Source for marine seismic acquisition and method

1. A seismic vibro-acoustic source element configured to generate acoustic waves in water, the seismic vibro-acoustic source element comprising:

an enclosure having first and second openings;

first and second pistons configured to close the first and second openings and to contact the water;

an actuator system provided inside the enclosure and configured to translate first and second shafts connected to the first and second pistons, respectively, to generate a wave having a first frequency; and

a pressure mechanism attached to the enclosure and configured to control a pressure of a fluid inside the enclosure such that a pressure of the fluid is substantially equal to an ambient pressure of the enclosure.

2. The seismic vibro-acoustic source element of claim 1 , wherein the pressure mechanism is also configured to actuate the first and second rigid pistons to generate a wave having a second frequency different from the first frequency, wherein the first and second frequencies are simultaneously generated.

3. The seismic vibro-acoustic source element of claim 1 , further comprising:

a wall configured to separate the enclosure into a first chamber and a second chamber.

4. The seismic vibro-acoustic source element of claim 3 , wherein the actuator system is an electro-magnetic actuator system that comprises:

a first actuator provided in the first chamber; and

a second actuator provided in the second chamber,

wherein the first and second actuators are configured to act simultaneously on the first and second pistons.

5. The seismic vibro-acoustic source element of claim 4 , wherein,

the first shaft connects the first piston to the first actuator; and

the second shaft connects the second piston to the second actuator.

6. The seismic vibro-acoustic source element of claim 5 , further comprising:

a first guiding system configured to guide the first shaft along an axial direction.

7. The seismic vibro-acoustic source element of claim 6 , further comprising:

an end-stop mechanism configured to restrict a translation of the first shaft along an axial direction.

8. The seismic vibro-acoustic source element of claim 1 , further comprising:

a cooling system configured to cool the actuator system.

9. The seismic vibro-acoustic source element of claim 1 , further comprising:

a control system provided on or inside the enclosure and configured to control the actuator system and the pressure mechanism.

10. The seismic vibro-acoustic source element of claim 9 , wherein the control system is configured to make locally control decisions for the actuator system and the pressure mechanism.

11. The seismic vibro-acoustic source element of claim 9 , further comprising:

a pressure port configured to supply the fluid under pressure to the pressure mechanism;

a data port configured to transmit data between the control system and a vessel to which the seismic vibro-acoustic source element is connected to; and

an electrical power port configured to receive electrical power for the actuator system.

12. The seismic vibro-acoustic source element of claim 9 , wherein the control system is configured to drive the actuator system so that the first and second pistons generate an acoustic wave having a frequency between 0 and 32 Hz.

13. The seismic vibro-acoustic source element of claim 9 , wherein the control system is configured to drive the pressure mechanism so that the first and second pistons generate an acoustic wave having a frequency between 0 and 4 Hz.

14. The seismic vibro-acoustic source element of claim 9 , wherein the control system is configured to drive the electro-mechanical actuator system and the pressure mechanism so that the piston simultaneously produces two waves having different frequencies.

15. A source array for generating under water seismic waves, the source array comprising:

at least one seismic vibro-acoustic source element, wherein the seismic vibro-acoustic source element includes,

an enclosure having first and second openings;

first and second pistons configured to close the first and second openings and to contact the water;

an actuator system provided inside the enclosure and configured to translate first and second shafts connected to the first and second pistons, respectively, to generate a wave having first frequency; and

a pressure mechanism attached to the enclosure and configured to control a pressure of a fluid inside the enclosure such that a pressure of the fluid is substantially equal to a pressure of an ambient of the enclosure.

16. A method for assembling a seismic vibro-acoustic source element configured to generate acoustic waves under water, the method comprising:

providing an enclosure having first and second openings;

installing an actuator inside the enclosure;

attaching to the actuator system first and second shafts that are configured to translate along a longitudinal axis, the first and second shafts being connected to first and second pistons, respectively, in such a way to close the first and second openings and to contact the water; and

installing a pressure mechanism to the enclosure to control a pressure of a fluid inside the enclosure such that a pressure of the fluid is substantially equal to an ambient pressure of the enclosure.