Downhole percussion drilling apparatus

Abstract

A downhole percussion drilling apparatus includes a housing and a piston rotatably supported within an interior bore of the housing. A first engagement surface serves as a cam surface. A second engagement surface serves as a follower surface. The cam surface has a plurality of inclined planes each of which terminates in a drop off. With each rotation of the piston, the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a downhole percussion drilling apparatus

BACKGROUND OF THE INVENTION

[0002] U.S. Pat. No. 5,396,965 (Hall et al 1995) entitled “down-hole mud actuated hammer” and U.S. Pat. No. 5,680,904 (Patterson 1997) entitled “in-the-hole percussion rock drill” both describe downhole percussion drilling apparatus with reciprocating piston hammers which are adapted to moved axially in relation to a housing. The piston hammers are moved by drilling mud pumped down the drill string under high pressure.

SUMMARY OF THE INVENTION

[0003] The present invention relates to an alternative downhole percussion drilling apparatus.

[0004] According to the present invention there is provided a downhole percussion drilling apparatus which includes an elongate tubular housing adapted for insertion down a borehole. The housing has an outer surface and an inner surface which defines an interior bore. A piston is rotatably supported within the interior bore of the housing. The piston has an exterior surface, a first end and a second end. The first end is adapted for connection to a downhole motor assembly that imparts a rotary motion to the piston. The second end is adapted for connection to a drill bit assembly. A first engagement surface is non-rotatably coupled to and projects from the inner surface of the housing into the interior bore. A second engagement surface is non-rotatably coupled to and projects from the exterior surface of the piston into the interior bore. One of the first engagement surface and the second engagement surface serves as a cam surface and the other of the first engagement surface and the second engagement surface serves as a follower surface. The cam surface has a plurality of inclined planes each of which terminates in a drop off. With each rotation of the piston, the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston. Springs are provided within the interior bore between the inner surface of the housing and the outer surface of the piston to maintain the first engagement surface and the second engagement surface engaged during rotation of the piston and allow limited axial travel of the piston relative to the housing during the percussive hammering impacts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:

[0006] FIG. 1 is a side elevation view, in section, of a first embodiment of downhole percussion drilling apparatus constructed in accordance with the teachings of the present invention.

[0007] FIG. 2 is a side elevation view, in section, of the first engagement surface (cam surface) and the second engagement surface (follower surface) of the downhole percussion drilling apparatus illustrated in FIG. 1.

[0008] FIG. 3 is a front elevation view of the first engagement surface (cam surface) of the downhole percussion drilling apparatus illustrated in FIG. 1.

[0009] FIG. 4 is section view taken along section lines A-A of the first engagement surface (cam surface) illustrated in FIG. 3.

[0010] FIG. 5 is section view of the first engagement surface (cam surface) illustrated in FIG. 4 engaged with the second engagement surface (follower surface).

[0011] FIG. 6 is a side elevation view, in section, of an alternative embodiment of downhole percussion drilling apparatus constructed in accordance with the teachings of the present invention.

[0012] FIG. 7a is section view of the first engagement surface (cam surface) illustrated in FIG. 5 engaged with the second engagement surface (follower surface).

[0013] FIG. 7b is section view of the first engagement surface (cam surface) illustrated in FIG. 7a engaged with the second engagement surface (follower surface) as follower surface begins to rise up inclined planes of cam surface.

[0014] FIG. 7c is section view of the first engagement surface (cam surface) illustrated in FIG. 7a engaged with the second engagement surface (follower surface) as follower surface continues to rise up inclined planes of cam surface.

[0015] FIG. 7d is section view of the first engagement surface (cam surface) illustrated in FIG. 7a engaged with the second engagement surface (follower surface) as follower surface begins falls down each of drop offs of cam surface.

[0016] FIG. 7e is section view of the first engagement surface (cam surface) illustrated in FIG. 7a engaged with the second engagement surface (follower surface) where follower surface has fallen down drop offs of cam surface.

[0017] FIG. 8 is a detailed side elevation view, in section, of a hydraulic damper added to shield the off-bottom bearing from hammering impacts.

[0018] FIG. 9 is a detailed side elevation view, in section, of an internal coupling configuration used to turn the hammering action on and off, with the hammer action turned on.

[0019] FIG. 10 is a detailed side elevation view, in section, of an internal coupling configuration used to turn the hammering action on and off, with the hammer action turned off.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The preferred embodiment, a downhole percussion drilling apparatus generally identified by reference numeral 10, will now be described with reference to FIGS. 1 through 5, and FIGS. 7a through 7e. An alternative embodiment, generally identified by reference numeral 100, will be described with reference to FIG. 6.

[0021] Structure and Relationship of Parts:

[0022] Referring to FIG. 1, there is provided a downhole percussion drilling apparatus 10, which includes an elongate tubular housing 12 adapted for insertion down a borehole. For ease of assembly, housing 12 includes a first section 14, a second section 16, a third section 18 and a forth section 20, which are secured together by threaded connections to form housing 12. Housing 12 has an outer surface 22 and an inner surface 24 which defines an interior bore 26. A piston 28 is rotatably supported within interior bore 26 of housing 12. For ease of assembly, piston 28 is formed from a first section 30 and a second section 32. Piston 28 has an exterior surface 34, a first end 36 and a second end 38. First end 36 is adapted for connection to a downhole motor assembly 40 that imparts a rotary motion to piston 28 and second end 38 is adapted for connection to a drill bit assembly (not shown). A first sleeve 39 and a second sleeve 41 are positioned in end to end relation overlying piston 28 within interior bore 26. First sleeve 29 is non-rotatably coupled to inner surface 24 of housing 12 by means of spline 43. Spline 43 is best illustrated in FIG. 2. A first engagement surface or cam surface 42 is positioned at one end 45 of first sleeve 39. Referring to FIG. 1, second sleeve 41 is non-rotatably coupled to exterior surface 34 of piston 28 by means of spline 47. Spline 47 is best illustrated in FIG. 2. A second engagement surface or follower surface 44 is positioned at one end 49 of second sleeve 41.

[0023] Referring to FIG. 3,4 and 5, cam surface 42 has a plurality of inclined planes 50 each terminating in a drop off 52. Referring to FIGS. 7a through 7e, with each rotation of piston 28 illustrated in FIG. 1, follower surface 48 rises up each of inclined planes 50 and then falls down each of drop offs 52 of cam surface 42 thereby imparting a series of percussive hammering impacts to piston 28 illustrated in FIG. 1.

[0024] Referring to FIG. 1, a first set of springs 54 are provided within interior bore 26 between inner surface 24 of housing 12 and exterior surface 34 of piston 28 to maintain follower surface 42 in engagement with cam surface 44 during rotation of piston 28 and allow limited axial travel of piston 28 relative to housing 12 during the percussive hammering impacts. Axial travel of piston 28 is limited to between ⅛ to ⅜ of an inch. A second set of springs 56 provide off bottom loading to thrust bearings 70 when downhole percussion drilling apparatus 10 is placed in tension.

[0025] Radial bearings or bushings 58 are disposed between inner surface 24 of housing 12 and exterior surface 34 of piston 28, thereby transmitting radial loads from piston 28 to housing 12. Sealing assemblies 60 and 62 are provided a first end 36 of piston 128 to limit entry of abrasive drilling fluids. Sealing assemblies 60 and 62 include seals 64 positioned in grooves 66 in sealing elements 68 disposed in interior bore 26. Thrust bearings, generally referenced by numeral 70, are provided to transmit axial thrust loads from piston 28 to housing 12. As previously stated, springs 56 are provided to maintain loading on thrust bearings 70 when the tool is placed in tension.

[0026] A floating piston seal 72 is provided between inner surface 24 of second section 16 of housing 12 and exterior surface 34 of piston 28. Floating piston seal 72 is provided to protect thrust bearings 70 and springs 56 from abrasive drilling fluids. It also serves a pressure balancing function placing lubricants which lubricate thrust bearings 70 under the same the same hydrostatic pressure as fluids external to the tool. For this purpose ports 71 are provided through housing which enable drilling fluids to pass into interior bore 26 to exert pressure upon floating piston seal 72. A seal 74 is also provided between inner surface 24 of housing 12 and exterior surface 34 at second end 38 of piston 28 to prevent entry of debris or abrasive drilling fluids into interior bore 26.

[0027] Lubrication ports 76 are positioned along housing 12, in order to add lubricants after assembly of downhole percussive drilling apparatus 10.

[0028] Operation:

[0029] The use and operation of downhole percussive drilling apparatus 10 will now be described with reference to FIGS. 1 through 7e. Referring to FIG. 1, during drilling operations piston 28 is rotated within housing 12 by downhole motor assembly 40. As piston 28 rotates, springs 54 maintain follower surface 44 engaged with cam surface 42. Referring to FIGS. 7a through 7e, as piston 28 illustrated in FIG. 1, rotates, follower surface 44 alternatively rises up one of inclined planes 50 and then falls down one of drop offs 52 of cam surface 42. Referring to FIG. 1, this imparts a series of percussive hammering impacts to piston 28. The number of percussive impacts per minute that are imparted to piston 28 is determined by the speed at which of piston 28 rotate coupled the number of drop offs 52 on cam surface 42. It is anticipated that piston 28 will rotate within housing 12 at between 90 and 350 rotations per minute. There will be generated approximately 900 percussive impacts per minute with the stroke being approximately ⅛ to ⅜ of an inch.

[0030] Variations: Referring to FIG. 1, in downhole percussive drilling apparatus 10, two sets of springs 54 and 56 were used. First set of springs 54 was used to maintain follower surface 44 engaged with cam surface 42 during rotational movement of piston 28 while allowing piston 28 limited axial movement. Second set of springs 56 was used to allow thrust bearings 70 to withstand axial loading both when in tension and when in compression. Referring to FIG. 6, the purpose of illustrating second embodiment 100 is to demonstrate that these functions can be combined to provide a shorter tool. A shorter tool is, of course, desirable when directional drilling tight radius boreholes.

[0031] Referring to FIG. 6, there is provided second embodiment of downhole percussive drilling apparatus 100 which includes an elongate tubular housing 112 adapted for insertion down a borehole. With second embodiment, housing 112 includes only a first section 114, a second section 116, and a third section 118. Housing 112 has an outer surface 122 and an inner surface 124 which defines an interior bore 126. A piston 128 is rotatably supported within interior bore 126 of housing 112. For ease of assembly, piston 128 is formed from a first section 130 and a second section 132. Piston 128 has an exterior surface 134, a first end 136 and a second end 138. First end 136 is adapted for connection to a downhole motor assembly 140 that imparts a rotary motion to piston 128 and second end 138 is adapted for connection to a drill bit assembly (not shown).

[0032] As with first embodiment 10, second embodiment 100 includes a first sleeve 139 and a second sleeve 141 positioned in end to end relation overlying piston 128 within interior bore 126. First sleeve 129 is non-rotatably coupled to inner surface 124 of housing 112 by means of spline 143. A first engagement surface or cam surface 142 is positioned at one end 145 of first sleeve 139. Second sleeve 141 is non-rotatably coupled to exterior surface 134 of piston 128 by means of spline 147. A second engagement surface or follower surface 144 is positioned at one end 149 of second sleeve 141. Cam surface 142 and follower surface 144 of second embodiment 100 operate in the same manner as with first embodiment 10. A single set of springs 154 are provided within interior bore 126. Springs 154 serve to maintain loading on thrust bearings 170 when the tool is placed in tension. By virtue of the positioning of shoulders 167 and 169, springs 154 also serve to force end 145 of first sleeve 139 engaged with end 149 of second sleeve 141 to maintain follower surface 144 in engagement with cam surface 142 during rotation of piston 128 and allow for limited axial travel of piston 128 relative to housing 112 during the percussive hammering impacts. Radial bearings or bushings 158 are provided to withstand radial loads. Seals 174 are provided between inner surface 124 of housing 112 and exterior surface 134 of piston 128 to limited entry of debris or abrasive drilling fluids into interior bore 126. Lubrication ports 176 are positioned along housing 112, in order to add lubricants after assembly of downhole percussive drilling apparatus 100.

[0033] Features:

[0034] The downhole percussive drilling apparatus, as described above has a number of advantageous features.

[0035] the input power can be produced by a positive displacement progressive cavity air or mud system;

[0036] the axial and radial bearings are oil lubricated, sealed and pressure balanced to prolong bearing life;

[0037] the apparatus is capable of handling higher radial and axial loads than air hammers—without stalling;

[0038] the torque and impacts per minute can be controlled by the operator.

[0039] Best Mode Disclosure:

[0040] Some field testing and commercial exploitation of the invention has now taken place. It was determined that off bottom bearing 70 was experiencing some wear from the hammering action. Referring to FIG. 8, a hydraulic damper, generally identified by reference numeral 200, has now been added to the tool to shield off-bottom bearing 70 from hammering impacts. Springs 56 still are used to provide off bottom loading for off-bottom bearing 70. However, during hammering impacts, hydraulic damper 200 absorbs the hammering impacts to protect off-bottom bearing 70 from wear. The movement which must be absorbed is equal to the axial travel of piston 28 which is between ⅛ to ⅜ of an inch. Hydraulic damper has an inner hydraulic housing 202, an outer hydraulic housing 204 and an hydraulic piston 206. Hydraulic piston has a seal 208 which engages inner hydraulic housing 202 and a seal 210 which engages outer hydraulic housing 204.

[0041] There are a spectrum of rock formations. At one end of the spectrum are hard rock formations. At the other end of the spectrum are soft rock formations. The remaining rock formations fit somewhere in between. During the course of drilling, more than one type of rock formation will be encountered. When drilling through hard rock formations, it is desirable to obtain the maximum hammering impacts the tool is capable of producing. When drilling through soft rock formations, it is better to drill without hammering impacts.

[0042] When drilling through rock formations which are in between soft and hard, it may be desirable to adjust the hammering impact. A mechanism has, therefore, been developed which enables the hammering impact to be reduced in intensity or turned off. Referring to FIG. 10, first engagement surface 42 is carried by housing 12 and second engagement surface 44 is carried by piston 28 (as was previously described). Referring to FIG. 9, springs 56 maintain first engagement surface 42 and second engagement surface 44 engaged, until sufficient bit weight is placed upon the drill string to overcome the biasing force of springs 56 and separate the engagement surfaces. As illustrated in FIG. 9, first engagement surface 42 and second engagement surface 44 remain engaged, indicating that the hammering action remains on. Referring to FIG. 10, first engagement surface 42 and second engagement surface 44 are shown as being separated, so that the hammering action is turned off. The best way to understand how this works is to review a few examples. We will assume for each of the examples, that springs 56 are pushing first engagement surface 42 and second engagement surface 44 together with a force of 10,000 pounds.

EXAMPLE 1

[0043] weight on bit is negligible—therefore, the first engagement surface 42 and the second engagement surface 44 are fully engaged with the hammer impact being 10,000 pounds.

EXAMPLE 2

[0044] weight on bit is 5000 pounds—therefore, the first engagement surface 42 and the second engagement surface 44 are only partially engaged, half of the spring force which provides the hammer impact has been negated, with the remaining hammer impact being 5,000 pounds.

EXAMPLE 3

[0045] weight on bit is 9000 pounds—therefore, the first engagement surface 42 and the second engagement surface 44 are only partially engaged, nine tenths of the spring force which provides the hammer impact has been negated, with the remaining hammer impact being 1,000 pounds.

EXAMPLE 4

[0046] weight on bit is 11,000 pounds—therefore, the first engagement surface 42 and the second engagement surface 44 are fully disengaged, the entire spring force which provides the hammering impact has been negated.

[0047] In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.

[0048] It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the claims.

Claims

1. A downhole percussion drilling apparatus, comprising:

an elongate tubular housing adapted for insertion down a borehole, the housing having an outer surface and an inner surface which defines an interior bore;

a piston rotatably supported within the interior bore of the housing, the piston having an exterior surface, a first end and a second end, the first end being adapted for connection to a downhole motor assembly that imparts a rotary motion to the piston and the second end being adapted for connection to a drill bit assembly;

a first engagement surface non-rotatably coupled to and projecting from the inner surface of the housing into the interior bore;

a second engagement surface non-rotatably coupled to and projecting from the exterior surface of the piston into the interior bore;

one of the first engagement surface and the second engagement surface serving as a cam surface and the other of the first engagement surface and the second engagement surface serving as a follower surface, the cam surface having a plurality of inclined planes each terminating in a drop off such that with each rotation of the piston the follower surface rises up each of the inclined planes and then falls down each of the drop offs of the cam surface thereby imparting a series of percussive hammering impacts to the piston; and

springs within the interior bore between the inner surface of the housing and the outer surface of the piston to maintain the first engagement surface and the second engagement surface engaged during rotation of the piston and allow limited axial travel of the piston relative to the housing during the percussive hammering impacts.

2. The downhole percussion drilling apparatus as defined in claim 1, wherein the biasing force exerted by the springs to maintain the first engagement surface and the second engagement surface engaged, decreases as bit weight increases, thereby allowing the force behind the percussive hammering impacts to be adjusted by altering the bit weight.

3. The downhole percussion drilling apparatus as defined in claim 2, wherein the first engagement surface and the second engagement surface become disengaged the bit weight exceeds the biasing force exerted by the springs to maintain the first engagement surface and the second engagement surface in engagement.

4. The downhole percussion drilling apparatus as defined in claim 1, wherein a first sleeve is positioned in the interior bore which is non-rotatably coupled to the inner surface of the housing, the first engagement surface being carried by the first sleeve; and

a second sleeve is positioned in the interior bore which is non-rotatably coupled to the exterior surface of the piston, the second engagement surface being carried by the second sleeve.

5. The downhole percussion drilling apparatus as defined in claim 1, wherein an off bottom bearing is provided and an hydraulic damper is provided to shield the off bottom bearing from the percussive hammering impacts.