Apparatus and method of applying force to a stuck object in a wellbore

1. An apparatus for applying a force to a stuck object in a wellbore, comprising:

a work string extending in the wellbore;

a vibrating string having a vibrator engaged with the stuck object, the vibrator driving the vibrating string to impart the force to the stuck object; and

an isolator in the wellbore placed between the work string and the vibrating string decoupling a portion of a motion of the vibrating string from the work string.

2. The apparatus of claim 1 , wherein the vibrator drives the vibrating string in an axial motion.

3. The apparatus of claim 1 , wherein the vibrating string has a predetermined length L.

4. The apparatus of claim 3 , wherein vibrator operates substantially at a fundamental axial resonant frequency of the vibrating string determined by the equation, f=c/4L, where “f” is the fundamental axial resonant frequency and “c” is the speed of sound in the vibrating string.

5. The apparatus of claim 3 , wherein the vibrator operates substantially at a harmonic of a fundamental axial resonant frequency.

6. The apparatus of claim 1 , wherein the vibrator operates in a frequency range of 5-30 Hz.

7. The apparatus of claim 1 , wherein the vibrator operates at a peak-to-peak amplitude of at least 1 inch.

8. The apparatus of claim 1 , further comprising a sensor detecting the motion of the vibrating string and generating a sensor signal in response thereto.

9. The apparatus of claim 8 , further comprising a controller for controlling the vibrator based on the sensor signal.

10. The apparatus of claim 9 , wherein the controller is located at one of: a surface location, and a downhole location.

11. The apparatus of claim 1 , wherein the vibrator is attached proximate a top end of the vibrating string.

12. A method of applying a force to a stuck object in a wellbore, comprising:

extending a work string in the wellbore from a surface location;

engaging a vibrating string with the stuck object;

driving the vibrating string by a vibrator in the wellbore at a frequency to apply the force to the stuck object; and

isolating the work string from the vibrating string by an isolator in the wellbore between the vibrator and the work string such that a portion of the motion of the vibrating string is decoupled from the work string.

13. The method of claim 12 , wherein driving the vibrating string comprises driving the string in an axial motion.

14. The method of claim 12 , wherein the resonant string has a predetermined length L.

15. The method of claim 14 , wherein driving the vibrating string at a frequency comprises driving the string at a fundamental axial resonant frequency determined by the equation, f=c/4L where “f” is the fundamental axial resonant and “c” the speed of sound is the vibrating string.

16. The method of claim 14 , wherein driving the vibrating string at a frequency comprises driving the vibrating string at a harmonic of a fundamental axial resonant frequency of the vibrating string.

17. The method of claim 12 , wherein driving the vibrating string at a frequency comprises driving the vibrating string in a frequency range of 5-30 Hz.

18. The method of claim 12 , wherein driving the string at a frequency comprises driving the vibrating string at a peak-to-peak amplitude of at least 1 inch.

19. The method of claim 12 , further comprising detecting the motion of the vibrating string with a sensor and generating a sensor signal in response thereto.

20. The method of claim 19 , further comprising controlling the motion of the vibrating string based on the sensor signal.

21. The method of claim 12 , wherein driving the vibrating string at a frequency to apply the force to the stuck object induces a motion in the stuck object of sufficient frequency and amplitude to induce liquefaction of a substantially unconsolidated material in contact with the stuck object.