Abstract:
The method of shearing drill collars used in the drilling of oil and gas wells, comprising providing an outer sleeve of a first material for carrying structural loads, providing a second material within the outer sleeve which is lower in shear strength and is greater in unit weight than the first material, and providing a hole in the second material for the circulation of fluids.

Description:
TECHNICAL FIELD  
       [0001]    This invention relates to the method of shearing drill pipe for drilling oil or gas wells, especially in deep water. 
       CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0003]    Not applicable 
       REFERENCE TO A “MICROFICHE APPENDIX” 
       [0004]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    The drill bit for drilling oil and gas wells is facilitated by having a heavy load applied to assist in crushing and pulverizing the formation being drilled. The formation material must be reduced to particles small enough that the flow of drilling mud up to the surface will carry it to the surface. Drill collars are connected to the drill bit to provide the heavy load for this purpose. 
         [0006]    The drill bit and drill collars are part of a drill string which also includes drill pipe which extends to the drilling rig at the surface. 
         [0007]    The drill pipe which extends to the surface is thin walled. Its primary design requirement is to support the weight of the drill string including the drill collars during running and retrieving of the drill string. 
         [0008]    Conversely, the drill collars are at the bottom of the drill string and they only support themselves. The drill pipe can be 20,000 feet long or longer and drill collars seldom exceed 1,000 feet in length. Although the drill collars are heavier, there is much more length in drill pipe, and the drill pipe must support the drill collars and the drill pipe. 
         [0009]    Drill collars have as small a bore as practical and as large an outer diameter as is practical so that they will be heavy. The drill collars have metal sealing threaded connections on each end. These threaded connections are benefited by being made of high strength steel. As a result the entire drill collar is made of high strength steel. They are extremely strong as a result, but do not have a requirement for being extremely strong. They are characteristically so strong that the average person presumes they need to be strong, because they always are. 
         [0010]    A problem resulting from this is that the thick cross section of high strength steel cannot be sheared by the blind shear rams in the primary well control device, the blowout preventer stack. The blind shear rams are to cut the pipe in the bore and seal across the bore to keep a well from blowing out. When as much as 1000 feet of drill collars pass in front of the blind shear rams, the well bore literally cannot be closed. 
         [0011]    On land or platform wells this is not a major concern as in unexpected pressure situations there is always a closable valve on the top of the drill string except for the short time for making connections at the surface. For the annular area between the outside diameter of the drill string in the well and the bore of the blowout preventer stack, there are annular and ram type blowout preventers which are well known in the art and can be closed to seal this annular area. 
         [0012]    In deepwater drilling situations from a floating vessel the situation is different. In the worst case scenario the vessel can be blown off location or can have a steering computer accidental drive off when you are in an unexpected pressure situation. If this happens when the drill collars are in the bore in front of the blind shear rams, you cannot close the blowout preventers and you cannot let go of the pipe string. In other words you have a blowout. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The object of this invention is to provide a drill collar which can be sheared with conventional blowout preventer shear rams. 
         [0014]    A second object of this invention is to provide drill collars of a higher unit weight such that the length of the drill collars to provide a desired weight on the bit will be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a view of a deepwater drilling system using the drill collars of this invention 
           [0016]      FIG. 2  is a half section of a drill collar of conventional design. 
           [0017]      FIG. 3  is a cross section of the drill collar of  FIG. 2  taken along lines “ 3 - 3 ”. 
           [0018]      FIG. 4  is a half section of a drill collar of this invention. 
           [0019]      FIG. 5  is a cross section of the drill collar of  FIG. 4  taken along lines “ 5 - 5 ”. 
           [0020]      FIG. 6  is a half section of one and one half drill collars of this invention 
           [0021]      FIG. 7  is a half section of a cylindrical tube which might be used to manufacture the drill collar of this invention. 
           [0022]      FIG. 8  is a half section of the tube of  FIG. 7  which is rolled and forged to an appropriate shape. 
           [0023]      FIG. 9  is a half section of the tube of  FIG. 8  machined. 
           [0024]      FIG. 10  is a half section of the tube of  FIG. 9  with a spacer ring added to the bottom and an internal tube added. 
           [0025]      FIG. 11  is a half section of weight material added to the components of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Referring now to  FIG. 1 , a view of a complete system for drilling subsea wells  20  is shown in order to illustrate the utility of the present invention. The drilling riser  22  is shown with a central pipe  24 , outside fluid lines  26 , and control lines  28 . 
         [0027]    Below the drilling riser  22  is a flex joint  30 , lower marine riser package  32 , lower blowout preventer stack  34  and wellhead  36  landed on the seafloor  38 . 
         [0028]    Below the wellhead  36 , it can be seen that a hole was drilled for a first casing string, that string  40  was landed and cemented in place, a hole drilled thru the first string for a second string, the second string  42  cemented in place, and a hole is being drilled for a third casing string by drill string  44  which includes drill bit  45 , heavy weight drill collars  46 , and lighter weight drill pipe  47 . 
         [0029]    The lower Blowout Preventer stack  34  generally comprises a lower hydraulic connector for connecting to the subsea wellhead system  36 , usually 4 or 5 ram style Blowout Preventers, an annular preventer, and an upper mandrel for connection by the connector on the lower marine riser package  32 . 
         [0030]    Below outside fluid line  26  is a choke and kill (C&amp;K) connector  50  and a pipe  52  which is generally illustrative of a choke or kill line. Pipe  52  goes down to valves  54  and  56  which provide flow to or from the central bore of the blowout preventer stack as may be appropriate from time to time. Typically a kill line will enter the bore of the Blowout Preventers below the lowest ram and has the general function of pumping heavy fluid to the well to overburden the pressure in the bore or to “kill” the pressure. The general implication of this is that the heavier mud will not be circulated, but rather forced into the formations. A choke line will typically enter the well bore above the lowest ram and is generally intended to allow circulation to circulate heavier mud into the well to regain pressure control of the well. 
         [0031]    Normal drilling circulation is the mud pumps  60  taking drilling mud  62  from tank  64 . The drilling mud will be pumped up a standpipe  66  and down the upper end  68  of the drill pipe  47 . It will be pumped down the drill pipe  47 , out the drill bit  45 , and return up the annular area  70  between the outside of the drill pipe  47  and the bore of the hole being drilled, up the bore of the casing  42 , through the subsea wellhead system  36 , the lower blowout preventer stack  34 , the lower marine riser package  32 , up the drilling riser  24 , out a bell nipple  72  and back into the mud tank  64 . 
         [0032]    During situations in which an abnormally high pressure from the formation has entered the well bore, the thin walled central pipe  24  is typically not able to withstand the pressures involved. Rather than making the wall thickness of the relatively large bore drilling riser thick enough to withstand the pressure, the flow is diverted to a choke line  26 . It is more economic to have a relatively thick wall in a small pipe to withstand the higher pressures than to have the proportionately thick wall in the larger riser pipe. 
         [0033]    When higher pressures are to be contained, one of the annular or ram Blowout Preventers are closed around the drill pipe and the flow coming up the annular area around the drill pipe is diverted out through choke valve  54  into the pipe  52 . The flow passes up through C&amp;K connector  50 , up pipe  26  which is attached to the outer diameter of the riser  24 , through choking means illustrated at  74 , and back into the mud tanks  64 . 
         [0034]    On the opposite side of the drilling riser  24  is shown a cable or hose  28  coming across a sheave  80  from a reel  82  on the vessel  84 . The cable  28  is shown characteristically entering the top of the lower marine riser package  32 . These cables typically carry hydraulic, electrical, multiplex electrical, or fiber optic signals. Typically there are at least two of these systems, which are characteristically painted yellow and blue. As the cables or hoses  28  enter the top of the lower marine riser package  32 , they typically enter the top of the control pod to deliver their supply or signals. When hydraulic supply is delivered, a series of accumulators are located on the lower marine riser package  32  or the lower Blowout Preventer stack  34  to store hydraulic fluid under pressure until needed. 
         [0035]    Referring now to  FIG. 2 , conventional drill collar  100  comprises a central thick wall section  102 , an upper female thread  104 , a lower male thread  106 , an upper sealing shoulder  108  and a lower sealing shoulder  110 . 
         [0036]    Referring now to  FIG. 3 , a cross section of  FIG. 2  is shown along lines “ 3 - 3 ” showing the thick cross section required to be sheared. 
         [0037]    Referring now to  FIG. 4 , a half section of the drill collar  120  of the present invention is shown being made of a thin wall formed tube  122  with an upper thread  124 , a lower thread  126 , upper sealing shoulder  128  and lower sealing shoulder  130 . Ring  132  lands on shoulder  134  and supports thin walled tube  136 . Heavy weight material such as lead  138  is melted and poured into the area between tube  122  and thin walled tube  136 . 
         [0038]    Referring now to  FIG. 5 , a cross section of  FIG. 4  is shown along lines “ 5 - 5 ” showing the majority of the section required to be sheared is of the lower shear strength material such as lead. As the density of steel is 0.283 lbs. per cubic inch and the density of lead is 0.410 lbs. per cubic inch, lead is approximately 45% heavier than steel. This means that the length of the drill collars of this invention could be up to 45% shorter than conventional drill collars. 
         [0039]    Referring now to  FIG. 6 , a drill collar  140  of this invention is shown with a portion of a second drill collar  142  attached at thread  144 . This illustrates that even the connection of the drill collar of this invention has a smaller cross section of steel than that of a conventional drill collar such as is shown in  FIG. 2 . 
         [0040]    Referring now to  FIG. 7 , a simple thin wall tube  150  is shown which can be used as material for a portion of the drill collar of the present invention. 
         [0041]    Referring now to  FIG. 8 , tube  150  of  FIG. 7  is rolled tube  160  to a suitable profile, with some forging upset occurring at locations  162  and  164  where thicker cross sections will be beneficial for machining. This is especially important when the connections are tapered threads. 
         [0042]    Referring now to  FIG. 9 , is shown with the rolled tube  160  of  FIG. 8  is a machined tube  170  with a lower thread  172 , an upper thread  174 , a lower sealing shoulder  176 , an upper sealing shoulder  178 , and an internal shoulder  180 . 
         [0043]    Referring now to  FIG. 10 , machined tube  170  has ring  132  and thin walled tube  136  installed. 
         [0044]    Referring now to  FIG. 11 , lead  190  is poured into the assembly of  FIG. 10  and allowed to solidify. As lead tends to shrink when solidifying, percentages of bismuth, antimony, and tin can be added to eliminate the shrinkage or to cause a slight expansion if desired. Alternately, a temporary tube can be placed in the bore for molding and then be removed. 
         [0045]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.