A pump down tool includes a resilient cup on the tool exterior to minimize leakage of pumped fluid around the outside of the tool when the tool is pumped into a well. The resilient cup is concave toward an upper end of the tool so it expands upon application of pressure to pump the tool into the well. The resilient cup is capable of expanding to a diameter sealing against the inside of the casing string. A fluid bypass around the resilient cup allows a fraction of the pumped fluid to stir up any proppant lying in the path of the tool thereby allowing the tool to move through a horizontal well without having to plow through the proppant.

This application is based on Provisional Application Ser. No. 61/795,104, filed Oct. 9, 2012, priority of which is hereby claimed. 
    
    
     This invention relates to a well tool that may be pumped into a well and more particularly to an improved tool that requires a smaller volume of liquid to pump the tool to its desired location. 
     BACKGROUND OF THE INVENTION 
     There are a number of situations in hydrocarbon wells where it is necessary or desirable to position a tool at a predetermined location in the well. In vertical wells, tools are conventionally run on the bottom of a wire line and use gravity to cause the tool to fall into the well. In horizontal wells, gravity can be used in the vertical leg but only for a very short distance into the horizontal leg. It has become customary to pump the tool on the end of a wire line to its desired location in the horizontal leg of a well. Pumping a liquid into the pipe string creates a dynamic pressure differential across the tool thereby propelling it along the horizontal leg. Because the tool is on the end of a wire line, the distance the tool is pumped can be controlled. 
     One problem with this approach is that substantial quantities of the pumped liquid, which is usually raw or treated water, are needed because creating a dynamic pressure drop across the tool requires that a large volume of liquid be pumped across the tool. It is not surprising to require twenty barrels of water a minute to propel a tool at an appropriate velocity in the horizontal leg of a hydrocarbon well. The volume required to pump the tool to its desired location is a simple multiplication of the pump rate and the pump time. It is not unusual to consume many hundreds of barrels of water to propel a tool a substantial distance in the horizontal leg of a hydrocarbon well. 
     A conventional approach is to provide a more-or-less rigid pump down collar on the exterior of pump down tools as shown in U.S. Printed Patent Applications 20100263876; 20110277989; 20120118561 and 20120145379 to reduce the gap between the outside of the tool and the inside of the pipe string. 
     Other disclosures of some interest relative to this invention are found in U.S. Pat. Nos. 2,644,523; 3,346,045; 3,347,196; 4,356,865; 4,392,528; 4,423,783; 4,828,291; 4,961,465; 5,095,980; 5,180,009; 5,209,304; 5,927,402; 6,138,764; 6,460,616; 6,467,541; 6,739,391; 6,973,971; 7,025,142; 7,182,135; 7,261,153; 7,322,421; 7,434,627; 7,686,092 7,753,130 and 8,079,413 and U.S. Printed Patent Application 20050241824. 
     SUMMARY OF THE INVENTION 
     As used herein, upper refers to that end of the tool that is nearest the earth's surface, which in a vertical well would be the upper end but which in a horizontal well might be no more elevated than the opposite end. Similarly, lower refers to that end of the tool that is furthest from earth's surface as measured along the well bore. Although these terms may be thought to be somewhat misleading, they are more normal than the more correct terms proximal and distal ends. 
     As disclosed herein, a pump down tool includes a resilient cup on the bottom of the tool that is captivated between a tool body and an anti-rotation device on the extreme bottom end of the tool. The tool body may include a stub having threads extending from its end terminating short of the junction between the stub and the larger tool body. The anti-rotation device may thread onto or slide onto the stub short of the tool body at a position captivating the resilient cup. In some embodiments, the cup may move axially between one position more-or-less abutting the tool body and a second position more-or-less abutting the anti-rotation device. 
     It is an object of this invention to provide an improved pump down tool requiring a smaller volume of water to propel the tool to its desired location. 
     Another object of this invention is to provide an improved pump down tool incorporating a resilient cup captivated between the tool body and an anti-rotation device on the bottom of the tool. 
     These and other objects and advantage of this invention will become more fully apparent as this description proceeds, reference being made to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial vertical cross-sectional view of a pump down tool; 
         FIG. 2  is an exploded partial view of a resilient cup and its support from  FIG. 1 ; and 
         FIG. 3  is a view similar to  FIG. 2  showing another embodiment of a resilient cup and support. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-2 , a pump down tool  10  may comprise, as major components, a body  12  having a passage  13  therethrough, one or more sets of slips  14 ,  16 , one or more conical or wedge-shaped sections  18 ,  20 , a malleable, rubber, packing element or seal  22  and an anti-rotation device or mule shoe  24 . The body  12  may include an upper section  26  and a lower section  28  connected together in a suitable manner, such as by threads  30 . The tool  10  is illustrated as of a type that can be converted between a bridge plug, a flow back plug, a check valve plug or otherwise by installing or removing a component in an insert  32 . The component may be a plug, a valve ball, a soluble ball or the like as shown in U.S. patent application Ser. No. 12/317,497, filed Dec. 23, 2008, the disclosure of which is incorporated herein by reference. 
     The insert  32  may be attached to the upper body  26  by suitable threads  34  and may include internal threads  36  for connection to a conventional setting tool (not shown) connected to a wire line or other work string extending to the surface. The setting tool (not shown) may act in a conventional manner by pushing down on the top of a collar  38  and pulling up on the threads  36 . This shears a pin (not shown) and allows the collar  38  to move downward relative to the slips  14 ,  16  thereby expanding the slips  14 ,  16  into gripping engagement with the casing  40 . 
     The slips  14 ,  16 , the wedges  18 ,  20  and the packing element  22  may be of a conventional type as shown in U.S. patent application Ser. No. 12/317,497, filed Dec. 23, 2008 so the tool is set in a conventional manner. During setting of the tool  10 , the slips  14 ,  16  ride along the wedges  18 ,  20  to expand the slips  14 , and fracture them into a number of segments in gripping engagement with the interior of a casing string  40  which may be cemented in a well bore (not shown). At the end of the setting of the tool  10 , the insert  32  fails or breaks at a neck  42  thereby detaching the threads  36  and the setting tool (not shown) so the setting tool and wire line may be removed from the well. 
     The anti-rotation device  24  acts to minimize or prevent rotation of the tool when it is being drilled up by interacting with a subjacent tool. This may be accomplished in a number of ways, one of which is to provide angled faces  42 ,  44  on the bottom of a body  46  of the anti-rotation device  24 . 
     There comes a time when it may be necessary or desirable to drill up the tool  10 . Thus, many of the components of the tool  10  may be easily drillable such as composite materials, aluminum, brass and the like although slips  14 ,  16  are often cast iron. The slips  14 ,  16  normally fracture into small pieces which are more easily removable and don't necessary have to be drilled up. Those skilled in the art will recognize the tool  10  as heretofore described as being more-or-less conventional. 
     A resilient cup  48  may be part of the tool  10  adjacent a lower end thereof and may be captivated between the body  12  and the anti-rotation device  24 . A preferred embodiment of the cup  48  may be a commercially available swab cup of a diameter matched with the I.D. or O.D. of the casing string  40 . In other words, for use in 4½″ casing, a swab cup of that size may preferably be used on the tool  10 . 
     It may be preferred to captivate the cup  48  between the anti-rotation device  24  and the body  12 . To this end, the lower body section  28  may include a stub  50  of reduced size providing threads  52  which terminate well short of a flared end  54  of the lower body section  28 . The anti-rotation device  24  may include threads  56  received on the threads  52  and stopping at a distance from the flared end  54  greater than the thickness of the cup  48 . In this manner, the cup  48  may be free to move slightly along the stub  50  so there is no requirement for an exact dimensional tolerance between the anti-rotation device  24 , the lower body section  28  and the cup  48 . A set screw  58  may be used to prevent the anti-rotation device  24  from unthreading from the stub  50 . 
     In the alternative, the anti-rotation device  24  may slip over the stub  50  and be pinned in place to captivate the cup  48 . Similarly, the cup  48  may be attached to the stub  50 , or to the anti-rotation device  24 , in any suitable manner, as by extending a fastener (not shown) through a passage  60  in the cup  48 . 
     The resilient cup  48  may typically be made of rubber or similar elastomeric material and is sufficiently flexible so a lip  62  stays more-or-less in contact with the interior of the casing string  40  when the tool  10  is horizontal and the lip  60  is distorted by the weight of the tool  10  resting on its side. It will be seen that the lip  62  is formed from converging sides  64 ,  66  so that pressure from above spreads the lip  62  into a more secure engagement with the interior of the casing string  40 . Many conventional swab cups include a metal reinforcing rim  68  and such features do not detract from operation of the cup  48  for present purposes. The cup  48  may be concave toward the upper end of the tool  10  so that pressure applied from above may spread or enlarge the diameter of the cup  48  from a size approximating the diameter of the tool  10  in its running in configuration to a size larger than the set diameter of the slips  14 ,  16 . 
     There is an advantage of the cup  48  being on or near the bottom of the tool  10  rather than on the top. If the cup  48  were above the slips  14 ,  16  and the tool  10  were to strike an obstruction while moving through the casing  40 , there is a risk that the shear pin (not shown) will shear off and the tool  10  will set prematurely at a location where it is not wanted. 
     When going into the vertical leg of a well, where the tool may be falling by gravity, the resilient cup  48  may abut the inside of the casing  40  but the flexibility and orientation of the resilient lip  62  allows liquid to bypass the resilient cup  48  on its exterior. In other words, the lip  62  may not substantially impede falling of the tool  10  in the vertical leg of a well. In this manner, the tool  10  may fall into the well in much the same manner that a swab falls into a vertical well. 
     One of the problems with the prior art devices is that when the tool is horizontal, it is eccentric to the casing, meaning that the gap between the tool and the casing becomes very large on the non-weight bearing side of the tool. This reduces the efficiency of the tool, meaning that a higher pump rate is required to produce the necessary dynamic pressure differential to pump the tool through the horizontal leg of a well. Thus, it is not unusual to require pumping at a rate of 15-20 barrels/minute to propel a tool at a recommended rate of 150-250′/minute. At 200′/minute it takes fifty minutes to pump a tool through a 10,000′ horizontal leg. At a pump rate of 20 bpm, this is 1000 barrels. 
     When the tool  10  reaches the horizontal leg of a horizontal well, the weight of the tool  10  tends to compress the cup  48  on the weight bearing side of the tool  10  and move away from the casing interior on the non-weight bearing side. Three factors tend to mitigate the cup  48  from unsealing relative to the casing  40 . First, the cup  48  may have considerable flexibility thereby allowing it to remain more-or-less engaged with the non-weight bearing side of the tool  10 . Second, pressure from above, represented by the arrow  74 , stiffens the cup  48  and pushes the lip  62  on the weight bearing side of the tool  10  toward the casing interior and thereby acts as a centralizer to center the tool  10  in the casing  40 . Pressure from above also biases the non-weight bearing side of the lip  62  toward the casing interior keeping it in more-or-less sealing engagement ith the casing interior. 
     It will be seen that the resilient cup  48  prevents most of the liquid pumped into the casing  40  from passing around the tool  10  in an uncontrolled manner. This means that the tool can be pumped to its desired location in the well by pumping into the well a liquid volume substantially equal to the volume of the pipe string from the heel of the horizontal leg to its desired location. This volume is much smaller than is conventionally required. For example, consider a situation of a horizontal well having a 10,000′ long lateral cased with 4½″ O.D., N-80, 11.6 #/ft pipe having a nominal I.D. of 4.000 inches subject to normal manufacturing variations or tolerances. Casing of this size has a volume of 67 linear feet per barrel, so it would take a minimum of 10,000/67 or about 150 barrels of liquid to pump the tool  10  from the heel to the end of the horizontal lateral. This is much smaller than the volume of liquid needed to create a dynamic pressure drop across the tool and propel it 10,000′. To achieve a nominal 150-250′/minute rate of movement of the tool  10  inside the pipe string above, with perfect sealing of the resilient cup  48 , it will be seen that a pump rate of 2.2-3.7 bpm is required—much less than the 15-20 bpm of the prior art. 
     In fact, it may be desirable to provide one or more small bypasses  70  may be provided around the resilient cup  48 . Many of the tools  10  are used in conjunction with the fracing of hydrocarbon wells so it is not uncommon to find proppant, such as sand, accumulated in the horizontal leg of such a well. Providing one or more small bypasses around the resilient cup  48  allows a small stream of liquid to disperse any proppant accumulated in front of the tool  10  as it is propelled along the horizontal leg of the well. The bypasses  70  work by diverting part of the pumped liquid in a controlled manner through the lower end of the passage  13  and through a passage  72  in the anti-rotation device  24  as suggested by the arrow  76 . This bypass liquid is sufficient to stir up and disperse any proppant in front of the tool  10  as it is being pumped along the horizontal leg of the well so the tool  10  doesn't have to plow its way through the accumulated proppant. Consequently, a pump rate of 6-9 bpm may be more typical of pump rates with the tool  10 . Thus, to pump the tool  10  through a 10,000′ horizontal leg may require 10-15 bpm less than with a prior art device. Manifestly, the smaller the bypass  70 , the smaller the pumped volume but with less proppant dispersion—both of which are of importance. An optimum size for the bypass  70  is sufficient to barely disperse proppant collecting in the casing  40 , the amount and concentration of which are unknown. Thus, the optimum size of the bypass  70  is normally unknowable and some compromise is in order. 
     Another advantage of the bypass  70  is that it allows the tool to be pulled from the well without swabbing the casing  40 . Occasionally, something occurs which makes it desirable to remove the tool  10  from the well without setting it. The bypasses  70  allow the tool  10  to be pulled toward the surface and allow liquid in the casing  40  to pass from above the cup  48 , through the bypass  70  and out the passage  72  without delivering liquid at the surface. Although the size and number of the bypasses  70  will differ depending on the size of the casing  40 , the desired rate of pulling the tool  10  from the well and other factors, two passages of ⅜″ diameter have been found to be sufficient with normal production sized casing, i.e. 4½″ and 5½″ O.D. 
     Referring to  FIG. 3 , another embodiment of this invention includes a tool  100  including an anti-rotation device  102  on the end of a body section  104 . A resilient cup  106  of somewhat different configuration is captivated between the device  102  and the body section  104 . One or more bypass channels  108  may be provided, either alone or in conjunction with a passage comparable to the passage  70 . The channels  108  pass through threads  110  securing the anti-rotation device  102  to the lower body section  104 . Thus, the threads  110  are interrupted threads but are still of sufficient capacity to secure the anti-rotation device  102  to the lower body section  104 . It will be seen that the bypass channels  108  have the same function as the bypass  70  so a bypass stream flows through the channels  108 , through a slot  112  in the anti-rotation device  102  and out of the bottom of the tool  100  through a passage  114  in the anti-rotation device  102  as suggested by the arrow  116 . A set screw  118  may be provided in the anti-rotation device  102  to prevent it from unthreading from the body section  104 . The cup  106  may be concave toward the upper end of its tool so that pressure applied from above may spread or enlarge the diameter of the cup  106  from a size approximating the diameter of its tool in its running in configuration to a size larger than the set diameter of the slips carried by the tool. 
     Although this invention has been described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and the combination and arrangement of parts may be resorted to without departing from the scope of the invention as hereinafter claimed.