Patent Publication Number: US-2015060040-A1

Title: Downhole Cutting Tool Having A Jetted Top Bushing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 61/602,707, filed Feb. 24, 2012, for all purposes. 
    
    
     BACKGROUND 
     Various downhole tools, deployed on a drillstring, have been used to sever and/or cut windows or sections in wellbore tubulars, namely casing strings. The terms “tubulars,” “tubular strings” and “casing strings” are used in their broadest sense in this application, to include without limitation such tubulars commonly known in the industry as casing, tubing, conductors, etc. 
     One broad type of such tools employs a movable piston disposed in the bore within the main body of the tool. The piston is moved in a downhole direction by fluid flow through the drillstring and the bore of the tool and piston. A bore through the piston, typically having a removable jet therein, permits some fluid flow therethrough, albeit in a restricted manner, thereby pushing the piston downward and actuating a mechanism which rotates blades and cutters into position to cut the casing wall. An example of such tool is disclosed in U.S. Pat. No. 7,063,155. 
     One problem which can arise in connection with use of such tools is related to removal of metal cuttings (resulting from cutting and/or section milling of the casing) from the wellbore, by circulation of the drilling fluid. It can be readily understood that if not removed, such metal cuttings can form a mass sufficient to stick the cutting tool downhole. A relatively high circulating rate, combined with circular flow patterns in and around the cuttings, assists in cuttings removal. 
     Another issue can arise in connection with use of such tools, related to available rig pump capacity and consequent fluid (which will be called “drilling fluid” for purposes of this application) circulating rate, and available flow area through the tool, namely through the flow passage or bore of the actuating piston. It is understood that fluid flow, and resulting pressure drop, across the piston is what moves the actuating piston downward to in turn move the blades and cutters into cutting position. The actuating piston has a removable insert or jet in its bore, which enables flow area through the piston to be changed by installing jets with different hole sizes. Different flow areas may be warranted depending upon the rig&#39;s pump capacity and consequent flow rate capability. For example, a rig with low pump capacity of 1½ barrels per minute (BPM) may require a relatively small flow area through the piston, to provide sufficient pressure drop to actuate the piston. On the other hand, such small flow area restricts the total fluid flow through the tool, and consequently the fluid flow rate available to lift cuttings to the surface and clean the hole, so in settings requiring a higher flow rate and with a pump capable of delivering it, the flow rate is constrained to an unacceptably low value. While changing the piston jet to one having a larger flow area could address these situations, from a practical matter such change is difficult and time consuming to do at the well location (on the rig). This is because the tool must be disassembled to access the piston, and the tool typically comes to the rig pre-torqued and not easily disassembled on the rig. As a result, the tendency exists for the tool to be run in less than optimum hydraulic flow conditions. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a downhole casing cutting and/or milling tool (referred to as a “cutting tool”) of the type having an inner operating piston with a piston bore therethrough. As is well known, the cutting tool is run downhole into a casing string (or other tubular) in a wellbore, on a drillstring. The cutting tool has one or more fluid outlets positioned above (that is, in an uphole direction from) the cutting surfaces (usually blades with attached cutters, or other types of cutting surfaces thereon). Preferably, the fluid outlets are positioned in a top sub or bushing, threadably connected to the top of the main body of the tool, which may be referred to as a “jetted top bushing.” A portion of the total drilling fluid stream (pumped down the bore of the drillstring) can flow from the bore of the drillstring into the drillstring/casing annulus, through the fluid outlets. The fluid outlets are preferably positioned and aligned so as to direct fluid in an angled-downward direction, generally toward the cutting surfaces. In the preferred embodiment, each fluid outlet comprises a threaded hole, into which various flow control inserts or jets can be installed; if desired, a “blank” can be installed, so as to completely close off the flowpath, or an insert having a desired jet diameter (essentially, a hole through which fluid will flow) can be inserted. Other embodiments may comprise inserts held in place by pins or other means known in the art. It is a simple and quick action on the jobsite to install jets, externally at the wellsite, with any desired flow area. As a result, instead of changing the size of the flow area in the inner piston to accommodate a given desired circulating rate, which as described above is a time-consuming task requiring disassembly of the cutting tool which may not be feasible on the rig, the present invention permits the size of the flow area through the jets to be changed as desired quickly and easily. The total fluid flow stream can thus be divided in an optimum manner, with a portion directed into the drillstring/casing annulus and preferably toward the cutting surfaces, and the remainder down through the bore of the tool, the piston bore, out the bottom of the tool and then back uphole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view in partial cross section, of a cutting tool embodying the present invention. 
         FIG. 2  is another side view of a cutting tool embodying the present invention, including the jetted top bushing. 
         FIG. 3  is a view showing exemplary fluid flowpaths resulting from fluid flow through the jetted top bushing. 
         FIG. 4  is a view of the jetted top bushing alone (separate from the remainder of the cutting tool) showing fluid flow through the jets. 
         FIGS. 5A and 5B  are views of an alternate embodiment of the jetted top bushing. 
         FIG. 6  shows additional detail of a jet in position to be installed in a fluid outlet. 
     
    
    
     DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT(S) 
     With reference to the drawings, some of the presently preferred embodiments of the invention can be described. 
       FIG. 1  is a side view of an exemplary cutting tool embodying the principles of the present invention. The cutting tool  10  comprises a main body  20  with a lower end  22  preferably having a threaded connection  23  for connecting various tools below cutting tool  10 . A longitudinal bore  21  extends through main body  20 . Typically, cutting tool  10  will have both bottom ( 24 ) and top ( 26 ) bushings which are threadedly attached to main body  20 . As can be seen in the drawings, especially  FIG. 1 , cutting tool  10  typically comprises a plurality of blades  30 , each having cutting surfaces  32 , typically having one or more cutters per blade, which actually contact and cut the casing or other tubular. It is understood that cutting surfaces  32  may take a number of different forms, including carbide “buttons,” carbide layers on blades  30 , etc. Blades  30  are rotatably attached to main body  20  typically by pins, and are rotatable between a first position generally retracted within main body  20 , and a second position as shown in  FIG. 1 , extending outwardly from main body  20 . 
     Cutting tool  10  comprises a means for rotating blades from the first position to the second, outward position as shown in  FIG. 1 . In a presently preferred embodiment, this means for rotating comprises, generally, a piston disposed in the bore of main body  20 , which is moved downward under the influence of drilling fluid being pumped downhole through the drillstring and tool, and which bears on heel portions of blades  30  and rotates them outwardly. 
     In more detail, piston  40  is slidably disposed in a bore in bore  21  of main body  20 . Piston  40  has a bore  42  therethrough, through which fluid can be pumped. Piston  40  typically also has a removable jet  44  in bore  42 , by which the flow area through the piston can be adjusted. As is well known in connection with tools of this type, fluid flow through the tool forces piston  40  in a downward position (due to the restricted flow area), the piston in turn pushes against a heel section  33  of blades  30  and rotates them outward into the position of  FIG. 1 . 
     As noted above, cutting tool  10  preferably has a jetted top bushing  26  threadably connected to its upper end. Top bushing  26  has a threaded connection  28  at its upper end, to permit attachment of the tool to a drillstring. It is understood that other embodiments of the cutting tool comprise a more unitary arrangement, with one or both of the threaded connections  23  and  28  being integral to main body  20 . 
     As seen in the drawings, one or more, preferably a plurality, of fluid outlets  50  are arranged around the circumference of main body  20 , in this example top bushing  26 . Preferably, four or more fluid outlets  50  are provided and spaced equally around the circumference. Each of fluid outlets  50  is preferably adapted to engage a removable insert or jet  52 , preferably by threading, pinning or other similar means well known in the art. The removable inserts or jets  52  can be “blanks,” which permit no fluid flow through the jet, or can have a hole therein forming a desired flow area therethrough. The fluid outlets  50  and jets  52  are preferably aligned generally angled downward, so that fluid flow through the fluid outlets and jets is angled downward toward cutting surfaces  32  of blades  30 , as is later described. It can be readily appreciated that changing jets  52  is a relatively simple and quick task, involving no disassembly of cutting tool  10  beyond the actual changeout of the inserts, which can be done externally and without disassembly of the balance of the tool. It is therefore easy to change the resulting flow area by inserting a jet having the desired size hole for fluid flow, from no hole at all (as mentioned above, a “blank”), to one of a range of hole sizes and consequent flow area. It is understood that jets with different sizes of holes could be inserted in the fluid outlets, e.g. some of them with relatively smaller holes, some with relatively larger holes.  FIG. 3  is a drawing of representative fluid flow paths (the arrowed lines) through fluid outlets  50  (and jets  52 ), downward toward blades  30  and surrounding area, then back uphole. The representative flow path illustrates how a circulatory path is created by fluid flow through the jets, and assists in lifting metal cuttings to the surface for removal. 
       FIG. 4  shows more detail of top bushing  26 , fluid outlet  50  and jet  52  arrangement (separated from the rest of cutting tool  10 ). Fluid flow (represented by the arrowed lines) through bore  21  of top bushing  26 , and out of fluid outlets  50 /jets  52 , is shown. Note that fluid flow from the jets is angled downward (in a downhole direction), toward the blades and cutting surfaces. 
     It is understood that other placements of fluid outlets  50 /jets  52  is possible within the scope of the invention, all of such placements generally being at a position above (uphole from) the blades and cutting surfaces and angled so as to create a downwardly angled flow path.  FIGS. 5A and 5B  show one such alternative placement. In this embodiment, fluid outlets  50 /jets  52  are positioned higher up (in an uphole direction) in the drillstring, above the tool joint upset in top bushing  26 . 
     It is further understood that the invention encompasses arrangements in which fluid outlets  50  have no removable jets therein, but are simply holes drilled in top bushing  26  (or another part of cutting tool  10  uphole from blades  30 ). Preferably, such holes would be oriented to yield the downward flow direction desired. 
     As described above, the direction of fluid flow out of fluid outlets  50  and jets  52  is preferably in an angled downhole direction, toward the cutting surfaces of blades  30 . However, it is understood that the invention encompasses a tool having any fluid flow direction, from generally angled downhole, to outwardly at near right angles from cutting tool  10 , to angled in an uphole direction. Different of fluid outlets  50  and jets  52  could be angled in different directions (some uphole, some downhole, some at right angles), should particular applications call for such fluid flow patterns. 
       FIG. 6  shows additional detail of top bushing  26 , fluid outlets  50 , and an example of jets  52 , in position to be inserted into and secured in fluid outlet  50 . In the illustrated embodiment, jet  52  is threadably engaged in fluid outlet  50 ; as previously described, other means of attachment include pinning. etc. or any other means of removably attaching jet  52 . 
     It can be readily understood that the placement of the jets permits quick and easy external replacement thereof, by the operator with the tool at the surface. Therefore, the flow area through the jets can be easily varied from zero (if blanked off) to any desired value, to accommodate any particular flow conditions at the wellsite. 
     CONCLUSION 
     While the preceding description contains many specificities, it is to be understood that same are presented only to describe some of the presently preferred embodiments of the invention, and not by way of limitation. Changes can be made to various aspects of the invention, without departing from the scope thereof. For example:
         the size, number, and circumferential placement of the fluid outlets and jets can be varied   the placement of the fluid outlets and jets along the length of the tool can be varied   various combinations of jet sizes can be used   the jetted feature can be employed on any manner of downhole cutting tool having a tool body which can accommodate flow outlets and inserts   the jet inserts can be fixed within the fluid outlets by threads, pins, or other means well known in the art.       

     Therefore, the scope of the invention is to be determined not by the illustrative examples set forth above, but by the appended claims and their legal equivalents.