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US 2011/0085422 A1Published application
Marine seismic source
AssigneeBP Exploration Operating Company Limited
InventorsMartin Thompson, Mark Francis Lucien Harper
Life of this patent
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AssigneeBP Exploration Operating Company Limited
InventorsMartin Thompson, Mark Francis Lucien Harper
Estimating the term…
A low frequency sound source has a radiating piston (3) of the order of a few metres across backed by a gas spring (13, 15) containing a fixed mass of gas. The gas pressure in the spring is kept at levels for which the natural frequency of the piston (3) loaded by the fluid (41) lies in the seismic band and may be as low as 0.5 Hz. The piston (3) is given an initial displacement and begins to oscillate. Its oscillations are sustained by an actuator (27, 29) whose drive signal is derived from the velocity of the piston (5) via a velocity or displacement sensor. The sound source is caused to perform a frequency sweep by gradually compressing the gas in the gas spring (13, 15) so that the spring becomes stiffer both because of the rising pressure and because of the reducing length of the gas spring spaces (13, 15). This double effect allows large changes in stiffness to be produced and hence allows the source to operate over at least three octaves of frequency.
A marine seismic source for producing seismic signals over a band of frequencies the source comprising:
A marine seismic source according to any preceding claim including means to vary the length of the gas chamber whilst the piston is vibrating so as to cause the piston to generate and radiate a signal comprising a sweep of frequencies.
A marine seismic source according to any preceding claim in which the piston has a diameter of at least one metre.
A marine seismic source according to any preceding claim in which the gas spring is held within a gas-filled shell one wall of which is formed by the piston.
A marine seismic source according to any preceding claim comprising a detector to detect displacement or velocity of the piston and means to control an actuator acting on the piston based on the detected changes in displacement and/or velocity of the piston.
A marine seismic source according to any of the preceding claims including means for initially displacing the piston from an equilibrium position and then releasing it.
A method of generating seismic signals over a band of frequencies the method comprising vibrating a piston to generate the seismic signals;
A marine seismic source suitable for producing seismic signals over a band of frequencies the source comprising:
A means of producing a swept-sine signal that will contain sufficient energy for a marine seismic survey down to 0.5 Hz and extending to higher frequencies over a band of at least three octaves, by causing a radiating piston of order a few metres diameter loaded by the mass of surrounding water and backed by a gas spring containing a fixed mass of gas which is compressed by a secondary piston to oscillate with large enough amplitude to radiate the desired acoustic signal.
Dependencies are inferred from the claim text.