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BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates generally to cutting devices or systems and, more particularly, to a cutting device or system operable for repeatedly cutting drill pipe, tubing, coiled tubing, and/or wireline so as to be especially suitable for use in a lightweight intervention package and/or in substitutions for replacing at least one BOP in an intervention package. 
     Background of the Invention 
     Blowout Preventer (B.O.P.) stacks are frequently utilized in oilfield well bore Christmas trees and subsea intervention operations such as, for instance, lower riser packages in offshore wells. B.O.P. stacks may include a first set of rams for sealing off the wellbore and a second set of rams for cutting pipe such as tubing, wireline and/or intervention tools. However, B.O.P. stacks are quite bulky and heavy, which are undesirable features especially in lower riser packages for undersea operation where space is often at a premium. B.O.P. stacks tend to be expensive for installation and removal due to the need for heavy lifting equipment. Moreover, if maintenance is required, then the high maintenance costs for utilizing B.O.P. stacks for intervention purposes severely limits the wells that can be economically reworked. B.O.P. stacks may frequently require maintenance after cutting pipe. For instance, the cut pipe may become stuck within the B.O.P. stack blocking other operations. 
     Consequently, those skilled in the art will appreciate the present invention that addresses the above problems. 
     The following patents discuss background art related to the above discussed subject matter: 
     U.S. Pat. No. 6,601,650, issued Aug. 5, 2003, to A. Sundararajan, which is incorporated herein by reference, discloses apparatus and methods for replacing a BOP with a gate valve to thereby save space, initial costs, and maintenance costs that is especially beneficial for use in offshore subsea riser packages. The method provides a gate valve capable of reliably cutting tubing utilizing a cutting edge with an inclined surface that wedges the cut portion of the tubing out of the gate valve body. A method and apparatus is provided for determining the actuator force needed to cut the particular size tubing. 
     U.S. Pat. No. 8,353,338, issued Jan. 15, 2013, to J. Edwards, discloses a well bore control valve comprising a housing defining a throughbore, the throughbore adapted to receive a first tubular. The valve further comprises first and second gates located within the housing, the gates being movable in different directions transverse to the throughbore between the throughbore open position and the throughbore closed position. Movement of the gates from the throughbore open position to the throughbore closed position, in use, shares a tubular located between the gates. The valve also comprises a first seal seat performing a seal of one of the gates in the throughbore closed position to seal the throughbore. 
     U.S. Patent Application No. 20100218955 discloses an oil field system comprising a main body having a bore therethrough, the main body having a connection at one end of the bore for, in use, connecting the main body to an existing wellhead, tree or other oil field equipment, a transverse cavity through the bore, the cavity having at least one opening to the outside of the main body, a plurality of flow control systems for insertion, at different times, into the cavity in order to selectively control fluid flow through the bore, wherein the plurality of flow control systems includes a gate valve and drilling BOP rams. 
     The above prior art does not disclose the cutting system operable for cutting drill pipe while still being very lightweight as described in the present specification. Consequently, those skilled in the art will appreciate the present invention that addresses the above and/or other problems. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved cutting apparatus and/or system. 
     Another possible object of the present invention is to provide a non-sealing compact cutting device to cut drill pipe at least up to 3½ inches and allows use with a gate valve for sealing the wellbore with the combination to substitute for a much heavier BOP. 
     Yet another possible object of the present invention is to provide a compact cutting system with a short stroke length and/or piston rod assemblies and/or lesser fluid volumes at different vertical heights. 
     Accordingly, a compact cutting system is provided that is operable for cutting 4½ inch 16.60 lb/ft drill pipe, coiled tubing, wireline and sinker bar. The cutting system comprises a housing defining a throughbore, a first gate and a second gate mounted within the housing. The first gate and the second gate are moveable transversely with respect to the throughbore between an open position and a closed position. In one embodiment, the first and second gates comprise openings therein that prevent sealing of the throughbore in the closed position. 
     The compact cutting system may further comprise a gate valve wherein the compact cutting system is operable for substitution of at least one BOP. 
     In one possible embodiment, the system may comprise a first piston and a first piston rod operably connected to the first gate with a first stroke length. A second piston and a second piston rod is operably connected to the second gate with a second stroke length. The first and second stroke lengths are less than a diameter of the throughbore. 
     In one possible embodiment, the first gate and the second gate each comprise a gate bore therethrough, in the open position each gate bore is in surrounding relationship to or form a portion the throughbore. In one embodiment, the gate bore is elliptical. 
     In one possible embodiment, when the throughbore is oriented vertically then the first piston and first piston rod is mounted to the housing at a higher vertical position than the second piston and second piston rod. 
     In one embodiment, the first piston and the second piston each comprise a piston surface with a diameter between one and one-half and two and one-half times as large as a diameter of the throughbore. 
     The compact cutting system may further comprise a first piston chamber for the first piston and a second piston chamber for the second piston. The first piston and the second piston are mounted so that all of each piston surface is available for engagement with hydraulic fluid for use in closing the gates. The piston rod end of the piston may then be utilized for opening the gates. 
     In one possible embodiment, the cutting system may comprise a first seat mounted in the throughbore adjacent the first gate. The first seat has a first seat interior. The first seat interior decreases in diameter with distance away from the first gate. A second seat is mounted in the throughbore adjacent the second gate. In a similar manner, the second seat interior decreases in diameter with distance away from the second gate. In one embodiment, the interior of the seats may be elliptical. 
     In one possible embodiment, the compact cutting system may comprise a first seat mounted in the throughbore adjacent the first gate, a second seat mounted in the throughbore adjacent the second gate. The first gate and the second gate may comprise a passageway therethrough to prevent sealing between the first gate and the first seat and between the second gate and the second seat. 
     In one possible embodiment, the first piston rod and the second piston rod comprise a length less than two and one-quarter times as large as a diameter of the throughbore. The first piston and the second piston each comprise a piston surface with a diameter between one and one-half and two and one-half times as large as a diameter of the throughbore. 
     These and other objects, features, and advantages of the present invention will become clear from the figures and description given hereinafter. It is understood that the objects listed above are not all inclusive and are only intended to aid in more quickly understanding the present invention, not to limit the bounds of the present invention in any way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above general description and the following detailed description are merely illustrative of the generic invention, and additional modes, advantages, and particulars of this invention will be readily suggested to those skilled in the art without departing from the spirit and scope of the invention. A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts and wherein: 
         FIG. 1  is a front elevational view, in section, of a compact cutting system in the open position in accord with one possible embodiment of the present invention. 
         FIG. 2  is a front elevational view, in section, of a compact cutting system in the closed position in accord with one possible embodiment of the present invention. 
         FIG. 3  is a side elevational view, in section, of a compact cutting system in accord with one possible embodiment of the present invention. 
         FIG. 4  is a top elevational view of a compact cutting system in accord with one possible embodiment of the present invention. 
         FIG. 5  is a front elevational view of a compact cutting system in accord with one possible embodiment of the present invention. 
         FIG. 6  is an exploded view of a compact cutting system in accord with one possible embodiment of the present invention. 
         FIG. 7A  is an enlarged view of a gate in accord with one possible embodiment of the present invention. 
         FIG. 7B  is an enlarged view of a gate oriented in a reversed position with respect to  FIG. 7A  in accord with one possible embodiment of the present invention. 
         FIG. 8  is a schematic view of a compact cutter and gate valve that may be utilized in a subsea installation is place of at least one BOP (blowout preventer) in accord with one possible embodiment of the present invention. 
         FIG. 9  is an elevational view of a cutter in accord with one possible embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner. 
     Abbreviations include the following: 
     API—American Petroleum Institute 
     DNV—Det Norske Veritas (The Norwegian Veritas) 
     ISO—International Standardization Organization 
     ROV—remotely operated vehicle 
     NACE—National Association of Corrosion Engineers 
     QTC—Qualification Test Coupon 
     The use of CCD  10  complies with codes and standards including: 
     API 6A, Specification for wellhead and Christmas tree equipment, 20th Edition, October 2010; 
     API 16A, Specification for Drill-through equipment, 3rd Edition, June 2004; 
     API 16D Control Systems for Drilling Well control Equipment, 2nd Edition, July 2004; 
     NORSOK D-002, Well intervention equipment, Revision 2, June 2013; 
     DNV-OS-E101, Drilling Plant, October 2013; 
     ISO 13533, Drilling and production equipment—Drill-through equipment, 1st Edition, December 2001; 
     API 17G, Recommended practice for completion/workover risers, 2 nd  Edition, July 2006 
     NACE MR0175/ISO 15156, Petroleum and natural gas industries—materials for use in H2S-containing environments in oil and gas production, 2nd Edition, October 2009. 
     Referring now to the drawings and more particularly to  FIG. 1 , there is shown one possible embodiment of a compact cutting device or system which may be referred to herein as CCD  10 . Housing  12  defines throughbore  14  with axis  16 . Flange connection  18  at the bottom end, which may comprise studs or the like, may be utilized for connection with well equipment such as subsea installations, well intervention equipment, and the like. Another flange connection at the top end may connect to other well equipment such as a gate valve or the like. One embodiment of CCD  10  comprises a 7⅜ inch throughbore, with a 10K psi pressure rating. The top and bottom connectors may comprise a 13⅝ inch 10K psi studded connectors and/or flange connections. In one embodiment, CCD  10  is operable to cut pipe  68  (see  FIG. 9 ) which may comprise 3½ in 13.3 lb/ft Grade E 75 drill pipe (Table 18, API 16A/ISO 13533) without leaving any snag or slug after cutting. In one embodiment, CCD  10  operates very quickly and can cut the drill string in less than 2 seconds when using an accumulator. The tests to be conducted for CCD  10  for use in an intervention package include NORSOK D-002 (API 16A/ISO 13533 Annex C) in one possible embodiment for cutting only, without the need for sealing tests as explained hereinafter. Further in one embodiment, CCD  10  weighs less than 12,000 pounds. Combined with a gate valve, the combination is much less than the weight of a BOP, which provides an opportunity for a highly desirable substitution in an intervention package. The light weight makes possible reworking of wells much less expensive than using a BOP. 
     Cylinder housings  20  and  22  are utilized to house pistons  24  and  26 , respectively, which drive piston rods  28  and  30  to move gates  44  and  46  between an open position and a closed position.  FIG. 1 ,  FIG. 3 , and  FIG. 9  show gates in an open or open throughbore position.  FIG. 2  shows the gates in a closed position. As discussed below, in one possible embodiment moving the gates to the closed position does not necessarily provide a seal but instead in one presently preferred embodiment fluid flow may occur past the gates. However, if desired, the gates could also be made to provide a seal when closed. 
     In one embodiment, stroke length  32  and  34  of the pistons is relatively short so as to be less than the diameter of throughbore  14 . In one embodiment of a 7⅜ inch throughbore, the stroke length may be in the range of 5 inches. However, larger and smaller stroke lengths could be utilized. In one embodiment, compact cutting system CCD  10  advantageously utilizes considerably less volume of hydraulic fluid to operate in comparison to other units with cutting capability, e.g. a BOP. In one embodiment, the present invention utilizes less than 12 liters of hydraulic fluid for opening or closing the gates. 
     It will be noted that when CCD  10  is vertically oriented that piston  24 , rod  28 , gate  44 , and the axis of movement  36  of rod  28  is vertically higher than piston  26 , rod  30 , gate  46  and axis  38  of rod  30 . Likewise, piston housing  20  with associated bolts is vertically higher than piston housing  22  as shown in  FIG. 1 ,  FIG. 2 ,  FIG. 5 , and  FIG. 9 . The applied force is therefore directed along axis  36  and  38  of the pistons, piston rods and gates, which reduces bending forces acting on the piston rods  28  and  30  due to cutting forces applied by the gates, which are at different vertical heights. 
     In  FIG. 2 , valve cavity  98  can be irregularly shaped due to the different vertical heights of the components. In one embodiment, the diameter of the opening into housing  12  for the components used with each cylinder is almost the same diameter of the pistons and may be used for inserting the seats, gates, and other components. 
       FIG. 4  shows the top elevational view whereby it can be seen that from an external view, cylinders  20  and  22  are aligned in top view, which may be considered the x-y plane. Accordingly, their associated pistons, piston rods, gates, piston axes are also aligned from this view. This is in contrast to  FIG. 5 , which shows that cylinder  20  is vertically higher than cylinder  22 , which might be considered along a z-axis. 
     Referring again to  FIG. 1 , upper seat  40  and lower seat  42  are mounted in throughbore  14  in respective recesses in housing  12 . Seats  40  and  42  may or may not seal with gates  44  and  46  when in the closed or closed throughbore position. In one embodiment, referring to  FIG. 2  that shows CCD  10  in the closed position, openings are formed in gates  44  and  46  that positively prevent sealing when in the closed position as indicated by flowpath  56  through the gates  44  and  46 , which allows for fluid flow even in the closed or closed throughbore position. For example, slots may be milled into gates  44  and  46  as shown in  FIG. 7A  and  FIG. 7B  at  65  and  67 . In another embodiment additional openings, passageways, or the like may be formed with in the gates. 
     In another embodiment, if desired, and which is not necessarily a preferred embodiment, one or both gates could be made to seal with seats  40  and  42 , with a metal to metal seal. 
       FIG. 2  also shows hydraulic fluid volumes  52  and  54  that are filled with pressurized hydraulic fluid to move the gates to the closed position. It will be appreciated that the entirety of piston surfaces  58  and  60  can be utilized to create force to drive the cutters in the gates to cut drill pipe or the like within throughbore  14 . In one embodiment, diameter  62  of piston surfaces  58  and  60  may be in the range of 1½ to 2½ times the diameter of throughbore  14 . In another embodiment the diameter may be between 1½ to 2 times the diameter of throughbore  14 . In this way, a significant cutting force relative to pipe within throughbore  14  is produced, which allows the high speed powerful cutting. Use of surfaces  58  and  60  to create the force to drive the cutters takes advantage of the full surface of the pistons rather than using the side of the piston to which the piston rod is attached. Use of the piston rod side to drive the cutters would reduce the area on which the pressurized hydraulic fluid operates. Significant gate opening force is also available to open the gates by applying hydraulic fluid to the interior side of pistons  24  and  26 . The piston rods connected to the interior size limit the force to some extent and in this embodiment may result in interior piston surfaces in the range of 132 square inches. Accordingly somewhat less hydraulic fluid is required for opening. 
     In one embodiment, the use of a shorter piston rod also helps produce a compact size for CCD  10 . In one embodiment, piston rods  28  and  30  comprise a length less than 2¼ times the throughbore diameter and in another embodiment less than 2 times the throughbore diameter when measured from the inner surface of the piston to the end thereof. 
     As noted above, the cutting action is performed by moving the gates towards the wellbore so the full hydraulic piston surface area is used (not the rod end). This allows maximization of the performance and utilization of the hydraulic pressure available. 
     Using two gates  44 ,  46  causes the tool string to be centralized during the cut action rather than it being pushed to one side. The tool string is captured inside the two gate bores  64 ,  66  to provide crushing action to yield and cut the string in an area away from the upper and lower seats  40 ,  42 . Gate bores  64 ,  66 , comprise a minimum diameter of the throughbore, which in one embodiment is 7⅜ inches. 
     In one embodiment, the gate bores  64 ,  66  may be oval so that the minimum of 7⅜ is along one axis of the oval with the other axis of the oval being greater than the borehole diameter. Likewise, upper and lower seat  40 ,  42  may comprise an oval interior to match that of the gates. 
       FIG. 6  shows an exploded view of CCD  10 , including piston seals  82 ,  84 , piston rod seals  86 ,  88  and cylinder housing bases  90 ,  92 . Other components have already been discussed but are shown here in a perspective view. It will be noted that external shapes of upper seat  40  and lower seat  42  as well as that of other components is shown. 
       FIG. 7A  and  FIG. 7B  show enlarged views of gates  44  and  46  as well as cutter inserts  94  and  96 . Gates  44  and  46  may or may not utilize cutter inserts such as cutter inserts  94  and  96 . Utilizing cutter inserts  94 ,  96  allows the cutting surfaces to be changed out. Cutting face or surface  76  is shown in  FIG. 7A . As discussed hereinbefore, gate openings or bores  64  and  66  preferably encircle throughbore  14  and drill pipe or the like within the throughbore when in the open position. In one embodiment openings or bores  64  and  66 , with the corresponding cutter inserts  94 ,  96  are preferably circular or as shown in this embodiment, are oval. Openings  65 ,  67  and/or other openings can be milled into the gates and utilized to provide that the gates do not seal with the seats and allow fluid flow through the throughbore in the closed position as discussed hereinbefore. However, if desired, the openings may not be used and the gates could seal with the seats, although that is not the presently preferred embodiment. It will be noted that a T-slot connection can be used on the ends of the gate with corresponding T connector on the piston rods if desire. 
     In one embodiment, the taper angle at the cutting edge of the gates is unique. Cutting inserts may or may not be used. If desired, hard facing or case hardening process may not be used on the gates. 
       FIG. 8  shows a schematic of intervention package  100  that comprises CCD  10 , which may be utilized with gate valve  102  in conjunction with subsea installation  104  in substitutions for a much heavier BOP in accord with one embodiment of the invention. CCD  10  may be utilized to cut 3½ in. 13.3 lb/ft Grade E-75 drill pipe without leaving any snag after cutting in accord with Table 18, API 16A/ISO 13533 and may be utilized to cut up to 4½ IN 16.60 lb/ft drill pipe. The use of CCD  10  in place of the much heavier BOP for use in an intervention package complies with codes and standards including: 
     API 6A, Specification for wellhead and Christmas tree equipment, 20th Edition, October 2010; 
     API 16A, Specification for Drill-through equipment, 3rd Edition, June 2004; 
     API 16D Control Systems for Drilling Well control Equipment, 2nd Edition, July 2004; 
     NORSOK D-002, Well intervention equipment, Revision 2, June 2013; 
     DNV-OS-E101, Drilling Plant, October 2013; 
     ISO 13533, Drilling and production equipment—Drill-through equipment, 1st Edition, December 2001; 
     API 17G, Recommended practice for completion/workover risers, 2nd edition, July 2006 
     NACE MR0175/ISO 15156, Petroleum and natural gas industries—materials for use in H2S-containing environments in oil and gas production, 2nd Edition, October 2009. 
       FIG. 9 , which is another embodiment of a cutting system, namely cutting system  10 A, shows openings  64  and  66  in gates  44 ,  46  which surround throughbore  12  and pipe  68 . Cutting system  10 A utilizes longer cylinder rods and housing. 
     It will also be seen that gate opening  64  decreases in inner diameter with distance away from seat  40  as indicated by interior surface profile  52  until coming to cutting face  74  at the bottom of upper gate  44 . Likewise, the inner diameter of gate opening  66  decreases with distance away from seat  42  as indicated by interior surface profile  55  until coming to a cutting face  76  at the top of lower gate  46 . The changes in inner diameter of the openings  64 ,  66  through the gate can also be seen in  FIG. 1 ,  FIG. 2 , and  FIG. 3 . 
     In this embodiment, the interior or inner diameter of upper seat  40  decreases in diameter with distance away from gate  44  as indicated by interior surface profile  48 . The interior of lower seat  42  also decreases in diameter with distance away from lower gate  46  as indicated by interior surface profile  50 . The decrease in diameter of the upper and lower seats discussed above leads to the throughbore diameter at about the midpoint of the seats, which in one embodiment may be 7⅜ inches. In other words, both the seats and the gates comprise openings which are larger than the throughbore diameter in some regions and then either approach or are at the throughbore diameter, e.g. at the cutting faces and at the upper portion of upper seat  40  and the lower portion of lower seat  42 . The minimum diameter is the throughbore diameter. As discussed above, both the interior of the seats and the gates may be oval. 
     Upper seat seal surface  70  is recessed into housing  12  and seals with upper seat  40 . Lower seat seal surface  72  is recessed into housing  12  and seals with lower seat  42 . Face  78  is provided between first gate  44  and seat  40 . Face  80  is provided between second gate  46  and seat  42 . As discussed hereinbefore, in one embodiment the seats do not seal off throughbore  12  even when the gates are in the closed position. However, if desired, a metal to metal seal could be provided at face  78 ,  80  to seal off throughbore  12  with the gates in the closed position. 
     In one embodiment, CCD  10  is operable to cut pipe  68  which may comprise 3½ in 13.3 lb/ft Grade E 75 drill pipe (Table 18, API 16A/ISO 13533) or 4½ IN 16.60 lb/ft drill pipe. 
     In summary, the present invention provides a compact cutting system or device. In one embodiment to provide a 7⅜ throughbore, the compact cutting system or device may be in the range of 40 to 50 inches in height, in the range of 65 to 75 inches at maximum width, and with a diameter in the range of 20-25 inches, with a weight in the range of 11,000 to 12,000 pounds. In one embodiment, a relatively short stroke is utilized. In one embodiment, the piston rods are at different vertical heights. The openings in the gates preferably surround the throughbore or form part of the throughbore in the open position. In the closed position, the gates may be modified to provide that they do not seal with the seats. 
     The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description only. It is not intended to be exhaustive nor to limit the invention to the precise form disclosed; and obviously many modifications and variations are possible in light of the above teaching. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.

Summary:
As compared to a BOP, a compact lightweight cutting system may have two gates with cutters moveable in opposite directions to cut drill pipe. The system utilizes a relatively short stroke and relatively less hydraulic oil for subsea operation. An opening through the gates surrounds the wellbore in the open position. The cutting elements are mounted within the openings. The piston rods and pistons are vertically offset with respect to each other. The compact cutting system with a gate valve can be used to substitute for a BOP to significantly reduce the size and weight required in an intervention system.