Inline distortion vibration damping mechanism for an oil drilling jig

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to oilfield equipment, and in particular to mitigation of torsional vibration in downhole tools.BACKGROUND

[0002] Conventional drill bits include drag-type drill bits with polycrystalline diamond compact (PDC) inserts and cutters, which use a shearing action to break the material of the formation. Such PDC cutters and inserts are suitable for continuous loading, but are subject to failure under vibration, chatter, and impact forces.

[0003] Accordingly, torsional vibration is a significant concern when drilling using PDC bits. One prevalent cause of torsional vibration is a phenomenon known as "stick-slip." Stick-Slip occurs when the rate of bit rotation suddenly slows or stops, such as when a hard interface or stringer is encountered by the bit. Although the drill bit momentarily slows or stops rotating, the drill string above continues to rotate, causing the drill string to wind up and torsionally store potential energy. This is the "stick" phase of the stick-slip cycle.

[0004] As the drill string winds up, drill string torque increases and drill string length decreases. At some point, either due to the increased drill string torque or decreased drill string length causing the bit to take a lesser bite of the formation, the formation shears and the bit rotates again. Due to the high energy stored in the drill string, the drill bit breaks free violently and over speeds as the drill string unwinds. This is the "slip" phase of the stick-slip cycle.

[0005] Stick-slip causes chatter, repeated impacts of the PDC cutters against the rock face, and drill string oscillation. Stick-slip is typically addressed by either increasing the bit speed or reducing the weight on bit. It is desirable, however, to provide a tool that mitigates torsional vibration without the need to increase the bit speed or reduce the weight on bit.

[0006] WO 2012 / 069858 A2 discloses that a downhole drilling or reaming tool comprises a drive assembly including a reciprocating hydraulically powered drive element arranged in a housing which is fixed to the lower end of a tubing string, for example, a drill string or a casing string.

[0007] US 2011 / 214963 A1 discloses a locking clutch to selectively transmit torque from a stator of a downhole tool to a rotor of the downhole tool.

[0008] US 4,199,201 discloses that an in-hole fluid driven motor has a stator and a rotor to drive a bore hole drilling bit.SUMMARY OF INVENTION

[0009] The invention is set out in the appended set of claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Embodiments are described in detail hereinafter with reference to the accompanying figures, in which: Figure 1 is a block-level schematic diagram of a drilling system, showing a drill string and an inline torsional vibration mitigation system such as that of Figure 2 for drilling a bore in the earth; Figure 2 is a block diagram of an inline torsional vibration mitigation system, showing a drill collar, an overrunning clutch assembly, a torsional dampener, and a bottom hole assembly; Figure 3 is an axial cross section of the overrunning clutch assembly and torsional dampener of Figure 2; Figure 4 is an enlarged exploded diagram in axial cross section of a portion of the overrunning clutch assembly of Figure 3, less its thrust bearing, and a portion of the torsional dampener of Figure 3, both shown with the output shaft removed for clarity; Figure 5 is an elevation in axial cross section of the assembly of Figure 4 illustrating the connection between the overrunning clutch assembly and the torsional dampener, showing an outer clutch housing and inner clutch mandrel of the overrunning clutch assembly and an outer dampener housing and inner dampener mandrel of the torsional dampener; Figure 6 is a perspective view of the bottom end of the overrunning clutch assembly of Figure 4, showing an outer clutch housing having interior asymmetrical serrations, an inner clutch mandrel having outer longitudinal grooves, and wedges positioned therebetween for creating a freewheel effect; Figure 7A is a detailed view of a portion of the overrunning clutch assembly of Figure 6, showing the wedge in an radially outward position engaging the outer clutch housing; Figure 7B is a detailed view of a portion of the overrunning clutch assembly of Figure 6, showing the wedge in a radially inward position disengaged from the outer clutch housing; Figure 8 is a detailed perspective view of a centering guide member of the overrunning clutch assembly of Figure 6; Figure 9 is a detailed perspective view of a wave-shaped spring of the overrunning clutch assembly of Figure 6; Figure 10 is a perspective view of the bottom end of the torsional dampener assembly of Figure 4, showing an outer dampener housing having interior grooves, an inner dampener mandrel having outer longitudinal protrusions, and wiper blades slideably positioned within the protrusions; Figure 11 is a detailed perspective view of the wiper blade of the torsional dampener assembly of Figure 10; Figure 12 is a detailed view of a portion of the torsional dampener assembly of Figure 10, showing the dampener mandrel and housing forming a closed fluid chamber and the wiper blade in an radially outward position engaging the outer circumferential wall of the dampener housing for providing fluidic resistance to relative movement between the dampener mandrel and housing; Figure 13 is a qualitative graph of rotational speed plotted over time, showing rotational speed variations in the bottom hole assembly with and without the tool of Figure 2 in the event of torsional vibration; and Figure 14 is a flow chart illustrating a method of torsional vibration mitigation. DETAILED DESCRIPTION

[0011] The foregoing disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed. Further, spatially relative terms, such as "beneath," "below," "lower," "above," "upper," "uphole," "downhole," "upstream," "downstream," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as being "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" can encompass both an orientation of above and below. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0012] Figure 1 illustrates a drilling system 120 including an inline torsional vibration mitigation system 10. Drilling system 120 may include land drilling rig 122. However, teachings of the present disclosure may be satisfactorily used in association with offshore platforms, semi-submersible, drill ships and any other drilling system satisfactory for forming a wellbore extending through one or more downhole formations.

[0013] Drilling rig 122 and may be located proximate well head 124. Drilling rig 122 also includes rotary table 138, rotary drive motor 140 and other equipment associated with rotation of drill string 132 within wellbore 160. Annulus 166 may be formed between the exterior of drill string 132 and the inside diameter of wellbore 160.

[0014] For some applications drilling rig 122 may also include top drive motor or top drive unit 142. Blow out preventers (not expressly shown) and other equipment associated with drilling a wellbore may also be provided at well head 124. One or more pumps 148 may be used to pump drilling fluid 146 from fluid reservoir or pit 130 to one end of drill string 132 extending from well head 124. Conduit 134 may be used to supply drilling mud from pump 148 to the one end of drilling string 132 extending from well head 124. Conduit 136 may be used to return drilling fluid, formation cuttings and / or downhole debris from the bottom or end 162 of wellbore 160 to fluid reservoir or pit 130. Various types of pipes, tube and / or conduits may be used to form conduits 134 and 136.

[0015] Drill string 132 may extend from well head 124 and may be coupled with a supply of drilling fluid such as pit or reservoir 130. The opposite end of drill string 132 may include bottom hole assembly 190 and rotary drill bit 100 disposed adjacent to end 162 of wellbore 160. Rotary drill bit 100 may include one or more fluid flow passageways with respective nozzles disposed therein. Various types of drilling fluids 146 may be pumped from reservoir 130 through pump 148 and conduit 134 to the end of drill string 132 extending from well head 124. The drilling fluid 146 may flow through a longitudinal bore (not expressly shown) of drill string 132 and exit from nozzles formed in rotary drill bit 100.

[0016] At end 162 of wellbore 160, drilling fluid 146 may mix with formation cuttings and other downhole debris proximate drill bit 100. The drilling fluid will then flow upwardly through annulus 166 to return formation cuttings and other downhole debris to well head 124. Conduit 136 may return the drilling fluid to reservoir 130. Various types of screens, filters and / or centrifuges (not shown) may be provided to remove formation cuttings and other downhole debris prior to returning drilling fluid to pit 130.

[0017] Bottom hole assembly 190 includes an inline torsional vibration mitigation system 10. Bottom hole assembly 190 may also include various other tools 191, such as those that provide logging or measurement data and other information from the bottom of wellbore 160. Measurement data and other information may be communicated from end 162 of wellbore 160 through drill string 132 using known measurement while drilling techniques and converted to electrical signals at well surface 124, to, among other things, monitor the performance of drilling string 132, bottom hole assembly 190 and associated rotary drill bit 100.

[0018] Figure 2 illustrates a block diagram of a rotational vibration mitigation tool 10. Tool 10 is primarily a mechanical tool that does not require any electronics and controls. Tool 10 includes an overrunning clutch assembly 12 and a torsional dampener assembly 14, and it may be connected between a drill string or drill collar 16 and a bottom hole assembly 18.

[0019] Overrunning clutch assembly 12 allows torque transfer from the drill string or drill collar 16 to bottom hole assembly 18 in one direction only. During the "slip" portion of a stick-slip cycle, when the bit has a tendency to over speed, overrunning clutch assembly 12 decouples the bottom hole assembly 18 from the end of the drill string or drill collar 16 to which the overrunning clutch assembly 12 is connected.

[0020] Torsional dampener assembly 14 dampens the rotational impact loads coming from sudden engagement during operation of overrunning clutch assembly 12. Additionally, torsional dampener assembly 14 dampens rotational vibration originating from other sources or mechanisms as well, including vibration transferred by the drill string.

[0021] Figure 3 is an axial cross section of tool 10. The upper end of tool 10 includes an upper clutch housing 20, which connects to drill string or drill collar 16 (Figure 2) in a conventional manner known to routineers in the art, such as by threading. For example, a pin end (not illustrated) may be provided. The lower end of tool 10 may include a box connector 22, for example, for connection to the bottom hole assembly 18 (Figure 2).

[0022] Box connector 22 is formed at the lower end of an output shaft 30, which is in turn rotatively carried by upper clutch housing 20 by a thrust bearing assembly 40 located within overrunning clutch assembly 12. The axial weight on bit is transferred from drill string or drill collar 16 to bottom hole assembly 18 (Figure 2) via upper clutch housing 20, thrust bearing assembly 40, and output shaft 30.

[0023] Referring to Figures 3-7B, overrunning clutch 12 includes a lower clutch housing 24 that is threaded or otherwise connected to the bottom of upper clutch housing 20. As best seen in Figures 6-7B, the interior surface of lower clutch housing 24 has asymmetrically tapered longitudinallyoriented serrations 26 formed therein.

[0024] A generally tubular clutch mandrel 50 is coaxially positioned within lower clutch housing 24. Clutch mandrel 50 is characterized by longitudinal grooves 52 being formed in its outer circumferential surface. Although not necessary, the number of grooves 52 in clutch mandrel 50 preferably corresponds to the number of serrations 26 in lower clutch housing 24.

[0025] Referring to Figures 7-9, in each groove 52, an elongate wedge 54, a spring 56, and two centering guide members 58 are positioned. Spring 56 urges wedge 54 radially outward from clutch mandrel 50. Centering guide members 58 angularly center spring 46 and wedge 54 within groove 52. In an example, spring 56 is a linear wave spring that is compressed easily by wedge 54 so as to minimize wear and tear.

[0026] As illustrated in Figure 7A, during normal drilling operation, lower clutch housing 24 rotates in the direction shown by arrow 55. Wedge 54 of overrunning clutch assembly 12, urged radially outward by spring 56, will always be in contact with the sharply angled portion 27 of serration 26 of lower clutch housing 24 so that the entire drilling torque gets transferred from lower clutch housing 24 to clutch mandrel 50 in the same manner as an ordinary spline drive.

[0027] In a stick-slip condition, torque is transferred in stick phase as drill string 16 (Figure 2) continues to rotate. When the drill bit finally breaks free and drill string unwinding begins, the bottom hole assembly 18 will tend to over-speed due to the stored torsional potential energy in the drill string. If mandrel 50 rotates faster than lower clutch housing 24, as shown by the relative speed vector 57 in Figure 7B, wedge 54 contacts and is forced radially inward by the gentle tapered slope surface 28 of serration 26, compressing spring 56 and thereby allowing serration 26 to slip past wedge 54. In this manner, lower clutch housing 24 is torsionally decoupled from mandrel 50 when mandrel 50 rotates faster than lower clutch housing 24.

[0028] Because of overrunning clutch assembly 12, the bottom hole assembly 18 remains decoupled from surface torque until its speed is reduced by friction, at the bit and stabilizers for example. When the bottom hole assembly speed becomes equal to the speed of the drill string where it connects to the overrunning clutch assembly 12, wedge 54 again engages portion 27 of serration 26, and torque transfer begins again. Persons of ordinary skill in the art will appreciate that the engagement surfaces of the corresponding components may be formed of materials with specific frictional properties to achieve a desired threshold before slip occurs. For example, wedge 54 may be formed of a material with a friction coefficient selected to slip relative to slope 28 upon a particular force or rotational speed. Likewise, springs 56 may be adjusted to achieve the desired frictional engagement between wedge 54 and slope 28.

[0029] In order to minimize impact loading during re-engagement of overrunning clutch 12, torsional dampener assembly 14 is provided. Referring to Figures 3-5 and 10-12, torsional dampener assembly 14 includes a tubular upper dampener housing 60 and a tubular lower dampener housing 62. Lower dampener housing 62 is connected to upper dampener housing 60 via a threaded connection or other suitable means as is known to routineers in the art. Upper dampener housing 60 has an upper end with a reduced diameter that is received within and connected to the lower end of clutch mandrel 50 of overrunning clutch 12, by threads, press-fit, or other suitable means. Accordingly, upper dampener housing 60 and lower dampener housing 62 receive drill string torque during normal drilling but freewheel during over-speed conditions.

[0030] Within upper and lower dampener housing 60, 62, torsional dampener assembly 14 includes a coaxially positioned dampener mandrel 70. The inner wall of lower dampener housing 62 has an number of longitudinal grooves 64 formed therein, and the outer circumferential surface of dampener mandrel 70 includes an equal number of longitudinal protrusions 72 formed thereabout. The protrusions 72 fit and are captured within the grooves 64 like a spline fitting, except that the angular dimension of each protrusion 72 is less than the angular dimension of each groove 64 so that there is an amount of rotational play between dampener mandrel 70 and lower dampener housing 62. That is, the lower dampener housing 62 is capable of limited rotational movement with respect to the dampener mandrel 70. The void between dampener mandrel 70 and grooves 64 define a closed fluid chamber 76. Although not illustrated for clarity, one of ordinary skill in the art understands that the upper and lower ends of fluid chamber 76 is sealed by appropriate structure. Fluid chamber 76 contains a viscous fluid damping of the torsional vibrational energy, as described below.

[0031] With particular reference to Figure 12, within each protrusion 72 on dampener mandrel 70, a radially-oriented longitudinal wiper recess 74 is formed. A wiper blade 78 functions as a flow restrictor and is slideably received within each wiper recess 74 and is urged radially outward by a spring 79 so as to make contact with the outer circumferential surface of groove 64 and thereby obstruct or restrict the free flow of the fluid within groove 64. The viscous fluid must overcome the force of spring 79 to force wiper blade 78 inward in order to pass by the blade to allow dampener mandrel 70 to move relative to lower dampener housing 62. In this manner, torsional dampener assembly 14 provides a damping effect during re-engagement of overrunning clutch assembly 12.

[0032] Referring to Figures 4-6 and 10, the interior circumferential surface of clutch mandrel 50 and dampener mandrel 70 may have an interior profile 34 disposed to engage a complementary raised portion 32 of output shaft 30 (Figure 3). Interior profile 34 and raised portion 32 preferably include flats or splines for transferring torque. In the embodiment shown, raised portion 32 of output shaft mates only with interior profile 34 of torsional dampener assembly 14. Torque is transferred from the drill string or drill collar 16 to the bottom hole assembly 18 via upper clutch housing 20, lower clutch housing 24, wedges 54, clutch mandrel 50, upper dampener housing 60, lower dampener housing 62, dampener mandrel 70 and output shaft 30.

[0033] In an alternative embodiment not falling within the scope of the claimed invention, torsional dampener assembly 14 is not included. In this case, raised portion 32 of output shaft 30 mates with interior profile 34 of overrunning clutch assembly 12. Torque is transferred from the drill string or drill collar 16 to the bottom hole assembly 18 via upper clutch housing 20, lower clutch housing 24, wedges 54, clutch mandrel 50, and output shaft 30.

[0034] Figure 13 is a qualitative graph that illustrates the effect of tool 10. Typically, when a drill string is subject to torsional vibration, the entire string is oscillates rotationally due to an excitation force predominately at a single frequency close to the natural frequency of vibration of the system. Such natural unmitigated response is shown in the upper solid line 80 of Figure 13. With tool 10, the overrunning clutch assembly 12 disengages the bottom hole assembly 18 from the drill string during over-speed conditions. This disengagement results in a sudden change in the system natural frequencies for torsional vibrations and causes a reduction in synchronous excitation due to external forces. Torsional dampener 14 further dampens vibrations. The combined effect of overrunning clutch assembly 12 and torsional dampener 14 upon the natural rotational vibration response 80 is shown by dashed line 82 in Figure 13. That is, Figure 13 shows the rotational speed (RPM) variations in the bottom hole assembly 18 with and without tool 10 with respect to torsional vibration.

[0035] Figure 14 is a flow chart that illustrates a method for mitigating torsional vibration carried out by the tools and system described above. At step 200, a wellbore is drilled by rotating a drill string to rotate a drill bit. During ordinary operation, torque is transferred from the drill string to the drill bit in a first direction. At step 202, upon the occurrence of a predetermined condition, the drill string is dis-engaged or decoupled from the drill bit (or bottom hole assembly, as the case may be). As a result, torque is not transferred from the drill string to the drill bit. That is to say, when the drill bit over-speeds, the drill string is decoupled. The predetermined condition, therefore, is that the rotational speed of the drill bit (or bottom hole assembly) is less than the rotational speed of the drill string. Once the difference between the rotational speed of the drill string and the drill bit falls below a predetermined threshold, the drill sting and the drill bit re-engage.

[0036] At step 204, any impact loads, such as from engagement of the overrunning clutch, is dampened. Specifically, a viscous fluid may be utilized to dampen torsional vibration between the drill string and the drill bit.

Claims

1. A downhole tool (10) for mitigating torsional vibration, comprising: an overrunning clutch assembly (12) arranged for connection between a drill string (16) and a drill bit (100), wherein said overrunning clutch assembly (12) comprises a first member (24) coupled to said drill string (16) and driven by rotation of said drill string (16) in a first direction; and a second member (50) coupled to said drill bit (100), wherein said first member (24) and said second member (50) are configured to engage to allow no relative motion between said first member (24) and said second member (50) and thereby transfer torque from said drill string (16) to said drill bit (100) when said drill string (16) rotates in said first direction, and disengage to allow relative motion between said first member (24) and said second member (50) and thereby prevent transfer of torque from said drill string (16) to said drill bit when said drill string (16) rotates in a second direction opposite said first direction, characterised in that said downhole tool further comprises a torsional dampener assembly (14) coupled to said overrunning clutch (12) assembly, wherein said torsional dampener assembly (14) is configured to dampen engagement of said first member (24) and said second member (50), wherein said torsional dampener assembly (14) comprises a third member (62) coupled to said second member (50), wherein said third member (62) is a tubular dampener housing (62) defining an interior wall with a groove (64) formed therein; a fourth member (70) coupled to said drill bit (100) and driven by rotation of said third member (62) and capable of limited rotational movement with respect to said third member (62), said third member (62) and said fourth member (70) collectively defining a fluid chamber (76) therebetween, wherein said fourth member is a dampener mandrel (70) coaxially disposed within said dampener housing (62) and defining an outer wall with a protrusion (72) formed therein, said protrusion (72) being received in said groove (64); a flow restrictor (78) disposed in said chamber (76); and a fluid received in said chamber (76), wherein said fourth member (70) is configured to move relative to said third member (62) to engage said third member (62) such that torque can be transferred from said drill string (16) to said drill bit (100) when said drill string (16) rotates in said first direction, wherein said relative movement between said fourth member (70) and said third member (62) causes said fluid to move relative to said flow restrictor (78), and said flow restrictor (78) resists movement of said fluid to thereby dampen said relative movement.

2. A downhole tool (10) as claimed in claim 1 further comprising: an output shaft (30) connected to and rotatively driven by said dampener mandrel (70), said output shaft (30) having a lower end adapted for coupling to said drill bit (100); and a thrust bearing (40) coupled between said overrunning clutch (12) assembly and said output shaft (30); wherein said dampener mandrel (70) is tubular, and a portion of said output shaft (30) is coaxially disposed within said dampener mandrel (70).

3. A downhole tool (10) as claimed in claim 1 wherein the first member is a generally tubular clutch housing (24) defining an interior wall with a tapered serration (26) formed therein; the second member is a clutch mandrel (50) coaxially disposed within said clutch housing and defining an outer wall with a groove (52) formed therein; and wherein said overrunning clutch assembly (12) further comprises: a wedge (54) captured within said groove (52) and urged radially outward against said interior wall of said clutch housing (24); wherein said wedge (54) engages said serration (26) to prevent unlimited relative rotation of said clutch housing with respect to said clutch mandrel in the first direction and disengages said serration to allow unlimited relative rotation of said clutch housing with respect to said clutch mandrel (50) in the second direction.

4. A downhole tool (10) as claimed in claim 3, wherein a spring (56) is disposed between said wedge (54) and said groove (64) so as to urge said wedge (54) radially outward against said interior wall of said clutch housing (24).

5. A downhole tool (10) as claimed in claim 1, wherein: said overrunning clutch assembly (12) automatically mechanically engages to transfer torque from said drill string (16) to said drill bit (100) in the first direction of rotation and disengages to prevent transfer of torque from said drill string to said drill bit in the second direction.

6. A method for mitigating downhole torsional vibration, comprising: providing a downhole tool (10) as claimed in any one of claims 1 to 5; connecting said overrunning clutch assembly (12) between a drill string (16) and a drill bit (100); rotating said drill string (16) in a first direction; engaging said overrunning clutch assembly (12) to allow no relative motion between said drill sting (16) and said drill bit so as to transfer torque from said drill string (16) to said drill bit (100); and disengaging said overrunning clutch assembly (12) to allow relative motion between said drill string (16) and said drill bit (100) so long as said drill bit (100) rotates in said first direction faster than said drill string (16) so as to prevent transfer of torque between said drill string (16) and said drill bit (100), the method further comprising: providing said torsional dampener assembly (14) positioned between said overrunning clutch assembly (12) and said drill bit (100); and dampening by said torsional dampener assembly (14) an impact load of said overrunning clutch assembly (12) engaging.

7. A method as claimed in claim 6 further comprising: automatically engaging said overrunning clutch assembly (12) to transfer torque from said drill string (16) to said drill bit (100) when said drill string (12) is urged to rotate faster than said drill bit (100); and automatically disengaging said overrunning clutch assembly (12) to prevent transfer of torque between said drill string (16) and said drill bit (100) when said drill bit (100) is urged to rotate faster than said drill string (16).

8. A drilling system, comprising: a drill string (16) carrying a drill bit (100); and a downhole tool (10) as claimed in any one of claims 1 to 5; the overrunning clutch assembly (12) being connected between said drill string (16) and said drill bit (100), said overrunning clutch assembly (12) engaging to transfer torque from said drill string (16) to said drill bit (100) in said first direction of drill string rotation and disengaging to prevent transfer of torque from said drill string (16) to said drill bit (100) in said second drill string direction of rotation opposite said first direction.