Abstract: Method and systems are provided for processing c-wave data resulting in less sensitivity to errors in p-wave velocity analysis. Therefore, according to one aspect of the invention, a process is provided for processing c-wave data, the process comprising: providing zero-offset gather without a hyperbolic movement correction; performing migration on the zero-offset gather; performing velocity analysis on the migrated zero-offset gather; and performing NMO on the migrated data using the velocity from the velocity analysis.

Abstract: A transducer is described especially for use in providing acoustic transmission in a borehole. The transducer includes a multiple number of magnetic circuit gaps and electrical windings that have been found to provide the power necessary for acoustic operation in borehole while still meeting the stringent dimensional criteria necessitated by boreholes. Various embodiments conforming to the design are described. Moreover, the invention includes transition and reflector sections, as well as a directional coupler and resonator arrangement particularly adapted for borehole acoustic communication.

Abstract: A position and speed sensor comprising a circular element (1) rotatably driven about its axis. The circular element (1) has two position indicators (3, 4) of different angular width. A sensor means (5) is fixed in position with respect to and adjacent to the circular element (1). The sensor means (5) has a sensing element for sensing the passage of each of the position indicators (3, 4) past the sensing clement. An electrical signal is produced by the sensor means (5) corresponding to the passage of each of the sensed position indicators (3, 4). The signal has a duration corresponding to the angular widths of the sensed position indicators (3, 4). Also included is a means to process the electrical signal to produce information as to the angular position and angular velocity of the circular element. A method for reverse rotation detection using the position and speed sensor means (5) is also disclosed.

Abstract: Methods are provided for automatic detection of linear seismic events and the detected events are used in correction of statics and geometry error.

Abstract: An inductance change detection circuit for detecting a change in inductance with a simple circuit design, having a series circuit having a resistor and a coil of which an inductance changes according to a position of an object; a pulse power supply 1 for applying a pulse voltage to the series circuit; a first signal generator for generating a first signal when an output voltage of the resistor in the series circuit becomes a specific voltage level; a second signal generator for generating a second signal responsive to a pulse voltage of the pulse power supply; and a comparison pulse generator for generating a pulse signal having a duty ratio responsive to the coil inductance based on the first signal and second signal.

Abstract: A sonic logging method involves the pre-processing of a detection signal by a downhole processing device to determine the arrival time of a sonic signal at a receiver which is then transmitted to the surface. A suitable sonic logging downhole tool includes a control device for controlling generation and reception of the sonic signal, an A-D converter for digitizing the detected signal at a predetermined sampling interval, a first memory for storing the digitized waveform, a second memory for storing a program for processing the digitized waveform, and a microprocessor capable of executing the stored program so as to determine an arrival time of the sonic signal arriving at the receiver.

Abstract: A method and an apparatus are provided for matching the response of hydrophones 22 to the response of geophones 24 and significantly reducing response variations between hydrophones caused by inherent characteristics. The method includes the steps of determining a capacitance 66 for each of the hydrophones 22 in an operating environment, configuring a filter 36 based on the capacitance 66, and modifying a response of a channel of the hydrophone 22 using the filter 36. The apparatus includes an acquisition unit 20 having a geophone 24 and a hydrophone 22, a recording unit 30, a processing unit 31 and a filter 36 for correcting for variation between hydrophones 22 and changing a first order low frequency response of the hydrophone 22 to appear like a second order response like that of the geophone 24.

Abstract: A signal scaling system and methodology for use in a signal measurement system such as a digital or analog oscilloscope, logic analyzer, network analyzer, spectrum analyzer or waveform generator that has a graphical user interface which controls a waveform display region on a display device. The signal scaling system determines one or more displayed waveform scaling parameters to cause portions of selected displayed waveforms appearing within a rescaling rectangle to occupy a predetermined portion of the waveform display region other than the rescaling rectangle. For each of the selected displayed waveforms, the scaling parameters may include horizontal scaling, horizontal offset, vertical scaling and vertical offset. Preferably, the predetermined portion of the waveform display region comprises the entire waveform display region and the selected displayed waveforms include all waveforms at least partially within the rescaling rectangle.

Abstract: The proposed device comprises a primary detector and a measuring amplifier, the primary converter comprising a central cylindrical core and an external cylindrical core arranged coaxially along a longitudinal axis, a movable member being mounted coaxially with the cores, a measuring winding arranged on the central core along the longitudinal axis in such a manner that the turns of the winding encompass the central core in a transverse direction, and an additional winding having a common electrical connection point with the measuring winding and disposed on one of the cores so that its turns encompass the core in a longitudinal direction and pass through the corresponding central axial opening. The measuring winding and the additional winding are connected with the measuring amplifier, and alternating current voltage is fed to the input thereof.

Abstract: A method of determining the acoustic impedance of a fluid in a borehole, by gating a reflected acoustic signal into a plurality of time slots, and comparing received energies of the signal for the time slots to obtain a value indicative of the acoustic impedance of the fluid. The value may be normalized to yield the acoustic impedance of the fluid using the acoustic impedance of, e.g., water as a calibration point. The comparison is performed by comparing a ratio of an integration of a first ring down time slot and a second ring down time slot, to an integration of an internal reflection time slot. The acoustic pulse may be generated using a transducer immersed in an intermediate fluid contained within a chamber defined in part by a plate in contact with the borehole fluid and having a thickness such that a mechanical resonance frequency of the plate in a thickness mode is substantially equal to a resonance frequency of the transducer.

Abstract: A low profile non-contacting position sensor for rotational engagement with a shaft. A pole piece has a first and a second piece. A backstrap retains the first and second pieces in parallel and opposing relationship. A shaft passes through at least one of the pieces. The pole piece is held to the shaft by a shaft retainer. A first and second magnet is disposed on the first and second pieces, respectively. A magnetic sensor is positioned between the first and second magnets. A magnetic field sensor such as a hall effect sensor is positioned in an gap and operates to provide an output signal representative of the field strength of the magnet as the shaft rotates. The output signal changes magnitude in relation to the relative position of the magnet with respect to the magnetic field sensor.

Abstract: Methods and apparatus are described for the seismic exploration of strata adjacent to a borehole, wherein an arrangement of geophones is lowered into the borehole and clamped to the wall. The geophones are clamped at essentially equal angular distances along the circumference of the borehole. A plurality of such arrangements can be positioned along the longitudinal axis of the borehole. By combining the outputs of the geophones noise signals generated by symmetric guided waves are attenuated. The arrangement can be used for cross-well seismic acquisition and in combination with seismic sources and/or attenuator so as to form an single-unit exploration tool for borehole seismics.

Abstract: A method for determining a degree of acoustic non-linearity of an earth formation from seismic signals transmitted into the formation from within one wellbore and received from the formation in another wellbore. The seismic signals include two selected discrete frequencies. The method includes spectrally analyzing the received signals, determining from the spectral analysis the presence of a frequency representing a sum of the two selected frequencies, and determining a relative amplitude of the sum frequency with respect to the amplitudes of the two selected discrete frequencies. In a particular embodiment, the method includes determining the presence of a frequency in the spectrally analyzed signals representing the difference between the selected discrete frequencies, and determining the presence of harmonic multiples of one of the two selected discrete frequencies.

Abstract: In mutually opposite directions, two light signals traverse an optical series circuit including a first multi-mode fiber, a first polarizer, a Faraday sensor device, a second polarizer and a second multi-mode fiber. An intensity-normalized measuring signal is derived with the aid of direct signal components from light intensities of the two light signals after traversal of the series circuit.

Abstract: A system for selectively tuning the buoyancy of a marine seismic streamer or underwater cable. Trimming weights are positioned along the streamer cable and can be integrated within a solid buoyancy member or can be located within an outer streamer sheath. The weights overcome the flotation forces provided by an internal buoyancy section to control the elevation of the streamer section. The outer streamer sheath can be opened to permit the removal or addition of trimming weights to the streamer section, and can be resealed to prevent water from intruding into the streamer interior. A single trimming weight can be positioned along the buoyancy member, or a plurality of trimming weights can be used. The trimming weights permit a tight buoyancy range to be accomplished without increasing water drag forces or noise as the streamer is towed.

Abstract: A magnetic sensor device comprising a magnetic element and a wire wound around the magnetic element. The magnetic element has a cross-sectional area of not more than 0.55 mm.sup.2 and a saturation magnetostriction constant .lambda.s whose absolute value is smaller than 1.times.10.sup.-6, with Sw/Sm being equal to or smaller than 9, provided that Sw is the cross-sectional area of the wire and Sm is the cross-sectional area of the magnetic element. Preferably, the magnetic element has an elastic limit .sigma.m greater than 1,000 MPa, and the elongation the magnetic element experiences upon application of a stress equal to the elastic limit .sigma.m is between 1.0% and 5.0%. It is also preferable that the magnetic element and the wire are covered with a resin layer to form an integral unit.

Abstract: A method and system of dual wavefield reinforcement or increasing the contributions to each image point in the seismic image can be accomplished by aligning the upward traveling energy, U, and the downward traveling energy, D, and then summing U and D in the stacking process. A method of dual wavefield reinforcement includes receiving seismic data having both up going and down going wavefields. The up going wavefields are separated from the down going wavefields. Pre-NMO and post NMO statics for each of said up going and said down going wavefields are calculated. The determined pre-NMO static is applied to each of the up going and the down going wavefields. NMO/DMO stacking velocities for the seismic data on an up going wavefield floating datum is determined.

Abstract: A method for planning continuity logging surveys and for detecting the presence of a continuous or discontinuous low-velocity inclusion in a subterranean geological formation. To detect the presence of a continuous or discontinuous low-velocity inclusion, a seismic source is inserted into a source borehole located at either a boundary or a center of a low velocity inclusion. Seismic energy is generated coupled to the low-velocity inclusion using the seismic source. The seismic energy propagates as seismic waves through the low-velocity inclusion and is measured and recorded by at least one detector disposed in a receiver borehole. The seismic waves are analyzed for the presence of at least one seismic signature from which the distance of a discontinuity, if any, of the low-velocity inclusion with respect to the receiver borehole can be determined.

Abstract: A molded protective body member for seismic cable hydrophone and geophone sensors and their cable splice connections from underwater obstructions and pay-out and retrieval apparatus. The body member is a one piece polymeric member having interior cavities, risers and apertures. When in use, the body member is folded longitudinally in half around the seismic cable at a hydrophone or geophone splice joint and secured in place with recessable molded straps having threaded fasteners passing through each of the body halves thus clamping the body to the cable. At least one interior diametrical cavity is provided consistent with the type seismic cable sensor used. With the sensor and its associated cable and connector positioned within the protective body member, tie wraps are threaded through apertures along and adjacent the longitudinal edges of each half thus closing the interior of the body member. Cavities are also provided internally for placing lead weights.

Abstract: A back-to-back locator instrument includes a first portion with an array of two or more magnetic sensors, and an indicator arrangement. A second portion of the instrument includes an array of correspondingly located magnets. Each of the first and second portions includes a marking arrangement, which either allows marking of the underlying surface, or viewing of a mark on the surface for properly locating the instrument portion thereon. When the two portions are congruent or registered, the indicator arrangement gives a maximum indication of corresponding locations. In a particular use, corresponding locations on the inside and outside of a tank are identified. The indicator arrangement may include a separate indicator for each magnetic sensor. A flux concentrator may be associated with each magnetic sensor.