Patent Publication Number: US-11384616-B1

Title: Multi-string section mill

Description:
PRIORITY 
     This application claims priority to United States provisional patent application Ser. No. 63/012,674 entitled “Multi-String Milling Tool” filed on Apr. 20, 2020, the entire content of which is thereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates to the field of sub-surface wellbore tools and equipment and, more particularly, to an apparatus for severing or cutting sections through multiple strings of wellbore casing or similar tubulars disposed in a wellbore. 
     BACKGROUND OF THE INVENTION 
     Section milling tools are often utilized to cut through sections of wellbore tubulars such as strings of casing pipe or other oilfield tubulars disposed in a wellbore for drilling and production of oil and gas wells. These strings may be concentrically placed in the wellbore or they may be placed eccentrically placed such that the strings are offset from one another in the wellbore. A variety of section milling tools has produced to perform such milling operations. Typically, such section milling tools are attached to a pipe string such as a drill pipe string or coiled tubing string which is run or placed downhole in a wellbore through one of the tubulars to be milled to a location where a milling operation is to be conducted. Generally, mining tools employ one or more retractable cutters that extend radially outward from the milling tool to engage the area of the casing or other tubing which is to be milled. Surface equipment such as a rotary table, a power swivel or the like is utilized to rotate the milling tool and its associated cutters to facilitate the cutting process. The cuttings from the milling operation are then circulated out of the wellbore by means of circulating wellbore fluid. 
     Problems associated with such milling tools, which reduce milling efficiency, increase wear and tear on the milling tool, and increase the cost of milling operations, include wobbling, oscillation, and vibration of the cutters during rotation of the milling tool, the failure of the extendable cutters to fully extend from the milling tool, inadequate radial force on the cutters resulting in incomplete or inadequate cuts in the tubular being milled, and excessive wear on the cutters and the cutter drive system that prevents efficient cutting of multiple strings of tubulars. The present invention is designed to address the foregoing problems in order to reduce tool vibration, cutter wobbling, and increase the reliability of cutter extension from the section milling tool, and reduce milling costs. 
     SUMMARY OF THE INVENTION 
     The proposed invention provides a new section milling tool for milling a window, a cutout, or a cutoff in multiple strings of oilfield tubing or casing. The section milling tool has a longitudinally extending tubular mill body threadedly attached to a top sub which is attached to a work string. The mill body of the section milling tool has a central bore and is provided with retractable mill carriers having an army of cutters that re deployed radially inward and outward from the central bore of the tubular mill body through a mill window by a translatable drive plunger at the lower end of the mill body. 
     The section milling tool has a translatable piston and a stationary thimble sealing the central bore of the tubular mill body to create a fluid pressure chamber. The piston has upper and lower elongated stems in fluid communication with the central bore of the milling tool. A coiled compression spring may be placed around the upper piston stem between the piston and the top sub to bias the piston downward to a downhole position away front the top sub. The lower piston stem is inserted through a central bore in the thimble and attached in fluid communication to a flow tube. The translatable drive plunger is attached to the lower downhole end of the flow tube below the thimble. The mill carriers are mounted between upper follower links pivotally attached to the mill body and low drive yoke links pivotally attached to the drive plunger. 
     Fluid circulating through the work string enters the tubular mill body and the flow tube. This circulating fluid flows through the flow tube and enters the fluid chamber through fluid ports in the lower piston stem. Changes in the pressure of the fluid in the fluid chamber moves the piston and attached flow tube upward and downward with respect to the thimble as the lower piston stem slides through the central bore of the thimble and, correspondingly, moves the drive plunger upward and downward. 
     Upward uphole movement of the piston and attached flow tube and the corresponding upward movement of the drive plunger will pivot the lower drive yoke links radially outward, and correspondingly the upper follower links radially outward, to mow the pivotally attached mill carriers radially outward through a mill window in the mill body. The radially outward movement of the mill carriers from the mill window will engage the cutters with the inner wall of a casing in which the work string and milling tool is deployed. Milling is conducted by rotation of the work string. An expansion limiter may be provided to limit the radial outward position of the mill carriers and corresponding cutters during use. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a longitudinal view of an assembled section milling tool of Applicants&#39; Invention with the milling assembly in its retracted position. 
         FIG. 2  is a partial longitudinal cross-section view of the section milling tool shown in  FIG. 1  showing the dive plunger in its retracted or downward position. 
         FIG. 3  is a longitudinal view of an assembled section milling tool of Applicants&#39; invention with the milling assembly in its extended position. 
         FIG. 4  is a partial longitudinal cross-section view of the section milling tool shown in  FIG. 1  showing the drive plunger assembly in its extended or upward position. 
         FIG. 5  is an exploded view of the section milling tool shown in  FIG. 1  illustrating the assembly of its various components. 
         FIGS. 6A and 6B  are longitudinal cross-section views of the section milling tool shown in  FIG. 1  positioned in a wellbore. 
         FIG. 7  is an enlarged cross-section view of the piston assembly of the section milling tool designated as detail  7  in  FIG. 6A . 
         FIG. 8  is an enlarged cross-section view of the milling assembly of the section milling tool designated as detail  8  in  FIG. 6B . 
         FIG. 9  is an enlarged cross-section view of the plunger assembly of the section milling tool designated as detail  9  in  FIG. 6B . 
         FIGS. 10A and 10B  are longitudinal cross-section views of the section milling tool shown in  FIG. 1  positioned in a wellbore showing the retractable mill carriers of the milling assembly deployed radially outward. 
         FIG. 11  is an enlarged cross-section view of the piston assembly of the section milling tool designated as detail  11  in  FIG. 10A . 
         FIG. 12  is an enlarged cross-section view of the milling assembly of the section milling tool designated as detail  12  in  FIG. 10B . 
         FIG. 13  is an enlarged cross-section view of the plunger assembly of the section milling tool designated as detail  13  in  FIG. 10B . 
         FIG. 14  is a partial longitudinal cutaway view of the section milling tool shown in  FIG. 1  showing the piston assembly, the milling assembly, and the plunger assembly. 
         FIG. 15  is an enlarged view of the upper follower links of the milling assembly of the section milling tool shown in  FIG. 1  designated as detail  15  in  FIG. 14 . 
         FIG. 16  is an enlarged view of the drive yoke links and follower links of the milling assembly of the section milling tool shown in  FIG. 1  designated as detail  16  in  FIG. 14 . 
         FIG. 17  is a schematic view of the section milling tool shown in  FIG. 1  shown in place in a wellbore of an oil and as well. 
         FIG. 18  is an enlarged cross-section view of the cutter assembly of the section mill of  FIG. 1  utilized to mill through multiple pipe strings within wellbore. 
         FIG. 19  is an exploded view of an expansion limiter utilized to limit the radial outward position of the mill carriers of the section milling tool shown in  FIG. 1 . 
         FIG. 20  is a partial longitudinal cross-section view of the section milling tool shown in  FIG. 1  showing the drive plunger with the expansion limiter shown in  FIG. 19 . 
         FIG. 21  is an exploded view of a mill carrier of the section milling tool of  FIG. 1  having an embodiment of a detachable and interchangeable cutter shoe. 
         FIG. 22  is an exploded view of a mill carrier having another embodiment of a detachable and interchangeable cutter shoe. 
         FIG. 23  is a horizontal cross-section view through the cutting window of the section milling tool of  FIG. 1  taken from section  23  of  FIG. 12  showing the position of the mill carrier and cutters during cutting of window in a liner pipe. 
         FIG. 24  is a horizontal cross-section view through the embodiment of the detachable and interchangeable cutter shoe taken from section  24  of  FIG. 22 . 
     
    
    
     These drawings may omit features that are well established in the art and do not bear upon points of novelty in the interest of descriptive clarity. Such omitted features may include threaded junctures, weld lines, sealing elements, O-rings, pins and brazed junctures. 
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to de drawings, particularly  FIGS. 1-5, 6A and 6B , the section milling tool  100  of Applicants&#39; invention has an upper uphole end  111 , a downhole lower end  113 , a longitudinally extending tubular mill body  310  having a central bore  112 , and a top sub  120  that is attached to a work string  200 . The tubular mill body  110  of the section milling tool  100  has longitudinally extending centrally located mill windows  116  that open into the central bore  112 . Positioned within the central bore  112  of section milling tool  100  are an upper piston assembly  101  and a lower plunger assembly  102 . A mill assembly  103  is positioned adjacent the mill windows  116  between the piston assembly  101  and the plunger assembly  102 . 
     Section milling tool  100  also has a tubular top sub  120  headedly connected to mill body  110  by a top sub pin connection  117  and a mill body box connection  114 . The top sub  20  is threadedly connected to mill body  110  by a top sub pin connection  117  and a mill body box connection  114 . The top sub  120  has an upper box connection  118  for attachment to a pin connection  202  at the lower downhole end of the work string  200 . Top sub  120  also has ports  119  that re in fluid communication with its central bore  121 . The ports  119  are drilled and tapped to receive nozzles or fluid jets  122 . The nozzles or fluid jets  122  allow for pressure adjustments within the section milling tool  100  to enhance its function and facilitate mill swarf removal during milling. The ports  119  in the upper top sub  120  may also be drilled and tapped to receive a plunger or flapper-type float valve. The plunger or flapper-type float militates against the effect of U-tubing to prevent debris from entering the mitt body  110  when pumping ceases or when a connection is required. 
       FIGS. 6A and 6B  show longitudinal cross-section views of the section milling tool  100  and its components attached to the end of the work string  200  and placed within the central bore  301  of a casing or liner pipe string  300  lining a wellbore  400 . As shown in  FIG. 7 , a detail view from  FIG. 6A , the piston assembly  101  of section milling tool  100  is positioned within mill body  110  below the tubular top sub  120  with the central bore  121  of the top sub  120  in fluid communication with the central bore  201  of the work string  200 . 
     The piston assembly  101  has a slidably positionable drive piston  126  upward from a stationary thimble  122 . The drive piston  126  has a longitudinally extending upper piton stem  125   a  and a lower piston stem  125   b . A central piston bore  127  in fluid communication with the central bore  121  of the top sub  120  extends through the drive piston  126  and piston stems  125   a  and  125   b . The lower piston stem  125   b  extends through the polished thimble bore  129  of a stationary thimble  128  that is positioned a desired distance below the drive piston  126  within the central bore  112  of the tubular mill body  110  to seal the central bore  112 . The lower end of the central bore  121  in the bottom pin connection  117  of the top sub  120  may be fitted with an O-ring  123  where it engages the piston stem  125   a  to maintain the required fluid movements and pressures during activation of the milling tool  100 . 
     The piston assembly  101  may also have a coiled compression release spring  124  located around the upper piston stem  125   a  between the top sub  120  and the drive piston  126 . The compression string  124  serves to bias the drive piston downward toward the stationary thimble  128 . The space between the drive piston  126  and the stationary thimble  128  creates a fluid pressure chamber  136  for movement of the drive piston  126 . The lower piston stem  125   b  has fluid ports  135  that allow fluid circulating through the lower piston stem  125   b  from the central bore  121  of the top sub  120  to enter the fluid pressure chamber  136 . A longitudinally extending flow tube  130  having a central bore  132   s  threadedly attached at its upper end  130   a  to the lower piston stem  125   b.    
     Flow tube  130  extends through the central bore  112  of the mill body  110  to engage with the plunger assembly  102  shown in  FIG. 9 , a detail view from  FIG. 6B . The plunger assembly  102  has a drive plunger  154  slidably positioned within the central bore  112  of the mill body  110 . The drive plunger  154  has an elongated cylinder upper body section  153  that transitions to a lower body section  155  to create a shoulder  156 , and a central bore  159 . The upper body section  153  of drive plunger  154  is threadedly attached to the longitudinally downward lower end  130   b  of the flow tube  130  with time flow tube central bore  132  in fluid communication with the central bore  159  of the drive plunger  154 . 
     The flow tube  130  allows fluid from the central bore  201  of the work string  200  to circulate through the central bore  121  of the top sub  120 , through the central bore  127  of the drive piston  126 , through flow tube central bore  132  of flow tube  130 , and through the central bore  159  of the drive plunger  154  of the section milling tool  100 . A flow-limiter  158  such as a fluid jet or nozzle is provided in the central bore  159  at the end of the lower body section  155  of the drive plunger  154  to allow for pressure adjustment within de flow tube  130 . 
     The fluid ports  135  in the lower piston stem  125   b  allow fluid circulating through the central piston bore  127  to the flow tube  130  from the central bore  121  of the top sub  120  to enter the fluid pressure chamber  136 . Variations in fluid pressure within the fluid pressure chamber  136  will move the drive piston  126  upward and downward with respect to the stationary thimble  128 . The attachment of the flow tube  130  between the drive piston  126  and the drive plunger  154  allows the drive plunger  154  to move upward and downward within the central bore  112  of the mill body  110  of the section milling tool  100  in response to upward and downward movement of the drive piston  126 . 
     Pivotally mounted between the piston assembly  101  and the plunger assembly  102  is the mill assembly  103  shown as detail  8  in  FIG. 6B . The mill assembly  103  of the section milling tool  100  is comprised of retractable mill carriers  144  that are deployed radially inward and outward from the tubular mill body  110  through mill windows  116 . The mill carriers  144  have a longitudinal array of attached cutters  148 . Each of the cutters  148  has a hardened cutting surface such as a carbide surface, a surface of polycrystalline diamond, or the like to facilitate milling through the wall of a pipe string  300  in which the section milling tool  100  is inserted. 
     Hardened stabilizer blades  149  may be provided and attached to the mill carriers  144  in conjunction with the cutters  148  to bear against the inner wall of a tubing segment in order stabilize the mill carriers  144  during the milling process. The cutters  148  and stabilizer blades may be provided as a unit or they may be provided individually and attached to the mill carriers  144 . The stabilizer blades  149  are recessed from the hardened cutting surface of the cutters  148  and have a wider beating surface that serves to prevent damage to the wall of adjacent pipe strings such as the wall of an outer liner pipe string when inner liner pipe string  300  is being milled. 
     Each of the mill carriers  144  may also be provided with a stabilizer pad  150  surface that is preferably positioned below the cutters  148 . The stabilizer pad  150  serves to assist in positioning mill carriers  144  at a desired location for milling through the interior wall  302  of liner pipe string  300 . The stabilizer blade  149  and stabilizer pad  150  are coated with a hard metal or provided with hard metal bearing inserts to increase wear resistance when section milling. 
     The mill carriers  144  are pivotally mounted between upper follower links  142  and lower drive yoke links  151 . The upper follower links  142  are attached to the mill carriers  144  by crown pins  143  and to the mill body  110  by studs  141 . The lower drive yoke links ISI at pivotally connected to the drive plunger  154  by crown pins  145  and to the mill carrier  144  by stud pins  147 . Intermediate follower links  146  are arrayed between the upper follower links  142  and the lower drive yoke links  151  and are pivotally mounted to the mill carriers  144  by crown pins  152  and to the mill body  110  by studs  139 . The upward movement of drive plunger  154  pivots the lower drive yoke links  151  downward and outward on crown pins  145  and stud pins  147  to move the pivotally attached intermediate follower links  146  and upper follower links  142  upward and outward to deploy the pivotally attached mill carriers  144  radially outward tom the mill window  116  in the mill body  110 . 
       FIG. 14  shows a partial cutaway view of the section milling tool  100  of  FIG. 1  displaying the relationship of the piston assembly  101 , the milling assembly  102 , and the plunger assembly  102 .  FIG. 13 , designated as detail  15  in  FIG. 14 , shows the upper follower links  142  pivotally attached to the mill body  110  by studs  141  and to the mill carriers  144  by crown pins  143 . Entry guides  140  with harden surfaces reinforce the upper follower links  142  as they pivot into and out of the mill body  110 . 
       FIG. 16 , designated as detail  16  in  FIG. 14 , shows the drive yoke links  151  pivotally attached to the mill carrier  144  by crown pins  145  and to the drive plunger  154  by stud pins  147 . The intermediate follower links  146  are arrayed between the upper follower links  142  and the lower drive yoke links  151  and are pivotally attached to the mill body  110  by studs  139  and to the mill carriers  144  by crown pins  152 . 
     For operation of the section milling tool  100 , the pin connection  117  of the top sob  120  is connected to the mill body box connection  114  and the box connection  118  of the top sub  120  is connected to a pin connection  202  at the lower downhole end of the work string  200  as shown in  FIG. 6A . The work string  200  and attached section milling tool  100 , with the mill as assembly  103  in a retracted position as shown in  FIG. 6B , is then inserted through the central bore  301  of the liner pip string  300  in a wellbore  400  of a drilling rig  500  to be milled as shown in  FIG. 17 . 
     Referring now to  FIG. 10A  and  FIG. 10B , fluid is pumped into the central bore  201  of the work string  200  to circulate though the central bore  121  of the top sub  120  to enter the central piston bore  127  and central bore  132  of flow tube  130 . Fluid from the central bore  121  of the top sub  120  circulates through the central piston bore  127  to the low piston stem  125   b  and enters the fluid pressure chamber  136  between the drive piston and the stationary thimble  128  through fluid ports  135 . Pressure created in the fluid pressure chamber  136  from the fluid entering through fluid ports  135  expands the fluid pressure chamber  136  and moves the drive piston  126  from the downwardly biased downhole position shown in  FIG. 7  to an upward or uphole position to compress the release spring  124  as shown in  FIG. 11 . 
     The upward movement of the drive piston  126  in turn moves the attached flow tube  130  upward through the stationary thimble  128  and correspondingly moves the attached drive plunger  154  upward from the downwardly biased downhole positon shown in  FIG. 9  to an upward uphole position as shown in  FIG. 13 . The upward movement of the attached drive plunger  154  will cause the pivotally mounted drive yoke links  151  of the mill carriers  144  to pivot downward and radially outward on crown pins  145  and stud pins  147  to move the mill carrier  144  radially outward from the mill body  110  through the mill window  116  as shown in  FIG. 13 . The upper follower link  142  and intermediate follow links  146  will pivot upward and radially outward to stabilize the mill carriers  144 . A lateral support ring  131  may be provided within the central bore  112  of the mill body  110  to support the flow tube  130  as it moves in response to movement of the drive piston  126 . 
     When extended through the mill window  116 , the mill carriers  144  and the cutters  148  will be positioned in the central bore  301  in the annulus between the mill body  110  of the section milling tool  100  and the liner pipe string  300  to bear against the interior wall  302  of liner pipe string  300  where the window or opening is to be milled. Milling is then conducted by rotating the work string  200  to engage the cutters  148  with and cat through the interior wall  302  of liner pipe string  300  shown in  FIG. 12  and in  FIG. 23 . The upper non-cutting stabilizer blade  149  and the lower non-cutting stabilizer pad  150  serves to prevent damage to an outer most casing while milling. Rotation of the work string  200  and the attached section milling tool  100  may be conducted by a rotary table  550  of the drilling rig  500  as shown in  FIG. 17  or another rotation mechanism such as a top drive. 
     Cuttings created during milling am carried away by fluid circulating through the central bore  112  of the top sub  120  and mill body  110  of the section milling tool  100  and upward in the annulus between the mill body  110  and the liner pipe being milled. 
     Once fluid pumping ceases, fluid in the pressure chamber  136  is evacuated though the fluid posts  135  in the lower piston stem  125   b  to relieve fluid pressure in the pressure chamber  136 . This release of pressure in the pressure chamber  136  allows the release spring  124  to expand shifting the drive piston  126  downward to a downhole position. The downward movement of the drive piston  126  moves the attached flow tube  130  and the attached drive plunger  154  downward to a downhole position. The downward movement of the drive plunger  154  will then pivot the drive yoke links  151  upward and radially inward on crown pins  145  and stud pins  147  to pivot the upper follower links  142  and intermediate follower links  146  downward and radially inward to move the mill carriers  144  into the mill body  110  through the mill window  116  and return the mill carriers  144  to the position shown in  FIG. 8 . Returning the mill carriers  144  to the position shown in FIG. g will allow the section milling tool  100  to be repositioned or removed from the wellbore. 
       FIG. 18  illustrates the section milling tool  100  utilized to mill through multiple strings of pipe. In  FIG. 18 , pipe string  300  is positioned within an outer interior pipe string  310  which is positioned within an exterior liner pipe string  350  lining wellbore  400 . A window opening has been through pipe string  300  from its interior wall  302  into the annulus  305  between pipe string  300  and outer interior pipe string  310 . The cutters  148  on mill carriers  144  of section milling tool  100  are shown positioned at the interior wall  312  of pipe string  310  for cutting a window opening through interior pipe string  310 . 
     In some embodiments, an expansion limiter  160  may be provided with the plunger assembly  102  to limit the radial outward position of the mill carriers  144  and corresponding cutters  148  when the mill carriers  144  are deployed. Such an expansion limiter  160  is shown  FIG. 2  and  FIG. 3  and in more detail in  FIGS. 19 and 20 . In this embodiment the expansion limiter  160  includes a threadedly adjustable sleeve  162  slidably positioned around the elongated lower body section  155  of the drive plunger  154 . 
     Sleeve  162  has threaded adjustment bares  163  that correspond with the bores  164  of an adjustment cap  165  and threaded groves  168  that extend along the lower body section  155  of the drive plunger  154 . Threaded adjustment bolts  166 , through bores sleeve bores  163 , engage with the adjustment cap bores  164  and the threaded drive plunger grooves  168  to allow the sleeve  162  to be positioned at a desired location along the lower body section  155  of the drive plunger  154 . When so positioned, the sleeve  162  may then be fixed in place on the lower body section  155  of the drive plunger  154  by pins  167 , such as cotter pins, in the adjustment cap  165  or by set screws. 
     A shoulder  115  in the lower end of mill body  110 , shown in  FIG. 20 , is provided to engage with sleeve  162  as it moves upward with de drive plunger  154  in response to the upward movement of the drive piston  126  and the attached flow tube  130 . The position of the sleeve  162  on the lower body section  155  of the drive plunger  154  when it engages the mill body shoulder  115  will limit the upward movement of the drive plunger  154  and correspondingly, the downward and radially outward movement of the drive yoke links  151  and the radial outward movement of the mill carriers  144 . Fixing the sleeve  162  at a desired position on the lower body section  155  of the drive plunger  154  by the adjustment bolts will limit the cutting range of the mill cutter  146  to a desired maximum or a desired minimum which serves to avoid overcuts in situations where there are additional outer pipe strings. 
     In some embodiments of the section milling tool, the cutters  148  and stabilizer blades  149  may be mounted on interchangeable releasably attachable and detachable cutter shoe module. Use of a cotter shoe module that is releasably attachable and detachable from the mill carrier  144  will facilitate the replacement of worn cutters, even in the field, which will lead to less downtime and at reduction in the cost of milling. One embodiment of a releasably attachable and detachable cutter shoe module  170  is shown in  FIG. 21 . Cutter shoe module  170  has a longitudinally extending army of cutters  148  and stabilizer blades  149  and an array of dovetailed slides  172  that slide into a corresponding army of dovetailed grooves  173  in the mill carrier  144 . A releasably attachable retainer block  174  secured by removable threaded pins or bolts  175  holds the cutter shoe module  170  in place on the mill carrier  144 . Multiple shoe modules  170  may be used on each mill carrier  144 . 
       FIGS. 22 and 24  show another embodiment of a releasably attachable and detachable cutter shoe module  180 . Cutter shoe module  180  is provided with one or more rows of cutters  148  with stabilizer blades  149  mounted on a base  181 . The base  181  has beveled dovetailed end.  182  and attachment tabs  183 . The base  181  of cutter shoe module  180  slides into a recess  186  on the mill carrier  144 . Recess  186  has beveled dovetail grooves  184  and the attachment slows  185  that receive, respectively, the beveled dovetailed ends  182  and attachment tabs  183  of the base  181 . An attachment plate  187  mounted on one edge of the base  181  of the cutter module  180  receives pins or bolts  188  to attach and hold the cutter module  180  in place a the edge of the mill carrier  144 . Additional attachment bolts  188  may be used to attach the cutter shoe module  180  at the top of the mill carrier  144 . 
     It is thought that the section milling tool  100  presented herein and its attendant advantages will be understood from the foregoing description. It will be apparent that various changes may be made in the form, construction and arrangement of the parts of the section milling tool  100  without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form described and illustrated are merely an example embodiment of the invention.