DOWNHOLE TRACTION TOOL AND METHOD OF USE

Abstract

The invention provides a downhole borehole traction apparatus (10) and method of use. The apparatus comprises a body comprising a borehole engaging section wherein the borehole engaging section comprises an outer surface comprising at least one thread. The at least one thread comprises a crest surface (32), a leading surface (30), and a trailing surface (28) having a curvilinear shape. The at least one thread has a low pressure generation means comprising one or more formations.

Claims

1. A downhole borehole traction apparatus comprising: a body comprising a borehole engaging section; wherein the borehole engaging section comprises an outer surface comprising at least one thread wherein the at least one thread comprises; a crest surface; a leading surface; and a trailing surface having a curvilinear shape; wherein the at least one thread has a low pressure generation means comprising one or more formations.

2. The downhole borehole traction apparatus according to claim 1 wherein the crest surface and leading surface form a wellbore traction section configured to engage the inner surface of the borehole.

3. The downhole borehole traction apparatus according to claim 1 wherein the crest surface has a generally curve or flat surface.

4. The downhole borehole traction apparatus according to claim 1 wherein the one or more formations are located upstream of the trailing surface and downstream of the leading surface.

5. The downhole borehole traction apparatus according to claim 1 wherein the one or more formations are located adjacent to the leading surface.

6. The downhole borehole traction apparatus according to claim 1 wherein leading surface and/or the trailing surface has a serpentine cross section.

7. The downhole borehole traction apparatus according to claim 1 wherein the one or more formation is a recess, cavity, pocket, concave or convex portion on the at least one thread.

8. The downhole borehole traction apparatus according to claim 1 wherein leading surface has a direction angle equal to or less than 45 degrees.

9. The downhole borehole traction apparatus according to claim 1 wherein the one or more formation comprises a serpentine or helically orientated shaped recess.

10. The downhole borehole traction apparatus according to claim 1 wherein the threads comprises a helix angle of less than 30 degrees.

11. The downhole borehole traction apparatus according to claim 1 wherein the borehole engaging section comprises an outer surface comprising a plurality of threads forming a threaded profile.

12. The downhole borehole traction apparatus according to claim 1 wherein the borehole engaging section comprises a screw member having a plurality of helical blades.

13. The downhole borehole traction apparatus according to claim 12 wherein the threaded profile is formed on an outer surface of each helical blade of the screw member.

14. The downhole borehole traction apparatus according to claim 1 wherein the borehole engaging section is configured to rotate about a longitudinal axis of the downhole borehole traction apparatus.

15. The downhole borehole traction apparatus according to claim 1 wherein the downhole borehole traction apparatus is connectable to a work string and/or a work string component.

16. The downhole borehole traction apparatus according to claim 1 wherein the downhole borehole traction apparatus is a unitary component.

17. The downhole borehole traction apparatus according to claim 11 wherein the traction profile is incorporated into a range of work string components selected from PDC bit gauge sections, stabilisers and/or collars.

18. The downhole borehole traction apparatus according to claim 1 wherein the downhole borehole traction apparatus is integral with a work string component and the borehole engaging section forms an outer surface of the work string component.

19. The downhole borehole traction apparatus according to claim 1 wherein the crest surface is the maximum outer diameter of the downhole borehole traction apparatus.

20. The downhole borehole traction apparatus according to claim 1 wherein the low pressure means is configured to allow the drill cuttings and debris in the wellbore to be attracted and recirculated.

21. A method of moving a work string in a borehole comprising the steps of: providing at least one downhole borehole traction apparatus comprising: a body comprising a borehole engaging section; wherein the borehole engaging section comprises an outer surface with at least one thread wherein the at least one thread comprises; a crest surface; a leading surface; and a trailing surface having a curvilinear shape; wherein the at least one thread has a low pressure generation means comprising one or more formations; connecting the at least one downhole borehole traction apparatus to a work string; rotating the work string to move the borehole engaging section to engage the inner surface of the borehole to urge the apparatus along the inner surface of the borehole in response to rotation of the body and/or the apparatus.

22. The method according to claim 21 comprising rotating the work string to rotate the borehole engaging section to bear against an inner wall of borehole to create a thrusting action to advance into the borehole in a downhole direction.

23. The method according to claim 21 comprising rotating the work string to rotate the borehole engaging section such that the at least one thread transfers weight on bit.

24. The method according to claim 21 comprising connecting and/or arranging more than one downhole borehole traction apparatus to a work string.

25. A downhole work string component comprising the downhole borehole traction apparatus according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0174] There will now be described, by way of example only, various embodiments of the invention with reference to the following drawings (like reference numerals referring to like features) in which:

[0175] FIG. 1A is a perspective view of a downhole traction apparatus module in accordance with an embodiment of the invention;

[0176] FIG. 1B is an enlarged longitudinal cross section of the threads of the helix section of FIG. 1A;

[0177] FIG. 10 is a developed elevation view of a thread configuration of the helix sections of the downhole traction apparatus module of FIG. 1A;

[0178] FIG. 1D is an enlarged profile view of two adjacent blades of the helix section of FIGS. 1A and 1B;

[0179] FIG. 1E is a schematic end view of the downhole traction apparatus module located on a work string in a wellbore.

[0180] FIG. 2 shows a side view of a work string component with four downhole traction apparatus modules of FIG. 1A connected;

[0181] FIG. 3A shows a perspective view of a downhole traction apparatus module in accordance with an embodiment of the invention;

[0182] FIG. 3B is an enlarged profile view of two blades on the helix section of FIG. 3A;

[0183] FIG. 3C is a developed elevation view of the thread of the four blades in the helix section of FIG. 3A; and

[0184] FIG. 4 is a side view of a work string component with three downhole traction apparatus modules of FIG. 3A integrated in to a drill sting;

[0185] FIGS. 5A and 5B are side and end views of a stabiliser showing the traction profile zones on the blades on the stabiliser;

[0186] FIG. 5C shows an enlarged profile view of two threads of the traction profile of FIGS. 5A;

[0187] FIG. 6 is a developed elevation view of a traction profile zones on the blades of the work string stabilizer in FIGS. 5A and 5B; and

[0188] FIG. 7 is an enlarged side view a downhole traction apparatus module of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0189] FIG. 1A shows a first embodiment of a downhole traction apparatus module 10 in the form of a sub 12. The sub 12 has a generally cylindrical body 13 provided with suitable threaded couplings at each end to allow it to be connected to a work string.

[0190] In this example the coupling is a standard API certified pin connection 14 and box screw threaded connection 16 at either end to enable the sub 12 to be included in a work string (not shown) such as a drill string (not shown).

[0191] Although in this example the downhole traction apparatus module is described as being connectable to a work string such as a drill string it will be appreciated that it could be integrated into a work string component. It will also be appreciated that multiple downhole traction apparatus modules may be connected on the same work string or drill string.

[0192] In-use the pin connection 14 is located at the vertically lower most end such that the pin connection 14 is positioned closest to the drill bit (not shown) and the box connection 16 is positioned closest to the surface. In alternative embodiments the box connection may be the vertically lower most end.

[0193] In this example, the sub 12 is advanced into the borehole 18 in the direction of arrow “A” as shown in FIG. 1A and the direction of the drilling mud and cutting flow in the annulus towards the surface as indicated by arrow “B” in FIG. 1A. As shown in FIG. 1E the sub 12 lies on low side 19a of the wellbore annulus due to gravity. Depending on the dimensions of the annulus and the sub, there may be an annulus space 19c on the high side 19b of the annulus 19.

[0194] The sub 12 has a wellbore engaging section 20 which has a generally cylindrical core 21 with an outer surface 22 with a thread profile 24 which acts a traction profile. In this example the thread profile is formed from a plurality of helical blades 26 located on the outer surface 22. The blades 26 may be fixed to or integral with the outer surface 22.

[0195] The threaded profile has a plurality of threads 27 which extend in a helical form along the length of the surface 22. In this example shown in FIG. 1A, four blades 26a, 26b, 26c and 26d are arranged on the wellbore engaging section forming four threads 27a, 27b, 27c and 27d. The threads 27 have a selected thread height, axial pitch, and a profile which enables the screw to engage the formation without scarring or digging into the formation.

[0196] FIG. 1B shows an enlarged longitudinal cross-section of three adjacent blades in the wellbore engaging section 20. The profiles of the three blade threads 27a, 27b and 27c are shown.

[0197] Each of the threads 27a, 27b, 27c is asymmetrical with a leading surface 30a, 30b, 30c, a trailing surface 28a, 28b, 28c, a crest surface 32a, 32b and 32c and a thread root 34a, 34b, 34c respectively. Each of the threads are parallel along the helix angle direction “H”. The leading surface 30a, 30b and 30c is the surface of the thread which first makes contact with the bore wall. The leading surface and trailing surface are asymmetric opposing curvilinear surfaces which flank the crest surface.

[0198] As best shown in FIG. 1D, each leading surface 30b and 30c has a first thread zone 40b, 40c and a second thread zone 42b, 42c. The first thread zone 40b, 40c has a surface which extends from the thread root 34b, 34c in a radially concave curvilinear shape to a tangent point 44 where the first thread zone meets and transitions into the second thread zone 42b, 42c where the outer surface of the leading surface 30b and 30c has a convex curvilinear shape.

[0199] The leading surface 30b, 30c has a leading angle of less than 70 degrees to the vertical shown as “L” in FIG. 1D. The trailing surface has a trailing angle “T” greater than the leading angle which results in a gentle sloping leading surface to assist in the low friction passage of the sub in the wellbore and a greater inclined leading surface to assist in the high efficiency traction of the crest surface and the generation of thrust force “F” as the sub in rotation around longitudinal axis “C” (shown in FIG. 1A).

[0200] In this example the leading angle is approximately 45 degrees. However, in certain embodiments the lead angle may range from between 30 to 80 degrees.

[0201] The crest surface 32b and 32c is generally a flat curvilinear shape to prevent the crest surface of the blade from cutting into or scaring the mud cake of the inner surface 18a of the borehole 18. The shape of the crest surface provides contact pressure distribution control. It will be appreciated that the crest surface may have other shapes including a convex shape for optimised pressure contact distribution. The shape of the crest surface provides controlled pressure distribution between the traction apparatus and the bore wall.

[0202] The blade crest surface 32b, 32b is the outer most diameter of the blades and the sub 12. The crest surface 32b, 32c is provided with a relatively hard facing material such as steel to be hard wearing to increase the life of the blades and therefore the sub 10.

[0203] As best shown in FIG. 1D, the crest surface 32b, 32c has a downstream tangential point “DT” where the second thread zone 42b, 42c meets and transitions into the crest surface 32b, 32c. The curve of the downstream tangential point has a tangential radius “RD”. The crest surface 32b, 32c has an upstream tangential point “UT” where the crest surface 32b, 32c meets and transitions into the trailing surface 28b, 28c. The curve of the upstream tangential point has a tangential radius “RU”. The tangential radius “RD” is generally lower than the tangential radius “RU”.

[0204] The trailing surface 28b, 28c consists of a third thread zone 50b, 50c and a fourth zone 52b, 52c. The surface of the third thread zone 50b, 50c extends from the upstream tangential point “UT” in a radially convex curvilinear shape to a tangent point 54 where the third thread zone 50b, 50c meets and transitions into the fourth thread zone 52b, 52c. The fourth thread zone 52b, 52c has a surface which extends from the tangent point 54 in a radially concave curvilinear shape to the thread root 34b, 34c.

[0205] Between each of the blade threads 27b, 27c is a thread groove 60 having a groove width “G”. The groove 60 is formed from the trailing surface of a first blade thread and the leading surface of an adjacent blade. The groove 60 extends from the upstream tangential “UT” point of one blade to the downstream tangential “DT” point of an adjacent blade. In use, the leading surfaces and crest surfaces of the threads form a wellbore traction section which bears against the surface of the wellbore. During rotation of the sub 12 a combination of forces is generated between wellbore traction section and the formation which encourages the sub 12 grip the formation and move the sub in the wellbore. As the sub 12 is rotated about its longitudinal axis “C” shown in FIG. 1A, the blades engage the inner surface 18a of the wellbore providing traction and resulting in a thrust force acting on the sub 12 in direction “F” shown in FIG. 1A. The thrust force moves the sub 12 and connected work string moving further downhole in direction “A” shown in FIG. 1A. If the work string is a drill string the thrust force provides weight on bit. It will be appreciated that reversal of the rotation direction may result in a thrust force in an opposing direction to direction “F”.

[0206] The blades have a helix pitch “P”, a lead “L” and a helix angle “α” as best shown in FIGS. 10 and 1D. The size of the helix angle α of the thread is determined by the outer diameter of the screw thread, the thread pitch and the thread height.

[0207] The helix angle in this example is 20 degrees to provide a gentle helix and prevent the screw from digging into the surrounding wellbore. It will be appreciated that the helix angle may range from 5 to 40 degrees. Preferably the helix angle is less than 30 degrees thus generating a maximum axial traction force

[0208] The combination of different convex and concave surfaces of the leading surface and the trailing surfaces creates a high pressure zone 62 and a low pressure zone 64 in each of the grooves 60 when fluid flow moves in direction Q over and/or through the grooves 60. The sudden and drastic increase in the axisymmetric mud flow passage over the convex and concave surfaces of the leading surface and the trailing surfaces creates the high pressure zone 62 and a low pressure zone 64 in each of the grooves 60.

[0209] In this example the Archimedes screw is a right-hand screw (same direction as Ω) with right hand blades forming right hand flow channel. Alternatively the Archimedes screw may be a left-hand screw with left hand blades forming left hand flow channels.

[0210] FIG. 2 shows a work string section 100 with four traction modules 112 in the form of subs 112. The traction module subs 112 are similar to the sub 12 described in FIGS. 1A to 1E above and will be understood from the above description of FIGS. 1A to 1E. Each of the traction modules 112 has a generally cylindrical body 113 provided with suitable threaded couplings to allow it to be connected to the work string 111. The sub 112 has a wellbore engaging section 120 which has a generally cylindrical core with an outer surface with a thread profile 124 formed from a plurality of helical blades 126 located on the outer surface 122. The blades 126 may be fixed to or integral with the outer surface 122.

[0211] Although in the above examples the modules are described as being threadedly connectable to the drill string or work string component, they may alternatively or additionally be integral with the drill string or a drill string component. Additional or alternatively the wellbore engaging section 120 may be integral with the drill string, a drill string component or a surface of drill string component thereof. In this example, the sub 112 is therefore advanced into a bore in the direction of arrow “A” as shown in FIG. 2.

[0212] The outer diameter wellbore engaging section 120 is preferably arranged to be the greatest diameter or at least equal to the greatest diameter of any other component included in the work string, such that the outer surface of the wellbore engaging section is the larger outer diameter of the whole of the work string to make contact with the inner surface of the borehole.

[0213] As the sub 112 is rotated from surface in the rotational direction shown as Ω in FIG. 2 about its longitudinal axis “C” (rotated at the surface in the clockwise direction) the blades engage the inner surface of the bore wall in an wellbore traction zone which includes the crest surface and the leading surface providing traction and resulting in a thrust force acting on each sub 12 in direction “F” shown in FIG. 2. The thrust force moves the sub 112 and connected work string 111 further downhole in direction “A” shown in FIG. 2. FIG. 3A shows a traction sub apparatus module 200 according to an embodiment of the invention. The sub module 200 is similar to the sub module 12 described in FIGS. 1A to 1E above and will be understood from the above description of FIGS. 1A to 1E. However the leading surface of the sub apparatus module in FIG. 3A comprises a recessed cavity or pocket on the leading surface to assist in the creation of a low pressure zone in the groove adjacent to leading surface to entrain and recirculate debris from the low side 19a of the wellbore annulus to the high side 19b of the annulus 19.

[0214] The sub 200 has a generally cylindrical body 213 provided with suitable threaded couplings to allow it to be connected to a drill string. In this example the coupling is a standard API certified pin connection 214 and box screw threaded connection 216 at either end to enable the sub 200 to be included in a drill string (not shown) such as a drill string (not shown).

[0215] In-use the pin connection 214 is located at the vertically lower most end such that the pin connection 214 is positioned closest to the drill bit (not shown) and the box connection 216 is positioned closest to the surface. In alternative embodiments the box connection may be the vertically lower most end nearest the drill bit (not shown) and the box connection 216 is positioned closest to the surface.

[0216] In the example, the sub 200 is therefore advanced and pushed into the borehole 218 in the direction of arrow “A” as shown in FIG. 3A and the direction of the drilling mud and cutting flow in the annulus towards the surface as indicated by arrow “B” in FIG. 3A.

[0217] The sub 212 has a wellbore engaging section 220 which has a generally cylindrical core 221 with an outer surface 222 with threaded profile 224 formed from a plurality of helical blades 226 located on the outer surface 222. The blades 226 may be fixed to or integral with the outer surface 222.

[0218] The blades 226 form threads 227 which extend in a helical form along the length of the surface 222. In the example shown in FIG. 3A, four blades 226a, 226b, 226c, 226d are arranged in a helical threaded arrangement on the wellbore engaging section forming four threads 227a, 227b, 227c, 227d. The threads 27 have a selected thread height, axial pitch, and a profile which enables the screw to engage the formation without scarring or digging into the formation.

[0219] FIG. 3B shows an enlarged axial cross-section of two adjacent blades 226b and 226c in the wellbore engaging section 220. The profiles of the two blade threads 227b and 227c are shown.

[0220] Each of the blade threads 227b, 227c are non-axisymmetrical with a leading surface 230b, 230c, a trailing surface 228b, 228c, a crest surface 232b, 232c and a thread root 234b, 234c respectively. All design elements follow the same helix angle α.

[0221] The leading surface 230b, 230c is the surface of the blade thread which first makes contact with the bore wall as the work string rotates. The leading surface and trailing surface are asymmetric opposing curvilinear surfaces which flank the crest surface.

[0222] As best shown in FIG. 3C, each leading surface 230b, 230c has a first thread zone 240b, 240c and a second thread zone 242b, 242c. The first thread zone 240a has a surface which extends from the thread root 234b, 234c in a radially concave curvilinear shape to a tangent point 244 where the first thread zone meets and transitions into the second thread zone 242b, 242c where the outer surface of the leading surface 230b and 230c has a convex curvilinear shape.

[0223] The concave curvilinear shape of the first thread zone 240b, 240c forms a recessed cavity 270 adjacent to the thread root 234b, 234c. The recessed cavity creates a zone of low pressure 264 as flow passes over the crest surface and blade trailing surface in the groove 260 followed by a sudden increase in groove flow passage.

[0224] The leading surface 230b, 230c has a leading angle of less than 45 degrees to the vertical shown as “L” in FIG. 1D. The trailing surface has a trailing angle “T” greater than the leading angle which results in a gentle sloping leading surface to assist in the low friction passage of the sub in the wellbore and a greater inclined leading surface to assist in the high efficiency traction of the crest surface and leading surface and the generation of thrust force “F” as the sub in rotation around longitudinal axis “C”.

[0225] In this example the leading angle is from 45 degrees. However, in certain embodiments the lead angle may range from between 10 to 80 degrees.

[0226] The crest surface 232b and 232c is generally a flat curvilinear shape to prevent the crest surface of the blade from cutting into or scaring the mud cake of the inner surface 218a of the borehole 218. The shape of the crest surface provides contact pressure distribution control. It will be appreciated that the crest surface may have other shapes including convex or quadratic shapes to secure adequate tangential radius at contact surface between thread crest and bore wall.

[0227] The blade crest surface 232b and 232b is the outer most diameter of the blades and the sub 212. The crest surface 232b and 232c is provided with a relatively hard facing material such as steel to be hard wearing to increase the life of the blades and therefore the sub 200. The crest surface is provided with hard materials directly on the apparatus body The crest surface 232b, 232c has an downstream tangential point “DT” where the second zone 242b, 242c meets and transitions into the crest surface 232b, 232c. The curve of the downstream tangential point has a tangential radius “RD”. The crest surface 232b, 232c has an upstream tangential point “UT” where the crest surface 232b, 232c meets and transitions into the trailing surface 228b, 228c. The curve of the upstream tangential point has a tangential radius “RU”. The tangential radius “RD” is generally lower than the tangential radius “RU”.

[0228] The trailing surface 228b, 228c consisting of a third thread zone 250b, 250c and a fourth thread zone 252b, 252c. The surface of the third thread zone 250b, 250c extends from the upstream tangential point “UT” in a radially convex curvilinear shape to a tangent point 254 where the third thread zone 250b, 250c meets and transitions into the fourth thread zone 252b, 252c. The fourth thread zone 252a has a surface which extends from the tangent point 254 in a radially concave curvilinear shape to the thread root 234b, 234c In other words the trailing surface 228b, 228c has a tapering or curvilinear convex contour shaped outer surface and which tapers from a first diameter D1 near the crest surface to a second diameter D2 near the thread root 234b, 234c.

[0229] Between each of the blade threads 227b, 227c is a thread groove 260 having a groove width “G”. The groove 260 is formed from the trailing surface of one blade thread and the leading surface of an adjacent blade. The groove 260 extends from the upstream tangential “UT” point of one blade to the downstream tangential “DT” point of an adjacent blade.

[0230] In other words, the leading surface 230b, 230c rapidly narrows or tapers in its outer diameter between the maximum outer diameter D3 at a first end of the blade leading surface to a narrower outer diameter D4, where the angle of the transition portion of the outer surface the crest surface curves very sharply forming a shoulder 272. The crest surface curves sharply from being parallel with the longitudinal axis of the apparatus 200 to being substantially perpendicular or deeply inclined to the longitudinal axis of the apparatus forming the shoulder 272.

[0231] The blade leading surface 230b, 230c then leads into a substantially rectilinear portion which forms the recessed cavity 270. The recessed cavity comprises an inclined surface 274 which can be considered to be inclined at a negative angle with respect to the direction of arrow B of FIG. 3B. The inclined surface 274 continues to curve from being substantially perpendicular to the longitudinal axis “C” of the sub 200 to be inclined at a negative angle in the region of 45 degrees to the perpendicular (with respect to the longitudinal axis “C).

[0232] The inclined angle surface 274 has a substantial or majority of its length at an angle of around negative 45 degrees to the perpendicular in a direction “B” with respect to the radially outwards pointing direction and so can be considered around a 45 degrees back angle.

[0233] The angle of the inclined surface 274 between the substantially parallel (with respect to the longitudinal axis “C”) outer surface of the crest surface and inclined surface is around 45 degrees.

[0234] The inclined surface 274 then leads into a lower leading surface which sharply curves back around through the perpendicular such that it heads back in the downstream direction. The lower leading surface has the majority of its outer surface lying at a positive angle of between 60 and 30 degrees to the perpendicular with respect to the longitudinal axis “C” of the sub 200 in an upstream direction (shown as “B” in FIG. 3b) with reference to the radially outwards pointing direction. Thus the leading surface has a serpentine cross section.

[0235] The outer diameter of the recessed cavity 270 on each blade changes very rapidly in a relatively short longitudinal length of the sub 200 and indeed due to the negative back angle, a pocket of low pressure is formed when flow passes over the recessed cavity. The low pressure is produced by a sudden and drastic increase in the flow passage.

[0236] The recessed cavity is therefore comprised of a combination of rectilinear (particularly the inclined surface 274 and curvilinear portions (particularly the first end of the blade leading which forms shoulder 272), and it is this geometry that enable the generation of an area of low pressure at the recessed cavity. The recessed cavity comprises an axisymmetric cavity which causes a low pressure is produced by a sudden and drastic increase in the axisymmetric flow passage. The recessed cavity comprises a serpentine or helically orientated shaped recess.

[0237] In use, the leading surfaces and crest surfaces of the threads form a wellbore traction section which bears against the surface of the wellbore. During rotation of the sub 212 a combination of forces are generated between wellbore traction section and the formation which encourages the sub 212 move in a downhole direction. As the sub 212 is rotated about its longitudinal axis “C” shown in FIG. 3A, the blades engage the inner surface 318a of the wellbore providing traction and resulting in a thrust force acting on the sub 312 in direction “F” shown in FIG. 1A. The thrust force moves the sub 312 and connected work string moving further downhole in direction “A” shown in FIG. 3A. If the work string is a drill string the thrust force provides weight on bit.

[0238] Fluid flow over the threads 227 and through the grooves 260 passes over the recessed cavity 270 which creates an low pressure zone 264 which attracts drill cuttings coming from the upstream cutting action and debris and drill cuttings on the low side 19a of the borehole 318 to be stirred and recirculated within the recessed cavity and the low pressure area.

[0239] Downstream of the recessed cavity the flow passes from the leading surface of the blades past the thread root and along the gradually tapering outer surface of trailing surface of the blades.

[0240] Drill cuttings suspended in and carried by drilling mud will flow along flow path 280 from the upstream end of the sub 200, around the crest surface of each blade and within the groove 260 of each blade, turbulently displaced or moved and therefore recirculated within the low pressure area created by the recessed cavity 270 and along the trailing face of the adjacent blade. In addition, drill cuttings that are already sedimented on a bed on the lower surface of the wellbore may be recirculated by the low pressure zone created by the recessed cavity 270 and scooped into the groove 260 between the blades and along the trailing face of the adjacent blade. In addition this cutting recirculation effect is enhanced and energised by the Archimedean screw effect, thus providing a powerful conveyor belt effect.

[0241] The blades have a helix pitch “P”, a lead “L” and a helix angle “Q” as best shown in FIG. 3C. The helix angle is preferably less than 30 degrees to provide a gentle helix and prevent the screw from digging into the surrounding wellbore.

[0242] FIG. 4 shows a drill string section 300 with tool joints 308 and three traction subs 312. FIG. 7 shows an enlarged view of one of the three traction subs 312. The traction sub modules 312 are similar to the sub 200 described in FIGS. 3A to 3C above and will be understood from the above description of FIGS. 3A to 3C. Each of the traction subs 312 has a generally cylindrical body 313 provided with suitable threaded couplings to allow it to be connected to the work string 311. In this example, as best shown in FIG. 7 each traction sub has seven blades 326. It will be appreciated the traction sub may have more or less than seven blades.

[0243] In use the drill string section 300 with three traction subs 312 is advanced into a bore in the direction of arrow “A” as shown in FIG. 4. As drill string 300 is rotated from surface in the rotational direction omega (Ω) about its longitudinal axis “C” (rotated at the surface in the clockwise direction) the blades 326 of the wellbore engaging section 320 of each sub 312 engage the inner surface of the bore wall providing traction and resulting in a thrust force acting on each sub 312 in direction “F” shown in FIG. 4. The thrust force moves the drill string section 300 and sub 312 and connected drill string 311 further downhole in direction “A” shown in FIG. 4.

[0244] As the drill bit (not shown) penetrates further downhole drilling mud flowing in the annulus in the direction “B” flows along the grooves between the blades in the Archimedes screw in the wellbore engaging section 320 of each sub. Fluid flow through the grooves 360 promotes movement of any drill cuttings resting on the low side of the annulus or flowing in the direction “B”.

[0245] The low pressure area created by the recessed cavity 370 on each of the blade threads attracts drill cuttings coming from the upstream cutting action and debris and drill cuttings on the low side of the borehole 318 and so will cause the drill cutting bed to be stirred, recirculated and directed through the grooves 260 to the high size of the borehole 318.

[0246] FIGS. 5A and 5B shows a stabiliser 400 with a generally cylindrical body 413 with suitable threaded couplings to allow it to be connected to a work string. In this example the coupling is a standard API certified pin connection 414 and box screw threaded connection 416 at either end to enable the sub 400 to be included in a work string (not shown) such as a drill string (not shown).

[0247] In-use the pin connection 414 is located at the vertically lower most end such that the pin connection 414 is positioned closest to the drill bit (not shown) and the box connection 416 is positioned closest to the surface. In alternative embodiments the box connection may be the vertically lower most end nearest the drill bit (not shown) and the box connection 416 is positioned closest to the surface.

[0248] The three equi-spaced blades 426a, 426b, 426c are peripherally mounted on the stabiliser body 413. The blades extend along the axial length of the body 413 in a helical configuration.

[0249] As best shown in FIG. 5C the outer edge surfaces 429 of the blades 426 has a threaded profile 424 formed from a plurality of threads 427. The threaded profile acts as a traction profile and bears against the inner wall of borehole to create a thrusting action to advance into the borehole in the downhole direction shown as arrow “A” in FIG. 5C and/or provide an enhanced weight on bit transfer.

[0250] As shown in FIG. 5C each of the blade threads 427a, 427b is asymmetrical with a leading surface 430a, 430b; a trailing surface 428a, 428b a crest surface 432a, 432b and a thread root 434a, 434b respectively. Each of the threads have a low pressure zone created by a recessed cavity 470.

[0251] The threaded profile 424 is similar to the threaded profiles 24, 124, 224 in FIGS. 1A to 3C and will be understood from the descriptions of FIGS. 1A to 3C.

[0252] FIG. 6 shows a developed elevation view of four helical threads 427a, 427b, 427c and 427d on the outer surface of the stabilizer blades 426a, 426b, 426c. The threads 427a, 427b, 427c and 427d have a selected thread height, axial pitch, and a profile which enables the stabiliser blades to engage the formation and provide a thrusting action.

[0253] The four helical threads are never parallel with the stabilizer blades 426a, 426b, 426c. The helix angle α of the four helical threads 427a, 427b, 427c and 427d is much smaller than the inclination angle β of the stabilizer blades 426a, 426b, 426c.

[0254] The thread profile (traction profile) including the crest surfaces and leading surfaces are made of hard materials or coated with hard materials and may act as stabilizer blade surface hard facing.

[0255] By providing a threaded profile with a general curvilinear geometry in combination with fluid bearing effect the rotational and axial stabilizer friction factors will drastically decrease reducing all static and dynamic loadings.

[0256] It will be appreciated that the traction profile may be incorporate into a range of work string component including PDC bit gauge sections and collars.

[0257] Although in the above examples the thread profile is formed from a plurality of blades it will be appreciated that the thread profile may be formed from a plurality of channels, grooves, ribs, ridges etc on a section of a work string component.

[0258] Although in the above embodiments the recessed cavity is described as being formed from an inclined surface having negative angle. It will be appreciated that the inclined surface could be modified to not actually require a negative back angle and instead the inclined surface could continue to be a positive angle of around 45 degrees because that may still provide some recirculation of drill cuttings in the drill cuttings bed but it is likely that it would not be as effective as the negative back angle of inclined surface as shown in FIG. 3A.

[0259] The invention provides a downhole borehole traction apparatus and method of use. The apparatus comprises a body comprising a borehole engaging section wherein the borehole engaging section comprises an outer surface comprising at least one thread. The at least one thread comprises a crest surface, a leading surface, and a trailing surface having a curvilinear shape. The at least one thread has a low pressure generation means comprising one or more formations.

[0260] The invention provides downhole traction apparatus which comprises a screw member having at least one helical blade for contacting the inner surface of the borehole. The least one helical blade comprises a helix angle of less than 30 degrees. The screw member is configured to engage the bore wall and generate thrust to displace the apparatus in a general downhole direction when the screw member is rotated.

[0261] The present invention in its various aspects provides an improved downhole traction apparatus and method of use. The invention provides a robust and reliable downhole traction tool which can provide a downhole traction force with low friction against the bore wall to mitigate damage to the bore wall with enhanced efficiency.

[0262] The invention also provides a downhole traction tool which can simultaneously provide traction to grip the wellbore traction and move drill cuttings settled on the lower side of the borehole thereby reducing the risk of loss of traction and the risk of drill string whirl.

[0263] The present invention may allow complete control over the movement of a downhole tool or equipment in a wellbore. The apparatus provides the operator with reliable control over the downhole movement of the apparatus by providing a traction apparatus capable of gripping and applying a traction force on the wellbore and clearing debris that may interfere with the ability to grip the wellbore The rotational movement required to grip and transport the apparatus in the wellbore is the same movement required to clear and/or recirculate the debris on a surface of the wellbore.

[0264] Throughout the specification, unless the context demands otherwise, the terms ‘comprise’ or ‘include’, or variations such as ‘comprises’ or ‘comprising’, ‘includes’ or ‘including’ will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[0265] Furthermore, relative terms such as, “lower”, “upper, “up”, “down”, “above”, “below”, “downstream”, “upstream” and the like are used herein to indicate directions and locations as they apply to the appended drawings and will not be construed as limiting the invention and features thereof to particular arrangements or orientations.

[0266] The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended.