A methodology and apparatus for cutting shape(s) or profile(s) through well tubular(s), or for completely circumferentially severing a well through multiple tubulars, including all tubing, pipe, casing, liners, cement, other material encountered in tubular annuli. This rigless apparatus utilizes a computer-controlled, downhole robotic three-axis rotary mill to effectively generate a shape(s) or profile(s) through, or to completely sever in a 360 degree horizontal plane wells with multiple, nested strings of tubulars. This is useful for well abandonment and decommissioning where complete severance is necessitated and explosives are prohibited, or in situations requiring a precise window or other shape to be cut through a single tubular or plurality of tubulars.

REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. § 119 to application No. 61/131,874, filed Jun. 14, 2008, entitled “Rotary milling casing cutter,” which is hereby fully incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    When oil and gas wells are no longer commercially viable, they must be abandoned in accord with government regulations. Abandonment requires that the installed tubulars, including all strings of tubing, pipe, casing or liners that comprise the multiple, nested tubulars of the well must be severed below the surface or the mud line and removed. Using explosive shape charges to sever multiple, nested tubulars in order to remove them has negative environmental impacts, and regulators worldwide are limiting the use of explosives. Therefore, a need exists for effective alternatives to the use of explosives for tubular severance in well abandonment. 
         [0003]    Mechanical blade cutting and abrasive waterjet cutting have been implemented in response to new restrictive environmental regulations limiting the use of explosives. 
         [0004]    The prior and current art of utilizing mechanical blade cutters from the inside of the innermost casing, cutting out through each successive tubular of the multiple nested tubulars, requires multiple trips in and out of the wellbore. Such mechanical blade cutters require a rotary rig or some means of rotary drive in order to rotate the work string to which the mechanical blade cutter is attached. Rotary drive systems are both cumbersome and expensive to have at the work site. An example of the prior art is disclosed in U.S. Pat. No. 5,150,755, which is deficient in that its mechanical blade cutters may break when they encounter non-concentric tubulars, defeating its aim of severing multiple strings of tubulars in a single trip. Another deficiency is the limitation on the number of nested tubulars that may be severed by this mechanical blade cutter. An “inner” and “outer” string are described as being severable in one trip, if generally concentrically positioned in relation to each other. There is no claimed capability of severing a greater number of tubulars, for example, five, nested tubulars, and certainly not in the event that such multiple, nested tubulars were to be non-concentrically positioned. 
         [0005]    Most advances in the mechanical blade cutting art have focused on cut chip control and efficiency, such as U.S. Pat. No. 5,181,564, or U.S. Pat. No. 5,899,268, rather than focusing the fundamental issues of blade breakage and required, multiple, undesired trips of the apparatus in and out of a well. Thus these fundamental problems of prior art in mechanical blade cutting persist. 
         [0006]    When cutting multiple, nested tubulars of significant diameters, for example 9⅝ inches outside diameter through 36 inches outside diameter, with at least two other nested tubulars of different sizes dispersed in between, the mechanical blade cutter must be brought back to the surface where the smaller, just-used cutting blades are exchanged for larger cutting blades. Exchanging the smaller blades for larger blades allows the downhole cutting of successively larger diameter multiple, nested tubulars. 
         [0007]    The access of the downhole mechanical blade cutter requires pulling the work string out of the wellbore and unscrewing the work string joints where the mechanical blade cutter is attached to the bottom work string joint. After exchanging the mechanical blade cutter for a larger cutting blade, the work string joints are screwed back together, one after another, and tripped back into the wellbore. The mechanical blade cutter trip back into the wellbore to the previous tubular cut location for additional cutting is compromised because the length of the work string varies due to temperature changes or occasionally human error in marking or counting work string joints. Many installed multiple, nested tubular strings in wells are non-concentric, meaning that the nested tubulars are positioned off center in relation to the innermost tubular, not having the same center diameter as the smallest tubular. As a result of the multiple, nested tubulars being stacked or clustered to one side, i.e. non-concentric to each other, the density or amount of material being cut will vary circumferentially during cutting. Mechanical cutter blades sometimes experience breakage when cutting multiple, nested tubulars positioned non-concentrically in relation to each other. The blade cutter often breaks from the contact with the leading edge of a partial segment of the casing that remains after another segment of that casing has been cut away. The remaining portion of the casing forms a “C” or horseshoe-type shape when viewed from above. The blade cutter extends to its fullest open cut position after moving across a less dense material or open space (because that material has been cut away) and when the blade cutter impacts the leading edge of the “C” shaped tubular, the force may break off the blade. The breaking of a cutter blade requires again tripping out and then back into the well and starting over at a different location in the wellbore in order to attempt severing of the multiple, nested tubulars. Non-concentric, multiple, nested tubulars present serious difficulties for mechanical blade cutters. Severing non-concentric multiple, nested tubulars can take a period of days for mechanical blade cutters. 
         [0008]    The prior art utilizing abrasive waterjet cutters also experiences difficulties and failures to make cuts through multiple, nested tubulars. Prior art methods and apparati are disclosed in U.S. Pat. No. 7,178,598 and also U.S. Pat. No. 5,381,631. These disclosures relate to abrasive waterjet cutting utilizing rotational movement in a substantially horizontal plane to produce a circumferential cut in downhole tubulars. However, the prior art in abrasive waterjet cutters for casing severance often results in spiraling cuts with narrow kerfs in which the end point of the attempted circumferential cut fails to meet the beginning point of the cut after the cutting tool has made a full 360 degree turn. In other words, the cut does not maintain an accurate horizontal plane throughout the 360 degree turn, and complete severance fails to be achieved. Another problem encountered by prior and current art abrasive waterjet cutting is the inability to cut all the way through the thicker, more widely spaced mass of non-concentrically positioned tubulars. In this situation, the cut fails to penetrate all the way through on a 360 degree circumferential turn. A further disadvantage of traditional abrasive waterjet cutting is that in order to successfully cut multiple, nested tubulars downhole, air is required to be pumped into the well bore to the area where the cutting is to take place, allowing the abrasive waterjet tool to function in air and not be impeded by water or wellbore fluid. The presence of fluid in the cutting environment greatly limits the effectiveness of prior art abrasive waterjet cutting. 
         [0009]    Verification of severance using waterjet cutting is accomplished by welding “ears” on the outside of the top portion of the tubulars under the platform, attaching hydraulic lift cylinders, heavy lift beams, and then lifting the entire conductor (all tubulars) to verify complete detachment has been achieved. When working offshore, this lifting verification process occurs before costly heavy lift boats are deployed to the site. This method of verification is time-consuming and expensive. 
         [0010]    Prior art has been devised to mill windows via longitudinal, vertical travel in casing. However, these milling methods do not completely sever multiple, nested non-concentric tubulars for well abandonment. A rotary milling method and apparatus was disclosed in U.S. Pat. No. 7,537,055. This milling method uses a whipstock, which must be deployed before the window milling process can begin. A rotary mill is then actuated against one side of a tubular along with a means of vertical travel, enabling a window to be cut through the tubular. This prior art does not permit 360 degree circumferential severance of multiple, nested tubulars and is not suited for the purpose of well abandonment. 
         [0011]    This invention responds to a need for a fast, inexpensive, safe and environmentally benign means of completely severing multiple, nested tubulars for well abandonment. This invention overcomes the difficulties encountered by mechanical blade cutting, abrasive waterjet cutting or other means of tubular milling in the prior art. As well as being environmentally “green,” this invention is a more efficient, rigless technology deployed downhole for severance of multiple, nested, non-concentric tubulars. 
         [0012]    This invention relates to a methodology and apparatus for cutting completely through multiple, nested strings of installed tubulars, concentrically or non-concentrically (eccentrically) positioned, by means of rotary milling. The downhole assembly is deployed in the innermost tubular and proceeds to rotary mill outward radially under computer control, cutting and completely severing all installed tubing, pipe, casing and liners as well as cement or other material encountered in the annuli between the tubulars. The severance process occurs during one trip into the well bore, obviating the need for retrieving and re-inserting the downhole milling assembly before job completion. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    This invention provides methodology and apparatus for efficiently severing all installed multiple, nested strings of tubulars, either concentric or eccentric, as well as cement or other material in the annuli between the tubulars, in a single trip into a well bore. This invention overcomes the difficulties encountered by prior art mechanical blade cutters by the rotary mill cutter machining through metal tubulars and other encountered material even if the nested tubulars and cement are not installed concentrically. 
         [0014]    The invention utilizes a computer-controlled robotic downhole rotary mill to effectively generate a shape(s) or profile(s) through, or completely sever in a 360 degree horizontal circumferential plane, all installed tubing, pipe, casing and liners as well as cement or other material encountered in the annuli between the tubulars. This process occurs under programmable robotic, computerized control, making extensive use of digital sensor data to enable algorithmic, robotic actuation of the downhole assembly and robotic rotary mill cutter. 
         [0015]    With this invention, for the purposes of complete severance of multiple, nested tubulars, the beginning and end points of the cut are immaterial as the robotic rotary mill cutter generates a wide swath or void. The severed casing will drop vertically at the surface platform, providing visual verification of the severance. The length, and therefore the reach of the spindle, is designed to extend beyond the outermost casing with any number of additional tubulars inside this outermost casing being extremely eccentrically positioned, even with each tubular abutting each successively nested tubular. This solves the cutting “reach” problems that are encountered with abrasive waterjet cutting when the waterjet has difficulty cutting through the thickest, most widely spaced mass of the eccentrically positioned tubulars and cement. The precision, programmable computer-controlled, sensor-actuated rotary milling process will take much less time to complete severance than mechanical blade cutters or abrasive waterjet cutting. The extremely precise, actively adjusted rotary milling, profile generation process greatly limits vibration and impact, preventing the impact breakage that plagues mechanical blade cutters encountering non-concentric, multiple, nested tubulars. Furthermore, this invention's capability of being deployed and completing the severance in one trip downhole provides a significant advantage over prior art. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0016]    Fig I. depicts the robotic rotary mill cutter  1 . The robotic rotary mill cutter  1 , shows the position of the vertical Z-axis, and the 360-degree horizontal rotary W-axis, and the milling spindle swing arm pivotal Y-axis. 
           [0017]      FIG. 2A  and  FIG. 2B  depict the robotic rotary mill cutter  1  (see  FIG. 1 ) enlarged and cut in half with the top of the robotic rotary mill cutter  1  (see  FIG. 1 ) shown in  FIG. 2A  and the lower portion of robotic rotary mill cutter  1  (see  FIG. 1 ) is shown in  FIG. 2B . 
           [0018]      FIG. 3  depicts an expanded view of an inserted carbide mill  17  that will be attached to milling spindle swing arm  14  (see  FIG. 2B ) with a bolt (not shown) running through the inserted carbide mill  17 . 
           [0019]      FIG. 4A  depicts a top view of multiple casings (tubulars)  18  that are non-concentric. 
           [0020]      FIG. 4B  depicts an isometric view of non-concentric casings (tubulars)  19 . 
           [0021]      FIG. 5A  depicts the bottom of the lower portion of robotic rotary mill cutter. 
           [0022]      FIG. 5B  depicts the lower portion of robotic rotary mill cutter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    This invention provides a method and apparatus for efficiently severing all installed tubing, pipe, casing, and liners, as well as cement or other encountered material in the annuli between the tubulars, in one trip into a well bore. 
         [0024]    Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts (elements). 
         [0025]    To help understand the advantages of this disclosure the accompanying drawings will be described with additional specificity and detail. 
         [0026]    The present disclosure generally relates to methods and apparatus for mill cutting through wellbore tubulars, including casing or similar structures. 
         [0027]    The method generally is comprised of the steps of positioning a robotic rotary mill cutter inside the innermost tubular in a pre-selected tubular or plurality of multiple, nested tubulars to be cut, simultaneously moving the rotary mill cutter in a predetermined programmed vertical X-axis, and also 360 degree horizontal rotary W-axis, as well as the spindle swing arm in a pivotal Y-axis arc. 
         [0028]    In one embodiment of the present disclosure the vertical and horizontal movement pattern(s) and the spindle swing arm are capable of being performed independently of each other, or programmed and operated simultaneously in conjunction with each other. The robotic rotary mill cutter is directed and coordinated such that the predetermined pattern is cut through the innermost tubular beginning on the surface of said tubular with the cut proceeding through it to form a shape or window profile(s), or to cut through all installed multiple, nested tubulars into the formation beyond the outermost tubular. 
         [0029]    A profile generation system simultaneously moves the robotic rotary mill cutter in a vertical Z-axis, and a 360-degree horizontal rotary W-axis, and the milling spindle swing arm swing arm in a pivotal Y-axis arc to allow cutting the tubulars, cement, and formation rock in any programmed shape or window profile(s). 
         [0030]    The robotic rotary mill cutter apparatus is programmable to simultaneously or independently provide vertical X-axis movement, 360 degree horizontal rotary W-axis movement, and spindle swing arm pivotal Y-axis arc movement under computer control. A computer having a memory and operating pursuant to attendant software, stores shape or window profile(s) templates for cutting and is also capable of accepting inputs via a graphical user interface, thereby providing a system to program new shape or window profile(s) based on user criteria. The memory of the computer can be one or more of but not limited to RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, floppy disk, DVD-R, CD-R disk or any other form of storage medium known in the art. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC or microchip. 
         [0031]    The computer of the present disclosure controls the profile generation servo drive systems as well as the milling cutter speed. The robotic rotary mill cutter requires load data to be able to adjust for conditions that cannot be seen by the operator. The computer receives information from torque sensors attached to Z-axis, W-axis, Y-axis, and milling spindle drive motor, and makes immediate adaptive adjustments to the feed rate and speed of the vertical X-axis, the 360 degree horizontal rotary W-axis, and the spindle swing arm pivotal Y-axis and the RPM of the milling spindle motor. 
         [0032]    Software in communication with sub-programs gathering information from the torque devices, such as a GSE model Bi-Axial transducer Model 6015 or a PCB model 208-M133, directs the computer, which in turns communicates with and monitors the downhole robotic rotary mill cutter and its attendant components, and provides feeds and speeds simultaneously or independently along the vertical Z-axis, and the 360 degree horizontal rotary W-axis, as well as the pivotal spindle swing arm Y-axis arc movement. 
         [0033]    The shape or window profile(s) are programmed by the operator on a program logic controller (PLC), or personal computer (PC), or a computer system designed for this specific use. The integrated software via a graphical user interface (GUI) or touch screen, such as a Red Lion G3 Series (HMIs), accepts inputs from the operator and provides the working parameters and environment by which the computer directs and monitors the robotic rotary mill cutter. 
         [0034]    The vertical Z-axis longitudinal computer-controlled servo axis will use a hydraulic cylinder, such as the Parker Series 2HX hydraulic cylinder, housing the MTS model M-series absolute analog sensor for ease of vertical Z-axis longitudinal movements, although other methods may be employed to provide up and down vertical movement of the robotic rotary mill cutter. 
         [0035]    In a still further embodiment of the present disclosure the vertical Z-axis longitudinal computer-controlled servo axis may be moved with a ball screw and either a hydraulic or electric motor, such as a computer controlled electric servo axis motor, the Fanuc D2100/150 servo, with encoder feedback to the computer system by an encoder such as the BEI model H25D series incremental optical encoder. Servo motors and ball screws are a know art and are widely available from many sources. 
         [0036]    In a still further embodiment of the present disclosure, the vertical Z-axis longitudinal computer-controlled servo axis may be moved with a rack and pinion, either electrically or hydraulically driven. Rack and pinion drives are a know art and are widely available from many sources. 
         [0037]    The rotational computer controlled W-axis rotational movement will be an electric servo motor, although other methods may be employed. The rotational computer-controlled W-axis servo motor, such as a Fanuc model D2100/150 servo, provides 360-degree horizontal rotational movement of the robotic rotary mill cutter through a specially manufactured slewing gear. 
         [0038]    The Y-axis pivotal milling spindle swing arm computer-controlled servo axis will use a hydraulic cylinder for ease of use, although other methods may be employed. The Y-axis pivotal milling spindle swing arm computer-controlled servo axis, may utilize the Parker Series 2HX hydraulic cylinder, housing the MTS model M-series absolute analog sensor inside the hydraulic cylinder to provide position feedback to the computer controller for pivotal spindle swing arm Y-axis arc movement. 
         [0039]    In a still further embodiment of the present disclosure that an inertia reference system such as, Clymer Technologies model Terrella6 v2, will provide information that the robotic rotary mill cutter is performing the movements commended by the computer controller as a verification reference. If the reference shows a sudden stop, the computer will go into a hold action stopping the robotic rotary mill cutter and requires operator intervention before resuming milling operations. 
         [0040]    The methods and systems described herein are not limited to specific sizes or shapes. Numerous objects and advantages of the disclosure will become apparent as the following detailed description of the multiple embodiments of the apparatus and methods of the present disclosure are depicted in conjunction with the drawings and examples, which illustrate such embodiments. 
         [0041]    One advantage of the present disclosure over the prior art is that the attendant costs of cutting through the wellbore tubulars, through casings, cement and into formation rock, will be relatively nominal as compared to current practices. The robotic rotary mill cutter may significantly decrease site and personnel time. 
         [0042]    Fig I. depicts the robotic rotary mill cutter  1 . The robotic rotary mill cutter  1 , shows the position of the vertical Z-axis, and the 360-degree horizontal rotary W-axis, and the milling spindle swing arm pivotal Y-axis. 
         [0043]      FIG. 2A  and  FIG. 2B  depict the robotic rotary mill cutter  1  (see  FIG. 1 ) enlarged and cut in half with the top of the robotic rotary mill cutter  1  (see  FIG. 1 ) shown in  FIG. 2A  and the lower portion of robotic rotary mill cutter  1  (see  FIG. 1 ) shown in  FIG. 2B . 
         [0044]      FIG. 2   a  depicts a collar  2  that is used to attach the umbilical cord (not shown) and cable (not shown) to the body of robotic rotary mill cutter  1 , (see  FIG. 1 ). Collar  2  may be exchanged to adapt to different size work strings (not shown) in case of the need for emergency removal of the robotic rotary mill cutter  1 , (see  FIG. 1 ). After the robotic rotary mill cutter  1 , (see  FIG. 1 ) is in the cut location, locking hydraulic cylinders  3 ,  FIG. 2   a  are energized to lock the robotic rotary mill cutter  1 , (see  FIG. 1 ) into the well bore (not shown). After the locks  3  have been energized, Z-axis hydraulic cylinder  6  is moved to a down position where hydraulic cylinder  6 , piston rod  4  allows the Z-axis slide  5  to extend. 
         [0045]      FIG. 2   b  a W-axis servo motor  8  rotates the W-axis under control of the computer (not shown). W-axis rotating body  10  houses the milling spindle swing arm  14  and the milling spindle swing arm is driven by motor  11  also housed in the W-axis rotating body  10 . Milling spindle swing arm  14  is driven by motor  11  through a half-shaft  12  such as Motorcraft model 6L2Z-3A427-AA. 
         [0046]    Half-shaft  12  has a C.V. joint (not shown) that allows milling spindle swing arm  14  to pivot in an arc from pivot bearing  13  that goes through W-axis rotating body  10 . Milling spindle swing arm  14  is moved by Y-axis hydraulic cylinder  16 . The rotation of W-axis rotating body  10  requires a swivel joint  9 , such as Rotary Systems Model DOXX Completion, to allow power and sense lines (not shown) to the motor  11 , Y-axis hydraulic cylinder  16  and load cell sense wires (not shown). Carbide cutter  15  is mounted to the milling spindle swing arm  14  (see  2 B) and is moved by Y-axis cylinder  16  into the cut under computer control. 
         [0047]      FIG. 3  depicts an expanded view of an inserted carbide mill  17  that will be attached to milling spindle swing arm  14  (see  FIG. 2B ) with a bolt (not shown) running through the inserted carbide mill  17 . 
         [0048]      FIG. 4A  depicts a top view of nested multiple casings (tubulars)  18  that are positioned non-concentrically. 
         [0049]      FIG. 4B  depicts an isometric view of nested multiple casings (tubulars)  19  that are positioned non-concentrically. 
         [0050]      FIG. 5A  depicts a view of the lower portion body of robotic rotary mill cutter  1 , (see  FIG. 1 ) before entering the nested multiple casings (tubulars)  18  (see  4 A). 
         [0051]      FIG. 5B  shows the nested multiple casings (tubulars)  18  (see  4 A) side view shows the void that has been removed by the profile generation system (not shown) that simultaneously moved the robotic rotary mill cutter  1  (see  FIG. 1 ) in a vertical Z-axis, and a 360-degree horizontal rotary W-axis, and the milling spindle swing arm  14  (see  2 B) in a pivotal Y-axis arc to allow cutting the tubulars, cement, and formation rock in any programmed shape or window profile(s) thereby cutting through the multiple casing (tubulars)  18  (see  4 A), cement or other encountered material in casing annuli (not shown).