GB2442303A

GB2442303A - Direction adjustment tool for downhole drilling apparatus

Info

Publication number: GB2442303A
Application number: GB0716856A
Authority: GB
Inventors: Rory Mccrae Tulloch
Original assignee: Geolink
Current assignee: Geolink
Priority date: 2006-09-26
Filing date: 2007-08-30
Publication date: 2008-04-02
Anticipated expiration: 2027-08-30
Also published as: GB0618880D0; GB2442303B; WO2008037947A1; GB0716856D0

Abstract

A direction drilling adjusting tool (102), such as a bent sub, comprises a first housing part (116), and a second housing part (118) which selectively pivots relative to the first housing part. A first actuator (162) moves relative to the first housing part between a first position and a second position to cause pivoting of the second housing part. A second actuator (146) additionally moves relative to the first housing part in response to a pressure differential between drilling fluid inside and outside of the housing between at a first position and a second position allowing the first actuator to move to the second position. The tool is therefore controlled more easily and reliably than by means of pressure drop generated within the tool housing.

Description

DIRECTION ADJUSTMENT TOOL FOR DOWNHOLE DRILLING APPARATUS

The present invention relates to direction adjustment tools for downhole drilling apparatus, and relates particularly, but not exclusively, to direction adjustment tools known as adjustable bent housings, to be fitted in a downhole mud motor (e.g. with Moineau power section), drilling apparatus and, to a lesser extent, to adjustable bent subs, to be fitted above a dowrihole mud motor drilling apparatus, for forming part of a down hole drill string for adjusting the direction of drilling. The downhole mud motor could also alternatively consist of a turbo drill or a vane motor or electro drill motor.

Downhole drilling apparatus are known, and it was for many years the case that in order to adjust the direction of drilling of a drill bit of the apparatus, it was necessary to retrieve the drilling apparatus from the hole, carry out the angular adjustment, and replace the tool in the hole, if a greater rate of direction change was required.

An attempt to provide a remotely operable direction adjustment tool operable while the drilling apparatus is dowrihole is disclosed in WO 98/31915, and is shown with reference to Figure 1. The apparatus 2 has an upper part including an inserting part 4 which is connected via an adjusting organ 6 to a lower part 8 to enable the lower part 8 to pivot relative to the upper part. A shaft 10 having widened portions 12, 14, 16 is arranged in the housing, which is provided with a constriction 18 surrounding the shaft 10. Adjustment of the orientation of the lower part 8 relative to the upper part (and therefore adjustment of the direction of drilling of the drilling apparatus incorporating the tool 2) is achieved by increasing the rate of flow of drilling fluid through the tool to locate constriction 18 around widened portion 14.

This causes the hydraulic force acting on piston parts 20, 22 to overcome the force of spring 24 so that piston parts 20,22, and therefore adjusting organ 6, move downstream to cause angular adjustment of lower part 8 relative to inserting part 4.

However, the arrangement shown in WO 98/31915 and in Figure 1 suffers from the drawback that the range of viscosity and density of drilling fluid used with the tool can fluctuate widely, as a result of which accurately calculating pressure drops in the tool before a job is. very difficult, so the required pressure drop is difficult to control. As a result, it is difficult to control operation of the tool sufficiently to ensure angular adjustment when intended or avoid angular adjustment when not intended. The pressure signal changes are also difficult to detect at the surface.

Preferred embodiments of the present invention seek to

overcome the above disadvantages of the prior art.

According to the present invention, there is provided a direction adjusting tool for a downhole drilling apparatus, the tool comprising:-a housing adapted to be incorporated into a drilling apparatus, in which drilling fluid flows from a location upstream of the tool to a drill bit downstream of the tool via an interior of said housing, and flows from the drill bit along an external surface of the housing, the housing having a first housing part, and a second housing part selectively pivotable relative to the first housing part between a first position thereof, in which the drilling apparatus drills along a first drilling direction, and at least one second position thereof, in which the drilling apparatus drills along a respective second drilling direction, different from said first driLling direction; a first actuator mechanism including a first actuator adapted to be moved relative to said first housing part between a first position thereof and at least one second position thereof to cause pivoting of said second housing part relative to said first housing part between said first position of said second housing part and a respective said second position of said second housing part; and a second actuator mechanism including a second actuator adapted to be moved relative to said first housing part, by means of pressure difference between drilling fluid inside said housing and outside said housing, between at least one first position thereof in which said first actuator is maintained in the first position thereof, and at least one second position in which said first actuator is caused to move to a respective second position thereof.

By providing a second actuator adapted to be moved relative to said first housing part by means of pressure difference between drilling fluid inside said housing and outside said housing, this provides the advantage of enabling the apparatus to be controlled significantly more easily and reliably than by means of pressure drop generated within the tool housing, since the pressure difference between the interior and exterior of the housing is easier to determine, both by calculation and by clownhole measurement, and is normally much larger in magnitude than 200psi.

The tool of the present invention also has the advantage over the arrangement of WO 98/31915 that the present invention does not require the use of a shaft inside a constrictor ring. As a result, the tool could be operated as a remotely adjustable bent sub run above a motor power section, since only the internal to external pressure drop is required to activate the tool, as opposed to pressure pulses within the tool. Since a universal joint or flexible shaft is generally only mounted between a mud motor rotor/stator and output shaft, and no such joint or shaft is needed above the motor power section, the present invention can therefore be operated above the power section.

Furthermore, because the tool of the present invention is activated by means of the existing drill bit pressure drop, this provides the advantage that the total system pressure does not need to be increased, as is necessary in the arrangement of WO 98/31915, from the additional dynamic head pressure drop as the drilling fluid flow passes through the annular gap between the constrictor ring and the universal centre shaft. No additional pressure drop therefore needs to be generated. Also, by avoiding the use of a constrictor ring over a universal centre shaft, the distance from the drill bit to the offset bend of the tool of the present invention can be made shorter than that of the arrangement of WO 98/31915.

S

In one embodiment, the second actuator includes at least one continuous track, and the second actuator mechanism includes at least one pin adapted to engage a respective said track to control movement of said second actuator between at least one said first position thereof and at least one said second position thereof by means of pressure difference between drilling fluid inside said housing and outside said housing.

By providing at least one pin adapted to engage a respective said track to control movement of said second actuator between said first position thereof and at least one said second position thereof, this provides the advantage of enabling the apparatus to be operated by simply switching on and off of pumping of the drilling fluid, and enables varying angular displacements of the first and second housing parts relative to each other to be selected by means of different profiles of the continuous track.

At least one said continuous track may include at least one respective first track portion adapted to be engaged by a said pin when the second actuator is in a respective said second position thereof.

At least one said continuous track may include at least one respective second track portion adapted to be engaged by a said pin when the second actuator is in a respective said first position thereof.

The tool may further comprise at least one first biasing device for biasing said second actuator towards at least one said first position thereof.

This provides the advantage of ensuring that the pins travel along the continuous track as the pumping of the drilling fluid is switched on and off.

At least one said continuous track may include at least one respective third track portion adapted to be engaged by a said pin such that reduction of fluid pressure difference between drilling fluid inside and outside of said housing causes movement of said pin relative to the track from at least one first or second track portion to a respective third track portion, and increase of fluid pressure difference between drilling fluid inside and outside of said housing causes movement of said pin relative to the track from at least one third track portion to a respective first or second track portion.

This provides the advantage of ensuring that the pin moves along the track in a single direction, which in turn enables the tool to be controlled simply by switching pumping of drilling fluid on or off.

The tool may further comprise at least one second biasing device for biasing the first actuator towards the first position thereof.

The tool may further comprise at least one first detent pin for releasably retaining the first actuator in the first position thereof.

This provides the advantage of preventing unintended movement of the apparatus out of its straight drilling mode, for example as a result of axial vibrations.

The tool may further comprise at least one first retaining device for limiting movement of said first actuator beyond at least one said second position thereof.

This provides the advantage of minimising excessive movement of the first actuator, for example as a result of axial vibrations in the apparatus.

At least one said first retaining device may comprise at least one respective second detent pin.

The tool may further comprise at least one second retaining device for opposing movement of said first actuator away from at least one said second position thereof.

This provides the advantage of enabling the apparatus to be locked in its bent drilling mode.

At least one said second retaining device may be adapted to restrict movement of first actuator relative to said second actuator.

This provides the advantage of simplifying construction of the tool.

Said second housing part may be located downstream of said first housing part in the direction of flow of drilling fluid to the drill bit.

This provides the advantage of locating the pivot axis of the first and second housing parts relative to each other closer to the drill bit, which maximises the effect of any angular adjustment during drilling. This also provides the advantage of minimising the effect of restriction of the interior of the housing by the radially offset member.

The first actuator mechanism may include an actuator member radially offset from a longitudinal axis of the tool and connected to said second housing part, and a sliding member arranged between said actuator member and said first actuator.

The tool may further comprise drive means in said housing for transmitting torque from a motor upstream of the tool to a drill bit downstream of the tool.

The drive means may include a flexible shaft.

In one embodiment, the flexible shaft passes through the actuator member and is provided with a male taper drive at each of its ends.

The drive means may include a respective universal joint adjacent each of its ends.

The tool may further comprise at least one locking ring for preventing separation of the first housing part from the second housing part, wherein at least one said locking ring comprises a plurality of locking members adapted to be abutted by said first housing part and mounted by means of pins to said first housing part.

The or each said pin may have a respective threaded shank portion for mounting to a respective said locking member.

This provides the advantage of enabling the locking ring to be assembled more easily and with less machining accuracy necessary for the locking members. The fact that the ring segments are retained in the grooves of the housing by a threaded pin means also that they can not be shaken out of position by the vibration from the motor power section or from the action of the drill bit.

The tool may further comprise indicator means for indicating whether the second housing part is in the first position thereof or at least one said second position thereof.

The indicator means may include at least one nozzle adapted to communicate between the interior and the exterior of the housing when the second housing part is in at least one said second position thereof.

The tool may further comprise at least one diffuser member for diffusing flow of drilling fluid through a respective said nozzle.

The indicator means may include at least one hole for allowing fluid leakage and a flow restrictor sleeve outside of at least one said hole.

The tool may further comprise at least one oil reservoir for accommodating lubricating oil, wherein at least one said oil reservoir contains a respective piston and biasing device for causing oil in said oil reservoir to have a higher pressure than the exterior of the oil reservoir.

An embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:-Figure 1 shows an existing direction adjustment tool for use in a downhole drilling apparatus; Figure 2A is a cross-sectional side view of a first part of an adjustable bent housing embodying the present invention in straight drilling mode with flow of drilling fluid turned off; Figure 3A is a cross-sectional side view of a second part of the adjustable bent housing of Figure 2A in straight drilling mode with flow of drilling fluid turned off; Figure 4A is a cross-sectional side view of a third part of the adjustable bent housing of Figure 2A in straight drilling mode with flow of drilling fluid turned off; Figure 5A is a cross-sectional side view of a fourth part of the adjustable bent housing of Figure 2A in straight drilling mode with flow of drilling fluid turned off; Figures 2B to 5B are views corresponding to Figures 2A to 5A respectively with the adjustable bent housing in straight drilling mode with flow of drilling fluid turned on; Figures 2C to 5C are views corresponding to Figures 2A to 5A respectively with the adjustable bent housing in offset/bent drilling mode with flow of drilling fluid turned on, in alternate sequence with respect to Figures 2B to 5B; Figures 6A to 6C are enlarged views of a control pin assembly of the tool part of Figures 4A to 4C respectively, radially offset from the pins shown in Figures 4A to 4C; Figures 7A to 70 are enlarged views of a detent pin assembly of the tool part of Figures 4A to 4C respectively, radially offset from the pins shown in Figures 4A to 4C; and Figure 8 is an opened out view of the tracking on the control ring of the apparatus of Figures 2 to 5.

Referring to Figures 2A to 5A, an adjustable bent housing 102 for forming part of a downhole drilling string is connected at its upstream end to a rotor-stator power section 104 of a downhole motor such as a moineau mud motor having a housing connector 106 and a rotor coupling 108.

The tool 102 is shown in the straight drilling mode with the flow of drilling mud switched off, and is connected at its downstream end to a housing connector 110 containing an output shaft coupling 112 leading to a motor output shaft assembly, to which a drill bit (not shown) is attached.

The tool 102 has a housing 114 having a first housing part comprising a female housing 116 and a second housing part comprising a male housing 118, part of which is inserted into the female housing 116 so that the male housing 118 can pivot relative to the female housing 116 about a pivot axis 120, the operation of which will be described in greater detail below. Rotary power is transmitted through the tool 102 from the Moineau rotor-stator power section 104 to the drill bit by means of a flexible shaft 122, which is connected to the rotor coupling 108 and to the output shaft coupling 112 by means of respective taper drives 124, 126 at its ends. Alternatively, a double universal joint assembly could be used with an extended centre shaft between the two joints.

An upper activation sleeve 128 is slidably mounted within the female housing 116 via seals 130, 132 and an anti-rotation guide pin 134, and is urged downwardly (i.e. in the direction of arrow A in Figure 3A) relative to the female housing 116 by means of an activation return spring 136 acting on a thrust bearing assembly 138 and a bearing nut 140. It has been found that the anti-rotation guide pin 134 can also be omitted. The activation return spring 136 is located in a chamber 142 communicating via small vents 144 in the female housing 116 with drilling fluid outside of the housing 114 at lower pressure than drilling fluid inside the housing 114.

Sliding of the upper activation sleeve 128 relative to the female housing 116 is controlled by means of a rotating control ring 146 which has a continuous track 148 (Figure 8) defining first, second and third track portions 150, 152, 154, respectively, the purpose of which will be described in greater detail below, and is mounted to the female housing 116 by means of three guide pins 156 mounted to the female housing 116 and engaging the continuous track 148 and two rows of ball bearings 158, 160 at its respective axial ends.

A lower activation sleeve 162 is slidably mounted within the female housing 116, and the upper part of the lower activation sleeve 162 is slidably mounted around the upper activation sleeve 128 by means of a pair of pins 164 in respective slots 166 of the lower activation sleeve 162, so that limited sliding movement of the lower activation sleeve 162 relative to the upper activation sleeve 128 is possible.

A telescopic joint spring 168 urges the lower activation sleeve 162 downwardly (i.e. in the direction of arrow A in Figure 3A) relative to the upper activation sleeve 128 and acts between the upper activation sleeve 128 at its upper end, and a coil spring retainer ring 170 at its lower end mounted to the lower activation sleeve 162 on a shoulder and retained by a circlip 172. A primary lubricating oil reservoir is formed by a primary reservoir sleeve 174 mounted via 0-rings 176, 178 to the internal surface of the lower activation sleeve 162, and a primary reservoir inner sleeve 180 defines a chamber in which a primary reservoir piston 182 is located and is urged downwardly by a primary reservoir coil spring 184 connected between the retainer ring 170 and the piston 182.

The primary oil reservoir lubricates (a) the areas of relative sliding between the upper 128 and lower 162 activation sleeves, i.e. the telescopic joint between the two, (b) the region of sliding of the lower activation sleeve 162 relative to the female housing 116, (c) the short region below the seal 132 on the upper activation sleeve 128 sliding relative to the female housing 116 (while the rotating control ring 146, the main activation sleeve return spring 136, thrust bearing 138 and two sets of ball bearings 158, 160 work in drilling mud), and (d) a sliding ring 206 which needs to rotate slightly inside two bearing rings 207 which each have a part-spherical internal surface.

This primary oil reservoir must move or change shape as the relative movements set out in (a) to (d) above occur, and must also accommodate a volume increase of the oil as a result of an increase in temperature of the lubricating oil as the tool 102 is run in a hole. The downhole pressure can also cause the reservoir volume to contract if air bubbles have been left in the oil reservoir at assembly of the tool 102. The piston 182 must be able to move in both the upward and downward directions at all times. The coil spring 184 acts on the piston 182 to maintain a small positive pressure to the main oil reservoir. The oil is filled via two inch NPT ports 183 in the female housing 116 near to its upper end. Two adjacent ports 185 (Figures 5A to 5C) are used to fill a secondary oil reservoir, as will be described in greater detail below.

As shown in greater detail in Figures 6A to 6C, further upward movement of the lower activation sleeve 162 relative to the female housing 116 when the tool 102 is bent and the flow of drilling fluid is on is limited by means of two control pins 190 mounted to the female housing 116 and sliding in a slot 192 in the lower activation sleeve 162. The control pins 190 are angularly offset from the pins 164 mounted to the upper activation sleeve 128, and the lower activation sleeve 162 is releasably retained in position relative to the female housing 116 by means of two detent pins 194 (Figures 7A to 7C) which are urged by means of a spring 196 into a recess, hole or turned groove 198 in the upper part of the lower activation sleeve 162.

Referring to Figures 4A to 4C and 5A to 5C, the male housing 118 has an angularly offset upper end 202 which carries a male housing sleeve 204, which slidably supports a cylindrical surface of a sliding ring 206, having a part spherical surface which slidably engages two sliding ring bearing rings 207 forming an internal spherical surface located on an internal surface of the lower activation sleeve 162 between the primary reservoir sleeve 174 and a corner ring 209 such that upward displacement of the lower activation sleeve 162 causes the sliding ring 206 to slide towards the distal end of the angularly offset upper end 202. The male housing 118 supports a joint shoulder ring 208, which has a part spherical surface slidably engaging a part spherical surface 210 on the lower end of the female housing 116. In this way, pivoting of the male housing 118 about pivot centre 120 relative to the female housing 116 is possible as the sliding ring 206 moves along the male housing sleeve 204.

P secondary oil reservoir is also provided in order to provide lubrication to a hinging spline connection 212 sealed between 0-rings 214, 216 on joint shoulder ring 208 and an o ring 218, 220 on joint compensation ring 222 and male housing 118 respectively. The secondary oil reservoir is separated from the primary oil reservoir and is pressure and temperature compensated by means of a spring-loaded piston 224. Oil is supplied via the two NPT plugged ports by means of a vacuum pump, in a similar manner to the primary oil reservoir. The secondary oil reservoir is larger in volume than the primary oil reservoir and only covers the spline connection 212 and the areas immediately adjacent to the spline connection 212, i.e. a joint pull ring formed by split rings 226 and a joint lock ring formed by split rings 228.

The joint pull ring 226 and joint lock ring 228 keep the female housing 116 and male housing 118 together when axial tension is applied to the tool 102, while the a joint thrust ring formed by split rings 230 acts as an axial compression shoulder for the male and female housings 118, 116 to hinge around more freely than on the spherical shoulder face 210.

The joint lock ring 228 consists of four segments held by means of cap screws 232 which thread into tappings in the centre of each segment of the lock ring 228. Each cap screw 232 has an unthreaded head 240 and a threaded shank 242. This provides the advantage of pulling and retaining the segments 228 tight into the grooves into which they are located, thus preventing axial vibration from causing the segments 228 to jump out of the grooves. The rings and pins are easier and quicker to assemble and with less machining accuracy than is necessary with the arrangement of Wa 98/31915, since the split rings 228 do not need to be parted off to a precise size and there is no need for more than one set of pins 232, as opposed to the arrangement of WO 98/31915, in which more than one size of pin is required in order to provide the necessary tight fit for the segment rings. Rings 230 and 226 are also split rings. The two halves of ring 226 are held together with dowel pins.

The tool 102 is also provided with a pressure indicator (not shown) to provide an indication at the surface that the tool 102 is in the bent drilling mode. A pressure drop will occur during operation of the tool 102 when the lower activation sleeve 162 lifts, since it exposes one or more nozzles 234 set in the side wall of the female housing 116. The size of the nozzles 234 can be chosen such that when matched with the drill bit nozzles (not shown) the total system pressure decreases by 200 to 300 psi when the bypass of some of the total flow rate out of the side nozzles 234 occurs instead of going through the drill bit nozzles. A diffuser shield 236 surrounding the nozzles rninimises any tendency of drilling fluid passing through the nozzle to undesirably enlarge the drilling hole in which the tool 102 is located. Alternatively, the pressure drop indicator could be removed by fitting blank nozzles in the ports of the female housing 116. An alternative would also be for the ports not to be fitted with nozzles and a flow restrictor sleeve to be fitted in place of the diffuser shield 236.

The operation of the tool 102 will now be described.

In the position shown in Figures 2A to 7A, the male housing 118 is oriented relative to the female housing 116 so as to enable the drilling string of which the tool 102 forms a part to drill straight ahead. When pumping of the drilling fluid is switched on, drilling fluid flows downwards (i.e. in the direction of arrow A in Figure 3A) in the interior of housing 114 to the drill bit (not shown), and upwards from the drill bit along the external surface of the housing 114.

Because of the pressure drop across the drill bit, the drilling fluid inside of the housing 114 is at a higher pressure than the drilling fluid outside of the housing 114. This pressure difference acts on the upper activation sleeve 128, which is moved upwardly relative to the female housing 116 against the action of the activation return spring 136, which in turn causes the rotating control ring 146 to move upwards relative to the female housing 116 to the position shown in Figure 4B. As a result of the upward movement of the control ring 146, the three circumferentially equispaced guide pins 156 move from the third track portion 154 in which it is located along the continuous track 148 on control ring 146, causing the control ring 146 to rotate relative to the female housing 116, until it is located at one of the second track portions 152. In this position, no further upward movement of the control ring 146 relative to the female housing 116 is possible. As a result of the upward movement of the control ring 116, the two pins 164 move from the bottom to the top of the slot 166 in the lower activation sleeve 162, but do not cause any upward movement of the lower activation sleeve 162. Since no upward movement of the lower activation sleeve 162 occurs, the male housing 118 retains its orientation relative to the female housing 116, and the drilling apparatus incorporating the tool 102 is maintained in the straight drilling mode. The two spring-loaded detent pin assemblies 194, 196, 198, together with the coil spring 168, prevent the lower activation sleeve 162 from moving upwards relative to the upper activation sleeve 128.

In order to adjust the direction of drilling of the drill string, the drilling fluid pump is first deactivated, as a result of which the pressure inside the housing 114 reduces, and the upper activation sleeve 162 is urged downwards by the activation return spring 136. This causes the control ring 146 to be urged downwardly relative to the female housing 116, as a result of which the three guide pins 156 move to one of the third track portions 154 in the track 148 on the control ring 146. When the pumping of the drilling fluid is started again, the pressure difference between the interior and the exterior of the housing 114 becomes sufficient to overcome the force of the activation return spring 136, and the upper activation sleeve 162 and control ring 146 are moved upwards relative to the female housing 116. As a result, the three guide pins 156 are displaced further along the track 148 and, because of thenon-symmetrical shape of the track 148, the three guide pins 156 are urged into engagement with one of the first track portions 150. When the control pins 156 are located in one of the first track portions 150, further upward movement of the control ring 146 and upper actuation sleeve 162 relative to the female housing 116 is possible because of the length of the slot forming the first track portion 150. As a result, the control ring 146 moves to the position shown in Figure 4C, and at the same time, the two pins 164 engage the upper end of the slot 166 in the lower activation sleeve 162, as a result of which the upper activation sleeve 128 moves the lower activation sleeve 162 upwards relative to the female housing 116 to cause the sliding ring 206 to slide upwards along the male housing sleeve 204 to angularly deflect the male housing 118 relative to the female housing 116 by an angle determined by the length of the slot 150 on the control ring 146.

The resistance of the two detent pins 194 and coil spring 168 must be overcome in order to allow the lower activation sleeve 162 to move upwards. When the guide pins 156 of Figures 4A to 4C and 8 are located in one of the first track portions 150, the lower activation sleeve 162 is prevented from moving upwards any more than is required by means of pins 190 which have moved from the top to the bottom of the slots 192 in the lower activation sleeve 162.

In order to return the apparatus to the straight drilling mode, pumping of the drilling fluid is switched off, as a result of which the control ring 146 is returned to the position shown in Figure 4A by means of the activation return spring 136. Vhen pumping of the drilling fluid is switched back on, the guide pins 156 move further along the track 148 until they reach the next second track portion 152, corresponding to the arrangement shown in Figures 2B to 7B. It can therefore be seen that the drilling apparatus can be reliably switched between its different drilling modes simply be repeated switching on and off of pumping of the drilling fluid. Each time the flow is off, the pins 156 return to the third track portions 154, while each time the pumps are switched on, the pins 156 alternately move to the first and second track portions 150, 152 respectively.

It will be appreciated by person skilled in the art that the above embodiment has been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, the design of the tool 102 can be enhanced by altering the number of pins 156 and the profile of the track 148 on control ring 146 to enable the tool 102 to be adjusted to a different angle offset from the tool axis so that the tool can be located in a straight and one or more angular positions. It will also be appreciated by persons skilled in the art that more than two angular offset positions may be provided, although the maximum number possible will be determined by constraints of strength of the control ring 146 and the track 148. It is also possible for a two position tool to operate between two "bent" angles, e.g. 0.5 degrees and 1.25 degrees, rather than 0 degrees and 1.25 degrees.

Claims

1. A direction adjusting tool (102) for a downhole drilling apparatus, the tool comprising:-a housing (114) adapted to be incorporated into a drilling apparatus, in which drilling fluid flows from a location upstream of the tool to a drill bit downstream of the tool via an interior of said housing, and flows from the drill bit along an external surface of the housing, the housing having a first housing part (116) , and a second housing part (118) selectively pivotable relative to the first housing part between a first position thereof, in which the drilling apparatus drills along a first drilling direction, and at least one second position thereof, in which the drilling apparatus drills along a respective second drilling direction, different from said first drilling direction; a first actuator mechanism including a first actuator (162) adapted to be moved relative to said first housing part between a first position thereof and at least one second position thereof to cause pivoting of said second housing part relative to said first housing part between said first position of said second housing part and a respective said second position of said second housing part; and a second actuator mechanism including a second actuator (146) adapted to be moved relative to said first housing part, by means of pressure difference between drilling fluid inside said housing and outside said housing, between at least one first position thereof in which said first actuator is maintained in the first position thereof, and at least one second position thereof in which said first actuator is caused to move to a respective second position thereof.

2. A tool according to claim 1, further comprising at least one first biasing device (136) for biasing said second actuator towards at least one said first position thereof.

3. A tool according to claim 1 or 2, wherein the second actuator includes at least one continuous track (148), and the second actuator mechanism includes at least one pin (156) adapted to engage a respective said track to control movement of said second actuator between at least one said first position thereof and at least one said second position thereof by means of pressure difference between drilling fluid inside said housing and outside said housing.

4. A tool according to claim 3, wherein at least one said continuous track includes at least one respective first track portion (150) adapted to be engaged by a said pin when the second actuator is in a respective said second position thereof.

5. A tool according to claim 3 or 4, wherein at least one said continuous track includes at least one respective second track portion (152) adapted to be engaged by a said pin when the second actuator is in a respective said first position thereof.

6. A tool according to any one of claims 3 to 5, wherein at least one said continuous track includes at least one respective third track portion (154) adapted to be engaged by a said pin such that reduction of fluid pressure difference between drilling fluid inside and outside of said housing causes movement of said pin relative to the track from at least one first or second track portion to a respective third track portion, and increase of fluid pressure difference between drilling fluid inside and outside of said housing causes movement of said pin relative to the track from at least one third track portion to a respective first or second track portion.

7. A tool according to any one of the preceding claims, further comprising at least one second biasing device (168) for biasing the first actuator towards the first position thereof.

8. A tool according to any one of the preceding claims, further comprising at least one first retaining device (190) for limiting upward movement of said first actuator relative to said first housing part beyond at least one said second position thereof, and/or limiting downward movement of said first actuator relative to said first housing part beyond at least one said first position thereof.

9. A tool according to any one of the preceding claims, further comprising at least one second retaining device (194) for opposing movement of said first actuator away from at least one said first position thereof.

10. A tool according to claim 9, wherein at least one said second retaining device comprises at least one first spring loaded detent pin (194) for releasably retaining the first actuator in the first position thereof.

11. A tool according to any one of the preceding claims, further comprising at least one third retaining device (164) adapted to restrict movement of first actuator relative to said second actuator.

12. A tool according to claim 11 wherein at least one said third retaining device is adapted to allow said second actuator (128) to move from a first to a second position thereof without said first actuator (162) moving to a second position thereof.

13. A tool according to claim 11 or 12, wherein at least one said third retaining device comprises a pin mounted on one of the first and second actuator, the pin adapted to slide in a slot (166) in the other of the first and second actuator.

14. A tool according to any one of the preceding claims, wherein said second housing part (118) is located downstream of said first housing part (116) in the direction of flow of drilling fluid to the drill bit.

15. A tool according to any one of the preceding claims, wherein the first actuator mechanism includes an actuator member (202) radially offset from a longitudinal axis of the tool and connected to said second housing part, and a sliding member (206) arranged between said actuator member and said first actuator.

16. A tool according to any one of the preceding claims, further comprising drive means (122) in said housing for transmitting torque from a motor upstream of the tool to a drill bit downstream of the tool.

17. A tool according to claim 16, wherein the drive means includes a flexible shaft.

18. A tool according to claims 15 and 17, wherein the flexible shaft passes through the actuator member and is provided with a male taper drive at each of its ends.

19. A tool according to claim 16, wherein the drive means includes at least one universal joint.

20. A tool according to claim 19, wherein the drive means includes a respective universal joint adjacent each of its ends.

21. A tool according to any one of the preceding claims, further comprising at least one locking ring (226, 228) for preventing separation of the first housing part from the second housing part, wherein at least one said locking ring comprises a plurality of locking members (226, 228) adapted to be abutted by said first housing part and mounted by means of locking pins (232) to said first housing part.

22. A tool according to claim 21, wherein the or each said locking pin has a respective threaded shank portion for mounting to a respective said locking member.

23. A tool according to any one of the preceding claims, further comprising indicator means for indicating whether the second housing part is in the first position thereof or at least one said second position thereof.

24. A tool according to claim 23, wherein the indicator means includes at least one nozzle (234) adapted to communicate between the interior and the exterior of the housing when the second housing part is in at least one said second position thereof.

25. A tool according to claim 24, further comprising at least one diffuser member (236) for diffusing flow of drilling fluid after exiting a respective said nozzle.

26. A tool according to any one of claims 22 to 25, wherein the indicator means includes at least one hole for allowing fluid leakage and a flow restrictor sleeve outside of at least one said hole.

27. A tool according to any one of the preceding claims, further comprising at least one oil reservoir for accommodating lubricating oil, wherein at least one said oil reservoir contains a respective piston and biasing device for causing oil in said oil reservoir to have a higher pressure than the exterior of the oil reservoir.

28. A tool according to any one of the preceding claims, wherein said first drilling direction is substantially parallel to a longitudinal axis of the apparatus.