Abstract:
Apparatus for drilling holes through concentric pipes is provided. The apparatus clamps on the exterior pipe and contains drilling assemblies that may be used for drilling sequentially or simultaneously two colinear holes.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to apparatus for drilling colinear (in the same line) holes in opposite directions through the walls of concentric pipes to form a single hole through the pipes. It is particularly applicable to large pipes such as casing used in wells. 
         [0003]    2. Description of Related Art 
         [0004]    After wells have produced to an economic limit it is necessary to remove pipes (casing) from the wells as part of abandoning the wells. There are normally several concentric casing strings to be removed. In offshore operations it may be desirable to reclaim a slot to drill a new well, eliminate a slot to reduce wave loading on a platform structure or to detach and remove a platform structure. When retrieving casing(s) it is normal practice to cold cut the casing(s) with an external saw into lengths that are within the safe lifting capacity of the available lifting apparatus. 
         [0005]    Prior to removal of casing at the surface of a well, the well is plugged and all tubing and production casing that are free are removed from the well. An internal mechanical cutter may then be used to cut the remaining casings at a predetermined depth below the mud line. Once the down-hole internal cut has been completed it is desirable to form a hole through the diameter of the concentric pipes. Once the hole has been formed, a metal pin is inserted through the hole. During the cutting operation, the internal pipes may become displaced from the external pipe, causing inefficient cutting time and or damage to the saw. There is a need to stabilize the location of the concentric pipes. 
         [0006]    The pin is left protruding out of the exterior pipe on each side of the concentric pipes. The first set of drilled holes is located at the upper end of the pipes, allowing sufficient metal above the holes for the metal pin to secure the inner pipes and to support the string weight of the pipes. The pin may then be used as a lifting device by attaching slings over the protruding ends of the pin and securing slings by sliding keeper plates with pin holes onto the pin against the slings and then installing keeper bolts through the pin diameter on each end. Once the slings are properly secured the pipes may then be safely lifted by means of winches, casing jacks, or a drilling rig to a selected length above the rig floor or work deck and then held in place by bowl and slips on the outermost casing. The process of forming holes simultaneously through the diameter of the pipes is then repeated a few feet above the bowl and slips and a second pin is installed through the pipes. Once the second pin has been installed, the pipes may then be cut with an external saw at a safe distance above the second pin to allow adequate casing material for the pin to secure the inner pipes and support the remaining string weight. Once the sawing operation is completed the first sectioned length of pipes may be removed and laid down Once the sectioned length of pipes has been laid down, the slings and the metal pin are removed. Wire cables may then be run through the drilled holes and secured with cable clamps to prevent internal pipes from sliding out during transportation. The securing cables are a safety precaution only and are not to be used as a lifting point. The process of securing the slings is then repeated onto the second pin, the slips are removed from the bowl, and the pipes may again be lifted to the determined length above the rig floor or work deck. The slips are then replaced into the bowl. The process of drilling, pinning, sawing, and laying down of sectioned pipes is repeated until the entire string of pipes has been removed. 
         [0007]    The procedure described above is a typical method of recovering pipes from a platform well. However, there may be variations to the procedure based on platform structure and available work space. The forming of holes, pinning, and sawing process, for example, may be performed at the well bay level or other levels of the platform structure. Also, when bowl and slips are not available or practical for a given project, support beams may be used to hold the string weight. This method requires the same process as described above with the exception of an additional drill- and pin-step. Once the downhole internal cut has been completed the first set of holes may be formed and pinned at the upper end of pipes to secure slings and lift the pipes to a determined length above the rig floor and/or work deck. The second set of holes may then be formed and pinned just above the support beams. The pipe string load is then lowered until the pin material protruding through each side of the diameter of the pipes comes to rest on the support beam to hold the string weight. A third set of holes may then be formed and pinned just above the second pin to be used later as a pick up point. The pipes may then be cut with an external saw above the third pin. The length of sectioned pipes is then laid down, the pin removed and cables installed through the holes. The pipe removal process is continued by securing the slings onto the remaining upper pin, lifting the pipe to a level for safe removal of the lower pin previously resting on support beam, and then lifting pipe to the determined length above the rig floor and/or work deck. The procedure is repeated until the entire pipe string has been removed. 
         [0008]    The hole through the concentric pipes may be formed by torch and by chipping cement between pipes. This procedure is slow and requires great care to remain safe. A drill may be used to drill a single hole through the concentric pipes, but this requires a long drill and consumes excessive time. What is needed is apparatus and method for forming colinear holes through concentric pipes and any material in the annuli between the pipes in a safe, efficient and cost-effective procedure. The apparatus should be adapted for use on concentric casings in wells that are located either on land or offshore at depths accessible to divers. 
       SUMMARY 
       [0009]    Apparatus is provided for cutting colinear holes through the walls of concentric pipes. Normally, the apparatus is used to drill simultaneously from opposite sides of the outside pipe. Drilling assemblies operated by hydraulic power include hydraulic motors to turn each bit and cylinders to move the bits linearly on a carriage adapted to move along rigid rods. The drilling assemblies are attached to clamping apparatus, which provides for rigid attachment to pipes over a range of sizes. Power may be controlled by a module attached to the drilling assemblies or by a remote module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of one embodiment of the disclosed apparatus. 
           [0011]      FIG. 2  is a top perspective view of a drill box assembly and remote control stand of the disclosed apparatus. 
           [0012]      FIG. 3  is an end elevation view of the drilling module with drill bit. 
           [0013]      FIG. 4  is a side elevation view of the carriage for the drill bit. 
           [0014]      FIG. 5  is a top view of a section of the clamp swing door and feed screw jaw. 
           [0015]      FIG. 6  is a schematic of a hydraulic circuit for the disclosed apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows apparatus  10  for drilling colinear holes through pipes. Drilling assemblies  13   a  and  13   b , normally identical, are disposed 180 degrees apart on clamp  11 , which is joined by hinge to clamp swing door  12 . Control modules  14   a  and  14   b  are joined to the drilling assemblies. Adjustable pick up bar  11   a , and two feed screw jaws:  11   b  and  11   c  are shown on clamp  11 . One feed screw jaw,  12   a , is shown on clamp swing door  12 . Each feed screw jaw may be adjusted according to casing size by means of adjustable mounting holes  12   b  and used to clamp a pipe by use of feed screws in the feed screw jaws. Clamp assembly  11  and  12  may be adapted to enclose up to a 36-inch pipe, for example. Clamp swing door  12  may be opened to allow apparatus  10  to be positioned on the external casing wall. When clamp swing door  12  is closed around the pipe and pinned to clamp body  11 , clamp swing door feed screw jaw  12   a  is extended into the pipe and compression is applied to all feed screw jaws through casing tong dies, which will be described in more detail below. Clamp and feed screw jaws are preferably adjusted such that drill bit guides  21  are preferably positioned near the inside diameter of the clamp and within 2 inches of the wall of the external pipe. This design feature helps keep the two drilling mechanism rigidly mounted 180° apart to ensure accuracy of the opposing colinear holes. The overall design of the apparatus minimizes set-up time in securing the drilling device to the external casing, which is important in drilling and well abandonment operations, and maximizes casing size-range adjustment. The two colinear holes may be drilled in sequence or simultaneously, but an important feature of the apparatus is that drilling the two holes simultaneously can cut the time required for drilling in half Particularly in areas where operation time is expensive, such as offshore, this saving in time is important. 
         [0017]      FIG. 1  also shows hydraulic cylinder  15   b , which provides a controlled linear force to move carriage  16   b  along rails, which are described below. Attached to carriage  16   b  is hydraulic motor  17   b  and pillow block spindle  18   b . Pillow block spindle  18   b  rotates drill bit  19   b . Drilling fluid, normally water, is directed through drill bits  19   a  and  19   b . The drill bit may be a variety of types such as a hole saw, core bit or plate cutter, and may range from 2-inch to 8-inch diameter with lengths up to 16 inches, for example. Safety guard covers  20   a  and  20   b  are preferably put in place over the drilling apparatus before it is started. 
         [0018]    Referring to  FIG. 2 , a top view of the bit guiding and driving parts of the apparatus is shown. Hydraulic cylinder  15  drives a carriage, which drives the bit, both of which are covered by safety guard cover  20 , It is important that the drive apparatus of the bit be rigid, so that sideways force on the bit does not significantly divert it from a line between the bits. The carriage moves along rods  22 , as will be shown in detail below, and the rods are held rigidly by rails  24 . The rails are preferably made of an aluminum alloy extrusion. The rigidity allows accurately drilled colinear holes from the drilling assemblies. Hitch  30  may be used to attach control modules  14  to the drilling assemblies. Control modules contain at least two controls—control  28  for hydraulic cylinder  15  and control  29  for hydraulic motor  17 . Alternatively, control module  14  may be located far remote from the drilling assemblies. For example, control module  14  may be in a boat and the drilling modules may be at the sea floor, or on another deck of a fixed or floating facility, connected by hoses. 
         [0019]    Referring to  FIG. 3 , pillow block bearings  26  ride on rods  22  supported by rigidly mounted rod support rails  24 . Carriage  16  provides a rigid mount for pillow block spindle  18 , which may utilize male 1¼ inch-diameter seven-thread spindle shaft  27  to rotate drill bit  19   b , as shown in  FIG. 1 . An elevation view is shown in  FIG. 4 , also showing hydraulic motor  17 , pillow block spindle  18  and spindle shaft  27 . 
         [0020]      FIG. 5  is a top view of clamp  12  with foot pad  52  bolted in place by bolts  57 . Holes in clamp  12  and holes  56   a  in screw body  56  of feed screw jaw  12   a  allow adjustment of the diameter of a circle passing through casing tong dies  54  for casing having different diameters.  FIG. 5  illustrates adjustment of apparatus  10  ( FIG. 1 ) for drilling through maximum diameter casing for which the clamp is constructed. 
         [0021]    Light-weight aluminum construction and modular design of the device allow for rapid assembly, disassembly, and adjustments in confined spaces such as on lower decks of offshore structures. The modular assemblies may be individually moved to confined space areas and quickly assembled. The two drill box assemblies  13  are secured onto clamp  11  by bolts. Remote control stands  14  may be attached to the clamp by inserting the 1½ inch square stock hitch  30 , shown in  FIG. 2 , into a 1½ inch inner dimension square tubing receiver mount and pinned with quick-release ball locking pins. 
         [0022]    Design features of the drilling device allow for use in subsea applications when operated by divers. The apparatus may be lowered to the seafloor and clamped to casing as on land. The remote control stand may be operated bottom-side by divers or may be removed from the hitch position on the clamp and used top-side with appropriate lengths of hose leads. 
         [0023]    Hydraulic circuits illustrating apparatus suitable for use with the drilling apparatus are shown in  FIG. 6 . Controls for hydraulic cylinder  15   a  are four-way valve with three-position centered detent  61 , pressure regulator  62  and flow control with by-pass  63 . Controls for hydraulic motor  17   a  are four-way valve with three position centered detent  64 , flow control with by-pass  65 , and pressure regulator  66 . 
         [0024]    For forming a hole through the wall of one or more strings of pipe, which may have cement in the annuli between the pipes, the apparatus is first clamped to the outside pipe. The drill bits are preferably fed by the single stage hydraulic cylinders into the wall of the external pipe at an optimal rate of speed until the casing wall has been penetrated. When the bit has entered cement, the feed rate may be increased to drill through a softer cemented annulus material until the next inner casing wall is reached. The feed rate may be reduced to an optimum feed rate for the harder metal casing inside the larger casing. This process is continued until the inner-most casing wall has been penetrated by each bit. The feed rate may be adjusted throughout the drilling process by monitoring hydraulic panel mounted gauges. The hydraulic cylinder gauge will register an increase in hydraulic pressure when drilling through the harder casing material, indicating the need to lower the pressure to slow down penetration rate, and will register a decrease in hydraulic pressure when drilling through the softer cemented annulus material, indicating the need to increase hydraulic pressure to increase the penetration rate. 
         [0025]    Although the process of drilling colinear holes using a pair of drilling assemblies and bits has been described assuming that the holes are drilled simultaneously, it should be understood that the holes may be drilled sequentially or at various drilling rates with each assembly and bit. This could be desirable, for example, if hydraulic power to the apparatus is limited. 
         [0026]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except as and to the extent that they are included in the accompanying claims.