Abstract:
A plug-dropping head in which the objects to be dropped are placed in individual discrete passages. A motor-driven or hand-operated rotating member orients an entrance to a passage going through it to, in series, individual passages in the housing for sequential dropping of objects downhole. A relief port is provided so that as the rotating outlet member moves from one passage in the housing to the next, the relief passage allows continuing flow delivered by the surface pump.

Description:
FIELD OF THE INVENTION 
     The field of this invention relates to surface-mounted equipment which can be used for dropping articles of various sizes and shapes downhole to facilitate downhole operations. 
     BACKGROUND OF THE INVENTION 
     Many downhole operations require sequential dropping of various objects downhole to facilitate a downhole operation. The sequence may involve dropping a ball on a ball seat to close off the wellbore to allow pressure to be built up to actuate tools such as packers or hangers or downhole valves. Cementing operations typically involve dropping one or more wiper plugs in a specific order to, for example, wipe the wellbore clean of the cement. These objects to be dropped downhole are frequently assembled in surface equipment referred to as a plug-dropping head. In the past, plug-dropping heads have been stacked vertically to accommodate the sequential dropping of objects downhole. Thus, the lowermost object would be dropped first and so forth up until the topmost plug-dropping head has released the object stored therein. The problem with this arrangement is that it gets to be quite tall and in most applications, the plug-dropping heads are inaccessible. One way the prior designs have compensated for this inaccessibility problem is to actuate the plug-dropping heads by remote control. Such techniques are described in U.S. Pat. Nos. 5,435,390 and 5,590,713. 
     One of the objects of the present invention is to provide a compact design which can be operable to insert a plurality of objects downhole within fairly confined vertical space limits at the surface. The object of the device is to present a compact design which can efficiently deliver a series of objects downhole. Another object of the invention is to allow circulation to continue as the device operates to sequentially drop objects downhole. These and other advantages of the present invention will become more apparent to those skilled in the art from a review of the description of the preferred embodiment below. 
     SUMMARY OF THE INVENTION 
     A plug-dropping head is disclosed in which the objects to be dropped are placed in individual discrete passages. A motor-driven or hand-operated rotating member orients an entrance to a passage going through it to, in series, individual passages in the housing for sequential dropping of objects downhole. A relief port is provided so that as the rotating outlet member moves from one passage in the housing to the next, the relief passage prevents deadheading of the surface pump. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional elevational view showing the apparatus in a position where one of the objects is being dropped downhole. 
     FIG. 2 is a section view along lines  2 — 2  of FIG.  1 . 
     FIG. 3 is the view of FIG. 2, with the outlet member rotated approximately 80° from the position shown in FIG. 2, showing the outlet member arriving close to the position where the next object will be dropped downhole. 
     FIG. 4 is a sectional elevational view showing a stackable configuration. 
     FIG. 5 is a topmost unit for a stackable configuration showing a spider  73  to stop reverse movement in an upflow situation. 
     FIG. 6 is a section view along line  6 — 6  of FIG.  4 . 
     FIG. 7 is a section view along line  7 — 7  of FIG.  5 . 
     FIG. 8 is a section view through guide  70 . 
     FIG. 9 is a section view showing a stacked arrangement of the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the apparatus A has a top sub  10  connected to a body  12 . Body  12  is connected to bottom sub  14 . These components together comprise the housing. Thread  16  is used to connect the surface pumping equipment (not shown) to the apparatus A. Thread  18  connects the apparatus A to the wellbore. A passage  20  extends through the top sub  10  and ultimately continues as passage  23  in the bottom sub  14 . A rotatably mounted outlet device  22  is secured in the bottom sub  14 . It has a gear  24  which is driven by a drive schematically shown as  26 . Operation of the drive  26  rotates the entrance  28  of a passage  30  which extends through the outlet device  22 . Entrance  28  is off-center from the longitudinal axis of body  12 . 
     Within body  12  there is a tubular component  32  which defines a series of passages  34 ,  36 ,  38  and  40 . Those skilled in the art will appreciate that varying the amount or size of these passages is within the spirit of the invention. These passages are illustrated in FIG.  3 . Each passage has, internally to it, a flapper or other retaining device  42  which is preferably pivotally mounted on a rod  44 . When the entrance  28  of the passage  30  on the outlet device  22  is not in alignment with, for example, passage  36 , a solid portion of the outlet device  22  is presented at the base of passage  36 , thus preventing the flapper  42  from pivoting about its pivot rod  44 . The same is true for the other passages except that the initial passage, which is shown in FIG. 3 as passage  34 , does not have a flapper. The apparatus A is configured for the start of operations with the passage  34  in alignment with the entrance  28  to the outlet device  22  with the objects to be dropped downhole positioned in passages  36 ,  38 , and  40 , as an example. 
     Another feature of the tubular component  32  is relief passage  46 . FIG. 3 illustrates that passage  46  still overlaps passage  34  as the entrance  28  approaches alignment with passage  40 . Thus, the flow from the surface pumping equipment can still go through passage  46 , through passage  34 , until the flapper  48  can swing open when entrance  28  is fully in alignment with passage  40 , as shown in FIG.  2 . The object in passage  40  can be dropped through the outlet device  22 . At this point in time, the passage  46  in the position shown in FIG. 2 is fully obstructed as it is aligned with the solid portion of the tubular component  32  between passages  34  and  40 . 
     As shown in FIG. 1, a curved component  49  in entrance  28 , upon further counterclockwise rotation of the outlet device  22 , will engage the flapper that is in the downward position shown in FIG.  1  and force it upwardly to the position also shown in FIG. 1 in the course of rotation of the outlet device  22 . While a curved component  49  is preferred, other shapes can be used without departing from the spirit of the invention. 
     The apparatus A shown in FIG. 1 can be operated in stacks as long as the lowermost units are aligned for flow-through. The dropping of objects can begin from the uppermost unit and proceed down to the lowermost unit, or vice versa. When being used as a flow-through unit, a guide  70  is rotated with outlet device  22  to provide a smooth fluid transition from flowpath  20  to outlet device  22 . This will allow alternate operation of the stacked plug-dropping heads. Plugs may be dropped in any sequence, regardless of the number of heads stacked. This will allow the sequence to be changed without reloading or stopping circulation. The bottom of guide  70  shown in FIG. 5 also includes passage  71 , which functions like passage  46 . A drive shaft  72  transmits torque from outlet device  22  to guide  70 . The base of guide  70  also covers the top of bores  36 ,  38 , and  40  to prevent possible damage or movement from unexpected flow events. 
     The top plug-dropping head will have a spider  73  to block upward exit of any of the balls, plugs, or other devices in case of reverse flow, planned or otherwise. 
     Any number of parallel passages can be provided in tubular component  32  depending on the space or weight limitations applicable. 
     It should be noted that there are no seals between the outlet device  22  and cavity  50  in the bottom sub  14  in which it is disposed. The only seals necessary are  52 , which seal around the drive  26  shown schematically in FIG.  1 . 
     Accordingly, the apparatus A is easy to fabricate and operates reliably to drop in sequence a multiplicity of objects downhole. The drive is simple and the sealing requirements are minimal, thus ensuring low maintenance for the apparatus A. 
     Additional performance enhancements can be added, such as remote operation, as well as some sort of flag device which indicates the position of the outlet device  22  with respect to the passages in the tubular component  32 . 
     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.