GB2515765A

GB2515765A - Drilling apparatus

Info

Publication number: GB2515765A
Application number: GB1311850.0A
Authority: GB
Inventors: James Julian Blackwell
Original assignee: HIGH MEAD DEVELOPMENTS Ltd
Current assignee: HIGH MEAD DEVELOPMENTS Ltd
Priority date: 2013-07-02
Filing date: 2013-07-02
Publication date: 2015-01-07
Also published as: GB201311850D0

Abstract

A drilling apparatus includes a shaft 21 and a helical flight 22 arranged around the shaft 21. There is an inlet 25 positioned above the flight 22 and an outlet 26 below the flight 22 to allow for flow of fluid. The fluid is used to support and maintain pressure in the bore that is being drilled. A cutter 24 is positioned at the end of the tool. The outlet 26 may have a cover (28, fig 7) which can be opened and closed such that when the bottom of the apparatus is forced against a solid surface the cover (28, fig 7) closes the outlet 26 and where the cover (28, fig 7) falls into an open position when the apparatus is not in contact with a surface thereby causing the outlet 26 to open when the apparatus is lifted from the bore.

Description

DRILLING APPARATUS

[0001] This invention relates to drilling apparatus in the field of rotary bored drilling, in particular but not exclusively to rotary bored drilling in a fluid supported bore.

BACKGROUND

[0002] Bored piling is normally carried out by one of the current well-established techniques, the choice of which is determined by considerations including the available headroom, the stability of the ground being drilled and the depth of the required bore. Brief descriptions of these techniques are provided below.

[0003] Continuous flight auger piling employs an auger with a continuous flight over its full length. The auger is rotated into the ground to the full depth of the required bore and then removed. The depth of bore possible depends on the length of the auger, although in low headroom the auger may be split into several discrete lengths. Further limitations on the depth and diameter of the bore may exist due to the high torque required to drive the auger and overcome the frictional resistance of the entire bore. These limitations may be particularly important if site considerations require the use of relatively small or lightweight plant.

[0004] Rotary bored piling with a Kelly bar employs a telescopically extendible kelly bar to rotate a short length of auger into the ground. Repeated extension of the kelly bar allows a bore to be drilled in discrete lengths. The depth of bore possible is typically limited by the total extended length of the kelly bars. This limitation may be particularly significant where headroom is low and so each individual kelly bar must be quite short. An improvement to this method, disclosed in GB2376248, overcomes this limitation by attaching further kelly bars as the depth of the bore is increased.

[0005] When unstable ground is encountered, it is common practice to install a length of temporary casing to support the unstable ground, to allow free passage of the auger through this zone to prevent the ground collapsing. This limits the depth of bore possible to the depth to which a casing can be installed.

[0006] Where unstable ground is encountered at a depth where it is impractical to install temporary casing, the ground may be supported by drilling support fluid which exerts a fluid pressure on the side of the bore to keep the bore open. The bore is filled with support fluid to a height above the water table, thus ensuring a positive pressure gradient from the inside of the bore to the outside of the bore. This pressure gradient acts to stabilise the bore. Suspended particles in the drilling support fluid seal the walls of the bore to so that the pressure gradient is maintained. Borehole instability may occur if the pressure gradient becomes negative.

[0007] Examples of a drilling support fluid include bentonite and polymer support fluid.

[0008] Where an auger or tool on a kelly bar is used to drill a hole under fluid, it needs to be possible for fluid from above the auger to flow past or through the auger to the underside of the auger, otherwise the auger will act as a piston, lifting the fluid above the auger and creating a negative pressure below the auger, ultimately resulting in loss of borehole stability.

[0009] The passage of fluid through an auger is normally accomplished by the creation of a secondary bypass flight which does not carry spoil but allows fluid to pass through the auger by following a downward spiral flow path along the flight.

[0010] The bypass flight of the auger is of a smaller cross-sectional area than the auger and accordingly the speed of the flow of the fluid through the auger must be faster than the speed at which the auger is moved through the fluid. In addition the path length around is the flight is several times longer than the overall length of the auger.

[0011] Use of a helical bypass flight path means that a significant proportion of the available volume of the auger tool is dedicated to the passage of fluid through the auger, rather than carrying spoil upwards. The faster flow of the fluid in the bypass flight compared with the speed of travel of the auger causes a significant pressure drop as the auger moves through the fluid.

[0012] The high fluid velocity and pressure drop have the potential to cause borehole instability through erosion of the side of the hole or loss of the supporting pressure gradient. To avoid this, the auger must be moved slowly through the fluid, increasing the time taken for each dig.

[0013] For all of the methods mentioned above the time taken to excavate the bore is a primary factor in determining the cost of the piling operation.

[0014] It is an objective of the present invention to address some of the problems described above and to provide a method which reduces the cost of drilling operations.

BRIEF SUMMARY OF THE DISCLOSURE

[0015] According to a first aspect of the present invention, there is provided drilling apparatus for drilling in a fluid supported bore, the apparatus including: a drilling tool having a first shaft and a helical flight arranged around said first shaft, the flight being capable of transporting spoil and maintaining pressure in a fluid-supported bore; coupling means for transmitting a torque to said drilling tool; and a cutting means located at or below a lowermost edge of the tool, the apparatus being characterised in that the tool includes a fluid bypass path located within the first shaft, the fluid bypass path having an inlet located at or above the S top of the helical flight and an outlet located at or below the bottom of the helical flight, the bypass path defining a generally linear path along which drilling fluid can pass downwardly through said central shaft from the inlet to the outlet.

[0016] As a result of the location of the bypass path within the central shaft, the length of the fluid bypass path is the shortest possible distance from the top of the tool to the bottom, with the result that the volume of the tool devoted to the transport of fluid is much reduced compared with an equivalently sized tool with a helical bypass flight. The tool is therefore able to carry proportionally more spoil with each dig.

[0017] The shorter fluid bypass path also reduces the pressure drop over the tool as it is withdrawn from the fluid-filled bore (compared to an equivalently sized tool with a helical bypass flight), allowing the tool to pass through the fluid at a greater speed without creating borehole instability through a loss of the supporting pressure gradient.

Furthermore, the passage of the fluid through a centrally-located bypass path rather than through a path at least partially adjacent the side of the bore, is much less likely to cause borehole instability by eroding the walls of the bore.

[0018] According to a second aspect of the invention there is provided a method of drilling a fluid-supported bore comprising the steps of: providing drilling apparatus as claimed in any of the preceding claims; lowering said tool into a bore containing drilling fluid such that drilling fluid can pass through said fluid bypass path; performing a drilling operation such that spoil is collected in said helical flight; lifting said tool from the bore such that drilling fluid can pass through said fluid bypass path; removing said tool from the bore and removing the spoil therefrom.

[0019] Preferred features of the invention are defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Preferred embodiments of the invention will be described, byway of example only, with reference to the following drawings, in which: Figure 1 is line drawing of a conventional auger for drilling in a fluid supported

bore (PRIOR ART);

Figure 2 is a schematic diagram showing the operation of a conventional auger in

a fluid filled bore (PRIOR ART);

Figure 3 is a side view of an auger according to an embodiment of the present invention; Figure 4 is a top view of the auger of Figure 3; Figure 5 is a cross-sectional view of the auger of Figure 3, on line A-A; Figure 6 shows the operation of the auger of Figure 3; Figure 7 is a cross sectional view of an alternative embodiment of the drilling tool having a closing member; Figure 8 is a top view of the tool of figure 7; Figure 9 is a perspective view of the closing member; Figure 10 is a perspective view of a collar for receiving the closing member; Figure 11 is a perspective view of a tool according to a further embodiment of the present invention; Figure 1 1A is a top view of the tool of Figure 11; Figure 12 shows an adaptor piece for engaging with the tool of Figure 11; Figure 13 is a side view of the tool of Figure 11, shown partly in cross-section, assembled with the adaptor piece and a driving shaft; and Figure 14 is a side view of the tool of Figure 11 with the adaptor piece and drive shaft locked into position.

DETAILED DESCRIPTION

(0021] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0022] Throughout the present application the terms defining orientation or position, e.g. "vertical" or "lowermost", are relative to the orientation of the bore which it is intended to drill with the apparatus. The lowermost end of the apparatus is therefore the end nearest the bottom of the bore, in use. Exemplary embodiments of the invention are described below in which the tool is an auger. The term "auger" is not intended to be limiting and the invention is defined in the appended claims.

[0023] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments.

The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0024] Figures 1 and 2 illustrate a conventional auger with helical bypass flight. The auger 10 has a central shaft 11 on which is arranged a helical flight 12 for carrying spoil and a helical bypass flight 13 for the passage of drilling fluid. A cutting edge 14 is located at the lowermost end of the auger.

[0025] As seen in Figure 2, the bore 15 which is being drilled is filled with drilling fluid 16 such as bentonite to a level above the water table 17. thus ensuring a positive pressure gradient from the inside of the bore to the outside of the bore. This pressure gradient acts to stabilise the bore.

[0026] When the auger 10, attached to a Kelly bar 18, is lifted upwardly (as indicated in Figure 2), spoil contained within the flight 12 is also lifted. In order to avoid the auger acting as a piston in the bore 15, drilling fluid 16 passes downwardly along the helical bypass flight 13 from the top to the bottom of the auger. This technique has the limitations outlined above in the introductory part of this application.

[0027] Figures 3-10 illustrate an improved tool or auger according to one embodiment of the present invention. The tool, which in this case is an auger 20. has a central first shaft 21 on which is arranged a helical flight 22 for carrying spoil but there is no helical bypass flight. A cutting edge 24 is located at the lowermost end of the auger. The auger has an outlet 26 on the lowermost face of the central shaft and an inlet in the form of apertures 25 radially disposed around the central shaft at a location above the helical flight. There are preferably four radially-spaced inlet apertures and one outlet aperture, although other configurations are envisaged, so long as there is at least one inlet aperture and one outlet aperture. The inlet and outlet communicate via an internal bore 27 in the central shaft 21 which forms a drilling fluid bypass path. The bypass path preferably comprises a generally cylindrical volume.

(0028] As seen in figure 6, the bore 15 which is being drilled is filled with drilling fluid 16 such as bentonite to a level above the water table 17, thus ensuring a positive pressure gradient from the inside of the bore 15 to the outside of the bore 15. This pressure gradient acts to stabilise the bore in a similar way to the pressure gradient illustrated by figure 2.

(0029] The auger 20 is attached to a Kelly bar 18 which transmits torque to the auger, in use, so as to drill the bore. When the auger 20, attached to a Kelly bar 18 is lifted upwardly, as indicated in figure 6, spoil contained within flight 22 is also lifted. In order to avoid the auger acting as a piston in the bore 15, drilling fluid 16 passes downwardly through the bypass path 27 in the central shaft of the auger, entering the bypass path through the inlet (upper apertures 25) and exiting through outlet 26, as illustrated in figure 6. This maintains the positive pressure gradient from the inside of the bore 15 to the outside of the bore 15 as the auger is lifted. This mitigates the problems outlined above because the drilling fluid bypass path is a direct, generally linear, route from top to bottom of the auger. The length of the bypass path is typically equal to the height of the auger, although the inlet and outlet apertures need not be exactly located at the top and bottom extremes of the auger so long as they are located above and below, respectively, the helical flight 22.

(0030] The shorter drilling fluid bypass path results in a lower proportion of the volume of the auger being devoted to the passage of drilling fluid, thus increasing the volume of spoil it is possible to remove with each dig.

(0031] The short bypass path also reduces the velocity of the drilling fluid therein and the pressure drop caused by lifting the auger at a given velocity when compared to the conventional auger shown in figure 2. Therefore, the auger shown in figure 6 may be lifted from the bore at a faster rate than the one in figure 2 without causing borehole instability.

This reduces the time needed for each dig.

(0032] The auger may optionally include a closing means located at the outlet of the bypass path, the closing means being capable of allowing drilling fluid to exit and being capable of substantially preventing spoil from entering the bypass path in the central shaft.

[0033] Figures 7 and 8 show a drilling tool having an axially-moveable closing member 28 disposed within outlet aperture 26'. In this embodiment, the inlet apertures 25' comprise four axially oriented apertures positioned on a top surface of the shaft 21'. When the bottom of the tool is forced against a solid surface, such as the bottom of a bore, the closing member 28 is forced axially upwardly into the bypass path so as to plug or block the outlet aperture.

[0034] Further detail of the closing member is shown in Figure 9. The closing member 28 has a plurality of radially arranged fins 210 with gaps between. Near the top of the closing member 28 is an upper ring 211 which joins the fins 210. At the bottom of the closing member 28 is a flange 212 which serves as a closing surface.

[0035] The closing member 28 is attached to the drilling tool by means of a collar 29 which is welded to the shaft 21' at the lowermost region of the tool. The closing member 28 and collar 29 are assembled together so that the collar 29 is located between the upper ring 211 and flange 212. The collar 29 has internal keyways 215 which receive the edges of the fins 210. In use, when the closing member 28 is forced downwardly against a solid surface it is pushed axially upwards, the fins 210 travelling in keyways 215 until closing surface 212 engages the lower surface 216 of collar 29, which acts as an endstop, closing outlet aperture 26'. A fluid-tight seal is not required, but the closing member 28 will close the outlet sufficiently to substantially prevent ingress of spoil.

[0036] When the bottom of the tool is no longer in contact with a solid surface, for example when the tool is being lifted, the closing member 28 drops out of the outlet aperture 26' under its own weight until the bottom surface of upper collar 211 engages the top surface of collar 29. This opens up the outlet for the passage of fluid which can move freely through the gaps between the fins 210.

[0037] Figure 9 also shows the closing member 28 having a conical end section 213 with cutting teeth 214 disposed thereupon.

[0038] As mentioned above, prior art patent GB2376248 describes a novel drilling apparatus having an auger which is liftable over the outside of interlocked Kelly bars and in which at least part of the lifting apparatus is rotatable with the auger.

[0039] Figures 11-14 show how the present invention can be applied to an arrangement of the type disclosed in GB2376248.

[0040] The tool, which in this case is an auger 20', has a central first shaft 21" on which is arranged a helical flight 22' for carrying spoil but there is no helical bypass flight. The auger 20" has, in this case, a dual entry flight wherein there is a dummy flight at the lower end of the auger 20". Moving upwardly from the dummy flight entry, the dummy flight

S

reduces in diameter and tapers out as shown in figures 13 and 14. A similar dummy flight is also shown in figure 7. As will be understood by those skilled in the art, the dummy flight enables the simultaneous use of two cutting edges but is not involved in providing a bypass path for drilling fluid. The auger has an outlet 26" on the lowermost face of the central shaft and an inlet in the form of an opening 25" in the top of the central first shaft 21". The inlet and outlet communicate via a fluid bypass path 27" in the central shaft 21 which is defined between the internal surface of the shaft 21" and the outer surface of a second, hollow inner shaft 32 which receives the drive shaft 30. In the illustrated embodiment, the fluid bypass path 27" comprises three vertically-extending passages, separated by support brackets which attach the inner shaft 32 to the first shaft 21".

(0041] The drive shaft 30 comprises a series of interlocked Kelly bars as described in G82376248. The lowermost Kelly bar (or "tool bar") includes a keyway or keyed region which is adapted to engage a corresponding keyed region or keyway on the interior of inner shaft 32 so as to enable torque to be transmitted to the tool 20", when drilling.

(0042] Figure 12 shows an adaptor piece 40, suitably sized and shaped to be able to cover and close outlet 26" when its upper surface 42 abuts or engages with a lower surface of the tool 20". As with the interior of inner shaft 32, the adaptor piece 40 is also provided with a keyway or keyed region 219 which is adapted to engage the corresponding keyed region or keyway in drive shaft 30. The adaptor piece 40 may also be provided with an arrangement of cutting teeth 41.

(0043] Figure 13 shows the tool 20" assembled with the drive shaft 30 and adaptor piece 40, as it would be lowered into a bore ready for a drilling cycle. As the tool 20" is lowered, drilling fluid is able to pass upwardly through the fluid bypass path 27" from the open outlet 26" (in this case serving as an inlet) to the openings 25" in the top surface of the tool 20".

(0044] When the tool reaches the bottom of the bore, torque is provided to the drive shaft 30, rotating in the digging direction to cause the tool bar, tool 20" and adaptor piece 40 to lock together by means of the internal keyways. Figure 14 shows the tool 20" assembled with the drive shaft 30 and adaptor piece 40, ready for drilling. The adaptor piece 40 is drawn up to be located adjacent the outlet 26" of the bypass path, above the base plate 33 of the lowermost Kelly bar or "tool bar". The diameter of the adaptor piece 40 varies along its length to accommodate the different diameters of the outlet 26" and the tool bar base plate 33. As shown in Figure 14, it can be seen that the adaptor piece 40 substantially closes the outlet 26" so as to reduce ingress of spoil. Further torque applied to drive shaft 30 will be transmitted to both the tool 20" and the adaptor piece 40 by the internal keyways or keyed regions to enable drilling of the bore.

[0045] When it is desired to lift the tool 20' to remove spoil, the drive shaft 30 is rotated in the opposite direction which causes the tool 20", adaptor piece 40 and tool bar to unlock from one another, again via the internal keyways. The tool 20" is then free to be lifted out of the bore, moving over the drive shaft as described, for example in GB2376248.

[0046] As the tool 20" is lifted, the adaptor piece 40 moves downwardly away from outlet 26", permitting drilling fluid to move freely through the bypass path 27" from the inlet openings 25" and out through outlet 26".

[0047] Once the tool 20" reaches the surface, it can be shaken to remove the spoil from the helical flight 22" and then lowered back into the bore to repeat the drilling cycle. 1 C)

Claims

CLAIMS1. Drilling apparatus for drilling in a fluid supported bore, the apparatus including: a drilling tool having a first shaft and a helical flight arranged around said first shaft, the flight being capable of transporting spoil and maintaining pressure in a fluid-supported bore; coupling means for transmitting a torque to said drilling tool; and a culling means located at or below a lowermost edge of the tool, the apparatus being characterised in that the tool includes a fluid bypass path located within the first shaft, the fluid bypass path having an inlet located at or above the Jo top of the helical flight and an outlet located at or below the bottom of the helical flight, the bypass path defining a generally linear path along which drilling fluid can pass downwardly through said central shaft from the inlet to the outlet.
2. The dulling apparatus of claim 1 further compuising a closing means located at the outlet of the bypass path, the closing means being capable of allowing drilling fluid to exit the outlet and being capable of substantially preventing the entry of spoil into the outlet.
3. The drilling apparatus of claim 2 wherein said closing means comprises a closing membeu disposed within the outlet and configured to permit axial movement of the closing member relative to the rest of the tool, said closing member having a closed position in which it closes the outlet, substantially preventing the entry of spoil into the outlet, and an open position in which drilling fluid is able to exit the outlet.
4. The drilling apparatus of claim 3 wherein the closing member is configured to be pushed into the closed position when the tool is forced against a solid surface such as the bottom of a bore and wherein the closing member is configured to fall into the open position under the action of its own weight when the bottom of the tool is not in contact with a solid surface.
5. The drilling apparatus of claim 3 wherein the closing member comprises an adaptor piece configured to be driven into the closed position by the application of torque to said coupling
6. The drilling apparatus of claim 3 or claim 4 wherein at least part of the cutting means is located on the closing member.
7. The drilling apparatus of any preceding claim wherein at least part of the cutting means is located on the lowermost edge of the helical flight.
8. The drilling apparatus of any preceding claim further comprising a second inner shaft for transmitting torque to the drilling tool via the coupling means, the second shaft being located within the first shaft, with the fluid bypass path being defined therebetween.
9. The drilling apparatus of claim 8 further comprising at least one Kelly bar, said kelly bar being interlockable with one or more other kelly bars such that a torque applied to an uppermost kelly bar is transmitted to a lowermost Kelly bar or tool bar.
10. The drilling apparatus of claim 9 wherein the coupling means comprises a keyway or a keyed region located on the interior of said second inner shaft, wherein said keyway or keyed region is configured to receive or be received by a corresponding keyed region or keyway on the lowermost Kelly bar or tool bar.
11. The drilling apparatus of claim 9 or claim 10 further comprising a lifting means for selectively raising or lowering the tool by sliding it over the outer surface of the or each Kelly bar.
12. The drilling apparatus of any preceding claim wherein the fluid bypass path inlet comprises one or more apertures oriented axially with respect to the first shaft.
13. The drilling apparatus of any preceding claim wherein the fluid bypass path inlet comprises one or more transverse apertures oriented radially with respect to the first shaft.
14. The drilling apparatus of any preceding claim wherein the fluid bypass path defines a generally cylindrical volume.
15. A drilling apparatus substantially as described herein with reference to and illustrated in any appropriate combination of figures 3-14.
16. A method of drilling a fluid-supported bore comprising the steps of: providing drilling apparatus as claimed in any of the preceding claims; lowering said tool into a bore containing drilling fluid such that drilling fluid can pass through said fluid bypass path; performing a drilling operation such that spoil is collected in said helical flight; lifting said tool from the bore such that drilling fluid can pass through said fluid bypass path; removing said tool from the bore and removing the spoil therefrom.
17. The method of claim 16 wherein, during said drilling operation, said fluid bypass outlet is substantially closed.
18. A method of drilling a fluid-supported bore substantially as described herein with reference to and as illustrated in any appropriate combination of Figures 3-14.