Positive displacement dump bailer and method of operation

1. A dump bailer assembly for use in a wellbore comprising:

a downhole power unit having a housing and a moveable shaft;

a dump bailer body operably associated with the housing, the dump bailer body having first and second ends;

a piston disposed within the dump bailer body, the piston releasably coupled to the moveable shaft;

an actuation assembly disposed within the dump bailer body between the first end and the piston, the actuation assembly comprising a compressible mechanical biasing element;

a barrier operably associated with the dump bailer body and positioned proximate the second end; and

a wellbore agent disposed within the dump bailer body between the barrier and the piston;

wherein, the downhole power unit is capable of retracting the moveable shaft to shift the piston toward the first end to energize the actuation assembly;

wherein, continued operation of the downhole power unit releases the moveable shaft from the piston such that the energized actuation assembly shifts the piston toward the second end; and

wherein, interaction between the piston and the wellbore agent opens the barrier and dispenses the wellbore agent from the dump bailer body.

2. The dump bailer assembly as recited in claim 1 further comprising at least one shearable member initially coupling the piston to the moveable shaft.

3. The dump bailer assembly as recited in claim 1 further comprising at least one wiper seal operably associated with the piston.

4. The dump bailer assembly as recited in claim 1 wherein the mechanical biasing element is selected from the group consisting of coil springs, compression springs and Belleville washers.

5. The dump bailer assembly as recited in claim 1 wherein the barrier further comprises a frangible disk member.

6. The dump bailer assembly as recited in claim 1 wherein the wellbore agent further comprises a cement slurry.

7. The dump bailer assembly as recited in claim 1 wherein the downhole power unit further comprises a self-contained power source for providing electrical power.

8. The dump bailer assembly as recited in claim 1 wherein the downhole power unit further comprises:

an electric motor including a rotor; and

a jackscrew assembly including a rotational member connected to the rotor, the rotational member operably associated with the moveable shaft to impart longitudinal motion to the moveable shaft.

9. A dump bailer assembly for use in a wellbore comprising:

a downhole power unit having a housing, a moveable shaft, a self-contained power source for providing electrical power, an electric motor having a rotor and a jackscrew assembly having a rotational member connected to the rotor, the rotational member operably associated with the moveable shaft to impart longitudinal motion to the moveable shaft;

a dump bailer body operably associated with the housing, the dump bailer body having first and second ends;

a piston disposed within the dump bailer body, the piston releasably coupled to the moveable shaft by at least one shearable member;

an actuation assembly disposed within the dump bailer body between the first end and the piston, the actuation assembly comprising a mechanical biasing element operably associated with the piston to exert a force on the piston to shift the piston toward the second element;

a barrier operably associated with the dump bailer body and positioned proximate the second end; and

a wellbore agent disposed within the dump bailer body between the barrier and the piston;

wherein, the downhole power unit is capable of retracting the moveable shaft to shift the piston toward the first end to energize the actuation assembly;

wherein, continued operation of the downhole power unit breaks the at least one shearable member releasing the moveable shaft from the piston such that the energized actuation assembly shifts the piston toward the second end; and

wherein, interaction between the piston and the wellbore agent opens the barrier and dispenses the wellbore agent from the dump bailer body.

10. The dump bailer assembly as recited in claim 9 further comprising at least one wiper seal operably associated with the piston.

11. The dump bailer assembly as recited in claim 9 wherein the mechanical biasing element is selected from the group consisting of coil springs, compression springs and Belleville washers.

12. The dump bailer assembly as recited in claim 9 wherein the actuation assembly further comprises an opposing magnet assembly.

13. The dump bailer assembly as recited in claim 9 wherein the wellbore agent further comprises a cement slurry.

14. A method for operating a dump bailer assembly in a wellbore, the method comprising:

disposing the dump bailer assembly at a target location in the wellbore, the dump bailer assembly including a downhole power unit having a housing and a moveable shaft and a dump bailer body operably associated with the housing;

operating the downhole power unit to retract the moveable shaft;

shifting a piston disposed within the dump bailer body toward a first end of the dump bailer body with the moveable shaft;

energizing an actuation assembly disposed within the dump bailer body responsive to shifting the piston, the actuation assembly comprising a mechanical biasing element;

releasing the moveable shaft from the piston responsive to continued operation of the downhole power unit;

shifting the piston toward a second end of the dump bailer body with the energized actuation assembly subsequent to releasing the moveable shaft;

opening a barrier, operably associated with the dump bailer body and positioned proximate the second end, responsive to interaction between the piston and a wellbore agent disposed within the dump bailer body between the barrier and the piston; and

dispensing the wellbore agent from the dump bailer body.

15. The method as recited in claim 14 wherein operating of the downhole power unit to retract the moveable shaft further comprises operating an electrical motor powered by a self-contained power source.

16. The method as recited in claim 14 wherein the mechanical biasing element is selected from the group consisting of coil springs, compression springs and Belleville washers.

17. The method as recited in claim 14 wherein energizing the actuation assembly responsive to shifting the piston further comprises energizing an opposing magnet assembly.

18. The method as recited in claim 14 wherein releasing the moveable shaft from the piston responsive to continued operation of the downhole power unit further comprises breaking at least one shearable member initially coupling the piston to the moveable shaft.

19. The method as recited in claim 14 wherein dispensing the wellbore agent from the dump bailer body further comprises dispensing a cement slurry.