Vibratory source for non-vertical boreholes and method
A reaction mass seismic survey source that is located in an underground casing. The seismic source includes a non-planar base plate; a reaction mass located on the non-planar base plate; and a flextensional element housed in a recess of the reaction mass and configured to vibrate the non-planar base plate when actuated, to generate seismic waves underground.
1. A reaction mass seismic source configured to advance through and operate in a non-vertical underground casing, the seismic source comprising:
a base plate;
a reaction mass located above the base plate to press the base plate toward a wall of the non-vertical underground casing; and
a flextensional element located between the reaction mass and the base plate and configured to generate seismic waves underground when actuated.
2. The seismic source of claim 1 , further comprising:
a guidance piston located between the flextensional element and the base plate.
3. The seismic source of claim 1 , wherein the flextensional element comprises:
a piezoelectric element that changes its size when actuated by a voltage; and
an elastic element located around the piezoelectric element and configured to change its shape when the piezoelectric element is actuated.
4. The seismic source of claim 1 , further comprising:
support devices located between the reaction mass and the base plate and configured to support a weight of the reaction mass such that the flextensional element is protected from the weight of the reaction mass.
5. The seismic source of claim 1 , wherein a weight of the base plate is between 200 and 400 kg.
6. The seismic source of claim 1 , wherein the flextensional element includes between one and ten flextensional elements.
7. The seismic source of claim 1 , further comprising:
a coupling element configured to be in a retracted state when the seismic source travels through the non-vertical underground casing and to press against the wall of the casing at a location opposite to where the base plate presses the wall when the seismic source is at a shooting location.
8. The seismic source of claim 1 , wherein a center of mass of the seismic source is lower than a geometric center so that the base plate remains below the reaction mass when the source travels through the non-vertical underground casing.
9. The seismic source of claim 1 , wherein the base plate has end portions along a moving direction to house the reaction mass.
10. A reaction mass seismic source configured to advance through and operate in a non-vertical underground casing, the seismic source comprising:
plural individual source elements connected to each other, each of the source elements comprising:
a base plate;
a reaction mass located above the base plate to press the baseplate toward a wall of the non-vertical underground casing; and
a flextensional element housed in a recess of the reaction mass and configured to vibrate to generate seismic waves when actuated.
11. The seismic source of claim 10 , wherein the flextensional element comprises:
a piezoelectric element that changes its size when actuated by a voltage; and an elastic element located around the piezoelectric element and configured to change its shape when the piezoelectric element is actuated.
12. The seismic source of claim 10 , wherein the source element further comprises:
support devices located between the reaction mass and the base plate and configured to support a weight of the reaction mass such that the reaction mass does not touch the base plate.
13. The seismic source of claim 10 , wherein flextensional element includes between one and ten flextensional elements.
14. The seismic source of claim 10 , wherein the source element further comprises:
a coupling element configured to be in a retracted state when the seismic source element travels through the non-vertical underground casing and to press against the wall of the casing at a location opposite to where the base plate presses with the wall when the seismic source element is at a shooting location.
15. The seismic source of claim 10 , wherein a center of mass of each of the seismic source elements is lower than a geometric center so that the base plate is below the reaction mass.
16. The seismic source of claim 10 , wherein the base plate has end portions along a moving direction to house the reaction mass.
17. A method for generating seismic waves in a non-vertical borehole, the method comprising:
positioning a source element inside the non-vertical borehole, with a reaction mass of the source element remaining over a base plate thereof;
extending a coupling element to push the base plate against a wall of the borehole;
actuating a flextensional element located in a recess inside the reaction mass, the recess opening toward the base plate; and
generating the seismic waves in the base plate by the actuated flextensional element.
18. The method of claim 17 , further comprising:
supporting the reaction mass with a support device so that the reaction mass does not touch the base plate.
19. The method of claim 17 , wherein the coupling element is attached to the base plate and extends through the reaction mass.
20. The method of claim 17 , further comprising:
retracting the coupling element within the reaction mass; and
moving the source element to a new position within the non-vertical borehole.