Abstract:
A plug-dropping head capable of dropping balls or plugs or other objects is disclosed. The plug-dropping head has a compact design with a cylinder having multiple chambers for storage of plugs and/or balls. The device can be actuated manually or automatically, locally or remotely, to rotate the cylinder to present a different bore in alignment with a flowpath through the housing. An exterior signal indicates that the object has fallen through the device. An indexing feature assures alignment of the individual bores in the cylinder which contain a plug or wiper with the main passage through the tool. Flow can be maintained through the tool as the cylinder is rotated. Rotation of the cylinder allows an obstruction device in the flowpath to move out of the way to allow the ball or plug to drop when sufficient alignment is reached.

Description:
FIELD OF THE INVENTION 
     The field of this invention relates to devices which can be used to drop objects into a wellbore, particularly balls or plugs used during the process of cementing liners. 
     BACKGROUND OF THE INVENTION 
     Devices have been used to drop balls or plugs into the wellbore, generally as part of a cementing process for a liner or casing. Balls can be dropped to actuate external packers or liner hangers, while wiper plugs are dropped during the cementing process, with one of the major purposes to wipe the cement from the casing or liner. In this patent application, reference will be made to plug-dropping head with the understanding that different types of objects can be dropped or inserted through it and the reference to plug-dropping head is meant for convenience to be all-inclusive. In situations that required multiple drops of plugs, plug-dropping heads in the past have been stacked vertically, one on top of the other, such that the assemblies could grow to a dimension of nearly 20 ft. or more. Typical of such devices is one made by Nodeco, designated as a top-drive cementing head for dual darts. This assembly is indicated as being approximately 2400 mm long. Other companies have made plug-dropping heads to drop multiple plugs and, in general, all these prior designs have vertically stacked similar or identical assemblies on top of each other so that plugs are arranged one on top of the next and can be dropped sequentially, starting with the lowermost plug. Since these plug-dropping heads are frequently inaccessible to the rig floor, devices have been developed to remotely actuate these plug-dropping heads so that one or more plugs can be dropped when desired. Patents which illustrate the remote actuation of plug-dropping heads are U.S. Pat. Nos. 5,435,390 and 5,590,713. These patents also incorporate the use of vertical stacking of plugs. 
     The problem with the prior art designs is that the assemblies were overly long, expensive to build, and time-consuming to assemble and effectively operate, primarily due to inaccessibility. What is needed is a compact device which could be simply operated which would also allow for dropping multiple plugs and/or balls. One of the objectives of the present invention is to provide such a compact design which could hold a multiplicity of plugs and/or balls in discrete chambers in a cylinder rotating about a vertical axis. Thus, the objective of a compact design is achieved with the present invention in view of its configuration. Another objective of the present invention is to provide an indexing feature which assures the desired alignment for dropping the plugs. Another objective of the present invention is to signal visually to rig personnel that a plug or ball or other object has been dropped. Yet another object is to allow actuation of the device with ongoing circulation and to configure the device in such a manner that circulation continues as the device is actuated. Yet another object is to construct the device in the manner so as to transmit torque therethrough without stressing threaded connections. Yet another objective is to provide a simple design which is not only compact but also reliable in operation. Those and other objectives of the present invention will become more apparent to those of skill in the art from a review of the preferred embodiment which is described below. 
     SUMMARY OF THE INVENTION 
     A plug-dropping head capable of dropping balls or plugs or other objects is disclosed. The plug-dropping head has a compact design with a cylinder having multiple chambers for storage of plugs and/or balls. The device can be actuated manually or automatically, locally or remotely, to rotate the cylinder to present a different bore in alignment with a flowpath through the housing. An exterior signal indicates that the object has fallen through the device. An indexing feature assures alignment of the individual bores in the cylinder which contain a plug or wiper with the main passage through the tool. Flow can be maintained through the tool as the cylinder is rotated. Rotation of the cylinder allows an obstruction device in the flowpath to move out of the way to allow the ball or plug to drop when sufficient alignment is reached. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional elevation of the device showing a ball the instant before it is to drop through the device when the support flapper has rotated out of the way. 
     FIG. 2 is the view seen along lines  2 — 2  of FIG.  1 . 
     FIG. 3 is the view along lines  3 — 3  of FIG.  2 . 
     FIG. 4 is an external elevational view of the apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The plug-dropping head P is shown in FIG. 1 to be made of several components. A lower housing  10  has a threaded outlet  12 . Threaded outlet  12  continues as bore  14 . The lower housing  10  has a top surface  16  which accepts the cylinder  18  in a sealing arrangement accomplished by O-ring or any other type of seal  20 . The cylinder  18  has a circumferential ring  22  also seen in FIG.  2 . Circumferential ring  22  has outer teeth  24  which mesh with gear  26 . Gear  26  is connected to crank  27  so that when crank  27  is rotated, the cylinder  18  is rotated with respect to the lower housing  10  and the upper housing  28 . It should be noted that the depicted technique for rotating the cylinder  18  with respect to the housings  10  and  28  is intended to be schematic and to also represent numerous alternative ways of accomplishing the relative rotational movement of the cylinder  18 . For example, cylinder  18  can be moved by a motor powered electrically, pneumatically, or hydraulically, connected to a drive to cylinder  18 . A stepper motor can be used which will accurately rotate the cylinder  18  the precise amount for alignment of the next ball or plug. Those skilled in the art will appreciate other techniques that can be employed to accomplish the rotation of cylinder  18 . While the lower end  30  of cylinder  18  extends into a receptacle  32  in lower housing  10 , the upper end  34  of cylinder  18  extends into a receptacle  36  of upper housing  28 . As previously stated, seal  20  seals adjacent the lower end  30  of cylinder  18 , while seal  38  seals adjacent the upper end  34  of cylinder  18 . Seal  38  is located within receptacle  36  of upper housing  28 . 
     Upper housing  28  has a threaded inlet  40  which extends into bore  42 , which is in alignment with bore  14 . It can be readily seen that the central axis  44  of the plug-dropping head P is offset from the central axis  46  of the cylinder  18 . This is more clearly seen in FIG. 2 where the central axes are marked in the plan view. 
     Referring again to FIG. 1, a soft metallic or nonmetallic thrust bearing  48  is installed in the lower housing  10  to facilitate the rotation of the cylinder  18  with respect to the lower housing  10  and upper housing  28 . The thrust bearing  48  can be made of brass or bronze or PTFE or any other compatible material which will facilitate the relative rotation while having sufficient strength to support the weight of the assembly of cylinder  18 . 
     A cover  50  has a series of slots  52  as shown in FIG.  4 . Tabs  54  extend into slots  52  after the cover  50  has been attached to the lower housing  10  at thread  56 . A bolt  58  holds the tab  54  in slot  52 . The upper housing  28 , as shown in FIG. 3, is secured to the cover  50  by nut  60  via threaded connection  62 . Cover  50  has a series of windows  64  through which a lug  66  held by bolt  68  is inserted and fastened. The purpose of lug  66  is to transmit torque from upper housing  28  to cover  50  and to avoid placing applied torque on the threaded connection  62 . Similarly, the tabs  54  act to transfer torque from the cover  50  to the lower housing  10  and avoid placing applied torque on the threaded connection  56 . Those skilled in the art will appreciate that during the cementing procedure, the liner being cemented may be rotated and the string supporting the liner will be connected to the plug-dropping head P through the connections  12  and  40  such that a turning force applied at the rig will be transmitted through the plug-dropping head P in some installations when the liner is being rotated. 
     As previously stated, the operation of the plug-dropping head P can be automated so that a remote signal can be received at the plug-dropping head P and electronics or other control mechanisms can be actuated to accomplish the turning of the cylinder  18  when desired. A space  70  exists between the cover  50  and the cylinder  18  due to the offset mounting of the cylinder  18  with respect to the axis  44  in which the control mechanisms and/or drive mechanisms can also be installed. 
     Referring to FIG. 2, the cylinder  18  is shown to have bores  72 ,  74 ,  76 , and  78 . These bores have centerlines which are preferably equidistant from axis  46 . Although four bores are shown, other configurations having greater or fewer numbers of bores in cylinder  18  can be employed without departing from the spirit of the invention. In the plan view of FIG. 2, bore  78  is in alignment with bores  14  and  42 . Bore  78  shows clear which can be the position during the pumping of the cement or other fluids. Ultimately, due to the rotation of the cylinder  18 , bores  76 ,  74  and  72 , respectively, can come into sufficient alignment with bores  14  and  42  so as to allow a ball or plug therein to drop through bore  14 . Looking at FIG. 2, the cylinder  18  rotates in a clockwise direction as shown by arrow  80 . A ratchet  82 , shown schematically in FIG. 2, permits only rotation in the direction of arrow  80  without reverse rotation. Those skilled in the art will appreciate that other types of ratcheting devices or their equivalents can ensure unidirectional rotation of the cylinder  18  without departing from the spirit of the invention. Similarly, rotation can be counterclockwise without departing from the spirit of the invention. 
     Referring again to FIG. 1, a plug  84  is secured by threads  86  in bore  88 . In the preferred embodiment, bore  88 , as shown in FIG. 2, is located adjacent the bore  78  such that balls or plugs can be loaded into bores  72 ,  74 , and  76  in conjunction with clockwise rotation of the cylinder  18  before any of the bores  72 ,  74  and  76  are brought into alignment with bores  14  and  42 , respectively, on the lower housing  10  and upper housing  28 . A bleed passage  89  is provided in upper housing  28  such that the threaded connection  86  continues the engagement of plug  84  to upper housing  28  as O-ring or any other type of seal  90  passes above bleed passage  89  to allow pressure to vent out of the plug-dropping head P through passage  88  before the removal of plug  84 . Plug  84  is removed for loading of balls or plugs into the bores such as  72 ,  74  and  76 . 
     Another feature of the present invention is the signaling feature. Referring to FIG. 3, a flapper  92 , which acts as an obstruction device, is shown in two positions. Flapper  92  pivots about rod  94  whose end can be seen in FIG.  3 . Rod  94  is shown more clearly in FIGS. 1 and 2. Rod  94  extends through lower housing  10 , with seal  96  preventing the escape of pressure in the plug-dropping head P. The lower end  30  of the cylinder  18  has a series of oval-shaped recesses  98 , shown in FIG.  2 . In the preferred embodiment, recesses  98  are oriented 90° from each other to correspond to alignment of bores  72 , 74 , 76  or 78  with bores  14  and  42 . Rod  94  has a cam  100  which normally rides on the bottom surface  102  of cylinder  18 . As any one of the bores illustrated in FIG. 1 come into alignment with bores  14  and  42 , the oval-shaped opening or recess  98  presents itself adjacent the cam  100 , thus allowing the weight of flapper  92  to initiate 90° rotational motion as tab end  104  rotates into recess  98 , as shown in FIG.  3 . At other times, recess  98  is rotated away from tab end  104 , causing a pivoting of the flapper  92  with rod  94 . Thus, referring to FIG. 3, the flapper  92  is shown in the open position where a ball or plug can be dropped and the same flapper  92 ′ is also shown in FIG. 3 in the closed position. The flapper  92 ′ remains in the closed position until there is near alignment or complete alignment between a given bore in the cylinder  18  and bores  14  and  42 . Attached to the end of rod  94  is indicating flag  106  which is oriented downwardly toward threaded outlet  12  when the flapper  92  is in the open position shown in FIG.  3 . FIG. 4 also illustrates the flag  106  indicating to rig personnel that a ball or plug has dropped through bore  14 . The other position of flag  106  is 90° rotated from the position shown in FIG.  4  and indicated as  106 ′ in FIG.  4 . 
     Those skilled in the art will appreciate that although a 90° rotating flapper  92  has been illustrated as the device to selectively retain a ball or plug prior to its being dropped through bore  14 , other devices can be used, and the primary objective of the assembly just described is to give rig personnel a signal that a ball or plug has become aligned with the bore  14  and the ball or plug has been dropped due to removal of a support which would keep the ball or plug from falling through bore  14 . Thus, a 90° rotating plug or a series of fingers could also be used as long as they were structurally sound to prevent the ball or plug from passing therethrough under circulating pump pressure internal to the plug-dropping head P. It should be noted that there is no need for the flapper  92  to close off the passage and, in fact, it is desirable to maintain circulation through the plug-dropping head P, even with the flapper  92 ′ in the closed position. Along those lines, to ensure the ability to flow sufficiently, particularly while cylinder  18  rotates, a bore  108  is provided in cylinder  18  along central axis  46 . In the preferred embodiment, the upper housing  28  has a cutaway  110  which allows flow through bore  42  to go in the direction of arrows  112  and  114  to accomplish flow through bore  108  back into bore  14 , while at the same time flow is going straight through from bore  42  through the aligned bore in cylinder  18  into bore  14 . Those skilled in the art will appreciate that the configuration shown in FIG. 2 will always allow flow through bore  108  of cylinder  18  through the recess  110  and its equivalent recess,  116  in bottom housing  10 . While the recesses have been shown in upper housing  28  and lower housing  10 , they could as easily be located in the cylinder  18  itself. The recesses can be configured for continuous flow through bore  108  or they can be sloped or tapered so that flow through bore  108  only occurs for a short period of time during rotation of cylinder  18  and effectively is significantly reduced or eliminated when a bore in cylinder  18  comes into alignment with bores  42  and  14 . 
     FIG. 3 also indicates an indexing feature which ensures proper alignment of a given bore in cylinder  18  with bores  14  and  42 . Circumferential ring  22  has a series of holes  118 , one of which is shown in FIG.  2 . Mounted to the lower housing  10  is a spring-loaded indexing pin  120 . In the manual version shown in FIGS. 2 and 3, the pin  120  is pulled down before the crank  27  is rotated. Once there has been some angular rotation of cylinder  18 , the pin  120  is released and cranking continues with crank  27 . Ultimately, when the next bore in cylinder  18  is in alignment with bores  14  and  42 , the pin  120  pops into hole  118  to prevent further rotation. Those skilled in the art will appreciate that other indexing devices, including those that are automatically operated, are also within the purview of the invention. Thus, especially if the cylinder  18  is motor-driven, a host of devices can be used to stop motor operation after a predetermined angular displacement of cylinder  18 . This can be accomplished by using, for example, a stepper motor to control the rotation of cylinder  18 . It can also be accomplished by putting targets on cylinder  18  and sensing the passage of such targets upon a predetermined rotation of cylinder  18 . The important thing is that there is a mechanism, be it manual or automatic, to ensure that movement of cylinder  18  stops when a given bore in cylinder  18  comes into sufficient alignment with bores  14  and  42 . 
     Those skilled in the art will appreciate that the figures are truly schematic in several senses. The illustration of a manual crank  27  is intended to be sufficiently schematic so as to encompass a power-driven cylinder  18  which is either locally controlled or remotely controlled from a location removed from the plug-dropping head P. The mechanism involving rod  94  is also intended to be schematic for alternative systems which retain a plug or ball from falling into bore  14  until there is sufficient alignment with the bore in cylinder  18 . Further, the schematic representation of the assembly involving flag  106  with rod  94  is also intended to broadly illustrate numerous alternative techniques of giving visual, audible or other signals to rig personnel that rotation of cylinder  18  has occurred and the ball or plug has dropped. It should be noted that FIG. 1 illustrates the presence of a ball  122  (which is normally dropped before plugs) suspended in bore  76  just instantaneously before it drops through bore  14  since the flapper  92  is in the open position. Thus, for example, one application of the plug-dropping head P can be the placement of a ball in bore  76  with a plug in bore  74  and bore  72  such that rotation in the direction of arrow  80  will result in first a ball being dropped and the next two rotations will allow plugs to be dropped. The plugs are not shown in the drawings for clarity, and the design of the plugs themselves is not a part of this invention. 
     Those skilled in the art will now appreciate that what has been demonstrated is a compact design for a plug-dropping head P which can be operated completely manually or automatically, locally or from a remote location and, in a very compact design, can allow rig personnel to drop one or more balls and/or one or more plugs in a very simple design which will operate reliably. 
     Also illustrated in FIG. 2 is a counter-balancing weight  124 . Since the cylinder  18  is mounted off-center from axis  44  and may be rotated during cementing, the counterbalancer  124  counterbalances the offset mounting of the cylinder  18  so that vibration is reduced or eliminated. Those skilled in the art will appreciate that the cylinder  18  is mounted in an offset manner on axis  46  so that its various bores can be rotated into a central position in alignment with longitudinal axis  44 . Other type of delivery systems can be used instead of cylinder  18  with bores thereon. Instead of a cylinder  18 , a ring with internal dividers can be used such that turning the ring on its vertical axis will position the next ball or plug for dropping. A belt with dividers can also be used so that rotating the belt about a vertical axis will position successive balls or plugs for dropping. 
     The compact design of the plug-dropping head P allows faster rig-up due to its lightweight nature and its compact design. The design is fairly simple and the sealing components, such as seals  90 ,  38 ,  20 , and  96  can be easily replaced, even by rig personnel, if necessary, at the location. The design incorporates a feature so as not to stress threaded connections  56  and  62  when torques are transmitted through the plug-dropping head P. A signaling system is also incorporated and the number and size of the bores in cylinder  18  can be varied to accommodate a particular application. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.