are calculated from measurements of the direct path first arrivals and of the velocity of the boundary waves propagating along the upper boundary of the near surface layer. The ratio of the near-surface shear-wave velocity vectors is used to scale the static time corrections attributable to seismic data received by shear wave sensors whose axes of responsivity coincide with the orientation of the microspreads.

Abstract: A marine seismic signal is transformed from time domain into frequency domain and represented by matrix D. The marine data signal is truncated in time, transformed into the frequency domain and represented by matrix D.sub.T. Eigenvalue decomposition D.sub.T =S.multidot..LAMBDA..multidot.S.sup.-1 of matrix D.sub.T is computed. Matrix product D.multidot.S is computed and saved in memory. Matrix inverse S.sup.-1 is computed and saved in memory. An initial estimate of the source wavelet w is made. Source wavelet w is computed by iterating the steps of computing diagonal matrix [I-w.sup.-1 .LAMBDA.], computing matrix inverse [I-w.sup.-1 .LAMBDA.].sup.-1, retrieving matrix product D.multidot.S and matrix inverse S.sup.-1 from memory, and minimizing the total energy in matrix product [D.multidot.S] [I-w.sup.-1 .LAMBDA.].sup.-1 S.sup.-1. Primary matrix P representing the wavefield free of surface multiples is computed by inserting computed value for w into the expression [D.multidot.S] [I-w.sup.-1 .LAMBDA.].sup.-1 S.

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.

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: Method and apparatus are disclosed for determining the water cut of an oil-water flow in a wellbore having a known deviation angle less than 90. A first step includes generating a set of predicted response curves where each response curve relates discrete selected values of the water cut to test values representative of a value of the flow mixture functionally related to measured responses of a selected logging instrument capable of distinguishing between the water and oil phases of the flow mixture for a selected oil-water total flow rate and at a borehole deviation within a selected range of deviation values that include the known borehole deviation. Then the selected logging instrument combination is introduced into the borehole for measuring the total flow rate of the oil-water mixture and the values representative of the responses of the selected logging instrument distinguishing between the oil and water phases of the oil-water mixture.

Abstract: A neutron detector sensitive principally to epithermal neutrons is disclosed. In a preferred embodiment of the invention, a neutron counter is substantially surrounded by a reflector composed of material having a high neutron scattering cross section. The reflector is then wrapped in a shield which is composed of a thermal neutron absorber. In a specific embodiment of the invention, the counter, reflector and shield are mounted inside a neutron moderator which can be composed of plastic.

Abstract: A method for measuring the velocity of shear waves in a formation beneath a body of water. The shear wave velocity is derived from the parameters of water density, water-bottom reflection coefficient, formation compressional wave, velocity and the propagation velocity of a submarine ground-roll wave front.