The disclosure herein generally relates to a device for use in marine seismic surveying. A displacement apparatus has a base and an actuated head. The actuated head is coupled to an actuation means comprising a shaft, a cam, and a motor. The cam is coupled to the shaft at a radial position from the center of the cam. A vacuum piston is optionally coupled to the actuation means. A variable resonance spring, such as an air spring, is coupled to the actuated head in order to tune the apparatus to operate in resonance at a range of frequencies.

Disclosed are acoustic logging systems and methods that involve correlating broadband acoustic signals acquired by a plurality of acoustic sensors at multiple depths within a wellbore to compute covariance matrices and their eigenvalues in the frequency domain for a plurality of frequency bins. In accordance with various embodiments, acoustic sources are detected and located based on the eigenvalues viewed as a function of depth and frequency.

A survey method includes generating a first amplitude modulation signal by amplitude-modulating a carrier wave repeating the same pattern at a predetermined cycle in each of a plurality of vibrators with a modulation signal whose cycle is 1/m times the predetermined period and is different for each of the vibrators, transmitting the seismic wave based on the first amplitude modulation signal, generating a second amplitude modulation signal in one or more receivers, the second amplitude modulation signal being identical to the first amplitude modulation signal generated by any one of the seismic vibrators, generating a reception signal in each of the one or more receivers by receiving a synthetic seismic wave in which the seismic waves generated by the seismic vibrators are synthesized, calculating a correlation value between the reception signal and the second amplitude modulation signal, and analyzing characteristics of the medium on the basis of the correlation value.

A data seismic sensing system and method for obtaining seismic refraction data and tomography data. The system may comprise a subsurface sensor array, wherein the subsurface sensor array is a fiber optic cable disposed near a wellbore, a seismic source, wherein the seismic source is a truck-mounted seismic vibrator comprising a base plate, and a surface sensor array, wherein the surface sensor array is coupled to the seismic source. The method may comprise disposing a surface sensor array on a surface, disposing a subsurface sensor array into a wellbore, activating a seismic source, wherein the seismic source is configured to create a seismic wave, recording a reflected seismic wave with the surface sensor array and the subsurface sensor array, and creating a seismic refraction data and a seismic tomography data from the reflected seismic wave.

An inline source can be used for a marine survey. For example, a marine survey vessel can tow source units in line. The source units can be actuated near-continuously to cause a respective signal emitted by each of the source units to be uncorrelated with signals emitted by other of the source units.

Downhole tools and method for a well. At least some of the example embodiments are methods of imaging a formation around a first borehole, including: focusing first outbound acoustic energy, launched from a tool with the first borehole, on a volume within the formation spaced away from the first borehole, the focusing creates a first virtual point source (VPS) that creates a first return acoustic energy; receiving the first return acoustic energy from the first VPS at a plurality of seismic sensors; and determining a parameter of the formation between the first VPS and a location of the seismic sensors using the first return acoustic energy.

An apparatus for detecting a location of an optical fiber having an acoustic sensor disposed subsurface to the earth includes an acoustic emitter configured to emit a first signal having a first frequency and a second signal having a second frequency that is higher than the first frequency, the first and second emitted acoustic signals being azimuthally rotated around the borehole and an optical interrogator configured to interrogate the optical fiber to receive an acoustic measurement that provides a corresponding first received signal and a corresponding second received signal. The apparatus also includes a processor configured to (i) frequency-multiply the first received signal to provide a third signal having a third frequency within a selected range of the second frequency, (ii) estimate a phase difference between the second received signal and the third signal, and (iii) correlate the phase difference to the location of the optical fiber.

It is proposed a positioning assistance system for a vibrator truck, that is configured to determine a vibration point distance between the vibrator truck and the vibration point location; determine a stopping distance for stopping the vibrator truck at a vibration point location, according to a determined current speed of the vibrator truck and according to a speed profile; determine a time for stopping the vibrator truck at the vibration point location according to the current speed of the vibrator truck, when the stopping distance corresponds to said vibration point distance; and trigger the lifting down of the baseplate of the vibratory system, when at least the following condition is met: said stopping time is inferior or equal to a time for lifting down the vibratory system to the ground. Corresponding vibrator truck and method are also proposed.

A modular downhole logging system includes a transmitter module having a local frequency, wherein the transmitter module transmits interrogation signals into a formation based on the local frequency. The downhole system also includes a receiver module axially-spaced from the transmitter module and that receives response signals corresponding to the interrogation signals, wherein the receiver module includes sampling logic and sync estimation logic. The sync estimation logic is configured to perform sync estimation operations including estimating the local frequency of the transmitter module based on analysis of response signal Fourier transform results corresponding to different frequencies. The sampling logic/clock is configured to sample the response signals based on the estimated local frequency of the transmitter module, wherein a processor derives formation property values using the sampled response signals.

A method for geophysical source steering including towing a first geophysical source through a body of water; and adjusting a first steering parameter of the first geophysical source while towing the first geophysical source. An apparatus for geophysical source steering including a first marine vibrator source having a first housing structure; a first vibrational surface functionally coupled to the first housing structure such that at least a portion of the first vibrational surface can vibrate relative to the first housing structure; and first steering control equipment.