Patent Publication Number: US-6220360-B1

Title: Downhole ball drop tool

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to a ball drop tool, and more particularly to a ball drop tool to be connected in a tool string lowered into a wellbore with coiled tubing. 
     In the drilling and completion of oil and gas wells, a wellbore is drilled into the subterranean producing formation or zone of interest. A string of pipe, e.g., casing, is typically then cemented into the wellbore. Oftentimes, a second string of pipe, commonly referred to as a liner, is attached at the lower end of the casing and extends further into the wellbore. Casing, when referred to herein, includes liners. A string of additional pipe, known as production tubing, is often lowered into the casing and/or the liner for conducting produced fluids out of the wellbore. 
     It is often necessary to lower downhole tools, such as packers or other tools into the casing, liner or production tubing to perform a desired operation. Many known downhole tools, such as but not limited to hydraulic disconnects, circulating subs and inflatable packers require a ball to be displaced down a tool string to engage a ball seat disposed in the tool. Typically, pressure is applied after the ball engages the seat to activate a mechanism in the tool. For example, with an inflatable packer, the ball may engage a seat to direct fluid into the inflatable elements of the packer, so that the packer will engage the casing, liner or production tubing. The foregoing are merely examples and there are a number of known tools that utilize and require a ball to engage a ball seat so that pressure can be applied in the tool above the seat to activate a mechanism in the tool string. 
     Coiled tubing is rapidly becoming a popular conveyance method for downhole tools, and the use of dropped balls to engage a seat in a tool lowered into the wellbore with coiled tubing is becoming more and more common. When coiled tubing is utilized to lower a tool into a wellbore, and it is necessary to drop a ball to engage a seat in the tool, the ball normally is manually inserted into the surface plumbing for the coiled tubing, so that the ball enters the coiled tubing at, or near the end of the tubing connected to the surface plumbing. The ball therefore enters the coiled tubing so that it must be pumped through the coiled tubing wraps on the reel, until it passes over a gooseneck which is utilized in connection with the coiled tubing. Pumping then continues for a period of time to insure that the ball has made its way through the coiled tubing to the seat in the downhole tool. Although such a method works in many circumstances, there are several drawbacks to this method. 
     The method described above for displacing a ball through coiled tubing is time-consuming and costly. It requires the usage of a large volume of fluid since at least one displacement volume of the coiled tubing is needed to get the ball around the wraps and to the downhole tool. Occasionally, balls are caught in the coiled tubing and never make it to the tool. For example, when small diameter balls are used in large coiled tubing, it is difficult to achieve a fluid velocity which will carry a small diameter ball through the wraps on the reel. 
     In addition, there are times when downhole devices above the ball seat have restrictions which would prevent a ball from passing therethrough to the ball seat in the tool. For example, filter screens are often run downhole to keep debris from plugging off small passages in the tools below. Actuating balls cannot pass through the screens. Likewise, it is possible that a tool having a small diameter would be positioned above the ball seat and thus would prevent the ball from passing therethrough. The present invention addresses the above needs by providing a downhole ball drop tool that can be positioned in the tool string below the coiled tubing and if necessary below any tools with restrictive diameters, and above the seat in the tool such that the ball does not have to pass through the coiled tubing wraps. 
     SUMMARY OF THE INVENTION 
     The present invention is a ball drop tool for use with coiled tubing which provides a method for dropping a ball into a downhole tool to engage a ball seat in the tool without the necessity of displacing the ball through the coiled wraps in a reeled coiled tubing. The ball drop tool comprises a ball drop housing having an upper end adapted for connection to a length of coiled tubing. The housing has a longitudinal opening therethrough and has a ball drop cage disposed therein. The ball drop cage has a closed upper end and an open lower end. A ball is disposed in the ball drop cage. A rocker arm having an upper end and a lower end is pivotally connected to the ball drop cage. 
     The ball drop tool may be connected to a lower end of the length of coiled tubing and lowered into the wellbore as part of a tool string having a ball seat therein. The ball drop tool has a retaining position and a releasing position. In the retaining position, the rocker arm is rotated such that a lower end of the rocker arm is positioned in an opening defined by the ball drop cage. The ball is trapped between the rocker arm and the closed upper end of the ball drop cage so that it cannot pass downwardly into the ball seat therebelow. The tool string can be lowered into a wellbore and once it has reached a selected location, fluid flow can be increased so that a flow, or pressure sufficient to begin to urge the ball drop cage downwardly in the ball drop housing is reached. The fluid will act on the upper cap and will also act on the balls through openings defined in the upper cap to cause the ball drop cage to begin to move downwardly in the ball drop housing. The rocker arm will pivot so that the lower end thereof is retracted from the opening defined by the ball drop cage. Once this occurs, the ball will be released and allowed to pass downwardly through the ball drop tool and into the tool having the ball seat disposed therein. Pressure can then be increased to activate any mechanism associated with the ball drop seat and ball. 
     Numerous objects and advantages of the invention will become apparent to those skilled in the art when the following detailed description of the preferred embodiment is read in conjunction with the drawings which illustrate such embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a cased well having a string of production tubing disposed therein and having a length of coiled tubing with a tool string including the downhole ball drop tool of the present invention inserted into the well by a coiled tubing injector and truck mounted reel. 
     FIGS. 2,  3  and  4  show cross sections of the ball drop tool of the present invention in different positions having actuating balls disposed therein. 
     FIG. 5 shows a partial section of the end view of the ball cage of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     After a well has been drilled, completed and/or placed in production, it is often necessary to perform any number of procedures therein such as but not limited to perforating, setting plugs, setting cement retainers, spotting permanent packers and the like. Such procedures are often carried out by utilizing coiled tubing. Coiled tubing is a flexible tubing, which can be stored on a reel when not being used. When used for performing well procedures, the tubing is passed through an injector mechanism, and a well tool is connected to the end thereof. A variety of tools may be connected in a tool string lowered in the well on the coiled tubing, and very often one of the tools will have a ball seat for receiving an actuating ball. Once the ball has engaged the seat, pressure can be increased to activate a mechanism in the tool string. The use of dropped balls through coiled tubing, and the use of ball seats in connection with a variety of tools, including but not limited to hydraulic disconnects, inflatable packers, hydraulic setting tools and pressure firing heads is common and is well known. 
     The injector mechanism pulls the tubing from the reel, straightens the tubing and injects it through a seal assembly at the wellhead, often referred to as a stuffing box. Typically, the injector mechanism injects thousands of feet of the coiled tubing with the well tool connected at the bottom end thereof into the casing string or the production tubing string of the well. A fluid, most often a liquid such as salt water, brine or a hydrocarbon liquid, may be circulated through the coiled tubing for operating well tools or for other purposes. The coiled tubing injector at the surface is used to raise and lower the coiled tubing and the well tool or tools during the service procedure and to remove the coiled tubing and well tools as the tubing is rewound on the reel at the end of the procedure. 
     Presently, when a tool having a ball seat is lowered into the coiled tubing, the ball is inserted into the surface plumbing and must be circulated through some or all of the coiled tubing wraps on the reel, out the bottom end of the coiled tubing and into the tool and the ball seat. The present invention provides a method and apparatus for positioning a ball between the bottom end of the coiled tubing and the ball seat. 
     Referring now to FIG. 1, a well  10  is schematically illustrated along with a coiled tubing injector  12  and a truck mounted coiled tubing reel assembly  14 . Well  10  includes a wellbore  16  having a string of casing  18  cemented therein in the usual manner. A string of production tubing  20  is also shown installed in well  10  within casing string  18 . Production string  20  may be made up of a plurality of tubing sections  22  connected by a plurality of joints or collars  24  in a manner known in the art. 
     A length of coiled tubing  26  is shown positioned in production tubing string  20 . A tool string  27  including a downhole tool  28  is connected to coiled tubing  26 . Tool  28  has a ball seat  29  therein for receiving a ball. The ball drop tool  30  of the present invention is generally designated in FIG. 1 by the numeral  30 . Ball drop tool  30  may be connected to the lower end of coiled tubing  26  with an adapter  31  or other tool or joint connector. Other well tools may be attached above or below tool  28 . 
     Coiled tubing  26  is inserted into well  10  by injector  12  through a stuffing box  32  attached to the upper end of tubing string  20 . Stuffing box  32  functions to provide a seal between coiled tubing  26  and production tubing string  20  whereby pressurized fluids within well  10  are prevented from escaping to the atmosphere. A circulating fluid removal conduit  34  having a shutoff valve  36  therein is sealingly connected to the top of casing string  18 . Fluid circulated into well  10  through coiled tubing  26  is removed from the well through conduit  34  and valve  36  and routed to a pit, tank or other fluid accumulator. 
     Coiled tubing injector  12  is of a kind known in the art and functions to straighten coiled tubing  26  and inject it into well  10  through stuffing box  32  as previously mentioned. Coiled tubing injector  12  comprises a guide mechanism  38 , commonly referred to as a gooseneck, having a plurality of internal guide rollers  40  therein and a coiled tubing drive mechanism  42  which is used for inserting coiled tubing  26  into well  10 , raising the coiled tubing or lowering it within the well, and removing the coiled tubing from the well as it is rewound on reel assembly  14 . 
     Truck mounted reel assembly  14  includes a reel  50  on which coiled tubing  26  is wound. A guide wheel  52  is provided for guiding coiled tubing  26  on and off reel  50 . A conduit assembly  54  is connected to the end of coiled tubing  26  on reel  50  by a swivel system (not shown). A shutoff valve  56  is disposed in conduit assembly  54 , and the conduit assembly is connected to a fluid pump (not shown) which pumps fluid to be circulated from the pit, tank or other fluid communicator through the conduit assembly and into coiled tubing  26 . Typically if an actuating ball is to be dropped without the use of the ball drop tool  30  of the present invention, the ball may be inserted in the piping between the coiled tubing and the shutoff valve  56 . Balls may also be introduced upstream of the valve and pumped therethrough. In either case, balls introduced in this manner must pass through the wraps of coiled tubing on the coiled tubing reel. 
     A fluid pressure sensing device and transducer  58  may be connected to conduit assembly  54  by connection  60 , and the pressure-sensing device may be connected to a data acquisition system  46  by an electric cable  62 . As will be understood by those skilled in the art, data acquisition system  46  may function to record the surface pressure of fluid being pumped through the coiled tubing. Other known methods may also be used to record fluid pressure. 
     Referring now to FIGS. 2-5, the details of ball drop tool  30  will be discussed. Ball drop tool  30  which may also be referred to as a ball drop assembly  30 , comprises a ball drop housing  70  having a ball drop cage  72  movably disposed therein. Ball drop cage  72  has a central opening  69  defined by a bore  71 . Ball drop tool  30  has at least one, and preferably three rocker arms  74 . Rocker arms  74  are pivotably connected to ball drop cage  72 . Each rocker arm  74  has a thickness  73  and a length  75 . 
     The ball drop assembly  30  of the present invention may be utilized with one or more balls, and the embodiment shown in FIGS. 2-4 has two actuating balls comprising a first or lower ball  76  and a second or upper ball  78 . In the embodiment shown, ball  76  is smaller than ball  78 . Balls of the same size may be used depending on the configuration of the tool and the ball seats to be utilized. Additional balls could be added simply by lengthening the tool  30  and placing balls therein. Ball drop cage  72  is movable from a retaining position  80 , which may be referred to as a first retaining position shown in FIG. 2, to a releasing position  82  as shown in FIG.  4 . The position shown in FIG. 3 may be referred to as a second retaining position  81 . Rocker arm  74  has corresponding first and second retaining positions  84  and  85  as seen in FIGS. 2 and 3 and a releasing position  86  as shown in FIG.  4 . 
     Housing  70  has an upper end  88 , a lower end  90 , an outer surface  92  and an inner surface  94 . Threads  96  are defined on inner surface  94  at the upper end of housing  70 . Housing  70  is thus adapted to be connected to the lower end of coiled tubing  26  with an adapter, joint or other tool which may be connected to ball drop assembly  30  at threads  96  and connected to coiled tubing  26 , thus connecting ball drop assembly  30  to coiled tubing  26 . Threads  100  are defined on the inner surface  94  of housing  70  at the lower end thereof and so that tool  30  may be connected to a tool, joint, or other threaded member therebelow. Ball drop assembly  30  is therefore adapted to be connected to the lower end of coiled tubing  26  and to be connected in tool string  27 . 
     Housing  70  has a first bore  102 , a second bore  104  and a third bore  106 . Second bore  104  has a smaller diameter than first bore  102  and is positioned radially inwardly therefrom. Third bore  106  has a diameter greater than second bore  104  and less than first bore  102 . Third bore  106  is thus positioned radially outwardly from second bore  104  and radially inwardly from first bore  102 . First or upper and second or lower cavities  108  and  110  respectively are defined in first bore  102 . First cavity  108  has first or upper and second or lower angular sides  112  and  114  connected by a base or flat portion  116 . Second cavity  110  is defined by first or upper and second or lower angular sides  118  and  120  connected by a flat or base portion  122  therebetween. Cavities  108  and  110  are spaced apart from one another in bore  102  such that they define a flat or fulcrum portion  124 . Fulcrum portion  124  defines a portion of bore  102 . Angular side  120  extends radially inwardly to bore  104  and thus may include an angular transition portion  126 . A downward facing shoulder  128  is defined by and extends between second and third bores  104  and  106  respectively. 
     Ball drop cage  72  has an upper end  129 , a lower end  131 , and essentially comprises a collet comprising a collet body  130 , and a plurality of collet fingers  132  having a first end  134  and a second end  136  extending therefrom. Upper end  129  is closed to prevent balls disposed therein from passing upwardly in the tool. Lower end  131  is open to allow the passage of balls therethrough. A plurality of collet heads  138  are defined at second end  136  of collet fingers  132 . Preferably, ball drop cage  72  comprises eight collet fingers. A first outer or collet body diameter  140  is defined on collet body  130 . Collet fingers  132  define a collet finger, or second outer diameter  142  positioned radially inwardly from first outer diameter  140 . Collet heads define a collet head diameter or third outer diameter  144  which extends radially outwardly from second or finger outer diameter  142 . An upward facing shoulder  146  is defined by and extends between second and third outer diameters  142  and  144  on ball drop cage  72 . A cap  148  is defined at the upper end  150  of collet body  130  which also comprises upper end  129  of ball drop cage  72 . Cap  148  has a plurality of openings  152  defined therein for allowing flow therethrough. 
     Slots  154  are defined in collet body  130  for receiving rocker arms  74 . A width  156  and length  158  of slot  154  are greater than thickness  73  and length  75  of rocker arms  74 . Openings  160  are defined in collet body  130  and intersect slots  154 . Rocker arms  74  have openings  162 . Openings  160  and  162  are for receiving pins, which are preferably self-locking pins  164 . Rocker arms  74  are thus pivotably attached to ball drop cage  72 , and preferably to the collet body portion  130  thereof. 
     Referring now to FIG. 2, ball drop cage  72  is received in ball drop housing  70  such that collet heads  138  are positioned in third bore  106 . Third bore  106  has an upper end  166  which is defined by shoulder  128  and a lower end  168 . A groove  170  is defined in bore  106  at the lower end thereof and has a retaining ring  172  received therein. A washer  174  is disposed in bore  106  and rests on retaining clip  172 . A spring  176  is disposed in bore  106  and, as shown in FIG. 2, engages washer  174  and collet heads  138 . Spring  176  thus biases ball drop cage  72  upwardly so that the collet heads  138  engage shoulder  128  to hold ball drop cage  72  in its first retaining position  80 . 
     Rocker arms  74  have a first or upper ends  182  and second or lower ends  184 . A first, or upper radially inwardly extending foot  186  is disposed at upper end  182  and a second or lower radially inwardly extending foot  188  is disposed at lower end  184  of each rocker arm  74 . In retaining position  80 , rocker arms  74  are rotated such that lower ends  184  thereof are rotated into opening  71  and engage first or lower ball  76 . Upper ends  182  of rocker arms  74  are rotated radially outwardly and are received in upper cavity  112 . 
     The operation of the invention is apparent from the drawings. Coiled tubing  26  is passed through tubing injector  12 . Tool string  27  which includes ball drop tool  30  is connected to the lower end of coiled tubing  26 . Ball drop tool  30  may be connected to the lower end of coiled tubing  26  with an adapter, joint or other tool or threaded connection therebetween. Ball drop tool  30  is thus positioned between the end of coiled tubing  26  and ball seat  29  disposed in downhole tool  28 , which is also connected in tool string  27 . Ball drop tool  30  is lowered into the well, along with the remainder of tool string  27  until a selected location in the well is reached. If desired, fluid may be circulated through the tool since ball drop tool  30  allows flow therethrough around ball drop cage  72  and through openings  152 . 
     Once the selected location is reached, flow rate can be increased to a sufficient rate such that the pressure acting across cap  148  of ball drop cage  72  and the balls will overcome the force of spring  176  and urge ball drop cage  72  downwardly. The increase in flow rate will act on the balls which will cause rocker arms  74  to pivot to the position shown in FIG. 3 which is referred to as second retaining position  81  since the actuating balls will not be released in that position. Continued flow will cause cage  72  to slide downward. Flat  124  acts similarly to a fulcrum, so that as cage  72  continues to slide downward, rocker arms  74  will pivot about pin  164  and rotate about flat  124  until lower foot  188  rotates radially outwardly and is received in lower cavity  110  as shown in FIG.  4 . First ball  76  is released and fluid flow therein will displace ball  76  downwardly until it reaches ball seat  29 . Ball drop cage  72  and rocker arm  74  can thus be referred to as a hydraulically actuated releasing means. Once ball  76  reaches seat  29 , pressure in the tool string can be increased to activate a desired mechanism associated with the ball seat, including those set forth above, or any other tool or mechanism that requires an increase in pressure, or a redirection of flow caused by a ball engaging a ball seat. 
     As is apparent from FIG. 4, which shows the sleeve in its releasing position, if a second or more balls are utilized, the balls are prevented from flowing downwardly by upper end  182  of rocker arm  74 . Once flow is slowed, or stopped to decrease pressure in the tool string, spring  176  will urge ball drop cage  72  back to its retaining position and, if a second ball is being utilized such as ball  78 , the ball will then take the position which was occupied by first ball  76  as shown in FIG.  2  and is ready to be dropped. 
     If a second ball is used, it may be necessary to increase the pressure to a sufficient amount to discharge the first ball and the first ball seat from the tool string or to open additional flow ports to allow flow through the tool so that the cage  72  can be moved to its releasing position. A second ball seat in the tool string can then be engaged by second ball  180 . Because first ball  76  is preferably smaller than ball  78 , it can pass through the seat which will be engaged by ball  78 . Once the first ball and ball seat have been removed or flow ports opened, flow can then be decreased so that cage  72  moves to its first retaining position  80  and is ready to drop second ball  78 . To drop second ball  78 , the process is simply repeated and flow is increased to move the cage from retaining position  80  to releasing position  82  and to displace the ball  78  downwardly until it is received in a second ball seat. Once second ball  78  engages the second ball seat, pressure can again be increased to activate a mechanism associated with the second ball seat. 
     Although ball drop tool  30  is shown disposed in a production tubing, it is apparent that the tool can be utilized in production tubing, or in the casing itself. It will be seen, therefore, that the ball drop tool of the present invention is well adapted to carry out the ends and advantages mentioned, as well as those inherent therein. The invention can be utilized with any tool which requires that a ball be dropped to engage a ball seat therein and is not limited by any of the specific examples provided. While presently preferred embodiments of the apparatus have been described for the purposes of this disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art. All such changes are encompassed within the spirit and scope of the appended claims.