[0001] This application claims benefit of U.S. Provisional Patent Application Serial No. 61/909,701 , filed November 27, 2013, the contents of which are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] Embodiments of the invention generally relate to a ball stack indicator of a ball dropper for indicating that a ball has been dropped from the ball dropper.

Description of the Related Art

[0003] In certain wellbore operations, a ball dropper may be used to drop one or more balls from the surface into a wellbore to actuate a downhole tool. The ball dropper may include a vertical ball stack that contains several balls stacked on top of each other. One or more of the balls are dropped as required for each wellbore operation. It is important to keep track of the number of balls in the vertical ball stack at all time, and to ensure that a ball has been dropped each time the ball dropper is operated. However, since the balls are hidden from view when disposed in the vertical ball stack, it is sometimes difficult to keep track of the number of balls and to verify that a ball was dropped when required.

[0004] Therefore, there is a need for a visual ball stack indicator. SUMMARY OF THE INVENTION

In one embodiment, a ball drop system may comprise a ball stack including a plurality of balls and a weighted member disposed on top of the balls; and a ball stack indicator including an inner magnet disposed within a tubular member and an outer magnet secured to an outer surface of the tubular member by a magnetic attraction to the inner magnet, the inner magnet being connected to the weighted member by a cable member. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] So that the manner in which the above recited features of the invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0006] Figure 1 illustrates a ball drop system having a ball stack and a ball stack indicator in a first position, according to one embodiment.

[0007] Figure 2 illustrates the ball drop system with the ball stack and the ball stack indicator in a second position, according to one embodiment.

[0008] Figure 3 illustrates the ball drop system having two ball stacks, according to one embodiment. DETAILED DESCRIPTION

[0009] Figure 1 illustrates a ball drop system 100 in an initial operating position. The system 100 includes a ball dropper 10, a ball stack 20, and a ball stack indicator 30. The ball dropper 10 includes a piston 2 coupled to a rod member 4 that is movably disposed in a cylinder 6. The rod member 4 includes a cavity 8, which may be a recess, pocket, or other type of opening formed in the body of the rod member 4 for receiving and/or transferring a ball from the ball stack 20. The cavity 8 may be used to move a ball from the ball stack 20, which is located at a position offset from a wellbore, to a position above the wellbore as further described herein.

[0010] A hydraulic power unit 3 powered by a generator 5 (such as a trailer mounted 10kw generator with a 220 VAC outlet) may be used to pressurize one or more chambers within the cylinder 6 that are separated by the piston 2 to extend and retract the rod member 4. Other types of power units may be used to pressurize the chambers in the cylinder 6 to extend and retract the rod member 4. Other types of actuation mechanisms, including pneumatic, hydraulic, and/or mechanical devices, may be used to extend and retract the rod member 4. [0011 ] In operation, the rod member 4 may be extended to move the cavity 8 to a position below the ball stack 20 such that a ball drops into the cavity. The rod member 4 may be retracted to move the ball to a position above the wellbore. The ball may drop out of the cavity 8 and into the wellbore by gravity. The wellbore may be cased or open hole as known in the art.

[0012] The cylinder 6 may be coupled to a center body 1 1 having a horizontal bore through which the rod member 4 moves and a vertical bore intersecting the horizontal bore. The center body 1 1 may be coupled to one or more spool members 12, a fracturing head 13, and a well head 14, each of which are in fluid communication with the vertical bore of the center body 1 1 . The center body 1 1 may include a fluid inlet 9 for pumping fluid through the vertical bore, through the cavity 8, and/or around the rod member 4, such as to pump a ball out of the cavity 8 and/or through the spool members 12, the fracturing head 13, and the well head 14. One or more valves 15 may be coupled to the spool members 12 to control fluid flow. [0013] The fracturing head 13 may include any type of fracturing head known in the art. One example of a fracturing head 13 may be the fracturing head 10 disclosed in U.S. Patent No. 8,100,175, the contents of which are herein incorporated by reference. The fracturing head 13 may be positioned below the ball dropper 10 and above the well head 14, and may be used to introduce pressurized fluid into the wellbore for conducting a well fracturing operation as known in the art. A pressurized fluid may be supplied into the wellbore through the fracturing head 13 to conduct a well fracturing operation, without having to flow through the ball dropper 10. The one or more valves 15 may be closed when flowing into the wellbore through the fracturing head 13 to fluidly isolate the ball dropper 10 from the pressurized fluid. [0014] The well head 14 may include any type of well head known in the art for controlling fluid flow into and out of a wellbore and/or for conducting one or more wellbore operations known in the art. In one embodiment, the cylinder 6, the center body 1 1 , the spool members 12, 17, 21 , the connecting body 16, fluid inlets 9, 24, the fracturing head 13, and/or the well head 14 may be coupled together using flanged, welded, threaded, and/or any other type of connections known in the art. In one embodiment, the cylinder 6, the center body 1 1 , the spool members 12, 17, 21 , the connecting body 16, fluid inlets 9, 24, the fracturing head 13, and/or the well head 14 may be tubular members having one or more bores disposed through the body of the tubular members.

[0015] The ball stack 20 may be coupled to the center body 1 1 by a connecting body 16 having a horizontal bore through which the rod member 4 moves and a vertical bore intersecting the horizontal bore. The vertical bore of the connecting body 16 may be in communication with the ball stack 20. Another spool member 17 may be coupled to the connecting body 16, and may also have a horizontal bore through which the rod member 4 moves. The spool member 17 may seal off one end of the ball dropper 20. [0016] The ball stack 20 may include a spool member 21 having a vertical bore that is in communication with vertical bore of the connecting body 16. One or more balls 22 may be stacked in the vertical bore of the spool member 21 . The balls 22 may drop into the connecting body 16, and may rest on the rod member 4. A weighted member 23 may be positioned on top of the stack of balls 21 to assist in forcing the balls 22 downward, such as into the cavity 8 of the rod member 4 when moved into a position below the stack of balls 22. The spool member 21 may include a fluid inlet 24 for pressurizing the ball stack 20 to assist in forcing the balls downward, such as into the cavity 8 of the rod member 4 when moved into a position below the stack of balls 22. [0017] The ball stack indicator 30 may be coupled to the ball stack 20. The ball stack indicator 30 may include a tubular member 31 that is coupled to the ball stack 20 and that is in sealed fluid communication with the bore of the spool member 21 via one or more ports 25 disposed through the wall of the spool member 21 . One or more inner magnets 32 may be disposed in the tubular member 31 , and may be connected to the weighted member 23 by a cable member 33 that extends through the port 25. One or more outer magnets 34 may be secured to and movable along the outer surface of the tubular member 31 by magnetic attraction to the inner magnet 32. The outer magnet 34 is moved along the outer surface of the tubular member 32 by the movement of the inner magnet 32 along the inner bore of the tubular member 31 . The tubular member 31 may be formed from any type of non-magnetic material, such as stainless steel, that does not interfere with the magnetic attraction between the inner magnet 32 and the outer magnet 34. [0018] One or more reed switches 35, as known in the art, may be coupled to the outer surface of the spool member 21 . The reed switches 35 may be spaced apart a predetermined distance, such as the amount of distance that the stack of balls 22 moves when one ball is removed from the stack of balls 22. The reed switches 35 may be located relative to the outer magnet 34 such that reed switch 35 closest to (or within a predetermined distance from) the outer magnet 34 is moved from an open circuit position to a closed circuit position by the magnetic field of the outer magnet 34. Conversely, each reed switch 35 may move from the closed circuit position to the open circuit position as the outer magnet 34 moves away or outside of a predetermine distance from the reed switch 35.

[0019] The reed switches 35 may be in communication with a visual indicator 40 and/or a ball counter 45 via a wired connection 41 and/or a wireless connection. The visual indicator 40 may include one or more LEDs or other lights that correspond to each reed switch 35 and that provide a visual indication of the reed switch 35 that has been switched to the closed position. The ball counter 45 may include an electronic device having a digital display that provides a visual count of each reed switch 35 that has been switched to the closed circuit position by the outer magnet 34. The electrical circuit that is opened and closed between the reed switches 35 and the visual indicator 40 and/or the ball counter 45 may be powered by a power source, such as a battery pack. The power source may also include the generator 5 or a trailer mounted 10kw generator via a plug-in outlet and direct current convertor (e.g. 12 VDC). The placement of the reed switches 35 relative to the movement of the outer magnet 34 and the inner magnet 35 via the connection to the weight member 23, relative to the height and position of the stack of balls 22 as each ball 22 is removed, provides an unobstructed and continuous visual indication of the number of balls 22 in the ball stack 20 and/or verification that a ball 22 has been removed from the ball stack 20 and dropped from the ball dropper 10.

[0020] Figure 1 illustrates the ball dropper 10 with the rod member 4 in a retracted position, such that the cavity 8 is positioned within the center body 1 1 above the well head 14.

[0021] Figure 2 illustrates the ball dropper 10 with the rod member in an extended position, such that the cavity is positioned within the connecting body 16 below the ball stack 20 and the stack of balls 22. As illustrated in Figure 2, one ball 22 from the stack of balls 22 drops into the cavity 8 of the rod member 4. The rod member 4 may be moved back to the retracted position to move the ball 22 in the cavity 8 into the center body 1 1 where the ball 22 may be dropped into the wellbore by gravity and/or pumped into the wellbore by pressurized fluid via the fluid inlet 9. [0022] Pressurized fluid may be supplied via the fluid inlet 9 and/or the fracturing head 13 to pump the ball 22 into the wellbore and/or to actuate a downhole tool. After the ball 22 has landed at a desired location within the downhole tool, pressurized fluid may be supplied through the fluid inlet 9 and/or the fracturing head 13 to pressurize and actuate the downhole tool. For example, the downhole tool may include a fracturing sleeve as known in the art, and the ball 22 and pressurized fluid may be used to open a port in the fracture sleeve to supply a fracturing fluid via the fracturing head 13 and/or the fluid inlet 9 into the wellbore.

[0023] As each ball 22 is removed and dropped, and the height of the stack of balls 22 is shortened, the weighted member 23 moves downward and pulls the inner magnet 32 upward via the cable member 33. As the inner magnet 32 is moved upward, the outer magnet 34 also moves upward along the outer surface of the tubular member 31 by attraction to the inner magnet 32. The outer magnet 34 opens and closes the reed switches 35 as it moves upward along the outer surface of the tubular member 31 after each ball 22 is removed from the ball stack 20 and dropped into the wellbore.

[0024] Each reed switch 35 may provide a signal to the visual indicator 40 and/or the ball counter 45 when switched by the outer magnet 34. As stated above, the reed switches 35 may be positioned along the outer surface of the spool member 21 to correspond to the position of each ball 22 in the ball stack 20. In this manner, the outer magnets 34 alone and/or in combination with the reed switches 35, the visual indicator 40, and/or the ball counter 45 may provide an unobstructed and continuous visual indication of the number of balls 22 in the ball stack 21 and/or verification that a ball 22 has been removed from the ball stack 20 and dropped from the ball dropper 10.

[0025] Figure 3 illustrates the ball drop system 100 according to one embodiment. The ball drop system 100 shown in Figure 3 includes many of the same components illustrated in Figures 1 and 2, which are identified by the same reference numerals. All of the embodiments described herein can be used with the system 100 illustrated in Figures 1 , 2, and 3. As illustrated in Figure 3, the ball drop system 100 includes two ball stacks 20A, 20B and two cavities 8A, 8B formed in the rod member 4. The rod member 4 may be movable disposed through cylinder 6, spool members 17A, 17B, connecting bodies 16A, 16B, and center body 1 1 . Each ball stack 20A, 20B may be configured with the ball stack indicator 30 discussed above and shown in Figures 1 and 2, but has been removed in Figure 3 for clarity.

[0026] Referring to Figure 3, as the rod member 4 is extended and retracted relative to the cylinder 6 (via the piston 2 and the hydraulic power unit 3), the cavities 8A, 8B are positioned relative to the ball stacks 20A, 20B and the center body 1 1 that one ball from one ball stack 20A, 20B is dropped from one cavity 8A, 8B into the wellbore, while one ball from the other ball stack 20A, 20B is dropped and loaded into the other cavity 8A, 8B. A single stroke of the rod member 4 loads one ball from one ball stack 20A, 20B into one cavity 8A, 8B, while dropping another ball from the other ball stack 20A, 20B from the other cavity 8A, 8B into the wellbore through the spool member 12 (and the fracturing head 13 and the well head 14 illustrated in Figures 1 and 2).

[0027] The ball stacks 20A, 20B may be positioned on opposite sides of the center body 1 1 , which is in communication with the wellbore. By using two ball stacks 20A, 20B, the overall height of each ball stack 20A, 20B may be reduced while maintaining the same number of balls 22 that can be dropped from the ball drop system 100 without reloading the ball stacks 20A, 20B. Also by using two ball stacks 20A, 20B, the ball drop system 100 may be able to drop the balls 22 faster and more efficiently with each stroke of the rod member 4 compared to a single ball stack system. [0028] In one embodiment, each one of the balls 22, 22A, 22B may be substantially the same size, including substantially the same diameter. In one embodiment, each one of the balls 22, 22A, 22B may have a different diameter than the diameters of the balls positioned above and/or below it. In one embodiment, the ball drop system 100 may be used to drop one or more balls 22, 22A, 22B into a wellbore to actuate one or more downhole tools for conducting one or more wellbore operations, such as a well fracturing operation. One example of a downhole tool that may be operated using one or more balls 22, 22A, 22B dropped from the ball drop system 100 is the downhole tool 10 disclosed in U.S. Patent Application Publication No. 2013/0025868, the contents of which are herein incorporated by reference.

[0029] While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.