Patent Publication Number: US-7909100-B2

Title: Reversible casing cutter

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of gas and petroleum exploration and production and, more particularly, to an apparatus for cutting multiple tubulars, such as casings in a well bore. 
     BACKGROUND OF THE INVENTION 
     In the offshore industry, the exploration and production of gas and petroleum is conducted through tubulars of various diameters that are cemented inside each other and extend to a distance below the sea floor, where the production zone is located. When the well is abandoned, the owner of the offshore rig is required to remove the casing at the depth of 20 feet below the mud line. After the casing is cut, the rig owner must cement the plug on the abandoned well to protect the marine life in the surrounding area. 
     To perform the cutting operation below the mud line, a cutting tool is lowered into the innermost casing, which usually has a relatively small diameter, and severs the tubulars. When the first inside casing is removed, another cutter with greater cutting diameter is lowered inside the pipe and the next diameter conduit is cut in a similar manner. This procedure continues until the multiple tubulars are cut at the required depth. 
     Conventionally, the industry uses a three-blade cutting tool, which will first cut the 7-⅝″ pipe, then another cutting tool that will cut 10-¾″ diameter pipe, etc. If the inner casing collapses, the job becomes even more complicated and the casing needs to be drilled out or severed by an explosive to remove the smallest diameter casing. The conventional three-blade tool has cutter blades equidistantly spaced about the circumference of the tool body. The distance between the cutter blades in a conventional tool suitable for fitting into the smallest diameter pipe is relatively small. Since the inner diameter of the tubular has very small tolerances, the cutter blades have to be sufficiently small, as well, to allow lowering into the small diameter innermost tubular. The cutter blades of a conventional tool are often damaged, requiring pulling the tool to the surface and starting the process again. The painstaking process takes several days over the use of conventional tools. 
     If the inner casing collapsed, it may become completely impossible to mill out the necessary portions of the tubulars. In that case, the casing must be cut from the outside, first excavating the mud around the casing to the required depth and then applying the cutting tool to do the job. Such procedure is also expensive and takes several days. 
     My casing cutter tool disclosed in U.S. Pat. No. 7,063,155 solves the above-described problems by providing a casing cutter that has a pair of cutter blades pivotally mounted on a support body. The blades are pivotally mounted for gradual movement outside of the support body when downward force is applied to proximate ends of the cutter blades. The support body is rotated inside the innermost of the multiple tubulars, while the cutter blades sever the tubulars of progressively increasing diameter. The cutting blades have a main top surface and a distal end wall. The cutting elements are located on the main top surface and on the distal end wall. When the cutter blades are gradually pivotally moved from an idle position recessed in the hollow body to a position substantially perpendicular to the vertical axis of the body the top surface mills out a window in the casing, severing the casing to allow a subsequent plugging operation to take place. 
     While the tool of the &#39;155 patent works satisfactory, it was observed during the tests that the cutter blades or the pivot pins carrying the blades sometimes become damaged, which requires that the tool be repaired with new blades or new pivot pins. Naturally, the blade or pin replacement takes time, which slows the casing cutting process. 
     The present invention contemplates elimination of the drawbacks associated with the prior art and provision of a casing cutter that can be used for cutting multiple tubulars in an efficient manner that allows to save time and expense of the operation. The cutting tool is reversible, allowing the tool to be turned 180 degrees, with new cutting blades to continue the casing milling operation. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a casing cutter that can be used for severing multiple tubulars below the mud line. 
     It is another object of the present invention to provide a casing cutter that can be used for cutting various diameter tubulars that have been cemented together in an expeditious and relatively inexpensive manner. 
     It is still a further object of the present invention to provide an apparatus for severing multiple tubulars while using the same support body provided with two or more locations for attaching the cutting blades. 
     These and other objects of the present invention are achieved through a provision of an apparatus and method for severing multiple tubulars in a well bore. The apparatus has a hollow support body of a generally cylindrical configuration and an outside diameter smaller than the inner diameter of the innermost of the tubulars. The support body has a longitudinal slot extending through diametrically opposite location of the support body. The ends of the support body are provided with external threads allowing reversible engagement of the support body to a downhole work string. 
     A pair of strong cutter blades is pivotally mounted in relation to the support body; the cutter blades are recessed in the support body when the apparatus is in an idle position. A piston mounted in the support body moves in a vertical direction pushing the cutter blades and causing the cutter blades to pivot, while gradually extending through the slot of the support body into contact with the tubulars. A rotational force is applied to the support body, causing the cutter blades to sever the innermost of the multiple tubulars by the surfaces of the cutter blades that are provided with cutting material, such as tungsten carbide. 
     The support body is provided with a second piston that remains idle while the first piston operates on the cutter blades. Should the original set of the cutter blades become unusable, the support body is turned over, the original cutter blades are detached, and a substitute set of the cutter blades is attached for movement by the second piston that is positioned in a mirror-image position inside the support body. The piston is then caused to contact the substitute set of the cutter blades and cause their movement into an operational position for cutting the tubulars. 
     Cutting material may be provided on a top surface of a cutter blade, or on both top and bottom surfaces of the cutter blades so that the cutting operation can be performed whether the support body is moved up or down within the tubulars. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will now be made to the drawings, wherein like parts are designated by like numerals and wherein 
         FIG. 1  is an elevation view of the preferred embodiment of the apparatus of the present invention shown with the blades fully extended and reversible knives in phantom lines. 
         FIG. 2  is an elevation, partially sectioned view illustrating the piston assemblies mounted inside the tool body. 
         FIG. 3  is a detail view illustrating one of the cutting knives in an engaged position and a reversible cutting knife in a disengaged position. 
         FIG. 4  is a detail view illustrating the cutting blades in a fully extended position. 
         FIG. 5  is a detail view showing a channel for delivering a wash liquid on top of the cutting knife. 
         FIG. 6  is a detail view illustrating the cutting knives in a fully extended position cutting through a casing wall. 
         FIG. 7  is a detail view illustrating an alternative embodiment of the cutting knives with opposing surfaces capable of performing a cutting operation. 
         FIG. 8  is detail, partially exploded view showing the piston assembly. 
         FIG. 9  is a detail view showing alternative embodiments of the cutter knives designs. 
         FIG. 10  is a detail view showing a cutter knife with a blunt edge having cutting capabilities. 
         FIG. 11  s a detail view showing a cutter knife with a tip of the knife without a cutting medium. 
         FIG. 12  illustrates an embodiment of the cutter knife with opposing surfaces and the tip of the distal portion having cutting medium located thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings in more detail, numeral  10  designates the cutting tool in accordance with the present invention. The cutting apparatus  10  comprises a cutter body  12  configured as an elongated hollow body with a pair of longitudinal slots  14  and  16  formed in the side wall of the body  12 . The slots  14  and  16  are open to the interior of the body  12 , forming a through opening that communicates with diametrically opposite sides of the cylindrical side wall. An upper annular shoulder  18  is formed above the slots  14  and  16 . A lower shoulder  22  is formed below the slots  14  and  16 . 
     An optional magnet retrieval tool  20  can be detachably secured to a first end  15  the tool body  12  and a second optional magnet retrieval tool  24  can be secured to the second end  17  of the tool body  12 . The ends  15  and  17  of the body  12  are provided with threaded subs  19 ,  21 , respectively allowing connecting of the cutter body  12  to a string (not shown) that lowers the tool body  12  into a well bore. 
     A pair of cutter blades or knives  32  and  34  is pivotally secured to the support body  12 . In an idle position, the blades extend in a generally parallel orientation in relation to the longitudinal axis of the body  12  and are recessed into the slots  14  and  16 . Each of the cutter blades  32 ,  34  has an elongated, rectangular in cross section, configuration. Each cutter blade  32 ,  34  is provided with openings  36 ,  38 , respectively for receiving pivot pins  40  and  42  therein. The knives  32 ,  34  have an upper surface  44 ,  46 , respectively, which is encrusted with cutting chips formed of hard non-corrosive material, for instance tungsten carbide. 
     The distal end of each knife  32 ,  34  has angularly cut corners  52 ,  54 . The tips  56 , Distal tips  56 ,  58  of the knives  32 ,  34  may be sharpened as at  57 ,  59  and encrusted with cutting chips, similar to the surfaces  44 ,  46  for performing the initial cut through an innermost casing, or can be formed blunt, such as  61 ,  63 , as shown in  FIGS. 3 and 5 . The blunt tips  61 ,  63  extend between the top surfaces  44 ,  46  and the angular corners  52 ,  54 ; the blunt tips  61 ,  63  may or may not be provided with cutting capabilities, depending on the needs of the operation.  FIG. 10  shows a cutter knife  32 , which has cutting chips positioned on the blunt end  61 , while  FIG. 11  shows a cutting knife  34 , which blunt tip  63  has no cutting capabilities. The blunt tips  61 ,  63  of the distal ends  56  and  58  are oriented at an approximately right angle in relation to the upper surfaces  44 ,  46  and at an obtuse angle in relation to the bottom surfaces  60 ,  62 . 
     A proximate end of the knife  32  has a “heel” portion  70  which extends forward of a vertical shoulder  72 . The heel portion  70  comprises a flat surface  74  and a rounded part  76  extending at a right angle to the vertical shoulder  72 . The pivot pin opening  36  extends through the heel portion  70  as well. 
     The knife  34  is a mirror image of the knife  32  and is similarly provided with a heel portion  80 , which has a top surface  82 , a vertical shoulder  81 , and a rounded part  84 . When the cutter blades  32  and  34  are secured on the body  12 , the heel portions  70  and  80  slightly overlap, as shown in  FIGS. 2 and 4 . 
     The body  12  is provided with a second set of opening  37 ,  39  that are configured for receiving the pivot pins  41 ,  43  of the reverse cutter knives  33 ,  35  therein. The knife  33  is substantially similar to the knife  34 , while the knife  35  is substantially similar to the knife  32 . When the pins  40 ,  42  become damaged, or the knives  32 ,  34  become unusable, an operator has an opportunity to continue the milling operation by first pulling out the tool  10  from the well bore and then engaging the end  17  of the tool body  12  in the upper position, in effect turning the tool  10  180 degrees about a vertical axis. In that case, the end  15  of the tool  10  is located below the end  17 . 
     The knife  35  has a cutting surface  135 , which carries the cutting material, for instance tungsten carbide. An opposite surface  136  of the knife  35  joins with a heel portion  138 . The heel portion  138  is provided with an opening  139  for receiving of the pin  43  therethrough. The heel portion  138  has a rounded part  176 , a vertical shoulder  172 , and a transverse shoulder  174 . The knife  35  has a distal end  140 , which has an angularly cut corner  142 . The tip  146  of the knife  35  can be sharpened or blunt (as in  FIGS. 1 and 11 ). If sharpened, the tip  146  may be provided with cutting material; if the tip  146  is blunt it may or may not be provided with cutting chips. 
     The knife  33 , similar to the knife  34 , also comprises a rounded heel, an upper surface with cutting chips, and a distal end with an angularly cut corner. The knife  33  is detachably pivotally engaged with the body  12 , similarly to the knives  32 ,  34  and  35  by a pivot pin . . . engaged within an opening  37 . 
     Apparatus  10  further comprises a means for transmitting a downward force on the cutter blades  32 ,  33 ,  34 , and  35 . The means for transmitting the downward force comprises a pair of opposing spaced-apart, independently operable piston assemblies  191 ,  192  configured for movement inside the hollow tool body  12 . Depending on the end that is the uppermost in the well bore, whether the end  15  or the end  17 , one of the piston assemblies  191 ,  192  is selectively actuated from the surface, while the piston assembly below the one that has been actuated remains idle. 
     Each of the piston assemblies  191 ,  192  comprises a piston body with an enlarged diameter upper portion  194  and a reduced size lower portion  196 . An O-ring  200  is fitted in a groove formed in the enlarged portion  194 . The upper portion  194  is configured to frictionally engage interior wall of the body  12  when the piston  191  moves through the body  12 . The lower portion  196  is unitary connected to the upper portion  194  and has a generally rectangular or square cross-section. 
     The upper portion  92  has a generally cylindrical configuration. The lower portion  196  has two side walls  197 ,  198  that extend below the upper portion  194  and terminate at the bottom surface  195  of the upper portion  194 . The lower portion  196  is configured to fit between vertical shoulders  72 ,  81  when the knives  32 ,  34  are pivoted on the pins  40 ,  42 . This design of the piston  191  allows backside of the knives to be reinforced by reducing tolerances needed for accommodating the tool  10  inside a small diameter tubular. This design provides additional strength, during the cutting or section milling operation. 
     An opening  202  is formed in the large portion  194  for allowing a wash liquid to be delivered from the surface to the area being cut. The opening  202  branches into a pair of channels  204 ,  206 , which direct the wash liquid in the direction of arrows  205  to the slots  14  and  16  to an area above the upper surfaces  44 ,  46  of the knives  32 ,  34 , respectively. The liquid washes away any cutting made by the knives  32 ,  34  and allows then to drop by gravity into the well bore. The cuttings can then be collected by the magnetic tools  24  or  20 , depending on which of these tools is below the body  12 . 
     In operation, the reduced size portion  198  of the piston  191  contacts the upper surfaces  74  and  82  of the heel portions  70  and  80 , respectively, when the piston  191  moves in the downward direction within a central opening  106  of the body  12 . The downward moving force applied to the piston assembly  191  may come from an electric, hydraulic, or pneumatic power source (not shown), to which the piston assembly  191  is connected in a manner known to those skilled in the art. 
     To ensure an axial movement of the piston assembly within the opening  106 , the assembly  191  further comprises a pair of piston alignment blocks  108 ,  110 . The piston alignment blocks are aligned to contact the surfaces  197 ,  198  of the lower portion  196 . The blocks  108  and  110  are configured as half disks, with straight surfaces  112 ,  114  and curved portions  116 ,  118 . The piston alignment blocks  108  and  110  are secured to the piston assembly  191  with the help of tightening members or screws  120  ( FIG. 8 ) such that the flat surfaces  112 ,  114  extend transversely to the flat surfaces  197 ,  198  of the lower portion  196 . The screws  120  extend through respective openings  121 ,  122  formed in the piston alignment blocks  108  and  110 . 
       FIGS. 6 ,  7 ,  9  and  12  illustrate the use of alternative cutter blades  232 ,  34  in the apparatus of the present invention. In this embodiment the cutter blades  232 ,  234  are provided with cutting surfaces formed on the top and bottom surfaces thereof. As can be seen in the drawings, each cutter blade  232 ,  234  has a first surface  236  and an opposing second surface  238 , which may be oriented parallel to the first surface  236 . Cutting chips, made for instance of tungsten carbide, are deposited on the surfaces  236  and  238 , allowing the cutter blade  232  to cut the casing  240  irrespective of whether the tool  10  is being moved downwardly or upwardly within the casing  240 . The cutter blade  234  has a similar structure with opposing cutting surfaces  242 ,  246 . 
     Similarly to the cutter blades  32 ,  34 , the blades  232 ,  234  are pivotally secured on the body  12  by suitable pivot pins  246 ,  248 , allowing the blades  232 ,  234  to move between a recessed, idle position within slots  250 ,  252  to a gradually extending position, and then to a fully extended position as shown in  FIGS. 6 and 9 . In this position the longitudinal axes of the blades  232 ,  234  are oriented substantially perpendicularly to the wall of the casing  240 . 
       FIG. 9  illustrates reversible substitute blades  262 ,  264 , which are configured for pivotal mounting on the body  12  through the use of pivot pins  266 ,  268 . The pins  266 ,  268  are sized and shaped to fit into openings  267 ,  269  formed in the body  12 . Securing bolts  270  secure the piston retaining blocks (not shown) with the body  12 . 
     Similarly to the embodiment described above, the substitute cutter blades  262 ,  264  are secured on the body  12  when the tool body  12  is turned 180 degrees about its vertical axis. The blades  262 ,  264  then perform the cutting operation cutting a “window” in the wall of the casing  240 . 
     In operation, the apparatus  10  is lowered into the smallest diameter pipe or casing  240  to a depth selected for performing the cutting operations. The required depth is such that the cutter blades  32 ,  34  or  232 ,  234  are positioned well below the mud line. In conventional oilfield operations the innermost casing  240  may have a diameter as small as 7-⅝″. The body of the apparatus  10  is caused to rotate within the casing  240 , while the piston  191  presses downward on the heels  70  and  80  of the cutter blades  32 ,  34  or  232 ,  234 . 
     Under the influence of the downward force on the piston assembly  191 , the cutter blades  32 ,  34  or  232 ,  234  pivot about the pivot pins  40 ,  42 , or  246 ,  248 , gradually extending through the slots  14  and  16  into a contact with the innermost tubular. The cutting surfaces of the distal ends  56 ,  58  begin the first cut through the casing  240 . Eventually, a window  280  of about 25 inches is cut through the wall of the casing  240  allowing the knives  32 ,  34  or  232 ,  234  to extend through the window. 
     The same cutting sequence is followed if the tool  10  is pulled upwardly or pushed downwardly within the casing  240 . Either the top surfaces or the bottom surfaces of the cutter blades perform the cutting operation. If desired, the cutting operation may start with using a pair of blades having sharpened tips and the subsequent milling operation can be performed using cutter blades with blunt tips so as not to damage or disturb the next size casing. 
     Once the first casing is severed, the tool  10  is retrieved to the surface, and a longer set of cutter blades is secured on the support body  12 . The longer set of the cutter blades still fits in the recesses formed by the slots  14  and  16 . Once the tool is lowered to the depth where the new set of the cutter blades is aligned with the previously cut slot in the casing  240 , rotational force is again applied to the body. At the same time, the new set of the cutter blades is extended through the pre-formed slot to continue the cutting operation through the next adjacent tubular and the cementing media. 
     Depending on the number of casings to be cut through, progressively longer blades are secured to the support body  12  and lowered into the well bore. The same support body  12  can carry the cutter blades for cutting large diameter tubulars, for instance a 30″ casing. In such cases, the cutter blades  32 ,  34  are pivoted to extend almost perpendicularly to the longitudinal axis of the support body  12  to a position schematically shown in the drawings. The casing cutting operation can be performed even if the cutter blades are not oriented strictly perpendicular to the longitudinal axis of the casing  240 . With partially extended cutter blades, the casing cutting operation can still be performed. The cutter blades of the apparatus of the present invention are allowed to self-align depending n the resistance offered by the casing wall of cementing medium in the casings. As a result, an operator can plug successively larger diameter casing, if necessary, while preventing oil leakage into the surrounding environment. This process continues until the outermost casing is severed. 
     The apparatus of the present invention allows severing of multiple casings that are cemented together using a two-bladed cutter. The support body  12  fits within the narrowest casings, while carrying cutter blades to cut even large diameter casings. The initial cut with the shortest set of knives  32 ,  34  is used for extending longer knife blades through the window and continue cutting operations at the same depth, while continuously increasing the lengths of the blades  32 ,  34  until the most outside casing is severed. 
     In comparison with conventional methods, the apparatus of the present invention allows to eliminate the milling from an outside of the casings, while severing the multiple tubulars at the desired depth in the matter of 1-½ to 2 days. The apparatus of the present invention allows severing of the multiple tubulars even when the tubulars are not co-axially aligned. 
     The cutting blade of the present invention allows cutting with the ends of the cutter blades  56 ,  58  and with the top surfaces  44 ,  46  of the blade, as well as bottom surfaces of the blades  232 ,  234 . In conventional three bladed cutters, the knives are about 1 inch wide. With the two bladed cutter of the present invention, the cutter blades can be up to 3 inches wide, which makes them stronger and allows to reach out into the outermost casing. 
     Many other changes and modifications may be made in the design of the present invention without departing from the spirit thereof. I, therefore, pray that my rights to the present invention be limited only by the scope of the appended claims.