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The present invention relates to an apparatus for dropping a ball into a wellbore. The apparatus is particularly useful for dropping a ball that has a diameter that is larger than the diameter of a bore within a wellbore tool above the apparatus. The ball-releasing apparatus first comprises a tubula

The present invention relates to an apparatus for dropping a ball into a wellbore. The apparatus is particularly useful for dropping a ball that has a diameter that is larger than the diameter of a bore within a wellbore tool above the apparatus. The ball-releasing apparatus first comprises a tubular body. The tubular body has a bore therethrough that is in fluid communication with the bore of the wellbore tool. A piston is placed within the tubular body. The piston has a top end disposed within the tubular body, and a bottom end disposed below the bore of the wellbore tool. The ball-releasing apparatus further comprises a connector for releasably connecting the piston to the ball. In one arrangement, the ball-releasing apparatus is connected to the bottom of a wiper plug for dropping a ball during a wellbore cementing operation. In one aspect, the ball is dropped by dropping a second ball having a diameter that will pass through the wellbore restriction, and then injecting fluid under pressure against the second smaller ball in order to actuate the releasable connection.

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1. An apparatus for releasing a first ball into a wellbore, the first ball having a diameter that is greater than the diameter of a restriction in the wellbore above the apparatus, and the apparatus being connected to a wellbore tool, the wellbore tool having a bore therethrough, the ball-releasing

1. An apparatus for releasing a first ball into a wellbore, the first ball having a diameter that is greater than the diameter of a restriction in the wellbore above the apparatus, and the apparatus being connected to a wellbore tool, the wellbore tool having a bore therethrough, the ball-releasing apparatus comprising: a tubular body, the tubular body having a fluid flow path therethrough in fluid communication with the bore of the wellbore tool; a piston having a top end and a bottom end, the top end being disposed within the tubular body, and the bottom end being disposed below the bore of the wellbore tool; and a connector for releasably connecting the piston to the first ball. 2. The apparatus of claim 1, wherein the tubular body is connected to the wellbore tool proximal to a lower end of the wellbore tool. 3. The apparatus of claim 2, wherein: the body further comprises threads at a top end; and the connection between the body and the wellbore tool is a threaded connection. 4. The apparatus of claim 2, wherein the tubular body further comprises one or more ports to permit fluid to flow through the apparatus and into the wellbore, the ports being disposed intermediate the wellbore tool and the first ball. 5. The apparatus of claim 4, wherein the tubular body further comprises an enlarged diameter portion proximate to the lower end, the enlarged diameter portion being essentially dimensioned to closely cover the top of the first ball. 6. The apparatus of claim 5, wherein the ball has a recess for receiving the bottom end of the piston as the connector is actuated. 7. The apparatus of claim 6, wherein: the wellbore tool is a wiper plug used during a wellbore cementing operation, the wiper plug having an inner mandrel; and the top of the tubular body is connected to the inner mandrel. 8. The apparatus of claim 6, wherein the connector is actuated in response to fluid pressure applied through the bore of the wellbore tool. 9. The apparatus of claim 8, wherein the connector is further actuated by dropping a second ball, the second ball landing on the top end of the piston and being urged downward against the piston by the fluid pressure. 10. The apparatus of claim 9, wherein the piston is maintained by a shearable connection, the shearable connection being sheared as pressure is applied downward by the fluid pressure and the second ball. 11. The apparatus of claim 10, wherein the shearable connection is a shear pin placed through the piston. 12. The apparatus of claim 11, wherein the piston further comprises: an upper shoulder at the top end of the piston; a lower shoulder at the bottom end of the piston; and a body intermediate the upper and lower shoulders for receiving the shear pin. 13. The apparatus of claim 12, wherein the body of the piston further comprises a reduced diameter portion for receiving the collet fingers as the piston is inserted into the recess. 14. The apparatus of claim 13, wherein the top end of the tubular body is threadedly connected to the mandrel of the wiper plug. 15. The apparatus of claim 9, wherein the connector is at the bottom end of the tubular body. 16. The apparatus of claim 15, wherein the first ball has a recess for receiving the bottom end of the piston as the connector is actuated, and a lip above the recess; wherein the connector comprises a collet, the collet having a body disposed above the recess of the first ball when the first ball is connected to the apparatus, and a plurality of fingers that extend downward from the collet body and into the recess of the first ball for holding the first ball; and wherein the fingers are pulled from the recess of the first ball as the bottom end of the piston is inserted into the recess of the first ball. 17. The apparatus of claim 16, wherein the tubular body further comprises a reduced diameter portion for receiving the ports and the second ball. 18. A wiper plug for a wellbore cementing operation, the wiper plug comprising: a ma ndrel having a bore therethrough; and a ball-releasing apparatus for releasing a first ball into a wellbore from below the wiper plug, the first ball having a diameter that is greater than a diameter of the mandrel, wherein the ball-releasing apparatus comprises: a tubular body, the tubular body having a bore therethrough in fluid communication with the bore of the wiper plug, and a top end connected to the mandrel of the wiper plug;a piston having a top end and a bottom end, the top end being disposed within the tubular body, and the bottom end being disposed below the bore of the wellbore tool; anda connector for releasably connecting the piston to the first ball. 19. The apparatus of claim 18, wherein the tubular body further comprises one or more ports to permit fluid to flow through the ball-releasing apparatus and into the wellbore, the ports being disposed intermediate the wiper plug and the first ball. 20. The apparatus of claim 19, wherein the tubular body further comprises an enlarged diameter portion proximate to the lower end, the enlarged diameter portion being essentially dimensioned to closely cover the top of the first ball. 21. The apparatus of claim 20, wherein the ball has a recess for receiving the bottom end of the piston as the connector is actuated. 22. The apparatus of claim 20, wherein the connector is actuated in response to fluid pressure applied through the bore of the wiper plug. 23. The apparatus of claim 22, wherein the connector is further actuated by dropping a second ball, the second ball landing on the top end of the piston and being urged downward against the piston by the fluid pressure, and the second ball having a diameter that is less than the diameter of the mandrel of the wiper plug. 24. The apparatus of claim 23, wherein the piston is maintained by a shearable connection, the shearable connection being sheared as pressure is applied downward by the fluid pressure and the second ball. 25. The apparatus of claim 23, wherein the shearable connection is a shear pin placed through the piston. 26. The apparatus of claim 25, wherein the connector is at a bottom end of the tubular body. 27. The apparatus of claim,26, wherein the first ball has a lip above the recess; wherein the connector comprises a collet, the collet having a body disposed above the recess of the first ball when the first ball is connected to the apparatus, and a plurality of fingers that extend downward from the collet body and into the recess of the first ball for holding the first ball; and wherein the fingers are pulled from the recess of the first ball as the bottom end of the piston is inserted into the recess of the first ball. 28. The apparatus of claim 27, wherein the tubular body further comprises a reduced diameter portion for receiving the ports and the second ball. 29. The apparatus of claim 28, wherein the piston further comprises: an upper shoulder at the top end of the piston; a lower shoulder at the bottom end of the piston; and a body intermediate the upper and lower shoulders for receiving the shear pin. 30. The apparatus of claim 29, wherein the body of the piston further comprises a reduced diameter portion for receiving the collet fingers as the piston is inserted into the recess. 31. The apparatus of claim 30, wherein the top end of the tubular body is threadedly connected to the mandrel of the wiper plug. 32. A ball releasing apparatus for use for with a downhole tool, the ball-releasing apparatus comprising: a tubular body having a flow path for communication with a bore of the downhole tool; a piston having a top end and a bottom end, wherein the top end being disposable within the tubular body; and a connector for releasably connecting the piston to a first ball, wherein the first ball has a diameter greater than a diameter of a restriction above the first ball. 33. A wellbore plug assembly for wellbore cementing operations, the assembly comprising: a plug carrying member; a first plug operatively connected to the plug carrying member; a second plug; a ball releasing apparatus for releasing a first ball into a wellbore, the first ball having a diameter that is greater than a restriction above the second plug. 34. The wellbore plug assembly of claim 33, wherein the second plug is operatively connected to the plug carrying member. 35. The wellbore plug assembly of wherein33, the second plug is operatively connected to the first plug. 36. The wellbore plug assembly of claim 33, wherein the ball releasing apparatus is operatively connected to the second plug. 37. A method for cementing a liner in a wellbore, comprising: placing a workstring having a wellbore plug assembly disposed at a lower end thereof in the wellbore, the plug assembly including: a mandrel having a bore therethrough; anda ball releasing apparatus having a tubular body, a release member operatively connected to the tubular body and a releasably connected member for connecting the release member to a first ball, wherein the first ball has a diameter greater than a diameter of a restriction above the first ball; activating the ball release apparatus, thereby releasing the first ball into a downhole tool below the plug assembly; pumping cement through the workstring; releasing the plug assembly from the workstring; and urging cement into an annulus formed between the liner and the wellbore. 38. The method of claim 37, further including pumping cement through a float shoe disposed at the lower end of the liner. 39. The method of claim 37, further including activating a float collar disposed in the liner to prevent cement backflow after the cement enters the annulus. 40. The method of claim 37, further including securing the liner in the wellbore by activating a liner hanger. 41. The method of claim 37, wherein a cementing head is disposed at the surface of the wellbore.