Patent Application
20090065262
In the following specification the term ‘conical sectional surface’ is deemed to mean a frustum of a generalised cone, the profile of the surface of which intermediate the base of the cone and its vertex may be straight, but may also be a generalised curve and may be continuous or discontinuous.
Conventional drill bits used in subterranean excavation are generally elongate structures with a generally circular cross-section comprising three main parts: First, there is a cutting face which contacts the material to be excavated. This usually comprises a plurality of cutting elements, the movement of which against the material to be cut causes matter to be cut or gouged away. Secondly, there are connecting means, usually located at an opposite end of the bit to the cutting face, for connecting the bit to a source of movement usually a rotary drill string. Thirdly, a so-called gauge region, intermediate the cutting face and connection means, the purpose of which is to contact sides of the hole being drilled in order to stabilise the movement of the bit. The gauge region may be generally free from cutting elements and has a diameter which is of similar size to that of the bore of the hole being drilled. The gauge region may also be provided with channels in its surface to allow cut material and drilling fluid to move away from the cutting face. This may occur as a result of drilling fluid being supplied to the cutting face by separate means, the drilling fluid displacing drilling fluid already present at the cutting face and cut material, causing it to flow through the gauge region channels away from the cutting face. The gauge region may be of generally uniform diameter, particularly if the drill bit is to be used in drilling straight holes. Gauge regions which incorporate a linear taper, i.e. where the diameter of the gauge region is reduced proportional to distance from the cutting face, resulting in a generally frusto-conical gauge region, have also been used.
It is well known to steer a drill bit so that it traces a curved path in a desired direction. In this situation part of the surface of the gauge region may be forced against the wall of the drill hole. This is a major problem, as it not only causes the drill bit to become unstable, but it also causes energy to be wasted in unnecessarily eroding the drill hole wall and/or the said surface of the gauge region. As the surface of the gauge region is also generally free of cutting elements, (but may have a hardened low-wear coating or covering) it means that its impacting with the drill hole wall will cause significant wear.
One method envisaged of overcoming this problem is the use of a drill bit with a curved profile gauge region. However, a drill bit of this type is less effective than a drill bit with a constant gauge cross section when utilised within a straight hole or a straight portion of a hole. This is due to the fact that curved profile of the gauge region will result in a portion of the gauge region not contacting the hole wall and therefore preventing it from stabilising the bit in the normal way.
Thus, a drill bit with a curved profile gauge region and a drill bit with a constant cross section gauge region are suitable for drilling either bent holes or straight holes respectively, but less effective in straight holes or bent holes respectively.
The proposed invention seeks to ameliorate the disadvantages hereinbefore described.
According to the invention there is provided a drill bit suitable, in use, for producing a hole, comprising a main body having an axis about which it is rotated in use; a cutting face, the movement of which, in use, across the surface of the material to be cut causes material to be gouged or scraped away; connecting means for, in use, attaching the bit to a source of rotary motion, said means also enabling the imparting of a force on the bit such that its cutting face is urged onto the material to be cut; a gauge region intermediate said cutting face and said connecting means, said gauge region comprising at least one member movable between a first position in which the gauge region is bounded by an imaginary tubular surface of constant cross-section co-axial to the axis of rotation; and a second position in which a portion of the member is located radially inwards, with respect to the axis of rotation, of its position when said member is in said first position, the gauge region whilst said member is in said second position being bound by an imaginary three dimensional conical sectional surface; and at least one actuator, each said member being mechanically linked to an actuator such that each member can be moved between said first and second positions by a said actuator.
Desirably, said actuator is actuated by a control signal in response to the desired path of the drill bit such that said member occupies said first position whilst the drill bit traces a substantially straight path and said member occupies said second position whilst the drill bit traces a curved path.
Preferably, the profile of said imaginary three-dimensional conical sectional surface is chosen so as to correspond to the curvature of the curved path the drill bit is tracing.
Desirably, the gauge region and in particular at least one movable member is devoid of cutting elements.
Preferably, the cross section of the gauge region with respect to the axis of rotation has a diameter equal to or less than that of the cutting face.
Desirably, said at least one movable member, which may contact the drill hole wall in use, incorporates at least one recess.
Advantageously, said at least one recess is a generally axial channel to allow the passage of cut material away from the cutting face. This prevents the cutting face from becoming clogged with cut material.
Desirably, said at least one member comprises a plurality of fingers disposed upon the main body, said fingers extending parallel to the axis of rotation and being hinged at a first end to the main body.
Preferably, said hinge is disposed intermediate the cutting face and an actuator mechanically linked to the finger.
Desirably, said at least one member comprises a plurality of similar segments disposed upon said main body so as to form a gauge disc co-axial with the axis of rotation.
Advantageously, there is a plurality of gauge discs each comprising a plurality of movable segments, the gauge discs being spaced along the axis of rotation of the drill bit.
Desirably, the means of permitting movement of said segments between first and second positions is a hinge connecting each segment to the main body.
Advantageously, the movement of each segment between said first and second positions is a radial rectilinear movement relative to the axis of rotation of the bit.
Preferably, there are a plurality of actuators and members, each actuator being associated with a member, said actuators operating such that the members move between said first and said second positions in a uniform simultaneous manner.
Advantageously, there are a plurality of actuators and members, each actuator being associated with a member, said actuators operating such that the members move between said first and said second positions in a sequential manner so as to effect a change in drilling direction of the bit.
Desirably, said at least one actuator is a ball screw actuator.
Advantageously, said at least one actuator is a hydraulic actuator and is energised by a supply of drilling fluid.
Advantageously, there are a plurality of actuators, at least one being a ball screw actuator and at least one being a hydraulic actuator.
Preferably, said drill bit additionally comprises a control unit, said control unit regulating said at least one actuator and controlling movement of said at least one member between the first and second positions.
Desirably, said drill bit additionally comprises means of connecting the drill bit to pumping means located remote to the drill bit, management of an output of said pumping means effecting control of the at least one actuator.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
As seen best in
Two kinds of gauge 18 region commonly used in current drill bits 10 include; a gauge region cylindrical about the axis of rotation A-A, of similar diameter to that of the cutting face 12, which is particularly suited to use in applications where it is desired to drill a straight hole; or, for use in steered drilling, where the path of the drill bit is curved, a tapered gauge region 18 where its diameter varies in relation to the distance along the axis of rotation A-A from the cutting face 12. The profile of such a tapered gauge region 18 may be straight and at an angle to the axis of rotation A-A or may be curved. It is common that the diameter of a tapered gauge region 18 decreases as a function of distance from the cutting face 12.
A cylindrical gauge region 18 is desirable for straight drilling as it provides the greatest contact between gauge region 18 and the wall of the hole being drilled. This results in the utmost possible stability of the bit 10 as it rotates in use. A tapered gauge region 18 is preferable for steered drilling as if a cylindrical gauge region 18 were incorporated into a steerable drilling system, then as the bit 10 executes curved paths, a portion of the gauge region 18 may be forced into the drill hole wall. Not only will this cause a waste of energy due to unnecessary friction, but it may also destabilise the bit, causing it to veer. As the gauge region 18 is worn if it is urged into the material which is being cut with any significant force, substantial wear will also occur in these situations, which may result in the bit becoming unusable, well before the cutting face 12 is worn out.
The profile of a tapered gauge region 18 is such that as the bit executes a curved path the gauge region 18 is not urged into the hole wall and as such the bit 10 is not restricted from rotating. However, light contact is still made between the hole wall and the gauge region 18 enabling stabilisation of the bit 10 as it rotates in use. Through a combination of preventing the gauge region 18 from being urged into the hole wall whilst enabling light contact between the hole wall and the gauge region 18, a tapered gauge region results in an increase in steering efficiency whilst drilling curved paths and a reduction in bit 10 generated vibrations. If a tapered gauge bit 10 were to be used in straight drilling it would be at a distinct disadvantage as a large portion of the gauge region 18 would not contact the hole wall and therefore not be able to stabilise the bit 10, as it rotates, in the normal manner.
Whilst drilling a hole it may be necessary to drill a combination of straight and curved sections. At present, if this is the case, either only one type of gauge bit 10 is used, it being suited to either straight or curved drilling and hence being inefficient at the other; or a different drill bit 10 must be used for each section. Swapping the drill bit 10 is a very labour intensive and time consuming process as drilling must be stopped, the drill string must be withdrawn, the bit 10 swapped and the drill string re-inserted into the hole before drilling may continue.
In order to overcome these disadvantages the current invention enables the gauge region 18 of the bit 10 to be changed between a cylindrical gauge region and a tapered gauge region whilst the drill bit 10 is in use. This results in improved drill hole, or wellbore, quality in straight sections without the expense of reduced steering response.
The ability to change between a cylindrical gauge region and a tapered gauge region whilst the drill bit 10 is in use also reduces the risk of the bit 10 sticking within the hole when used in an application such as using impregnated bits, which are typically very long gauge bits run at high speeds by turbines in excess of 500 rpm.
In a first embodiment of the present invention, shown in
Each finger 20, shown clearly in
Each finger 20 may be planar or curved and is generally shaped as a trapezium, with a greater width at the hinge 21 end compared to the end opposite the hinge 21. This is to enable the end opposite the hinge 21 of each finger 20 to sit adjacent one another at the reduced radial distance whilst the actuators are in said first state. If the finger 20 is curved, it may be curved in any direction, but preferably it is curved co-axially to the axis A-A as this minimises the contact of any edges of the finger with the hole wall on rotation of the bit 10.
In a separate embodiment of the present invention the gauge region 18 comprises a plurality of gauge discs 30 spaced along the axis of rotation A-A. As seen best in
As the gauge discs 30 are spaced along the axis A-A of the bit 10, then by altering the diameters of the discs it is possible to change the profile of the gauge region 18 parallel to the axis A-A. For example, the segments 32 of each disc 30 may be positioned by their respective actuators 36 such that the radially outermost surface 38 of each segment 32 of each disc 30 is bounded by an imaginary circle 40 of the same radius as the radius of the cutting face 12. In this way the gauge region 18 is bounded by an imaginary cylindrical surface, the drill bit 10 in this configuration being suitable for drilling straight hole sections.
In a different mode of operation of the bit 10 the segments 32 of each disc 30 are positioned by their respective actuators 36 such that the radially outermost surface 38 of each segment 32 of a first disc 30 is bounded by an imaginary circle 40 of lesser radius than the imaginary circle 40 bounding the radially outermost surface 38 of each segment 32 of a second disc 30 situated intermediate the cutting face 12 and first disc 30. In this mode of operation the gauge discs 30 are bounded by an imaginary conical sectional surface which is tapered and as such the bit 10 in this configuration is suitable for steered drilling, i.e. the drilling of curved hole sections.
Using either embodiment, the profile of the gauge region 18 parallel to the axis A-A may be chosen such that it matches the intended curvature of the drill hole resulting from a change in drilling direction whilst utilising the drill bit as part of a directional drilling system. Such a bit will be particularly efficient at drilling holes of said curvature.
In order to create a particular profile of gauge region 18 parallel to axis A-A the position of each actuator 24, 36 must be co-ordinated. Such co-ordination is provided by a control unit (not shown) which may be part of the bit 10 or located remote to it.
It is also envisaged that the actuators 24, 36 could be operated in a non-uniform or sequential way so as to impart a force in a specific direction to the hole wall as the drill bit rotates. This would allow steering of the drill bit 10 by the movable gauge region 18 members 20, 32. Again, the co-ordination of the actuators 24, 36 may be provided by a control unit which operates as a function of the steering response required and is either part of the bit 10 or remote to it.
The actuators 24, 36 may be of any type, but particular examples which are envisaged are ball screw type actuators and hydraulic actuators. The hydraulic actuators may be energised by drilling fluid or mud which is pumped to the bit 10.
The actuators 24, 36 may also be connected to pumping means (not shown) located remote to the drill bit 12, management of an output of said pumping means effecting control of the actuators. This output management may include cycling the pumping means, whereby the pumping means is turned on and off repetitively, each cycle being responsible for selecting one of a plurality of sequential actuator 24, 36 states. I.e. each cycle of the pumping means selects the next actuator state in the sequence.
It will be appreciated that a number of modifications can be made to the device within the scope of the invention. Examples of such modifications include, but are not limited to, the use of a different number of gauge discs (including just one), the use of a different shaped inner portion of the gauge region, the use of a different cutting face structure, integrating the shaft connection means into the gauge region, the use of different means for connecting the bit to the drive shaft; and the use of actuators which are the only means of connecting the movable gauge region members to the bit, said actuators moving radially relative to the axis A-A in a rectilinear manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0717623.3 | Sep 2007 | GB | national |
