Patent Publication Number: US-8534388-B2

Title: Dual pipe for increased fluid flow

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. Ser. No. 12/391,113 filed Feb. 23, 2009, which claims the benefit of provisional patent application Ser. No. 61/030,615 filed on Feb. 22, 2008, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to dual-member drill strings and specifically a system for ensuring unobstructed fluid flow through an annulus of a dual member drill string. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a pipe joint for use in drill strings in rotary boring applications. The pipe joint comprises a tubular outer member having a first end and a second end and having an inner surface and an outer surface, an inner member having a first end and a second end, and a spacing assembly having a first end and a second end. The inner surface forms an annular shoulder. The inner member is arranged generally coaxially within the outer member and forms an annular fluid flow path between the inner member and the inner surface of the outer member. The inner member defines a stop sized to restrict axial movement of the inner member in a first direction. The spacing assembly is disposed around a circumference of the inner member, and is positioned between the shoulder of the outer member and the stop of the inner member such that the first end of the spacing assembly is engageable with the shoulder and the second end of the spacing assembly is engageable with the stop. The spacing assembly defines a fluid flow passage in fluid communication with the fluid flow path. 
     In an alternative embodiment, the present invention is directed to a drill rod assembly, comprising an outer pipe, an inner drill rod, and a means for providing continuous fluid flow. The outer pipe comprises a first inner diameter and a second inner diameter the second inner diameter being greater than the first inner diameter, and a shoulder located at a transition between the first and the second inner diameters. The inner drill rod has a first and second ends. The inner drill rod is positioned within the outer drill rod such that a fluid flow path is defined between the inner and outer drill rods. The inner drill rod includes a knob sized to engage the shoulder of the outer drill rod to limit movement of the inner drill rod relative to the outer drill rod in a longitudinal direction. The means for providing continuous fluid flow is proximate the shoulder and the knob. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  is a partially cross-sectional cut-away side view of a Horizontal Directional Drilling (HDD) system with a dual member drill string built in accordance with the present invention. 
         FIG. 1   b  is a side view of the dual member drill string shown in  FIG. 1   a.    
         FIG. 2  is a partial cross-sectional side view of the drill string of the present invention having a first spacing assembly comprising a coil spring and a second spacing assembly comprising a coil spring. 
         FIG. 3  is a partial cross-sectional side view of an alternative embodiment of the drill string having a first spacing assembly comprising a flow spacer and a second spacing assembly comprising a sleeve. 
         FIG. 4  is a top left perspective view of an alternative embodiment of the flow spacer of  FIG. 3 . 
         FIG. 5  is a partial cross-sectional side view of a collar having a partially-slanted abutment surface. 
         FIG. 6  is a partially cross-sectional side view of an alternative embodiment of the pipe joint having a spacing assembly comprising a plurality of rolling elements. 
         FIG. 7  is a partially cross-sectional side view of another embodiment of the pipe joint having a spacing assembly comprising a plurality of rolling elements. 
         FIG. 8  is a partially cross-sectional side view of the drill string of  FIG. 1  having a spacing assembly comprising a plurality of rolling elements, a resilient element, and a collar having a partially-slanted abutment surface. 
         FIG. 9A  is a partially cross-sectional perspective view of an alternative drill string having a non-symmetrical knob. 
         FIG. 9B  is a perspective view of the knob of  FIG. 9A . 
         FIG. 10  is a partially cross-sectional side view of an alternative drill string having an offset knob. 
         FIG. 11  is a partially cross-sectional side view of an alternative drill string having a grooved knob. 
         FIG. 12A  is a cross-sectional side view of an outer member of a drill string having a modified bore. 
         FIG. 12B  is a sectional view of the member of  FIG. 12A  at reference line A. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Horizontal boring machines have now almost totally supplanted trenching techniques for laying underground utility lines and other conduits. Various systems are available for directional or steerable drilling. For example, when drilling in soil, a machine with a single drill string with a slant face drill bit is ideal. Drilling of the bore hole occurs while the drill string is rotated. Steering occurs when the slant face bit is advanced without rotating the drill string; the slanted face simply pierces the soil causing the drill bit to be deflected thus altering the angle of the axis of the drill string. 
     However, this technology is not effective in rocky conditions because the slanted face bit cannot be advanced through rock. Thus, for rock drilling applications, dual-member drill string systems are preferred. Dual-member drill strings are comprised of a plurality of pipe joints, each of which comprises an inner member supported inside an outer pipe or member. The inner member of the drill pipe constantly drives rotation of the boring head and drill bit to excavate the formation, and the outer member of the drill string is selectively rotated to align a steering mechanism to change the direction of the borehole while the rotating bit continues to drill. An exemplary HDD system is disclosed in U.S. Pat. No. 5,682,956, the content of which is incorporated herein in its entirety. 
     Turning now to the figures in general and  FIG. 1   a  specifically, a Horizontal Directional Drilling (HDD) system  10  using a dual-member drill string  12  built in accordance with the present invention is shown. The drill string  12  is comprised of a tubular outer member  14 , or outer pipe, and an inner member  16 , or rod. During the drilling operation, the outer pipe  14  is used for thrust and steering and supply of drilling fluid to a downhole tool  18 , whereas the inner rod  16  is used for transmission of power to the downhole tool. The inner rod  16  is arranged generally coaxially within the outer pipe  14 . As shown in  FIG. 1   b , this coaxial arrangement forms an annulus  20  between the outer pipe  14  and the inner rod  16 . The annulus  20  provides a space for an annular fluid flow path  22  for drilling fluid passing to the downhole tool  18 . 
     The drill string  12  is comprised of a plurality of pipe segments  28  which are adapted to couple at pipe joint connections  30 . Referring now to  FIG. 2 , there is shown therein a pipe joint connection  30  connecting the pipe sections  28   a  and  28   b . Each pipe segment  28  is comprised of the tubular outer member  14  and the inner member  16 . The tubular outer member  14  has a first end  32  and a second end  34  and an inner surface  36  and an outer surface  38 . For illustration purposes and as shown in  FIG. 2 , the first end  32  (uphole end) is shown as part of the pipe segment  28   b  and the second end  34  (downhole end) is shown as part of the pipe segment  28   a . One skilled in the art will appreciate that each pipe segment  28  of the drill string  12  has ends of the features described herein. 
     Preferably, the first end  32  comprises a pin end  40  and the second end  34  comprises a box end  42 , wherein the box end of the outer pipe  14  of the segment  28   a  is adapted to couple with the pin end of the outer pipe of the second pipe segment  28   b . More preferably, the pin end  40  will couple to the box end  42  in a threaded connection  46 . The inner surface  36  of the outer member  14  defines a first shoulder  48  at the second end  34  of the outer member. The inner surface  36  defines a second shoulder  50  proximate the first end of the outer pipe  14 . 
     A first end  52  of the inner member  16  comprises a box end  54  forming a geometrically shaped recess  56  and a second end  58  of the inner member comprises a geometrically-shaped pin end  60 . The recess  56  in the box end  54  of the inner member  16  is designed to correspond to the shape of the pin end  60  of the inner member such that the pin end of the inner member of the first segment  28   a  is slideably receivable within the recess of the box end of the inner member of the second pipe joint segment  28   b . In the preferred embodiment, the second end  58  of the inner member  16  is disposed within the second end of the outer member  14 . The first end  52  of the inner member  16  preferably extends beyond the first end  32  of the outer member  14 . More preferably, the first end  52  of the inner member comprises a radially projecting annular stop member  62 . Most preferably, the annular stop member  62  comprises a collar  64  secured to the inner member  16  with a set screw  66  or other retention apparatus. 
     The inner rod  16  is further contained by a protruding knob or stop  70  proximate the second end  58  of the inner member and sized such that it cannot pass through the first shoulder  48  of the outer member  14 . At the first shoulder  48  a first inner diameter of the outer pipe  14  is smaller than an outer diameter of the knob  70 , restricting axial movement of the inner rod  16  in a first direction. Preferably, the first direction is uphole relative to the outer member  16 . At the second shoulder  50  the inner diameter of the outer pipe  14  is smaller than an outer diameter of the collar  64  restricting axial movement of the inner rod  16  in a direction substantially opposite the first direction. In this arrangement, the inner pipe  16  and the outer pipe  14  must remain within a set of tolerances such that the plurality of collars  64  along a string of the dual-member drill string  12  always have enough engagement to transfer torque to the inner rod  16  of the next segment  28   b  without premature wear or breakage. Tolerances must also allow for elongation of the outer pipe  14  due to pulling the product drill string  12  during a backream operation and shrinkage of the outer pipe during drilling. These occurrences may obstruct the fluid flow path  22  across one or more pipe joints  30  along the drill string  12  due to the flow being restricted either around the collar  64  or at the knob  70 . If the knob  70  comes in contact with the first shoulder  48  or if the collar  64  comes in contact with the second shoulder  50 , fluid flow  22  may be restricted and flow through the pipe joint  30  to the downhole tool  18  may not be sufficient. The present invention is advantageous because it provides for the segment  28 , which both secures the inner rod  16  within the outer pipe  14  and allows for sufficient fluid flow  22  through the pipe joint  30  at both the first shoulder  48  and the second shoulder  50  during all aspects of drilling and backreaming operations. 
     With continued reference to  FIG. 2 , the drill string  12  pipe section  28  comprises a spacing assembly  80 . The spacing assembly  80  has a first end  82  and a second end  84 . The spacing assembly  80  is disposed around a circumference of the inner rod  16  and is positioned between the first shoulder  48  and the knob  70  such that the first end  82  of the spacing assembly is engageable with the first shoulder and the second end  84  of the spacing assembly is engageable with the knob. In the embodiment of the spacing assembly  80  shown in  FIG. 2 , the spacing assembly comprises at least a first coil compression spring  90 . As shown, the first compression spring  90  extends from the first end  82  at the first shoulder  48  to the second end  84  proximate the knob  70 . 
     Each pipe section  28  further comprises a second spacing assembly  100  comprising a second compression spring  102  which extends from a first end  104  proximate the collar  64  to a second end  106  proximate the second shoulder  50 . Preferably, spring force counteracts axial forces on the inner rod  16 , such as fluid drag, to hold the inner rod in the proper position. Spring  90 ,  102  centering prevents the knob  70  and collar  64  from contacting the shoulders  48 ,  50  when the outer pipe  14  stretches or compresses under high force. Preferably, the springs  90 ,  102  are arranged such that at least one gap  110  remains between the coils even when compressed. Thus, the fluid flow path  22  through the annulus  20  and pipe joint  30  is unrestricted. More preferably, the one spring  90 ,  102  is a right-handed spring and the other spring is a left-handed spring. The springs are positioned such that rotation of the inner pipe  16  does not cause the unwinding of either spring  90 ,  102 . Hardened washers (not shown), properly sized to not inhibit the fluid flow path  22  may be placed at one or both ends of the springs  90 ,  102  to improve wear life. 
     Turning now to  FIG. 3 , an alternative embodiment of the pipe segment  28  is shown. In  FIG. 3 , the spacing assembly  80  comprises a flow spacer ring  120 . The flow spacer ring  120  comprises a first end  122  and a second end  124 . As shown, the flow spacer ring  120  extends from the first shoulder  48  at the first end  122  to the knob  70  at the second end  124 . Preferably, the flow spacer ring  120  is wider at the first end  122  than at the second end  124 , and defines a gap  110  or slot between the first end and the second end such that the fluid flow path  22  can pass through the flow spacer ring. Alternatively, the flow spacer ring  120  may comprise a plurality of gaps or slots  110 . 
     With continued reference to  FIG. 3 , a second flow spacer  130  is disposed around the first end  52  of the second segment  28   b  of the inner member  16 . The second flow spacer  130  preferably comprises a sleeve  132 . The sleeve  132 , disposed around the circumference of the inner member  16 , extends between the collar  64  to or through the second shoulder  50 . The sleeve  132  comprises a gap  110  or flow slot which maintains an unrestricted fluid flow path  22  along a length of the inner rod  16 . 
     With reference again to  FIG. 3 , the knob  70  is shown having a flat abutment surface  134  which contacts the second end  124  of the flow spacer ring  120 . This allows a greater area of contact between the second end  124  of the flow spacer ring  120  and the knob  70  when the fluid spacer ring and the knob are in contact. 
     One skilled in the art will appreciate that such contact is not necessarily continuous. In a preferred embodiment, the fluid spacer ring  120  is not permanently engaged at either the first shoulder  48  or the knob  70 , but only engages the first shoulder and the knob when the position of the inner rod  16  and outer pipe  14  are subject to operational stresses. Likewise the sleeve  132  is not permanently engaged at the collar  64  or the second shoulder  50 . One skilled in the art can calculate how much the outer pipe  14  will compress or stretch under maximum forces. Therefore, the proper length of the particular fluid flow spacer  120  or sleeve  132  may be determined such that transfer of tension to the inner rod  16  may be avoided. 
     The embodiment of  FIG. 3  may also be utilized without a knob  70  comprising a flat surface. Alternatively, the spacing assembly  80  may comprise two fluid flow spacers  120  or two sleeves  132 . In another alternative, the spacing assembly  80  may comprise only one flow spacer ring  120 . The flow spacing assembly  80  may also be shaped to allow increased contact with a standard knob  70  without an abutment surface  134 . This is advantageous as it allows the inner rod to be manufactured with little or no modification to existing tooling. 
     Turning now to  FIG. 4 , an alternate embodiment of the flow spacer ring  120  is shown in detail. The first end  122  comprises a plurality of feet  136  adapted to engage the first shoulder  48 . The second end  124  comprises a ring surface  138  adapted to engage the knob  70 . The feet  136  are set wider than the ring surface  138  such that gaps  110  allow continuous fluid flow  22 . 
     With reference again to  FIG. 3 , the fluid flow spacer  120  or sleeve  132  which is most “upstream” relative to a direction of the fluid flow path  22  may not be necessary if the proper distance between the collar  64  and the second shoulder  50  is provided in the drill string  12 . If properly measured, drag forces against the knob  70  will hold the fluid flow path  22  around the knob open provided tolerances and impedances to flow are accounted for. 
     Referring now to  FIG. 5 , an embodiment which may be used in combination with one or more of the previous embodiments is shown. The collar  64  surrounding the inner rod  16  comprises a partially slanted abutment surface  150 . The abutment surface comprises an engagement surface  152  and a slanted surface  154 . The engagement surface  152  is engageable either at the second shoulder  50  or the spacing assembly  80  proximate the second shoulder. Alternatively, a partially slanted abutment surface  150  may be utilized with the knob  70  and the first shoulder  48 . The slanted surface  154  ensures that a portion of the collar maintains clearance between the stop member  70 ,  64  and the shoulder  48 ,  50 , defining the gap  110  for the fluid flow path  22 . 
     One skilled in the art will appreciate that the embodiment of  FIG. 5  may result in uneven wear of the stop  64  and the shoulder  50 . As shown in  FIG. 5 , a replaceable hardened ring  156  may be utilized at the shoulder  50 . Further, the collar  64  may be replaced when the engageable surface  152  wears down and the slanted surface  154  is lost or compromised. 
     With reference now to  FIG. 6 , an alternative spacing assembly  80  for the modified pipe segment  28  is shown. As shown therein, the spacing assembly comprises a plurality of rolling elements  160  located between the first shoulder  48  and the knob  70 . The rolling elements  160  are adapted to freely engage the first shoulder  48  and the knob  70  while defining a minimum distance between the shoulder and the knob. The inner surface  36  of the outer pipe  14  comprises a retaining element  162  located such that the knob  70  is between the first shoulder  48  and the retaining element. As shown, the spacing assembly  80  comprises a second plurality  164  of rolling elements  160  located between the retaining element  162  and the knob  70 , each of the plurality defining a minimum distance between the retaining element and the knob. The rolling elements  160  are disposed about the circumference of the inner rod  16  such that gaps  110  between the plurality of rolling elements provide for an unobstructed fluid flow path  22 . As shown in  FIG. 7 , the plurality of rolling elements  160  may likewise be placed between the collar  64  and the second shoulder  50 . Further, the spacing assemblies  80  of  FIGS. 6 and 7  may be utilized together, individually, or in combination with one or more of the other spacing assemblies discussed herein. Preferably, each of the plurality of rolling elements  160  comprises a hardened sphere, such as a bearing ball. 
     With reference now to  FIG. 8 , the spacing assembly  80  of  FIGS. 6 and 7  further comprises a resilient element  166 . The resilient element  166  is held within the collar  64  such that it is held between the pin end  60  of the inner rod  16  and the box end  54  of the inner rod of the second segment  28   b . When the adjacent inner rods  16  are connected, the plurality of rolling elements  160  of  FIG. 6  is held in place by the resilient element  166 . The resilient element  166  may comprise a compressible elastomeric material, a compression spring, or other similar element. 
     With reference now to  FIGS. 9A and 9B , an alternative embodiment of the pipe segment  28  is disclosed which allows an unobstructed fluid flow path  22  without the use of the spacing assembly. In this embodiment, the knob  70  comprises an additional knob feature that causes the knob to only partially engage the first shoulder  48 . As shown therein the knob  70  feature comprises a flat surface  170 , such that when the knob contacts the first shoulder  48 , the fluid flow path  22  is unobstructed due to a gap  110  created by the flat surface. A rod retainer  172  is provided on the inner surface  36  of the outer pipe  14  such that the knob  70  is kept in proximity of the first shoulder  48 . Alternatively, the retainer  172  may be placed on the inner rod  16 . 
     Referring now to  FIG. 10 , shown therein is the knob  70  on the inner member  16  having an alternative feature to that shown in  FIG. 9 . In the alternative embodiment, the knob  70  is not coaxial with an axis or centerline of the inner rod  16  and the outer pipe  14 , such that a gap  110  is created when the knob  70  contacts the first shoulder  48 . In this embodiment, the annulus  20  of the pipe section  28  must be sized such that 360° of rotational clearance is given for the knob  70  to prevent wear during rotation of the inner rod  16 . 
       FIG. 11  shows yet another alternative for the knob  70 , in which the knob feature comprises grooves  174  in the surface of the knob. The grooves  174  are preferably sized such that one or more gaps  110  are created when the knob contacts the first shoulder  48 . Preferably, there are not more than six such grooves  174  in the surface of the knob  70 . 
     Referring now to  FIGS. 12A and 12B , an alternative design for the outer pipe  14  of a pipe section  28  is described. As shown therein, a modified bore  180  of the inner surface  36  of the outer pipe  14  is proposed. Preferably, the modified bore  180  will comprise an elliptical cross-section, as shown in  FIG. 12B . When utilized with the knob  70  configurations previously discussed, the modified bore  180  ensures that only a portion of the knob abuts the elliptical cross-section of the first shoulder  48  so that the fluid flow path can never become restricted. The modified bore  180  may be tapered and need not extend a full length  182  of the interior of the pipe section  28 , provided it intersects the first shoulder  48 . Alternatively, the bore  180  may be machined to form shoulder at a right angle to the inner surface  36  of the pipe  14 . 
     Flow restriction problems may also be overcome for dual member drill strings  12  without significant modification by periodic insertion of a modified segment  28 . The modified segments  28  may be used at intervals appropriate to the forces placed on the drill string  12  due to thrust and pullback forces. One skilled in the art can envision other potential combinations of the principles disclosed in the above embodiments to create a dual-member drill string  12  composed of connected segments  18  that meet the previously stated objectives of containment of the inner rod  16  within and aligned with the outer pipe  14  longitudinally as well as concentrically, joining of dual-member drill string segments  28  together in a manner that assures an adequate fluid flow path  22  to downhole tools  18  across the broad expected range of drilling operations, and ease of manufacture and assembly. The inner rods  16  may be shortened to prevent their end-to-end stack up in long drill strings  12 , the amount of shortening being primarily determined by stack up of pertinent manufacturing tolerances and outer pipe length shrinkage under full thrust force.