Abstract:
The present invention provides an apparatus and method for severing casing as it is pulled from a wellbore. An apparatus is first provided, comprising a clamping assembly, a drilling assembly and a cutting assembly. In one aspect, the apparatus is disposed at the end of a telescopic arm, with the components being remotely operated by personnel using a control panel. The apparatus can be positioned adjacent casing and clamped thereto. Thereafter, the apparatus can drill a hole completely through the casing for the insertion of a retention pin. The apparatus can then severe the casing into manageable lengths to facilitate disposal, such as during a plugging and abandonment procedure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to a pending provisional patent application entitled “Methods and Apparatus for Severing Concentric Strings of Tubulars,” filed on Mar. 20, 2001. That application carries Serial Prov. No. 60/277,439.  
         [0002]    This application is also a continuation-in-part of U.S. patent application Ser. No. 09/355,439, filed Nov. 29, 1999. That application is entitled “Apparatus for Positioning a Tong, and Drilling Rig Provided with Such an Apparatus.”The parent application was the National Stage of International Application No. PCT/GB97/03174, filed Nov. 19, 1997 and published under PCT Article 21(2) in English, and claims priority of United Kingdom Application No. 9701790.9 filed on Jan. 29, 1997. Each of the aforementioned related patent applications is herein incorporated in its entirety by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    Field of the Invention  
           [0004]    The present invention generally relates to plugging and abandonment of oil and gas wells. More particularly, the present invention relates to the removal of a tubular from a wellbore in order to satisfy various environmental regulations. More particularly still, the invention relates to severing nested strings of tubulars that are cemented together in order to more easily handle the tubulars as they are removed from a wellbore during or subsequent to a plugging and abandonment operation.  
           [0005]    In the completion of oil and gas wells, boreholes are formed in the earth and thereafter are lined with steel pipe known as casing. An annular area formed between the outside of the casing and the wall of the borehole is typically filled with cement in order to secure the casing in the borehole and to facilitate the isolation of certain areas of the wellbore for the collection of hydrocarbons. In most instances, because of the depth of a wellbore, concentric strings of tubulars are disposed in the wellbore with each lower string of tubulars being necessarily smaller in diameter than the previous string. In some cases, especially in offshore oil and gas wells, the strings are run in a nested fashion from the surface of the well. In other words, a first string of casing is cemented into the wellbore and, subsequently, a second smaller string of casing is cemented into the first string to permit the borehole to be lined to a greater depth. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever-decreasing diameter.  
           [0006]    When a decision is made to no longer operate a hydrocarbon well, the wellbore is typically plugged to prevent formation fluids from migrating towards the surface of the well or into a different zone. Various environmental laws and regulations govern the plugging and abandonment of wellbores. These regulations typically require that the wellbore be filled with some amount of cement. In some instances, the cement must be squeezed into the annular area around the cemented casing in order to prevent fluids from migrating up towards the surface of the well on the outside of the casing through any cement gaps. In offshore wells, regulations typically require not only the foregoing steps, but also that a certain amount of wellbore casing be completely removed from the wellbore. For example, in some instances, the upper 1,000 feet of casing extending downward from the ocean floor into the wellbore must be removed to complete a plugging and abandonment operation.  
           [0007]    Various methods and techniques have been developed and are currently utilized in order to remove casing from an offshore wellbore. Most often, some type of cutting device is run into the wellbore on a wireline or string of tubulars. The cutting device is actuated in order to sever the casing at a predetermined depth, creating separate upper and lower strings of casing. Thereafter, the upper string is pulled and brought to the surface.  
           [0008]    Because of the great length and weight of the upper string of casing being removed, it is necessary to further sever the upper casing string as it is retrieved at the surface. Accordingly, the casing is further severed into predetermined lengths. This makes handling and disposal of the removed casing more efficient.  
           [0009]    In some instances, the severed upper string of casing includes more than one set of tubulars. In other words, there is a first outer string of casing, and then a second smaller string of casing nested therein. In one example, the outer casing string is 13⅜ inches in diameter, and the smaller casing nested therein is 9⅝ inches in diameter. These two strings of severed casing will typically be joined by a layer of cement within the annular area. This cement layer adds to the weight of the severed casing string, making it even more desirable to cut the retrieved pipe into manageable sections.  
           [0010]    A casing string is typically comprised of a series of joints that are 30 feet in length. The pipe joints are connected by threaded male-to-female connections. When retrieving a severed casing string during a plug and abandonment procedure, it is desirable to break the pipe string by unthreading the connected joints. However, this process is difficult where the severed string consists of outer and inner pipe strings cemented together. Further, there is little incentive to incur the time necessary to break the joints apart at the threads, as the pipe joints from an abandoned well will typically not be re-used. For these reasons, the severed casing is typically broken into smaller joints by cutting through the inner and outer strings at the surface of the well. The severed pipe sections are then recycled or otherwise disposed of.  
           [0011]    In a conventional plug and abandonment operation, casing strings are severed generally as follows:  
           [0012]    First, the casing string is severed within the wellbore. Typically, severance is accomplished at a depth of around 1,000 feet. Thereafter, the severed portion of casing is “jacked” out of the wellbore and raised to the surface of the rig platform using a platform-mounted elevator. As the upper end of the severed casing section reaches the floor of the platform, it is lifted to a predetermined height above a set of slips. The slips are then set, suspending the severed string of casing above the rig floor. A drilling machine then drills a hole completely through the casing, including any cement layer and smaller diameter casing which is cemented within the larger diameter casing. Thereafter, a pin or other retainer is inserted through the drilled hole to ensure that the smaller string of casing is anchored to the larger string. This method of drilling a hole through the casing and inserting a retainer pin is necessary to ensure that the smaller string of casing does not become dislodged from the larger string due to some failure of the cement layer there between.  
           [0013]    After the inner casing string and cement therearound is anchored to the larger outer string, a band saw is used to cut the severed tubular into a predetermined length. The band saw operates with coolant to avoid the use of high temperature cutters or the production of sparks. Typically, a length of between fifteen and thirty feet is selected, with the cut being made above the retention pin. The newly severed, ten-foot portion of string is then transported to a barge or other transportation means for disposal or salvage.  
           [0014]    With the slips disengaged, the elevator then raises the severed string of casing another length of approximately ten feet. The slips are then re-engaged and the drilling, anchoring and cutting procedure takes place again.  
           [0015]    While the foregoing apparatus and method are adequate to dispose of strings of concentrically cemented casing, the operation necessarily requires personnel to be at the drilling mechanism and the band saw during the operation. The presence of personnel on a platform inherently carries risk. The risk is magnified when the personnel must be in close contact with the operating machinery.  
           [0016]    There is a need, therefore, for a method and apparatus of disposing of concentric strings of tubular during a plugging and abandonment operation which does not require personnel to be located directly at the machinery performing the cutting operations. There is a further need for a method and apparatus which can be operated remotely by well platform personnel. There is yet a further need for an apparatus and method that can more safely and effectively sever strings of casing at a well site.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention generally provides an apparatus and method for severing predetermined lengths of nested casing above a drilling rig or workover rig platform. The apparatus includes a clamp assembly, a drill assembly and a cutting assembly. In one aspect, the clamp assembly, the drilling assembly and the cutting assembly are disposed at the end of a telescopic arm, and are remotely operated by personnel using a control panel. In accordance with the present invention, the clamp assembly is positioned adjacent a section of casing to be severed, and then clamped thereto. Thereafter, the drilling assembly is actuated so as to drill a hole completely through the casing strings. A retention pin is then inserted through the newly formed aperture. Finally, the cutting assembly, such as a band saw, is actuated so as to severe the casing above the pin. The newly severed portion of casing above the pin may then be disposed of. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    So that the manner in which the features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0019]    [0019]FIG. 1 is a perspective view of the tubular severing apparatus of the present invention, in one arrangement.  
         [0020]    [0020]FIG. 2 is a side, schematic view of the tubular severing apparatus of FIG. 1.  
         [0021]    [0021]FIG. 3 is a perspective view of a cross-sectional cut of a casing section. The pipe section is comprised of an outer casing string, an inner casing string and a layer of cement there between.  
         [0022]    [0022]FIG. 4 is a side view illustrating a drilling assembly of the present invention. The drilling assembly is shown drilling a hole through a casing section.  
         [0023]    [0023]FIG. 5 a  is a top view showing an alternate embodiment of a drill assembly of the present invention. FIG. 5 b  presents a side view illustrating the drill assembly of FIG. 5 a.    
         [0024]    [0024]FIG. 6 is a perspective view illustrating the tubular severing apparatus of FIG. 1. In this view, the clamping assembly is more clearly seen. The clamping assembly is shown clamping a casing section. Also visible is the band saw being used to cut through the casing section.  
         [0025]    [0025]FIG. 7 is also a perspective view illustrating the tubular severing apparatus of FIG. 1. In this view, features of an exemplary band saw are more clearly. The band saw is again shown cutting a casing section.  
         [0026]    [0026]FIG. 8 is an enlarged view of the band saw of FIG. 7.  
         [0027]    [0027]FIG. 9 is a perspective view of a control panel as might be used to control various portions of the severing apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    The present invention provides a method and apparatus for severing casing that has been removed from a wellbore.  
         [0029]    [0029]FIG. 1 provides a perspective view of a novel tubular cutting apparatus  100  of the present invention, in one embodiment. The apparatus  100  comprises a clamp assembly  130 , a drill assembly  150  and a cutting assembly  120 . The apparatus  100  is selectively movable. In one aspect, the apparatus  100  is disposed at the end of an extendable structure. In FIG. 1, the extendable structure is shown as a cantilevered arm  110 . The exemplary arm  110  defines an outer barrel  110  having at least one telescoping section  112  extending therefrom. An intermediate telescoping section (not shown) may also be incorporated. In such an arrangement, the end telescoping section  112  is slidably mounted in the intermediate telescoping section which is, in turn, slidably mounted in the outer barrel  110 .  
         [0030]    The arm  110  is supported by a base  114  secured to the floor of a rig platform (not shown). The arm  110  is disposed along a vertical support beam  116  vertically extending above the base  114 . In the parent application, the outer barrel of the arm  110  is described as being attached to the support beam  116  by means of a clamp (not shown in FIG. 1) bolted to the top of the beam  116 . The clamp maintains the arm  110  in position with respect to the beam  116 . In one aspect, the arm  110  is pivotally attached to the support beam  116  to permit the tubular severing apparatus  100  to pivot about a vertical axis and, alternatively or in addition, a horizontal axis. In one aspect, the clamp is releasably attached to the support beam  116 .  
         [0031]    An additional feature of the arm  110  described more fully in the parent application is that the outer barrel  110  of the arm itself may be selectively moved with respect to the support beam  116 . This means that the entire arm  110  may be retracted away from the casing section  200 ′. When the telescoping sections  112  are fully contracted, the free end of the arm  110  lies closely adjacent the support beam  116 . This retracting feature is shown in FIG. 4 of the parent application with respect to a tong, but may also be employed in the present application with respect to a tubular severing assembly  100 .  
         [0032]    In the arrangement of FIG. 1, the apparatus  100  is further supported by an overhead hoisting system. Cables  160  from the hoisting system are visible in FIG. 1. In one aspect, the hoisting system maneuvers the tubular severing apparatus  100 , with the telescoping section  112  of the arm  110  moving in response. In another aspect, the telescoping section  112  of the arm  110  is hydraulically powered, causing the apparatus  100  and the supporting cables  160  to advance and recede in response to movement of the arm  110 . Alternatively, the arm  110  and the hoisting system may be independently powered.  
         [0033]    Further details concerning the operation of a suitable telescoping arm are found in the pending application entitled “Apparatus for Positioning a Tong.” That application bears Ser. No. 09/355,439, and was filed on Nov. 29, 1999. That application is incorporated by reference herein, in its entirety.  
         [0034]    Also visible in FIG. 1 is a section of casing  200 ′. Casing section  200 ′ represents an upper, severed string of casing that is being retrieved from a wellbore (not shown in FIG. 1). The casing  200 ′ is being further severed into smaller portions for ease of manipulation and disposal. The exemplary casing string  200 ′ houses a smaller, inner string of casing  205  nested within an outer casing string  200 . The inner string  205  has been cemented into the outer string  200  in connection with earlier wellbore completion operations.  
         [0035]    [0035]FIG. 2 is a schematic view of the apparatus  100 , adjacent a section of casing  200 ′. Visible again in FIG. 2 is the clamp assembly  130 , the drill assembly  150  and the cutting assembly  120 . In this arrangement, the assembly  100  is again disposed at the distal end of the telescopic arm  110  and is suspended from above with cables  160 . The telescopic arm  110  again has at least one telescoping section  112 .  
         [0036]    In FIG. 2, the clamp assembly  130  is radially disposed about the section of casing  200 ′ so as to secure the casing section  200 ′ for severing. The casing  200 ′ is shown in FIG. 2 in cross-section. Visible in this view are the outer casing string  200 , the inner casing string  205  and a matrix of cured cement  210  in the annular region between the two casing strings  200 ,  205 .  
         [0037]    [0037]FIG. 3 is a perspective view showing a cross-section of the casing  200 ′ after it has been severed using the apparatus  100  of FIG. 2. As previously described, casing section  200 ′ defines an outer string of casing  200  which houses a smaller diameter casing  205 . A matrix of cement  210  is disposed in an annular area between the two casing strings  200 ,  205 . In this view, inner casing string  205  is eccentric relative to the surrounding outer casing string  200 , as is typical in a completed wellbore.  
         [0038]    Referring back to FIG. 2, the tubular string  200 ′ is shown being held above a floor member  170  by a set of slips  172 . The slips  172  permit the tubular string  200 ′ to be raised from below the surface of the platform to some height. Typically, elevators (not shown) are provided on a rig for maneuvering pipe relative to the wellbore. The slips  172  hold the casing  200 ′ so that it can be clamped and severed by the apparatus  100  after positioning of the casing  200 ′ by the elevators.  
         [0039]    As noted, the apparatus  100  includes a drill assembly  150 . The purpose of the drill assembly  150  is to form an aperture through the casing strings  200 ,  205  for insertion of a retention member  165 . Preferably, the retention member  165  defines a pin configured to be received within the formed aperture. Various pin types may be used, including, for example, a cylindrical bar, a cotter pin, or a cotter and key. In FIG. 2, a simple tubular pin is shown. The pin  165  serves to anchor any nested casing string  205  and cement  210  to the outer casing string  200 . Preferably, the aperture is formed completely through both the front and back walls of the outer casing string  200 , and the pin  165  is inserted completely through the outer casing string  200 .  
         [0040]    In the arrangement of FIG. 2, the drill assembly  150  is disposed below the band saw  120 . The drill assembly  150  is constructed and arranged to insert a rotating drill bit  151  essentially perpendicular to the longitudinal axis of the casing string  200 ′. In this way, a suitable aperture is formed. Any known drilling device may be employed for boring a through-opening into the casing section  200 ′. The drill assembly  150  of FIG. 2 utilizes a rotary motor (not shown) inside of a housing  153  to rotate a single drill bit  151 . A positioning device is further provided for selectively advancing the drill bit  151  towards and away from the casing section  200 . In one aspect, a hydraulic cylinder  156  is used to advance the drill bit  151  towards and away from the casing section  200 ′ by adjusting flow and pressure of hydraulic fluid.  
         [0041]    An enlarged perspective view of a drill assembly  150  in operation is shown in FIG. 4. The drill bit  151  can be more clearly seen penetrating the wall of the outer section of casing  200 . The drill assembly  150  typically operates with a source of coolant and advances forward towards the casing  200  by means of a telescoping positioning device, shown in FIG. 4 as a cylinder  156 . In one aspect, the drill assembly  150  is operated remotely from a control panel  125  as is shown in FIG. 2. The remote control panel  125  will be more fully described, infra.  
         [0042]    An alternative arrangement for a drill assembly is presented in FIGS. 5 a  and  5   b . FIG. 5 a  is a top view of an alternate embodiment of a drilling assembly for the present invention. FIG. 5 b  is a side view thereof. In this arrangement, a pair of opposing boring devices  155  are urged inwardly towards the center of the casing section  200 ′. Again, it is within the spirit of the present invention to employ any drilling assembly  150  capable of boring an aperture through the casing section  200 ′ for insertion of an anchoring pin  165 .  
         [0043]    Referring again to FIG. 2, it can be seen that the drill assembly  150  has been actuated to form an aperture through both casings strings  200 ,  205 . The pin  165  has been inserted through the formed aperture to anchor the inner casing  205  to the outer casing  200 .  
         [0044]    [0044]FIG. 6 is a perspective view of the apparatus  100  of FIG. 1. In this view, the clamp assembly  130  is more clearly seen. The clamp assembly  130  includes a frame  134  that selectively radially encompasses the casing section  200 ′ in order to secure the apparatus  100  to the casing section  200 ′. The clamp assembly  130  further comprises at least two clamp members  140  for frictionally engaging the casing  200 ′. In the arrangement of FIG. 6, the clamp members  140  each define a pair of angled support blocks which are moved into contact with the casing  200 ′. However, other arrangements may be employed, such as a single block having a concave surface.  
         [0045]    The clamp assembly  130  includes a gate member  135  that swivels about a hinge  133  mounted on the frame  134 . The hinge  133  permits the gate member  135  to be selectively opened and closed for receiving and for clamping the casing  200 ′. In the view of FIG. 6, the gate member  135  is closed about the casing  200 ′ while the casing section  200 ′ is being severed. The gate member  135  includes at least one clamp member  140  for engaging the casing  200 ′ in its closed position. The gate  135  preferably operated with hydraulic power, and is remotely operated from control panel  125 . A hydraulic arm  136  is shown to aid in remotely opening and closing the gate  135 .  
         [0046]    [0046]FIG. 7 presents the apparatus  100  of FIG. 1 in still greater detail. In this perspective view, the cutting assembly  120  is more clearly seen. The cutting assembly  120  is shown as a band saw. The band saw  120  first comprises a housing  122 . The housing  122  houses a pair of wheels (not seen in FIG. 7) about which a band saw blade  121  is tracked. The band saw blade  121  includes a plurality of teeth. The blade  121  is fed through pairs of roller members  123  which guide the blade  121  to cut in a direction substantially perpendicular to the longitudinal axis of the outer casing  200 . One pair of roller members  123  is preferably provided at the housing outlet for the blade  121 . In this respect, the blade  121  is fed through this first pair of roller members  123 . A second pair of roller members  123  is disposed at the opening in the housing  122  through which the blade  121  is received back into the housing  122 . The roller members  123  are more clearly seen in the enlarged view of FIG. 8.  
         [0047]    It is within the spirit of the present invention to utilize any cutting device  120  known for severing casing, so long as the cutting device  120  may be adapted to operate in conjunction with a clamp assembly  130  and a drill assembly  150 . In the exemplary arrangement for a cutting assembly  120  of FIG. 7, the cutting assembly defines a band saw  120 . Further, the band saw  120  includes a housing  122  that is offset from the angle of cutting by the blade  121 . In other words, the angle of the housing  122  of the band saw  120  is offset from the angle at which the teeth of the blade  121  engage the outer casing  200  during the cutting operation. The angle shown is approximately 30 degrees, though other angles may be used. In addition, an enlarged spacing  129  is provided in the housing  122  between the wheels. These features accommodate placement of and access to the drill assembly  150  and clamp assembly  130 . The spacing  129  in the housing  122  is more importantly sized to receive the casing  200 ′ as the blade  121  of the saw  120  advances through the casing  200 ′ during a cutting operation  
         [0048]    In the drawings of FIG. 7 and FIG. 8, the blade  121  of the band saw  120  has been actuated. In addition, the blade  121  is engaging the casing section  200 ′, and has advanced partway through the casing  200 ′ to form a cut that is substantially perpendicular to the longitudinal axis of the outer casing  200 .  
         [0049]    Referring again to FIG. 2, the band saw  120 , the clamp assembly  130 , and the drill assembly  150  are preferably controlled in an automated fashion from a control panel  125 . Control lines  126  are provided from the control panel  125  to control the assembly  100 , e.g., parts  120 ,  130 ,  150 ,  154 , etc. FIG. 9 is a more detailed perspective view showing a typical control panel  125  to be utilized with a tubular severing apparatus  100 . The illustrated control panel  125  in one aspect includes separate controls to operate the clamp assembly  130 , the drilling assembly  150 , and the band saw  120 .  
         [0050]    The band saw  120  and the drill assembly  150  are typically operated with similar controls. For example, the drill assembly  150  and saw  120  each require an on/off control and a rotational speed control to manipulate the rotation of the saw blade  121  or the drill bit  151 . Corresponding gauges illustrating the rotational movement of the drill bit  151  and the band saw  121  as shown in revolutions per minute may optionally be provided. In addition, a tool advancing control is provided to control the speed of advance of the drill bit  151  into the casing  200 ′ and the blade  121  of the band saw  120  into the casing  200 ′. Corresponding positioning devices  127  (shown in FIG. 1) and  156  (shown in FIG. 4) are provided for the band saw  121  and the drill assembly  150 . These positioning devices,  126 ,  156 , in one aspect, represent telescoping hydraulic cylinders. These devices permit the drill bit  151  of the drill assembly  150  and the blade  121  of the band saw  120  to be independently, selectively advanced towards the casing  200 ′ during the respective drilling and cutting operations and then withdrawn.  
         [0051]    In addition, both the band saw  120  and the drill assembly  150  optionally include pressure sensors to determine the amount of pressure placed upon the casing by the rotating drill bit  151  or the rotating saw blade  121 . Gauges may be provided at the control panel  125  indicating pressures on the drill bit  151  or the rotating saw blade  121 . For example, core heads and saw blades provided by Mirage Tool Co ltd. (U.K.) and core heads from Alf I Larsen (Norway) may be used.  
         [0052]    The clamp assembly  130  also has controls that are located on the control panel  125 . For instance, the clamp assembly  130  includes a panel-mounted control which opens and closes the gate  135  located on the clamp assembly  130 . Optionally, a gauge indicating pressure between the casing  200 ′ and a clamp  140  may be provided and pressure of the clamps  140 . A corresponding sensor is positioned on at least one of the clamp members  140  for sensing pressure of the clamp member  140  against the casing  200  when the gate  135  is closed. [Per: what type of sensor would work? Do you have an example?] Preferably, the sensor is placed on the clamp member  140  on the gate  135 .  
         [0053]    In use, the severing apparatus of the present invention operates as follows:  
         [0054]    First, a casing cutting means (not shown) is run into a wellbore. The cutting means is typically disposed on the end of a run-in string or wireline. The cutting means is placed in the wellbore at a predetermined depth, and then actuated. In this way, a selected length of casing is severed downhole. Thereafter, the severed portion of casing  200  is pulled or “jacked out” of the wellbore and lifted to the rig platform within an elevator.  
         [0055]    A predetermined amount of the severed portion of casing  200 ′ is pulled upwards past the slip  172  located at the level of the platform floor. The casing  200 ′ is held in place by the slip  172 , exposing the upper portion of the casing  200 ′ above the platform floor. Thereafter, a tubular severing apparatus  100  of the present invention is moved towards the casing  200 ′ by the telescopic arm assembly  110  with its extending and retracting sections  112 . As the apparatus  100  reaches a location proximate to the casing  200 ′, the clamp assembly  130  is actuated to open the gate  135  and to receive the casing  200 ′. The gate  135  is then closed around the casing  200 ′, and the clamp assembly  130  is secured to the casing  200 ′ by the clamping members  140 . In this way, the severing apparatus  100  is properly positioned with respect to the casing  200 ′.  
         [0056]    Thereafter, with the outer casing string  200  clamped in the apparatus  100 , the drill assembly  150  is operated. Preferably, remote actuation of the drill assembly  150  is conducted through the control panel  125 . The drill bit  151  disposed on the drill assembly  150  is rotated and advanced towards the casing  200  to form an aperture therein. The aperture is created through at least the front wall of the casing section  200 ′ at an angle substantially perpendicular to the longitudinal axis of the outer casing  200 . A retention mechanism such as a pin  165  is then inserted through the casing  200 ′ to ensure that any inner string of casing  205  is longitudinally fixed with respect to the outer string of casing  200 .  
         [0057]    The next step involves actuation of the band saw  120 . Preferably, actuation of the band saw  120  is performed remotely via the control panel  125 . The blade  121  of the band saw  120  is actuated, and is advanced through the casing  200 ′ at a point above the pin  165 . The retention pin  165  anchors the smaller diameter casing  205  within the larger diameter casing  200 . In this manner, the inner  205  and outer  200  casing strings in the lower section  200 ″ are prevented from separating below the rig floor. The severed portion of the casing section  200 ′ is then lifted away, leaving an upper end of the lower portion of casing  200 ″ remaining within the clamping assembly  130 .  
         [0058]    Once the severed piece of casing  200 ′ has been disposed of, an elevator or other lifting device works with the slips to lift the casing  200 ′ another predetermined distance upwards. The slips  172  are then used to re-grasp the casing  200 ′ for the operation to be repeated. Each time a severing operation is completed, the clamp assembly  130  is de-activated, and the gate  135  is reopened so that the apparatus  100  can move away from the severed piece of casing  200 ′. In addition, it is noted that the pin  165  may be retained in the newly lifted section of casing  200 ′ to be severed. A new pin  165  can then be inserted once a new aperture is formed within the casing  200 ′.  
         [0059]    As demonstrated in the foregoing disclosure, the apparatus  100  of the present invention provides a safe and efficient means for severing casing during a plug and abandonment operation. In one aspect, the apparatus  100  is operated via a remotely located control panel  125 .  
         [0060]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.