Patent Publication Number: US-7896108-B2

Title: Dual string orbital drilling system

Description:
This application claims the benefit of provisional application Ser. No. 61/068,383 filed Mar. 6, 2008. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to a dual string orbital drilling system for drilling bore holes in earth formations. The present invention has significant advantages when drilling through fractured rock. 
     Generally bore holes are formed by rotating a drill string which may be several hundred feet in length into an earth formation. Dual wall drilling systems are known. For example, U.S. Pat. No. 4,618,172 to Becker shows a dual wall drill pipe having an outer pipe with a drill bit mounted at the drilling end of the outer pipe and an inner pipe used for providing a passageway for returning drilling fluid directed to the drill bit returning the drilling fluid to the surface. U.S. Pat. No. 4,940,098 to Moss shows another dual wall drilling system where the inner pipe is used for returning drilling fluid to the surface and a drill bit is mounted at the drilling end of the outer pipe. 
     A need exists, however, for a dual string drilling system where both the outer drilling string and an inner drilling string are used together to drill a bore hole. 
     A need also exists for a drilling system which allows an inner drilling string to perform drilling operations while being supported by an outer drill string which then allows the outer drill string and the inner drill string to be of reduced diameter thereby enabling a user to use the drilling system for drilling small holes approximately 3″ in diameter for long depths such as 10,000 feet. 
     SUMMARY OF INVENTION 
     The present invention relates to a dual string drilling system for drilling a well bore in an earth formation, having a rotatable, tubular outer drill string and an upper rotatable, tubular inner drill string concentrically disposed in spaced apart relation with the outer drill string. An elongate tubular driver shoe is mounted to a distal end of the outer drill string. The driver shoe mounted to the outer drill string having an interior passageway having a longitudinal axis which is inclined with respect to the longitudinal axis of the outer drill string. The driver shoe mounted to the outer drill string further provided with a cutaway portion extending through a wall of the tubular outer drill string. A lower rotatable inner drill string is coupled to the upper rotatable tubular inner drill string for rotation therewith and is disposed within the interior passageway of the driver shoe mounted to the outer drill string. A drill bit is mounted to the distal end of the lower inner drill string and is sized to extend beyond the drive shoe mounted to the outer drill string. A passageway is provided for injecting drilling fluid through the tubular inner drill string to the drill bits in the well bore and then returning the drilling fluid through a passageway between the inner drill string performs the drilling operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein: 
         FIG. 1  is an elevational view of a dual string orbital drilling system according to the present invention; 
         FIG. 2  is a top view of the drilling system shown in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along the line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a left side elevation view of the drilling system shown in  FIG. 1 ; 
         FIG. 5  is a perspective view of an upper inner drill string used with the present invention; 
         FIG. 6  is an elevational view of the upper inner drill string shown in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view taken along the line  7 - 7  in  FIG. 6 ; 
         FIG. 8  is a perspective view of a lower inner drill string assembly used with the present invention; 
         FIG. 9  is an elevational view of the lower inner drill string assembly shown in  FIG. 8 ; 
         FIG. 10  is a cross-sectional view taken along the line  10 - 10  in  FIG. 9 ; 
         FIG. 11  is a detailed perspective view of the upper inner drill string and lower inner drill string assembly connected together; 
         FIG. 12  is an elevational view of the upper inner drill string and lower inner drill string shown in  FIG. 11 ; 
         FIG. 13  is a cross-sectional view taken along the line  13 - 13  in  FIG. 12 ; 
         FIG. 14  is a detail view taken at A in  FIG. 11 ; 
         FIG. 15  is a detail view taken at C in  FIG. 13 ; and 
         FIG. 16  is a diagrammatic representation of a conventional drilling rig having an inner drill string and an outer drill string connected thereto. 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     A dual string orbital drilling system  10  is shown in  FIGS. 1-3 . The drilling system  10  includes a tubular outer string  12  and an upper tubular inner string  14 . Each of the drill strings  12  and  14  are connected to a conventional drilling rig  15 , as shown in  FIG. 16 , located above the surface of the earth. The drilling rig  15  includes a drill head  17  connected to the outer string  12  and a second drill head  19  connected to the inner drill string  14  for rotating the drill strings independently of one another. 
     The outer string  12  is provided with an elongate outer string drill bit driver shoe  16  in which carbide bearing buttons  18  are mounted for bearing against the exposed bore hole surface when drilling a bore hole. 
     The upper inner drill string  14  is concentrically positioned inside the outer drill string  12 . The inner drill string  14  has an interior passageway  21  and the inner drill string  14  has an outside diameter smaller than the inside diameter of the outer drill string  12 , leaving a passageway  20  between the inner string  14  and the outer string  12 . At the lower end of upper inner string  14 , a chain sprocket  22  is formed on the outside wall of inner string  14  as shown in FIGS.  3  and  5 - 7 . 
     A lower inner drill string assembly  24  is positioned below the upper inner drill string  14  as shown in  FIG. 3 . The lower inner drill string assembly  24  is provided with a chain sprocket  26  as shown in FIGS.  3  and  8 - 10 . A conventional roller chain flexible coupling  28  is wrapped around sprockets  22  and  26  and is used to couple the upper inner drill string  14  and the lower inner drill string assembly  24  together as shown in  FIG. 3  and  FIG. 11-15  so that the upper inner drill string  14  and lower inner drill string assembly  24  rotate together. The lower inner drill string assembly  24  has an interior passageway  25  in fluid communication with the passageway  21  of the inner drill string  14  as shown in  FIG. 13 . 
     An inner bit  30  is attached at the bottom end of the lower inner drill string assembly  24  as shown in  FIG. 3  with the inner bit  30  extending beyond the outer string driver shoe  16 . In a preferred embodiment, bit  30  may be a conventional polycrystalline diamond bit. The inner bit  30  includes openings  31  in fluid communication with the passageway  25  as shown in  FIGS. 3 and 4 . The outside diameter of the inner bit  30  is larger than the outside diameter of the lower inner string assembly  24  providing a shoulder  32  as shown in  FIGS. 3 and 13 . Further, the lower inner drill string assembly  24  is provided with a shoulder  34  in spaced apart relation with the shoulder  32  as shown in  FIGS. 3 and 15 . A sleeve bearing  36  is positioned in surrounding relation to the lower inner drill string assembly  24  and is sized to fit between the shoulders  32  and  34 . Thus, the sleeve bearing  36  and inner drill string  24  are restricted from moving outwardly with respect to the outer drill string  12 . 
     The outer string driver shoe  16  is provided with an internal, inclined, off-center bore  38  as shown in  FIG. 3 . The outer string driver shoe  16  is also provided with a cutaway portion  40  as shown in  FIG. 1 . The lower inner drill string assembly  24  with sleeve bearing  36  is fitted within the off-center bore  38  and extends out through cutaway portion  40  as shown in  FIG. 3 . With this construction, as the outer string  12  is rotated, the inner bit  30  orbits around the center line of the outer string  12  during the drilling operation. 
     Drilling fluid may be injected to the inner bit  30  through the passageways  21  and  25 . Drilling fluid is then injected through opening  31  into the bore hole surrounding bits  30  and driver shoe  16 . The outer drill string  12  is provided with cutouts  42  as shown in  FIGS. 1-3 . Drilling fluid is then forced under pressure to move upwards to the earth&#39;s surface in the bore hole outside the outer drill string  12 , through cutouts  42  and then upwardly in the passageway  20 . 
     In a preferred embodiment, the inner string rotates at a faster rate than the outer string and the outer string can be rotated either in the same direction or in opposite direction as the direction of rotation of the inner string. 
     As can be seen, the inner bit and the inner drill string can be removed from the outer drill string without removing the outer drill string and outer drill string driver shoe. The orbital cutting by the inner drill string cuts a hole large enough for both drill strings to advance. With the present system, the inner string can be pulled leaving the outer string  12  in place during bit changes and tool insertions. This allows an operator to “case while drilling” so that the hole never falls in when the inner string drill bit  30  is pulled. 
     While the fundamental novel features of the invention have been shown and described, it should be understood that various substitutions, modifications, and variations may be made by those skilled in the arts, without departing from the spirit or scope of the invention. Accordingly, all such modifications or variations are included in the scope of the invention as defined by the following claims: