Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/10—Wear protectors; Centralising devices, e.g. stabilisers
  • E21B17/1085—Wear protectors; Blast joints; Hard facing
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/02—Couplings; joints
  • E21B17/04—Couplings; joints between rod or the like and bit or between rod and rod or the like
  • E21B17/042—Threaded
  • E21B17/0426—Threaded with a threaded cylindrical portion, e.g. for percussion rods

Definitions

• the present invention relates to percussive drilling, and, in particular, to a drill rod for use in such drilling.
• Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes.
• drill strings are typically used in which a plurality of drill rods are interconnected to advance the drill bit and increase the depth of the hole.
• a terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes.
• Drill rods used for this application usually have a male threaded end and a female threaded end and are commonly called MF-rods.
• the drill rods can also have a shoulder formed as a radially flared extension of the main length section of the drill close to the male threaded end.
• the shoulder provides increased efficiency in energy transfer between the drill rod and the drill bit.
• the shoulder on the first drill string rod that joins to the drill bit is exposed to high levels of wear as the hole collapses and rock cuttings gather behind the drill bit. The problem with this is that as the shoulder wears the strength of the coupling will weaken and the contact area between drill rod and drill bit will decreases which leads to a decreased transfer of energy between drill rod and drill bit.
• WO202169657 discloses a drilling assembly for percussion drilling where the shoulder is encased in both radial and axial direction inside the mounting sleeve of the drill bit.
• WO2020234259 discloses a drill string rod with a shoulder that is protected by a hard layer.
• the drill rod for percussive drilling comprises: a hollow elongate main length section, defining a longitudinal axis of the drill rod, extending axially between a leading male end, for connecting the drill rod to a drill bit, and a trailing female end.
• a through-going flushing channel comprises: a female end comprises a female thread and the male end comprises a male thread and a radially projecting shoulder between the male thread and the main length section.
• the main length section has a circular cross-section perpendicular to the longitudinal axis of the drill rod.
• the shoulder comprises a peripheral surface with a greater outer diameter than the outer diameter of the main length section.
• a crushing element is positioned adjacent a trailing end of the shoulder and a cross-section and a radially peripheral surface of the crushing element has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.
• a flushing channel that passes through the drill rod and exits at the front of the drill bit is used for directing a flushing agent such as air, or a fluid such as water, to the bottom of the drilled hole.
• the flushing agent will arrive at the bottom of the hole at a high pressure to flush the cuttings, produced during the drilling operation, to the exit of the drilled hole.
• the cuttings will pass between the wall of the drilled hole and the outside surface of the drill rods on its way to the exit of the drilled hole.
• Some cuttings, however, are too large to be effectively flushed out of the hole. Due to gravity, these large cuttings will accumulate at the trailing side of the shoulder of the drill rod that is attached to the drill bit. This accumulation of large cuttings will lead to wear on the shoulder. Heavy wear on the shoulder will decrease the efficiency of transmitting percussive energy from the drill rod, through the shoulder, to the drill bit. The drilling will thus be less effective.
• the present inventors have realized that having a crushing element at the trailing end of the shoulder solves this problem.
• the crushing element has a radially peripheral surface that has a non-constant distance to the longitudinal axis of the drill rod around the circumference of the radially peripheral surface of the crushing element.
• the crushing element radially extends the main length section in the area closest to the trailing end of the shoulder. Its radially peripheral surface has a non-constant distance to the longitudinal axis of the drill due to it being made of at least one protrusion or protuberance that extends in a certain direction(s) away from the longitudinal axis of the drill rod. There may be more than one protrusion or protuberance, for example 2, 3 or 4, that extends in different radial directions away from the longitudinal axis of the drill rod.
• the crushing element due to it extending away from the longitudinal axis of the drill rod, on at least one position, will impact and squeeze the large cuttings against the wall of the drilled hole. The large cuttings will then break into finer cuttings which can be flushed away from the drilled hole.
• a small transition surface may be positioned in the transition between the shoulder and the crushing element.
• the transition surface simplifies manufacturing of the crushing element and additionally decreases the stresses in the area between the shoulder and the crushing element.
• the transition surface is not part of the crushing element.
• the main length section of the drill rod has a circular cross-section with a radius Rm.
• the crushing element can be seen as the leading end part of the main length section where there is a protrusion or protuberance extending in a radial direction.
• the entire peripheral surface of the crushing element preferably extends further from the longitudinal axis of the drill rod than the radius Rm of the main length section.
• leading end refers to the end of the drill rod where the drill bit is attached.
• the leading end thus refers to the end closest to the bottom of the drilled hole.
• the trailing end refers to the end furthest away from the bottom of the drilled hole.
• the outer surface of the cross-section of the crushing element is smooth around the whole circumference of the outer surface of the cross-section.
• This configuration ensures that large cuttings are not just pushed in front of the crushing element but will instead get squeezed between the crushing element and the wall of the drilled hole.
• the peripheral surface of the crushing element is convex around its circumference. This ensures that there are no indents in the crushing element where cuttings may get stuck.
• the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is smaller than a radius Rs of the shoulder.
• This configuration ensures that the shoulder will act as a barrier for cuttings to stop cuttings from travelling back down the hole to the drill bit.
• the peripheral surface of the crushing element preferably has a minimum distance to the longitudinal axis that is approximately equal to the radius Rm of the main length section.
• a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod to the radius Rs of the shoulder is between 0,5-1,0. More preferably the ratio is between 0,7-0,95 and most preferably between 0,75-0,9.
• This configuration ensures that cuttings will be effectively squeezed and crushed between the crushing element and the wall of the borehole. This configuration further ensures that a large range of different sized cuttings will be crushed.
• the crushing element has a maximum distance Rc from the longitudinal axis of the drill rod that is larger than a radius Rm of the main length section.
• a ratio of the maximum distance Rc from the crushing element to the longitudinal axis of the drill rod and the radius Rm of the main length section is between 1,2-2,0.
• the ratio is more preferably between 1,25-1,6 and most preferably between 1,3-1,4.
• This configuration ensures that a large range of different sized cuttings will be crushed.
• the crushing element has an axial extension that is between 5-100 mm.
• the axial extension is more preferably between 10-40 mm.
• the drill rod is usually manufactured by friction welding a majority of the main length section to a male end and to a female end.
• the male end and the female end will however comprise a small part of the main length section. This manufacturing method simplifies the manufacturing of the drill rod compared to if the drill rod was manufactured in one piece.
• the crushing element should not have an axial extension from the shoulder that is too long since a certain free distance is needed to clamp the male end during the friction welding operation. Usually a free distance of 50-90 mm is needed.
• the axial extension of the crushing element must additionally have a certain minimum length to effectively crush cuttings.
• the crushing element is anti-symmetric with a central axis that is offset from the longitudinal axis of the drill rod.
• the crushing element is symmetric around the longitudinal axis of the drill rod.
• the crushing element has 2, 3 or 4 protrusions or protuberances that are symmetrically positioned around the longitudinal axis of the drill rod.
• the crushing element generally has a cylindrical peripheral surface and in that the central axis of the crushing element is offset from the longitudinal axis of the drill rod.
• This configuration ensures that the cuttings will be effectively crushed due to the peripheral surface of the offset cylinder having a distance from the longitudinal axis of the drill bit that progressively increases. Having a crushing element that is cylindrical in shape is also simple to manufacture.
• the crushing element has a peripheral surface that is generally elliptical in shape.
• a crushing element having a peripheral surface that is generally elliptical in shape has the advantage that it can have its central axis coinciding with the longitudinal axis of the drill rod and then the elliptical surface will extend in two radial directions, thus forming a crushing element with two symmetrically positioned protrusions or protuberances.
• the crushing element has a peripheral surface that slopes towards the longitudinal axis of the drill rod in a direction towards the trailing end of the drill rod.
• the slope can be any shape that slopes towards the longitudinal axis of the drill bit, for example a straight line, a concave or a convex shape.
• the crushing element will have the form of a truncated cone.
• the crushing element is integral with the main length section.
• This configuration increases the strength of the drill rod and especially the strength of the crushing element.
• the crushing element is in this configuration integrally formed with the main length section.
• the main length section may however be manufactured by friction welding a major part of the main length section with a male end and a female end, each of the male end and female end comprising a part of the main length section.
• the crushing element is integral with the shoulder.
• This configuration increases the strength of the drill rod.
• the invention furthermore relates to a drill string comprising at least one drill rod according to the definitions above and a drill bit.
• Fig. 1 shows a drill rod 12 releasably coupled to a drill bit 2 of conventional design.
• This assembly is especially used for top hammer drilling. Shockwaves generated by a surface piston (not shown) are translated through the mated surfaces from the drill rod 12 to the drill bit 2.
• the drill rod 12 comprises an axially extending main length section 14 and at one end a male end 16 and at a second opposite end a female end 18 and having a longitudinal axis 5.
• the drill rod 12 is capable of being coupled end-to-end with other adjacent drill rods 12 to form a drill string (not shown).
• the length of the drill rod 12 is usually between 3 to 6 m.
• the middle major part of the main length section 14 is usually friction welded to the male end 16 and to the female end 18.
• Figs. 2a-c shows a male end 16 of a drill rod according to a first embodiment of the invention.
• the male end 16 has at its leading end a male thread 17 for connecting to a drill bit 2.
• At the trailing end of the male 16 part of the main length section 14 is located.
• the main length section has a radius Rm.
• the trailing end is usually friction welded to a longer main length section 14 which at its other end is friction welded to a female end 18 to form the entire drill rod 12.
• a flushing channel 7 extends along the entire axial length for providing flushing media to the front of the drill bit 2.
• a shoulder 20 is positioned close to the rear end of the male thread 17. The shoulder 20 transfers percussive energy from the drill rod 12 to the drill bit 2.
• the shoulder has a radius Rs.
• a crushing element 30 Integral with, and at the rear end of the shoulder 20, a crushing element 30 is positioned. Between the shoulder and the peripheral surface of the crushing element 30 a transition surface 22 is positioned. The transition surface 22 smoothly connects the shoulder 20 with the crushing element 30.
• the crushing element 30 is cylindrical in shape and has a peripheral surface that is circular in a cross-section perpendicular to the longitudinal axis 5.
• the central axis of the crushing element 30 is offset from the longitudinal axis 5.
• the peripheral surface of the crushing element has a maximum distance Rc from the longitudinal axis 5. Due to the offset of the central axis of the crushing element 30 in relation to the longitudinal axis 5, this maximum distance Rc is located at a specific location around the circumference of the peripheral surface of the crushing element 30.
• the peripheral surface will be located closer to the longitudinal axis 5. At its smallest distance the peripheral surface has a distance to the longitudinal axis 5 that is approximately equal to the radius Rm of the main length section 14.
• the offset cylindrical crushing element 30 will, during rotation of the drill rod 12, squeeze cuttings between the crushing element 30 and the wall of the drilled borehole, thus crushing the cuttings into smaller pieces. These smaller cuttings can then be efficiently transferred to the exit of the borehole by the flushing media.
• the male end 16 is typically around 290 mm long.
• the radius Rs of the shoulder is typically 42 mm.
• the radius Rm of the main length section is typically 30 mm and the maximum distance Rc of the peripheral surface of the crushing element 30 to the longitudinal axis is typically 40 mm.
• the given numbers are only examples of values that can be used.
• Figs 3a-c shows a male end 16 of a drill rod according to a second embodiment of the invention.
• Most of the features of the second embodiment are identical to the first embodiment and the same reference numerals are used for identical features. Only the differences compared to the first embodiment will be described.
• the crushing element 40 has in this embodiment a radially peripheral surface that is elliptical in cross-section perpendicular to the longitudinal axis 5.
• the center of the elliptical cross-section is offset from the longitudinal axis 5.
• the elliptical shape results in that the crushing element 40 has a more sharp or pointy end compared to having a crushing element 30 with a cylindrical shape and it gets progressively sharper, or more curved, closer to the location where the peripheral surface's maximum distance Rc from the longitudinal axis 5 is located. This is highly efficient for crushing cuttings.
• the elliptical crushing element 40 may have its center coinciding with the longitudinal axis 5. The ellipse will then form two parts that symmetrically extend radially from the longitudinal axis 5.
• Figs 4a-c shows a male end 16 of a drill rod according to a third embodiment of the invention.
• Most of the features of the third embodiment are identical to the first and second embodiment and the same reference numerals are used for identical features. Only the differences compared to the first and second embodiment will be described.
• the crushing element 50 has a radially peripheral surface that slopes towards the longitudinal axis 5 when moving away from the shoulder 20 or moving towards the trailing end of the drill rod 12.
• the peripheral surface slopes in a straight line (as seen in a side view of the drill rod 12) but alternatives where the slope of the surface has a convex or concave shape in a side view is also possible.
• a cross-section of the peripheral surface of the crushing element 50 forms part of a circle and when the surface slopes with a straight line in a side view the crushing element 50 forms a part of a truncated cone.
• a cross-section of the peripheral surface of the crushing element 50 may alternatively form part of an ellipse.
• the crushing element 50 described forms a crushing element with a single protrusion or protuberance.
• the crushing element 50 may also be symmetrical (not shown) around the longitudinal axis 5.

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Citations (5)

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• 2024
  • 2024-06-04 EP EP24179779.4A patent/EP4660418A1/fr active Pending
• 2025
  • 2025-06-02 WO PCT/EP2025/065095 patent/WO2025252624A1/fr active Pending

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