Abstract: The present invention provides a method for forming wellbores. In one method, one or more wellbores are drilled along preplanned paths based in part upon seismic surveys performed from the surface. An acoustic transmitter conveyed in such wellbores transmits acoustic signals at a one or more frequencies within a range of frequencies at a plurality of spaced locations. A plurality of substantially serially spaced receivers in the wellbores and/or at surface receive signals reflected by the subsurface formations. The sensors may be permanently installed in the boreholes and could be fiber optic devices. The receiver signals are processed by conventional geophysical processing methods to obtain information about the subsurface formations. This information is utilized to update any prior seismographs to obtain higher resolution seismographs. The improved seismographs are then used to determine the profiles of the production wellbores to be drilled.

Abstract: The invention is a method for facilitating discrimination and identification of seismic or microseismic events by means of permanent pickups in an underground zone under development. The method comprises permanent installation of, in one or more wells, elastic wave receivers, geophones and hydrophones leaving the wells clear for development of the zone, at least one reference pickup with direct acoustic coupling with the technical zone development equipment (pickup pressed against a production string for example) for detection of events directly connected with the operation of the wells (valve opening and closure, etc.

Abstract: Methods and apparatus are described for seismic signal acquisition utilizing an odd number of vibratory sources arranged in line and positioning the sources for one sweep cycle at positions occupied by other sources during the previous sweep cycle. The method has advantages in particular for marine seismic acquisitions.

Abstract: A method for filtering noise from discrete noisy seismic signals in a time interval ([1, . . . , T]) is provided. The method comprising the steps of using the noisy seismic signals for determining at least one reference channel (x(t)) for the time interval as an estimate of the noise; determining coefficients for M temporally local filters (w(i, t)), the filters forming a filter bank, and M being a number equal to or larger than two, by minimizing a cost function (J(t)) representing a measure of the error of the output of the filter bank, and applying the filter bank to at least one estimate (x(t)) to determine M filtered estimates of the noise. The filtered estimates are multipled with temporal windows (h(i, t)).

Abstract: Apparatus and method for determining the location of the source of seismic energy around a well are provided. Multiple seismic receivers, each receiver having orthogonal seismic sensors, are axially spaced on a tool which is capable of sending real-time seismic signals to the surface. A method for calculating the location with respect to the receivers is also provided.

Abstract: An apparatus and method are disclosed for eliminating a noise signal from at least one source during an acoustic measurement of a subsurface geological formation or borehole. The apparatus includes a longitudinal body for positioning in the borehole and a transmitter supported by the body for transmitting acoustic signals into the formation and borehole. A sensor, substantially isolated within the body, is used to detect one or more noise signals and a receiver is carried by the body for receiving acoustic signals traversing the formation and borehole, and for receiving one or more noise signals. A processor is connected to the sensor and receiver for processing the acoustic signals and noise signals coupled from the receiver and the noise signal coupled from the sensor into a preferred formation or borehole signal by determining the noise signal received at the receiver using the noise signal received in the sensor and a propagation factor for the noise signal between the sensor and receiver.

Abstract: The invention relates to a device for exploring an underground formation crossed by a well, suited to work in well portions where the advance thereof under the effect of gravity is difficult, notably in horizontal well portions or in well portions greatly inclined to the vertical. A plurality of rigid exploration modules (Mi) are interconnected end to end, each one including a rigid pipe (1), a flexible leaf (11) fastened to each pipe (1) so as to press against the wall of the well at least one box (18) containing sensitive elements, a linking cable (32) connected to a surface central station (40), and a connecting block (26) comprising an acquisition system (37) connected to the various modules (M1-Mn) by a bundle of electric conductors running through the tubular elements (1), and a deferred electric connection useful in damp conditions between linking cable (32) and the acquisition system.

Abstract: A system for eliminating the tool mode signal from a received combined signal comprising both tool mode and formation mode components, comprising: a formation receiver for receiving said combined signal, a reference receiver for receiving a tool mode reference signal, a filter for processing said tool mode reference signal and generating a predicted tool mode component of the combined signal, and a summation element for subtracting said predicted tool mode component from said combined signal and generating a predicted formation mode component. The filter preferably incorporates a portion of the output of the summation element as an error signal, enabling the filter to adapt to changing conditions and update the algorithm on which it makes its predictions. According to an alternative system, an average value for the tool mode signal is updated according to a moving average to which new data points are added as they become available.

Abstract: A method for acquisition of seismic data from an area surveyed using a group of seismic energy sources and a group of seismic streamer cables, particularly a marine area, includes forming a first group A from at least two elements of either seismic energy sources S or seismic streamer cables C having a spacing X between said elements, forming a second group B from at least two of the other elements of sources S or cables C than that forming group (A), spacing the elements in group B a distance equal to X multiplied by the number of elements in group A, forming a group C from at least two subgroups each consisting of a group A, spacing said subgroups in group C in distance equal to the distance between two elements in group B multiplied by the number of elements in group B, the spacing between two adjacent subgroups being equal to the lateral distance between midpoints between the subgroups, and forming further groups as desired D, E, F etc.

Abstract: Apparatus and method for determining the location of the source of seismic energy around a well are provided. Multiple seismic receivers, each receiver having orthogonal seismic sensors, are axially spaced on a tool which is capable of sending real-time seismic signals to the surface over conventional wireline. A method for calculating the location with respect to the receivers is also provided, the method employing data from all the sensors and a performance function to minimize error in the determination of location, and a simplified method is provided for determining if a fracture has extended past a selected depth in a formation.

Abstract: A marine seismic surveying method recording with a first sensor a first signal indicative of pressure and with a second sensor a second signal indicative of motion, calculating a coupling mechanism filter for the second signal substantially correcting for the imperfect coupling of the second sensor, and applying a filter based on the coupling mechanism filter to at least one of the signals.

Abstract: Disclosed is a sonic well tool for performing acoustic investigations of subsurface geological formations penetrated by a borehole, and a method of logging formation data. The well tool generally includes a longitudinally extending body for positioning in said borehole. The tool also includes a transmitter supported by the body for transmitting acoustic energy, and at least two receivers. One of the receivers is positioned on the interior of the sonic tool to receive the acoustic signals that traverse the sonic well tool. The second receiver is positioned on the exterior of the sonic tool and receive sonic signals that traverse the sonic tool and those that traverse the formation. The apparatus further includes a processor for subtracting the well tool signal of the first receiver from the combined well tool and formation signal of the second receiver.

Abstract: A method for determining a unique signal representing the earth's response between a transmitter and receivers when conducting a seismic survey involves the steps of receiving a seismic signal set that comprises a plurality of different output frequency signals having known amplitude and phase characteristics, selectively combining the different output frequency signals to form the unique signal, and recording values of amplitude, phase, and frequency of the unigue signal. A method of conducting a modulated seismic survey involves the steps of providing seismic sensors capable of receiving a modulated seismic signal comprised of different frequency signals, transmitting modulated seismic energy information into the earth, and recording indications of reflected and refracted seismic waves sensed by the seismic sensors in response to transmission of the modulated seismic energy information into the earth.

Abstract: A method of acquiring and processing seismic data for repetitive monitoring of displacement of fluids impregnating a reservoir deep in the sub-surface below the surface weathered zone comprises the steps of: making at each point of a predetermined grid on the surface a vertical axis shallow borehole in the earth above the reservoir passing through the surface weathered zone; positioning in each borehole along its vertical axis a plurality of fixed receivers adapted to be connected separately to a seismic recorder on the surface; emitting near each borehole seismic waves into the earth by means of an emitter on the surface or close to the surface near the vertical axis of the borehole; recording for each borehole by means of receivers placed in the borehole the direct incident seismic waves and the seismic waves reflected at the interfaces of deep strata of the sub-surface, each receiver providing a separate record of an incident wave and a plurality of reflected waves; and carrying out the following processin

Abstract: The device comprises instruments for collection and recording of signals in seismic exploration of the substratum off-shore. The device is designed as a pole which is adapted to be forced down into the seabed and comprises a pointed lower end (7), an intermediate approximately cylindrically shaped main portion (6), a vibration-absorbing spacer (14) between the pointed end (7) and the intermediate main portion (6). The other end of the intermediate main portion (6) is connected to a top part (8) designed for inserting/pulling and other ways of handling the device. The pointed end (7) at least comprises geophones (15-17) and a hydrophone (23) is placed in the vicinity of the upper end of the device. The majority of the device's other instruments are placed in the intermediate main portion (6). The device is connected to a main cable (4) which extends to a seismic ship (29, 31).

Abstract: A method for obtaining seismic data in frigid regions without interference from flexural ice waves. In an exemplary embodiment, seismic data is produced by using an energy source to generate a seismic wave in a floating ice sheet. Seismic disturbances caused by the energy source are detected by one or more hydrophones and geophones, which produce hydrophone and geophone response signals, respectively. In a first embodiment, the hydrophone response signal is integrated. The integrated signal and/or the geophone response signal are scaled, and the two signals are then added. Alternatively, instead of integrating the hydrophone response signal, the geophone response signal may be differentiated prior to scaling and summing. A method is also disclosed for overcoming phase errors that might be introduced, for example, by the use of a transformer-coupled hydrophone.

Abstract: An element responsive to acoustic particle acceleration for sensing acoustic signals in a region of low acoustic pressure is disclosed. The element may be isolated from acoustic noise when positioned adjacent an acoustic noise generating high acoustic impedance structure by a baffle which provides isolation from radiated and evanescent acoustic signals and structure vibration.

Abstract: A seismic sensor platform comprises an open frame and a plurality of seismic motion sensors vertically positioned in a common horizontal plane in spaced relationship around the periphery of the open frame. A spike associated with each of the sensors extends beneath the open frame for anchoring each of the sensors in the earth. The frame includes a shield for protecting the sensors from physical damage and for shielding them from seismic noise. Second and third pluralities of horizontally positioned sensors may be provided on the frame, orthogonally positioned with respect to each other to sense orthogonal components of reflected seismic waves. The sensors may each be of a different natural frequency to optimize the multi frequency output of the sensor array.

Abstract: Doping the jacket of a data cable reduces the bulk volume resistivity of the jacket material allowing built-up static electricity to discharge. This reduces the likelihood of static charge interfering with data transmission.

Abstract: A remote seismic sensing system is provided which operates as a bipolarized, differential mode, LDI (laser differential interferometry) system to detect electrical signals produced at a remote location. In preferred embodiments, the system is used in seismic surveying to detect array signals. An amplified array signal (the electrical signal is coupled to an array retroreflector apparatus (target). The array signal is obtained from an array of seismic detectors, e.g., geophones or hydrophones. The amplified array signal increases the velocity of a Doppler shifting optical component on the target. The target converts a defused sensing beam into two polarized return sensing signals, both of the return sensing signals having been Doppler shifted by the target to contain frequency components that represent motions, e.g., ground motions and wind motions, that are common to both signals and to contain a difference signal which represents the array signal.

Abstract: A remote sensing system is provided which operates as a bipolarized, differential mode, LDI (laser differential interferometry) system to detect an electrical signal produced at a remote location. The system is adapted to reduce the effects of turbulence induced frequency fluctuations by using an array retroreflector apparatus which converts a single sensing beam into a single return beam having two, overlapping, transversely polarized sensing signals; thus, turbulence induced noise will be common mode to both return signals and cancel at the receiver.In preferred embodiments, the system is used to remotely detect an amplified array signal from a plurality of seismic detectors (e.g., geophones or hydrophones) connected to form an array at the remote location. The target is coupled to common motions at the selected location and the amplified array signal is coupled to an optical component within the target.

Abstract: A broadline seismic survey is carried out by positioning a plurality of areal arrays of seismic detectors along each of a plurality of broadline receiver lines along the surface of the earth. Array centers along an inline direction of each receiver line are staggered by one-half of an array interval from array centers along the inline direction of adjacent receiver lines. Each detector array on a given receiver line is elongated in a cross-line direction to such receiver line to effect an areal array coverage between broadline centers of the adjacent receiver lines being on opposite sides of the given receiver line. The seismic detectors in each array are connected in common to a recording means.

Abstract: The invention comprises a seismic recording apparatus and method. A multichannel recorder is connected to a cable formed from a plurality of signal conductors. Each of the signal conductors is connected to a different channel of the recorder via a multiplexer. The cable has a plurality of takeouts located at spaced distances along its length. Each of the takeouts is connected to a different signal conductor of the cable. A switch means is operably connected to one of the takeouts for selectively interconnecting the takeout and any one or more of several seismic detector connections upon receipt of a remotely generated signal. The invention also includes a number of detector conduits, each of which has one end operably connected to a different one of the seismic detector connections of the switch means. Each detector conduit has at least one geophone located along its length and operably connected thereto. A control means is provided for transmitting a signal to the switch means.

Abstract: A seismic sensor platform comprises an open frame and a plurality of seismic motion sensors vertically positioned in a common horizontal plane in spaced relationship around the periphery of the open frame. A spike associated with each of the sensors extends beneath the open frame for anchoring each of the sensors in the earth. The frame includes a shield for protecting the sensors from physical damage and for shielding them from seismic noise. Second and third pluralities of horizontally positioned sensors may be provided on the frame, orthogonally positioned with respect to each other to sense orthogonal components of reflected seismic waves. The sensors may each be of a different natural frequency to optimize the multifrequency output of the sensor array.

Abstract: A method and apparatus by which elastic properties of rock formations are determined includes a downhole logging device which has two internal accelerometers mounted within to measure the acceleration of the device. A reference displacement of the device is determined by measuring the acceleration outside the borehole while the device is suspended in air. The output of the accelerometers is measured in the borehole. Integrating the acceleration outputs of these accelerometers twice yields the displacement in the borehole. Changes in the displacement of the device are indicative of various elastic properties of formations surrounding the borehole. Using two accelerometers to determine displacement allows the continuous logging of Young's modulus and other elastic properties of rocks surrounding a well bore. In an alternate embodiment, geophones are used to measure the velocity of the device and their outputs are integrated once to yield displacement.

Abstract: A seismic directional sensor for solid-borne sound has at least one geophone with pronounced directional characteristic. The measuring electrical vibration signals, which are obtained at different circumferential angular positions of the radial longitudinal axis of the geophone and are to be compared with one another, are correlated with the direction of a seismic ray extending at right angles to the longitudinal axis of the geophone, which is ineffective in its neural circumferential angular position.The neutral circumferential angular position is determined by the ratio of the amplitude of the measuring signals which are determined on both sides adjacent to the neutral circumferential angular position in effective circumferential angular positions of the geophone. The vibration pattern of the measuring signals is antiphase in relation to the respective other side.

Abstract: An apparatus and method for detecting seismic waves traveling in an underground formation. The apparatus includes a hydraulic pressure source, preferably a downhole hydraulic pump; a plurality of small, light-weight, flexibly connected clamping detector units having hydraulically actuated clamps; conduit means connecting the hydraulic pressure source to the detector units so that the detector units may be hydraulically clamped to a wellbore with a large force by activation of the clamps; and means for conditioning signals from the detectors. The small, light-weight detector units are securely clamped to the side of the wellbore because of the high clamping force-to-weight ratio thereby allowing high frequency signals to be detected without interference.

Abstract: A method for using mode converted P- or S- wave data to delineate the surface of an anomalous geologic structure such as a salt dome is disclosed. Seismic wavefields are propagated from near the surface, through the earth, and through the anomalous geologic unit, so that a wavefield encounters the geologic unit at a non-normal incidence angle to generate a converted S- wave. Incidence angles of the direct arrival and converted waves are then determined. The intersection point of each converted S- wave raypath with each direct arrival raypath is determined, to provide a length of the raypaths. Travel times along the raypaths are determined, and a point on the interface of the anomalous geologic unit with the surrounding earth is determined by comparing raypath travel time differences with the recorded arrival time differences.

Abstract: An improved method and apparatus for conducting seismic prospecting is provided wherein more accurate estimates of the source wavelet can be achieved. Receivers (202) detect pulses at vertically offset locations. The pulses are converted to digital signals in a signal processor (212) and stored on a recorder (210). A processor (108) operates on the stored signals to produce an output wavelet A'(107 ,.theta.) in accord with the equation .intg.(P.G.sub.n -G.P.sub.n)dx.sub.g.

Abstract: The present invention relates to methods of seismic exploration utilizing vibrationally generated, elliptically polarized shear waves in an earth medium for subsequent detection of one or more dimensions of orthogonal particle motion. The invention relies upon a shear wave source of a type which couples a continually rotating longitudinal force into an earth medium thereby to propagate an elliptically polarized shear wave for refraction, reflection or subsurface detection, various forms of exploration being well within the capabilities.

Abstract: A non-destructive method of measuring physical characteristics of sediments to obtain a cross-sectional distribution of porosity and permeability values and variations, and of shear modulus and shear strength. A pair of boreholes have borehole entries spaced apart from each other at a predetermined distance, and a plurality of hydrophones are spaced at predetermined known positions. A source of seismic energy is placed into another borehole and activated to transmit seismic wave energy from the source to the hydrophones. Seismic wave characteristics are measured in a multiplicity of paths extending from the source to the hydrophones, using cross-bore hole tomography.

Abstract: A hydrophone is provided for use with a hydrophone array enclosed in a streamer cable that is deployed in a body of water. The active transducer elements of the hydrophone are electrically isolated from the sealed metal case in which they are mounted. The signal input and output terminals are protected from short-circuiting due to water invasion of a faulty streamer cable jacket.

Abstract: The invention comprises a seismic recording apparatus and method. A multichannel recorder is connected to a cable formed from a plurality of signal conductors. Each of the signal conductors is connected to a different channel of the recorder via a multiplexer. The cable has a plurality of takeouts located at spaced distances along its length. Each of the takeouts is connected to a different signal conductor of the cable. A switch means is operably connected to one of the takeouts for selectively interconnecting the takeout and any one or more of several seismic detector connections upon receipt of a remotely generated signal. The invention also includes a number of detector conduits, each of which has one end operably connected to a different one of the seismic detector connections of the switch means. Each detector conduit has at least one geophone located along its length and operably connected thereto. A control means is provided for transmitting a signal to the switch means.

Abstract: A signal receiving system adapted to be lowered into a drilling and suspended from an electro-bearer cable and adapted to be coupled with walls of the drilling so as to receive signals propagating in the surrounding formations. One or more expansible chambers are interconnected by ducts and suspended under a rigid body connected to the surface by the electro-bearer cable. Each expansible chamber includes flexible side walls into which are integrated at least one receiving element. The expansible chambers are adapted to be expanded by injecting a compressed fluid produced by a hydraulic system contained in the rigid body. The receiving elements are connected to a signal acquisition device disposed in the rigid body which communicates with a laboratory truck on a surface.

Abstract: A method for high-resolution seismic recording with increased bandwidth using detectors planted at shallow depths below the earth's surface. In one embodiment, an optimum depth where the amplitudes of high frequency signals increase relative to that of the noise during high-resolution recording is determined, geophones are then planted at that optimum depth and signals are recorded at that depth. To find this optimum depth, detectors are planted at various depths below the earth's surface in order to record the signals at those various depths. The frequency spectra for each detected signal is generated and a velocity profile of the depths covered by the detectors is also generated from the signals. The bandwidth of the frequency spectra and the velocity profile are used to determine a depth for planting the detectors that is closer to the earth's surface than the depths previously considered.

Abstract: A method of seismic exploration uses recordings from both surface receivers and buried sensors to determine the full elastic effect of the near surface layer on an applied seismic wave. The surface receivers are arranged relative to the seismic source location so that rotational effects may be detected. Buried sensors are located so that vertical effects may be detected. This full elastic effect may be used in subsequent seismic data acquisition to reconcile the effect of the near surface so that the response of the underlying rock formations may be known.

Abstract: A blasting system wherein the actuation of detonators at a plurality of blast holes is controlled by firing one or more test blasts and, at each blast hole, monitoring the resulting shock wave to derive data which is used to determine time delay criteria for the blast holes.Each detonator includes a shock sensitive device which detects the shock wave. Each detonator has on-board signal processing capability and optionally is connected to a central control computer.

Abstract: A method of acquiring seismic data is disclosed which includes a horizontal towed receiver array in conjunction with at least one vertically oriented receiver array formed from a plurality of receiver elements spaced apart vertically within a plurality of cable. By simultaneously recording the data from both arrays, seismic data can be acquired for locations directly beneath a fixed obstruction, which a towing vessel has had to steer around.

Abstract: Geophones are placed around pipelines to detect third parties, e.g., heavy construction vehicles. Associated computer equipment acquires data from the geophones and discriminates for the frequencies associated with heavy construction vehicles.

Abstract: In a method of acquiring seismic data in a prospecting area, an array of excitation vibration receivers is placed on or over the terrestrial surface. A plurality of excitation vibration sources is disposed in the vicinity of the array, each source emitting excitation vibrations with a frequency spectrum in a specific frequency band. These bands are adjacent and together cover the frequency band of usable seismic data signals. When the excitation vibrations are emitted by the plurality of sources, the excitation vibration echoes reflected from strata beneath the terrestrial surface are registered by the receivers. The above steps are repeated for a plurality of successive trace increment displacements to produce an emission figure and to cover the prospecting area. The method and the device implementing it can be used for acquisition of terrestrial or marine seismic data.

Abstract: A hydrophone (16) having a short-baseline array of transducers (12A, 12B, and 12C) as well as a long-baseline array of transducers (14A, 14B, and 14C) includes switches 30A, 30B, and 30C) for selectively connecting the outputs of the arrays to a cable (18) that carries the signals to processing circuitry (20) aboard an ocean-going vessel (24). The switches (30A, 30B and 30C) change state in accordance with the output of a narrow-band filter (42), which indicates whether the received signal is of a predetermined frequency and thus is likely to have been produced by an intended source. Due to the delay inherent in the narrow-band filter 42, the processing circuitry (20) thus processes the response of the long-baseline array to the first part of a beacon pulse and the response of the short-baseline array to the second part of the beacon pulse.

Abstract: A computer-integrated survey system which is useful in the location of underground obstacles, such as rocks, concrete, steel and ice is disclosed. Specifically, the detection system of the present invention is operated by a microcomputer, having a series of sensors, which integrate position-determining systems, time, sub-surface radar, sonar, seismograph, laser equipment and earth-resistivity functions to accomplish its stated purpose. The system is specially designed in a compact fashion so that it may easily be hand-held, if so desired. Simultaneous with the detection and measurement of underground obstacles, in a preferred embodiment of the present invention, a permanent record of all information may be constructed for subsequent review and print-out.

Abstract: An inventive method for simultaneously collecting depth-of-focus vertical seismic profiling (VSP) data and three-dimensional surface seismic data is disclosed. At least one seismic sensor is deployed at a predetermined depth of a borehole and raised in increments determined by the survey. A seismic source and a plurality of seismic sensor may be deployed at the surface along a partial arc offset from the top of the borehole by a distance inversely proportional to the depth of the sensor in the borehole. The seismic source generates a seismic signal at a plurality of points in a circular path around the borehole. Once a circle has been completed, the borehole sensor is raised, and the seismic signal generator and sensors are moved to the next largest circular path and the process is repeated. The seismic signals are simultaneously recorded by the borehole sensor and the sensors deployed in the arcuate path.

Abstract: A seismic exploration method and apparatus in which non-uniformly distributed noise signals generated by wind, machinery, or surface wave propagation and received by the sensing geophones are cancelled by the utilization of adaptive filter processing. A number of horizontally sensitive geophones are disposed along the surface of the earth to detect surface waves induced in the surface of the earth at a plurality of spaced locations throughout an entire area of investigation. Similarly, a number of wind noise and mechanical noise detectors are utilized to detect airwave and noise signals at a plurality of locations throughout the area of investigation.

Abstract: An endfire seismic array comprises one or more marine seismic cables having a plurality of acoustic-to-electrical hydrophone receivers spaced therealong, each being operatively connected in combination so that as a unit an endfire receiving beam pattern with respect to any frequency across the seismic band is formed by causing the signals from the individual hydrophone receivers to be additive for that frequency. A plurality of cables results in a more narrow beam than a single cable. A geologic or lithologic formation that is a dip change from the norm may be detected either as an extra strong increase or decrease in signal, depending on the mode of use.

Abstract: In an acoustic ground vibration detector for the detection of infrasound ground vibrations, comprising at least one three-component geophone probe, the three individual geophones of said geophone probe are electrically connected in series and act upon an operation amplifier whose output signal activates a Reed relay. The activated Reed relay switches on a sound signal transmitter which produces an audible acoustic signal for the duration of the ground vibration signal. The acoustic ground vibration detector is intended in particular for locating buried persons. Moreover, it serves to protect important objects by registering infrasound ground vibrations produced by footfall sound.

Abstract: A sensor for resolving the left-right ambiguity encountered in horizontal line hydrophone arrays consists of an orthogonal pair of dipole hydrophones, a monopole hydrophone, and a tilt sensor, the tilt sensor connecting the dipole hydrophones so as to provide a single dipole hydrophone which is always oriented horizontally. The tilt sensor consists of two variable capacitors made from hollow cylinders of high permittivity dielectric material, partially filled with a quantity of liquid mercury which forms the variable inner electrodes of the capacitors. The outer electrodes of the capacitors, on the outside of the cylinders, having a sinusoidally-shaped perimeter and being oriented at right angles to each other, are connected to the crossed dipoles in order to provide the required horizontal dipole hydrophone.

Abstract: A seismic prospecting method comprising the use of at least two vehicles for moving an acoustic wave emission assembly and a reception assembly such as a seismic streamer. The method consists in performing successive cycles of emission of acoustic waves, of reception and of recording of the acoustic waves coming from reflecting interfaces of the subsoil and combining the recording so as to provide multiple coverage. The vehicles follow paths such that the angle formed by the respective advancing directions remains greater than or equal to 90.degree. in absolute value.

Abstract: A cartridge retention system includes a cartridge carrying electronic, compressed gas or other components which has a spring-loaded button at one end and which is removably mounted in the breech of an adapter module connected either in a streamer section or between opposing ends of adjacent streamer sections of a towed array. The cartridge is demountably retained within the adapter by providing an adapter housing with a breech which is somewhat longer than the cartridge, and by providing the housing with an overlying two part shell which is rotatable about the housing, with one of the shell parts containing an aperture to accommodate cartridge insertion and with both parts containing an internal circumferential groove adapted to coact with the spring-loaded button on the cartridge to move the cartridge from one end of the breech to the other end upon rotation of the shell.

Abstract: A method of marine seismic investigation involves positioning or deploying at a predetermined point close to or within a multi-element seismic source array a calibration source which is an acoustic pressure wave point source which has a far-field seismic signature of broad bandwidth. The radiated pressure wave field of the calibration source (3) is weaker than that of the main source (2). The two sources are fired at separate instants within a predetermined time range, preferably with the calibration source (3) being fired about two seconds before the main source (2). The reflected response of the sub-surface strata is recorded and processed to generate seismic data. In one embodiment, the response is recorded with two hydrophone arrays - a short high-resolution array (4) and a conventional main array (5). The method can be used to determine the far-field signature of the main source array (2). It can also be used to obtain a high-resolution shallow seismic section simultaneously with a deep seismic section.