CA2311254C - A circulating sub apparatus and method - Google Patents

Abstract

A circulating sub apparatus and method is described. The apparatus has an outer body member and an inner body member each having one or more holes, and a displacement mechanism for producing relative movement between the outer body member and the inner body member. The inner body member and the outer body member may be moved between a first configuration, in which the one or more holes on the inner body member are substantially in fluid communication with the one or more holes on the outer body member, and a second configuration, in which fluid communication between the one or more holes on the inner body member and those on the outer body member is substantially prevented. The apparatus is arranged such that when the inner and outer body members are in the first configuration, fluid need not flow through the displacement mechanism. A restraint device for restraining movement of the inner body member with respect to the outer body member is also described, wherein the restraint device is disposed within a chamber which is isolated from fluid located outwith the chamber.

Description

1 "A Circulating Sub Apparatus and Method"
, 2 3 This invention relates to a circulating sub and a 4 method, and more particularly to a multi-opening circulating sub and method for use in energy 6 exploration, milling and drilling.

8 Conventional oil and gas drilling techniques utilise 9 drill-bits which are conveyed on individual lengths (usually 30 feet) of drill-pipe and rotated from the 11 surface of the drilling rig floor to produce the 12 necessary rotary cutting action required to drill well 13 bores. Alternatively, the rotary cutting action can be 14 supplied by using a Positive Displacement Motor (PDM) located above the drill-bit and connected to the 16 surface by either coil tubing that is provided in one 17 continuous length, or by more conventional drill-pipe.
18 The PDM produces the rotary action when.drilling fluid 19 is pumped through it from the surface. The main advantage of using coil tubing in conjunction with a ......~~_..

2 1 PDM is that of a decrease in the running-in time of the 2 equipment into the well-bore.

3

4 Debris or cuttings are produced from the cutting action, which are transported to the top of the well 6 bore by the drilling fluid. In order to clean the well 7 bore effectively the drilling fluid must be pumped at a 8 high enough flow rate to lift the cuttings to the 9 surface. However, only relatively low volumes of drilling fluid can be pumped through the complete 11 Bottom Hole Assembly (BHA) without a large pressure 12 drop at the surface.

14 This problem can be alleviated by using nitrogen to clean the well-bore which gives increased hole cleaning 16 capabilities.

18 However, the use of nitrogen gives rise to a second 19 problem, in that, nitrogen can only be pumped through a PDM motor for very short periods of time without 21 damaging the PDM motor. Hence, the benefits of using 22 nitrogen to clean the well-bore with existing 23 technology are limited.

Traditionally, this first problem is overcome by using 26 an additional tool in conjunction with the motor and 27 drilling/milling assembly, known as a drop-ball 28 circulating sub. This tool is run above the motor and 29 is operated by dropping a ball, from the surface, down the drill-pipe or coil tubing. The ball seats on top 31 of a piston within the tool and pressure is applied to 32 the upper end of the piston and ball. The pressure is 1 increased until shear pins, which are located within 2 the main body of the drop-ball circulating sub, break 3 allowing the piston to move axially downwards within 4 the main body thereby uncovering circulating holes in the main body drilled transverse to the centre-line of 6 the drop-ball circulating sub. These holes allow an 7 increased flow rate to be pumped through the drill-pipe 8 or coil tubing, thus giving a more effective hole 9 cleaning capability.
11 However, this tool has the disadvantage that once the 12 ball has been dropped to the circulating sub, no 13 further milling or drilling can take place as the fluid 14 path to the PDM has been blocked by the ball. If further milling or drilling is required then the tool 16 must be removed from the well-bore so that the ball can 17 be removed. Also, the length of time that the ball 18 takes to drop down the drill-pipe or coil tubing can be 19 considerable.
21 The second problem of pumping nitrogen is helped, but 22 not solved, by using a drop-ball circulating sub as the 23 drop-ball does not effect a complete seal on the piston 24 allowing nitrogen to flow through the motor.
26 The reader is directed to European Patent Application 27 No. 96306334.2 which describes a prior art circulating 28 sub apparatus and method.

According to a first aspect of the present invention, 31 there is provided a circulating sub apparatus having an 32 outer body member and an inner body member, the outer 1 body member and the inner body member each having one 2 or more holes, and a displacement mechanism for 3 producing relative movement between the outer body 4 member and the inner body member, such that the inner body member and the outer body member may be moved 6 between a first configuration, in which the one or more 7 holes on the inner body member are substantially in 8 fluid communication with the one or more holes on the 9 outer body member, and a second configuration, in which fluid communication between the one or more holes on 11 the inner body member and those on the outer body 12 member is substantially prevented, wherein the 13 apparatus is arranged such that when the inner and 14 outer body members are in the first configuration, fluid is permitted to flow through the one or more 16 holes on the inner and outer body members without 17 flowing through the displacement mechanism.

19 Typically, the apparatus further comprises a restraint device, which may be for restraining movement of the 21 inner body member with respect to the outer body 22 member, wherein the restraint device is preferably 23 disposed within a chamber which may be isolated from 24 fluid located outwith the chamber.
26 Typically, the chamber is formed between the inner and 27 outer body members, and preferably is provided with 28 hydraulic fluid therein. The chamber is typically 29 provided with upper and lower seals to isolate the chamber from other fluid located outwith the chamber.
31 Preferably, the pressure of fluid located within the 32 chamber is substantially equalised with the pressure of 1 fluid located outwith the chamber, and more preferably, 2 with the pressure of fluid located outwith the 3 apparatus. Typically, the upper and/or lower seal(s) 4 are moveable with respect to the outer and/or inner

5 body members, and preferably, one face of the upper

6 and/or lower seal(s) is exposed to the pressure of

7 fluid located within the chamber and another face of

8 the upper and/or lower seal(s) is exposed to the

9 pressure of fluid located outwith the chamber.
Preferably, at least one aperture is provided in the 11 outer body member to expose at least one of the upper 12 and lower seals to the pressure of fluid located 13 outwith the apparatus.

Preferably, the displacement mechanism is controlled by 16 fluid pressure, where the fluid pressure is typically 17 provided by fluid located within a throughbore of the 18 apparatus, and more preferably, the displacement 19 mechanism comprises a piston assembly and a restrictor nozzle in the fluid path.

22 Preferably, the restrictor nozzle is provided on the 23 inner body member such that fluid passing through the 24 inner bore of the circulating sub apparatus when the inner and outer body members are in the aligned 26 configuration, need not flow through the restrictor 27 nozzle.

29 Preferably, the restrictor nozzle is located on the inner body member such that it is located downstream of 31 the holes provided on the inner body member, in use.
32 Preferably, the restrictor nozzle is located on the 1 inner body member such that when the inner and outer 2 body members are in the aligned configuration, the 3 restrictor nozzle is located downstream of the holes 4 provided on the outer body member.

6 Typically, the restrictor nozzle is located on the 7 inner body member such that in use of the apparatus, 8 the restrictor nozzle is located vertically below the 9 holes provided on the inner body member. Typically, the restrictor nozzle is located on the inner body 11 member such that when the inner and outer body members 12 are in the aligned configuration in use of the 13 apparatus, the restrictor nozzle is located vertically 14 below the holes provided on the outer body member.

16 Typically, the holes are substantially transverse to 17 the longitudinal axis of the outer body member and/or 18 the inner body member.

Preferably, the outer and/or inner body members are 21 substantially tubular.

23 The displacement mechanism typically further includes a 24 restraining device which preferably restrains movement of the inner body member with respect to the outer body 26 member.

28 Typically, the inner body member and the outer body 29 member may be repeatably moved between the aligned configuration and the obturated configuration.

1 Preferably, when the outer body member and the inner 2 body member are positioned relative to one another in 3 the obturated configuration, fluid can pass from the 4 inner bore of the outer body member to the inner bore of the inner body member and out of the bottom end of 6 the inner body member.

8 Preferably, when the outer body member and the inner 9 body member are positioned relative to one another in the aligned configuration, a bypass passage is formed 11 that allows fluid to flow from the throughbore of the 12 circulating sub apparatus to the annulus between.the 13 outside diameter of the tool and the inside diameter of 14 the well bore, in use.

16 Typically, the piston assembly is coupled to the inner 17 body member.
18 Typically, an increase in the fluid pressure displaces 19 the inner body member in a downwards direction.
Typically, there is provided a return spring, one end 21 of which butts against the outer body member and the 22 other end butts against the inner body member.

24 Typically, the restraining device comprises at least one restraining member mounted on each of the inner and 26 outer body members, the restraining member(s) mounted 27 on the inner body member being selectively co-operable 28 with the corresponding restraining member(s) mounted on 29 the outer body member.

1 Typically, the restraining member(s) mounted on the 2 inner body member is/are mounted on the piston 3 assembly.

Typically, longitudinal movement of the inner body 6 member with respect to the outer body member moves the 7 restraining member mounted on the inner body member 8 into contact with the restraining member mounted on the 9 outer body member.

11 Preferably, one of the restraining member mounted on 12 the inner body member and the restraining member 13 mounted on the outer body member is adapted to rotate 14 the inner body member with respect to the outer body member, following continued longitudinal movement of 16 the inner body member with respect to the outer body 17 member.

19 Preferably, after a predetermined longitudinal movement of the inner body member, if necessary, the restraining 21 members of the inner and outer body members are adapted 22 to restrain the inner body member in a first 23 configuration from further rotation, and more 24 preferably, from further longitudinal movement.
26 Typically, a second restrained configuration is reached 27 upon longitudinal movement, if necessary, in the 28 opposite direction to the direction of longitudinal 29 movement for which the first restrained configuration was reached.

1 Typically, the direction of rotation of the inner body 2 member with respect to the outer body member for which 3 the first restrained configuration is reached is the 4 same direction of rotation for which the second restrained configuration is reached.

7 Preferably, the first configuration is the aligned 8 configuration and the second configuration is the 9 obturated configuration.

11 Alternatively, the first configuration is the obturated 12 configuration and the second configuration is the 13 aligned configuration.

Preferably, when the circulating sub is in the aligned 16 configuration, a sealing device deters the flow of 17 fluid through the bottom end of the circulating sub, 18 and more preferably deters the flow of fluid through 19 the bottom end of the inner body member. Typically, when the circulating sub is in the aligned 21 configuration, the sealing device seals the bottom end 22 of the inner body member.

24 Typically, the circulating sub has an initial and natural obturated configuration when there is no or 26 minimal fluid flow rate through the restrictor nozzle.
27 When the fluid flow rate through the restrictor nozzle 28 is increased, the inner body member will typically move 29 longitudinally (and preferably) downwardly within the outer body member, and the location of the restraining 31 member (which may be a pin) of the outer body member 32 with respect to the restraining member (which may be a 1 slot) of the inner body member will determine whether 2 the fluid continues to flow through the restrictor 3 nozzle and thereafter out of the circulating sub 4 through the bottom end thereof, or whether the fluid 5 can exit the circulating sub through the one or more 6 holes in the inner and outer body members, where the 7 one or more holes are preferably formed in the side 8 walls of the inner and outer body members.

10 The invention has the advantage that nitrogen gas may

11 be pumped through the circulating sub and through the

12 circulating holes, when the circulating sub is in the

13 aligned configuration, to clean the well bore without

14 damaging any tools located below the circulating sub.
16 According to a second aspect of the present invention 17 there is provided a method of drilling or milling in a 18 borehole, the method comprising (a) inserting in the 19 borehole a drill string which includes a drill or mill and a circulating sub in accordance with the first 21 aspect, (b) altering the flow rate of fluid to move the 22 body members to the obturated configuration to permit 23 drilling or milling, (c) altering the flow rate of 24 fluid to move the body members to the aligned configuration to permit circulation, and (d) repeating 26 steps (b) and (c) as required.

28 Preferably, the drill string also includes a fluid 29 operated motor, such as a positive displacement motor, and/or a reamer.

1 The fluid may be a liquid or a gas and is preferably a 2 drilling fluid. Alternatively, or in addition the 3 fluid may be nitrogen gas.

Embodiments of the invention will now be described, by 6 way of example, with reference to the accompanying 7 drawings wherein:-9 Fig. 1(a) is a cross-sectional view of the upper in-use portion of a circulating sub with minimal 11 or no fluid flow rate through the circulating sub;
12 Fig. 1(b) is a cross-sectional view of the middle 13 in-use portion of the circulating sub of Fig.

14 1(a);
Fig. 1(c) is a cross-sectional view of the lower 16 in-use portion of Fig. 1(a);
17 Fig. 2(a) is a schematic view of a first example 18 of a restraining or controlling device of the 19 circulating sub of Fig. 1(a), laid out flat for greater clarity, showing a full circulation cycle 21 of the sub;
22 Fig. 2(b) is a schematic view of a second example 23 of a restraining or controlling device;
24 Fig. 2(c) is a cross-sectional plan view of the restraining or controlling device of either of 26 Figs. 2(a) or 2(b);
27 Fig. 3(a) is a cross-sectional view of the 28 circulating sub of Figs. 1(a) to (c) during a 29 circulation operation;
Fig. 3(b) is a cross-sectional view of the 31 circulating sub of Figs. 1(a) to (c) during a 32 milling/drilling operation;

1 Fig. 3(c) is a cross-sectional view of a 2 circulating sub of Figs. i(a) to (c) with minimal 3 or no fluid flow rate through the circulating sub;
4 Fig. 4(a) is a repeat of Fig. 3(c) and is depicted alongside Fig. 4(b), which is a repeat drawing of 6 the restraining device of Fig. 2(b), to show the 7 relationship between the circulating sub and the 8 restraining device;
9 Fig. 4(c) and 4(d) are cross-sectional plan views of the circulating sub which show how locating 11 pins, which extend through an upper body of Fig.
12 21, locate in a packing spacer of Fig. 14(a) and 13 14 (b) ;
14 Fig. 5 is a cross-sectional view of an outer body section in the form of a top sub;
16 Fig. 6 is a cross-sectional view of an indexing 17 sleeve of the circulating sub of Figs. 1(a) to 18 (c) ;
19 Fig. 7 is a side view of an indexing pin of the circulating sub of Figs. 1(a) to (c);
21 Fig. 8 is a cross-sectional view of a bush, for 22 use with the indexing pin of Fig. 7;
23 Fig. 9 is a cross-sectional view of a restrictor 24 nozzle for use with the circulating sub of Fig.
1(a) to (c) prior to the restrictor nozzle having 26 a throughbore formed therein;
27 Fig. 10 is a cross-sectional view of a flow plug 28 packing retainer which is mounted on an upstanding 29 pin of Fig. 11 of the circulating sub of Figs.

i(a) to (c) ;
31 Fig. 11 is a cross-sectional view of a flow plug, 32 or bottom plug, which carries an upstanding pin, 1 and is incorporated in the circulating sub of 2 Figs. i(a) to (c) ;
3 Fig. 12 is a cross-sectional view of a top sub 4 spacer for use with the circulating sub of Figs.
l(a) to (c) ;
6 Fig. 13 is a cross-sectional view of a bottom sub 7 spacer for use with the circulating sub of Figs.
8 i(a) to (c) ;
9 Fig. 14(a) is a cross-sectional view of a packing spacer for use with the circulating sub of Figs.
11 i(a) to (c) ;
12 Fig. 14(b) is a sectioned view of the packing 13 spacer of Fig. 14(a);
14 Fig. 15 is a cross-sectional view of a seal bush;
Fig. 16 is a part cross-sectional view of a lower 16 piston or indexing mandrel;
17 Fig. 17 is a cross-sectional view of an upper 18 piston of an inner piston assembly of the 19 circulating sub of Figs. 1(a) to (c);
Fig. 18 is an outer body section, in the form of a 21 bottom sub, of the circulating sub of Figs. 1(a) 22 to (c) ;

23 Fig. 19 is an outer body section, in the form of a 24 lower body, of the circulating sub of Figs. 1(a) to (c) ;

26 Fig. 20 is an outer body section, in the form of a 27 mid body, of the circulating sub of Figs. 1(a) to 28 (c) ; and 29 Fig. 21 is a cross-sectional view of an outer body section, in the form of an upper body, of the 31 circulating sub of Figs. 1(a) to (c).

1 Fig. 1 shows an example of a multi-opening circulating 2 sub 50 in accordance with the present invention, 3 consisting of an outer tubular body formed by a number 4 of outer body sections 51, 53, 54, 55 and 57, and an inner tubular body in the form of an inner piston 6 assembly having an upper piston 52 and a lower piston 7 65. The upper piston 52 is coupled at its lower end to 8 the lower piston 65. A restrictor nozzle 60 is 9 provided at approximately the mid-point of the upper piston 52.

12 An indexing sleeve 10 is located around the outer 13 circumference of approximately the mid-point of the 14 lower piston 65, and as shown in the Figs. is radially and longitudinally secured thereto by means of set 16 screws (not shown) which project inwardly from the 17 indexing sleeve 10 to locate in apertures 8 formed 18 around the outer circumference of the lower piston 65.
19 A continuous "W" shaped slot 15 is formed around the outer circumference of the indexing sleeve 10, as more 21 clearly seen in Fig. 2. An indexing pin 13 is provided 22 on one of the outer body sections 54, and projects 23 radially inwardly therefrom, such that the innermost 24 portion of the indexing pin 13 locates within the continuous "W" shaped slot 15. A bush 14 is located 26 around the outer circumference of the pin 13, and is 27 free to rotate around the pin 13.

29 For a milling or drilling operation, drilling fluid flows from a coiled tubing that is connected to an 31 upper outer body section 53, through the restrictor 32 nozzle 60, through a bore 70 of the circulating sub 50, 1 out of the lower outer body section 57 and subsequently 2 onwards to equipment located below the circulating sub 3 50, such as a PDM.

5 Referring to Figs. 2(a) and 2(b), the circulating sub 6 50 is preferably set up by the operator so that the pin 7 13 and bush 14 are located within the continuous "W"
8 shaped slot 15 at position 13A, which is approximately 9 half distance of the axial extent of the slot 15, such 10 that the sub 50 is in a first restrained configuration, 11 or otherwise known as a "flow through" or drilling 12 configuration. In this initial configuration, the 13 sleeve 10, and thus the inner piston assembly 52, 65, 14 is restrained from downwards movement (or left to right

15 movement referring to Figs. 2(a) and 2(b)) with respect

16 to the outer body sections 51, 53, 54, 55 and 57 by

17 virtue of the surface 15A of the slot 15 being

18 restrained by the pin 13A. Accordingly, in this

19 initial configuration, the circulating sub 50 is arranged such that drilling fluid flows from the coiled 21 tubing through the bore 70 of the circulating sub 50, 22 and onwards to the equipment located below the 23 circulating sub 50.

To obtain a circulating operation, the fluid flow rate 26 through the circula-tion sub 50 is stopped, which 27 results in the sleeve 10 being moved upwardly (right to 28 left referring to Figs. 2(a) and 2(b)) until the slot 29 surface 15B contacts the pin at position 13B, this movement being caused by a return spring 63 which will 31 be detailed subsequently. Continued cessation of the 32 fluid flow rate causes the sleeve 10 to move further 1 upwards, and due to the action of the pin 13 at 2 position 13B, the sleeve 10 (and hence the inner piston 3 assembly 52, 65) also rotates with respect to the pin 4 13 and outer body sections 51, 53, 54, 55 and 57, until the slot surface 15C arrests upon the pin 13 at 6 position 13C.

8 The fluid flow rate is now increased through the 9 throughbore 70 of the sub 50, by an operator at the surface of the borehole, which creates a back pressure 11 of drilling fluid across the restrictor nozzle 60, and 12 which forces the piston assembly 52, 65 longitudinally 13 downwards within the outer body sections 51, 53, 54, 14 55.

16 Consequently, the sleeve 10 moves downwardly (from left 17 to right in Figs. 2(a) and 2(b)) with respect to the 18 pin 13 and bush 14, until the slot surface 15D strikes 19 the pin 13 at position 13D. The angled nature of surface 15D causes the sleeve 10 to rotate, and whilst 21 doing so, the sleeve 10 continues it's downward 22 movement until slot surface 15E arrests against the pin 23 13 at position 13E. The sleeve 10 is now in a second 24 restrained or "circulating" configuration.
26 When the circulating sub 50 is in the second restrained 27 position, the lower piston 65 has moved downwards so 28 that bypass ports 66 are now aligned with the 29 circulating holes 68. Drilling fluid will now flow down the bore 70 of the circulating sub 50 and out of 31 the circulating holes 68 via the bypass ports 66.

32 Thus, the various components of the circulating sub 50 1 are dimensioned such that when the sub 50 is in this 2 second restrained configuration, the bypass ports 66 3 located in the sidewall of the upper piston 52 move 4 into fluid communication with the circulating holes 68 located on an outer body section 51. A pack-off 6 sealing element 69 is mounted on an upstanding pin 17.
7 When the bypass ports 66 are aligned with the 8 circulating holes 68, the bottom end of the lower 9 piston 65 engages with the pack off sealing element 69 such that no drilling fluid can pass through an 11 aperture 71 in a bottom plug 72 (which carries the 12 upstanding pin 17) at the bottom end of the circulating 13 sub 50 to the equipment below. Further if nitrogen gas 14 is being circulated through the bore 70 of the circulating sub 50 and out through the circulating 16 holes 68, the seal between the pack off sealing element 17 69 and the lower piston 65 ensures that no nitrogen gas 18 can pass through any of the tools below the circulating 19 sub 50.

21 Once the circulating sub 50 has been operated for the 22 required period in the second restrained configuration, 23 that is in the circulating mode, to change to the other 24 operating mode, the drilling fluid flow rate is reduced. This action once again reduces the drilling 26 fluid back pressure across the restrictor nozzle 60. A
27 return spring 63 which acts between a shoulder 72 28 mounted on the outer body section 54 and a thrust 29 bearing 62 mounted on the lower piston 65, biases the lower piston 65 upwards, and consequently the piston 31 assembly 52, 65, and the sleeve 10, moves upward.

1s 1 The thrust bearing 62 ensures that any residual torque 2 retained in the return spring 63 is dissipated, and 3 hence does not interfere with the rotation of the 4 piston assembly 52, 65.

6 As the piston assembly 52, 65, and the sleeve 10, moves 7 upward, the indexing pin 13 contacts the continuous "W"
8 shaped slot 15 at slot surface 15F, which rotates the 9 sleeve 10 and piston assembly 52, 65. Continued reduction in the fluid flow rate to a minimal or zero 11 flow rate causes the sleeve 10 to move further upwards, 12 until the slot surface 15G is arrested by the pin 13 at 13 position 13G. Now, when the fluid flow rate is once 14 again increased by the operator at the borehole surface, the back pressure of fluid created across the 16 restrictor nozzle 60 forces the piston assembly 52, 65 17 longitudinally downwards within the outer body sections 18 51, 53, 54, 55, and hence the sleeve 10 moves downwards 19 until the slot surface 15A is once again restrained by the pin 13 in position 13A. The sleeve is therefore 21 back in the first restrained or "drilling"
22 configuration, having moved through 360 degrees of 23 rotation, and the entire axial extent of the slot 15.
24 Therefore, Fig. 2 shows the positional relationship for a complete cycle of the circulating sub 50, with the 26 components being shown laid out flat for clarity.

28 As has previously been described, the circulating sub 29 50 has two main modes of operation, drilling fluid flow through and circulation, for when the piston assembly 31 52, 65 is restrained in a first and a second position 32 respectively. Clearly, the sequence of appearance of 1 the modes of operation could be switched, for instance 2 to allow a circulation mode when the sub 50 and coiled 3 tubing are being re-run into an already drilled well, 4 by the operator adjusting the sub 50 at the surface such that it starts in an initial circulating 6 configuration.

8 A pair of seal stacks 67A, 67B are disposed, and act, 9 between the inner piston assembly 52, 65 and the outer body sections 51, 53, 54, 55, with the upper seal stack 11 67A being located above the circulating holes 68 and 12 the lower seal stack 67B being located below the 13 circulating holes 68. The pair of seal stacks 67A, 67B
14 prevents any leakage of drilling fluid between the bypass port 66 and the circulating hole 68, whilst the 16 circulating sub 50 is in the first restrained 17 configuration, and hence in drilling or fluid flow 18 through mode of operation.

The apparatus 50 also includes a hydraulic fluid 21 chamber 20 which is defined by the boundaries of the 22 inner surface of the outer body sections 51, 54, the 23 outer surface of the lower piston 65, a lowermost 24 sealing face of a seal provided on an upper balanced piston 21 and an uppermost sealing face of a seal 26 provided on a lower balanced piston 22. An operator at 27 the surface of the wellbore can inject or withdraw 28 hydraulic fluid into the chamber 20 as required via a 29 hydraulic fluid plug 32.

31 The hydraulic fluid provides a lubricating action to 32 both the restraining device as provided by the co-1 operation between the indexing pin 13 and the 2 continuous "W" shaped slot 15, and also provides a 3 lubricating action to the spring 63.

5 Upper apertures 29 formed in the side wall of the outer 6 body section 51 and lower apertures 30 formed in the 7 side wall of the outer body section 55 provide fluid 8 communication between the fluid located outwith the 9 apparatus 50 and the respective upper surface of the 10 upper balance piston 21 and the lower surface of the 11 lower balance piston 22. The upper balance piston 21 12 can move with respect to the outer body section 51 and 13 the lower piston 65 between a radially inwardly 14 projecting shoulder 24 provided on the outer body 15 section 51 and a radially outwardly projecting shoulder 16 25 provided on the lower piston 65. The lower balance 17 piston 22 can move with respect to the outer body 18 section 55 and the lower piston 65 between a radially 19 inwardly projecting shoulder 27 provided on the

20 lowermost end of the outer body section 54 and a

21 radially inwardly projecting shoulder 28 provided on

22 the outer body section 55.

23

24 Thus, this aspect of the apparatus 50 provides the advantage that there is substantially no differential 26 pressure between the hydraulic fluid located within the 27 chamber 20 and the fluid located outwith the apparatus 28 50.

It should be noted that the by-pass ports 66 are not 31 exactly transverse with the longitudinal axis of the 32 apparatus 50, but are angled downwardly from the inner 1 surface to the outer surface of the upper piston 52.
2 It should also be noticed that the circulating holes 68 3 are not exactly transverse to the longitudinal axis of 4 the apparatus 50, but are angled upwardly from the inner surface to the outer surface of the outer body 6 section 51. This respective downwards and upwards 7 angling of the by-pass ports 66 and the circulating 8 holes 68 advantageously aids the flow of fluid from the 9 bore 70 of the circulating sub 50 to the exterior of the apparatus 50 via the circulating holes 68.

12 The location of the by-pass port 66 vertically above 13 the restrictor nozzles 60 in use of the apparatus 50, 14 and hence the location of the by-pass port 66 upstream of the restrictor nozzle 60 in use of the apparatus 50 16 provides the advantages that, as the piston assembly 17 52, 65 travels longitudinally downwards, the restrictor 18 nozzle 60 passes the circulating holes 68. Therefore, 19 with the by-pass port 66 and the circulating holes 68 now in fluid communication with one another, the 21 requirement to pump the circulating fluid through the 22 restrictor nozzle 60 in the circulating mode has been 23 eliminated, and thus higher fluid circulation rates can 24 be achieved.

26 Modifications and improvements can be made to the 27 embodiments, without departing from the scope of the 28 invention.

For instance, the indexing sleeve 10 may be rotatably 31 mounted around the outer circumference of approximately 32 the mid-point of the lower piston 65, and in this 1 scenario, a thrust bearing (not shown) is provided at 2 each end of the indexing sleeve 10 to aid rotation 3 thereof. This embodiment permits the indexing sleeve 4 10 to rotate relative to the lower piston 65, and this embodiment has the advantage that the inner piston 6 assembly 52, 65 need not rotate when moving axially 7 between the "flow through" and "circulating"
8 configurations, which means that the friction generated 9 between the seal stacks 67A, 67B and the inner piston assembly 52, 65 is minimised.

12 In addition, two or more pins 13 and respective bushes 13 14 may be provided to locate within a modified 14 continuous "W" shaped slot 15. In this embodiment, the "W" shaped slot 15 has a corresponding number of 16 profiles as shown in Fig. 2(a) and 2(b) to match the 17 number of pins 13 and respective bushes 14, such that 18 if two pins 13 are provided, then two slot 15 profiles 19 are provided, with each profile circumscribing 180 of the slot 15, and the two pins 13 being arranged 21 diametrically opposite one another.

23 Hence, a corresponding number of profiles can be 24 repeated around the slot 15 to match the number of pins 13 and bushes 14 provided. This embodiment has the 26 advantage that the rotation required of the indexing 27 sleeve 10 is halved (if two profiles and two pins 13 28 are provided) or cut to 33% (if three profiles and 29 three pins 13 are provided, etc.).

31 Furthermore, the indexing sleeve 10, pins 13 and bush 32 14 mechanism can be replaced by a clutch type mechanism 1 (as described, for example, in EP Application No 2 96306334.2) which will also be contained within the 3 chamber 20, and this clutch mechanism may be preferred 4 for heavy duty operations with larger tools.

Claims (30)

CLAIMS: -

1. A circulating sub apparatus having an outer body member and an inner body member, the outer body member and the inner body member each having one or more holes, and a displacement mechanism for producing relative movement between the outer body member and the inner body member, such that the inner body member and the outer body member may be moved between a first configuration, in which the one or more holes on the inner body member are substantially in fluid communication with the one or more holes on the outer body member, and a second configuration, in which fluid communication between the one or more holes on the inner body member and those on the outer body member is substantially prevented, wherein the apparatus is arranged such that when the inner and outer body members are in the first configuration, fluid is permitted to flow through the one or more holes on the inner and outer body members without flowing through the displacement mechanism.

2. An apparatus according to claim 1, wherein the apparatus further comprises a restraint device for restraining movement of the inner body member with respect to the outer body member.

3. An apparatus according to claim 2, wherein the restraint device is disposed within a chamber.

4. An apparatus according to claim 3, wherein the chamber is isolated from fluid located outwith the chamber.

5. An apparatus according to claims 3 or 4, wherein the chamber is formed between the inner and outer body members.

6. An apparatus according to any one of claims 3 to 5, wherein the chamber is provided with hydraulic fluid therein.

7. An apparatus according to any one of claims 3 to 6, wherein the chamber is provided with upper and lower seals to isolate the chamber from other fluid located outwith the chamber.

8. An apparatus according to any one of claims 3 to 6, wherein the pressure of fluid located within the chamber is substantially equalised with the pressure of fluid located outwith the chamber.

9. An apparatus as claimed in claim 7, wherein the pressure of fluid located within the chamber is substantially equalised with the pressure of fluid located outwith the chamber.

10. An apparatus according to any one of claims 3 to 6, or 8, wherein the pressure of fluid located within the chamber is substantially equalised with the pressure of fluid located outwith the apparatus.

11. An apparatus according to claims 7 or 9, wherein the pressure of fluid located within the chamber is substantially equalised with the pressure of fluid located outwith the apparatus.

12. An apparatus according to claim 7, wherein at least one of the upper and lower seal are moveable with respect to at least one of the outer and inner body members.

13. An apparatus according to claims 9 or 11, wherein at least one of the upper and lower seal are moveable with respect to at least one of the outer and inner body members.

14. An apparatus according to any one of claims 7, 9, 11 or 13, wherein one face of at least one of the upper and lower seals is exposed to the pressure of fluid located within the chamber and another face of at least one of the upper and lower seals is exposed to the pressure of fluid located outwith the chamber.

15. An apparatus according to any one of claims 7, 9, 11, 13 or 14, wherein at least one aperture is provided in the outer body member to expose at least one of the upper and lower seals to the pressure of fluid located outwith the apparatus.

16. An apparatus according to any one claims 1 to 15, wherein the displacement mechanism is controlled by fluid pressure.

17. An apparatus according to claim 16, wherein the fluid pressure is provided by fluid located within a throughbore of the apparatus.

18. An apparatus according to any one of claims 1 to 17, wherein the displacement mechanism comprises a restrictor nozzle in the fluid path.

19. An apparatus according to claims 18 or 19 wherein the circulating sub has an initial and natural obturated configuration when there is no or minimal fluid flow rate through the restrictor nozzle.

20. An apparatus according to claim 18 or 19, wherein the restrictor nozzle is provided on the inner body member such that fluid passing through the inner bore of the circulating sub apparatus when the inner and outer body members are in the aligned configuration, need not flow through the restrictor nozzle.

21. An apparatus according to claims 19 or 20, wherein the restrictor nozzle is located on the inner body member such that it is located downstream of the holes provided on the inner body member, in use.

22. An apparatus according to any one of claims 19 to 21, wherein the restrictor nozzle is located on the inner body member such that when the inner and outer body members are in the aligned configuration, the restrictor nozzle is located downstream of the holes provided on the outer body member, in use.

23. An apparatus according to any one of claims 19 to 22, wherein the restrictor nozzle is located on the inner body member such that in use of the apparatus, the restrictor nozzle is located vertically below the holes provided on the inner body member.

24. An apparatus according to any one of claims 19 to 23, wherein the restrictor nozzle is located on the inner body member such that when the inner and outer body members are in the aligned configuration in use of the apparatus, the restrictor nozzle is located vertically below the holes provided on the outer body member.

25. An apparatus according to any one of claims 1 to 24, wherein the holes are substantially transverse to the longitudinal axis of the outer body member and/or the inner body member.

26. An apparatus according to any one of claims 1 to 25, wherein the inner body member and the outer body member may be repeatably moved between the aligned configuration and the obturated configuration.

27. A method of drilling or milling in a borehole, the method comprising:

(a) inserting in the borehole a drill string which includes a drill or mill and a circulating sub; wherein said circulating sub comprises an outer body member and an inner body member, the outer body member and the inner body member each having one or more holes, and a displacement mechanism for producing relative movement between the outer body member and the inner body member, such that the inner body member and the outer body member may be moved between a first configuration, in which the one or more holes on the inner body member are substantially in fluid communication with the one or more holes on the outer body member, and a second configuration, in which fluid communication between the one or more holes on the inner body member and those on the outer body member is substantially prevented, wherein the apparatus is arranged such that when the inner and outer body members are in the first configuration, fluid is permitted to flow through the one or more holes on the inner and outer body members without flowing through the displacement mechanism;

(b) altering the flow rate of fluid to move the body members to the obturated configuration to permit drilling or milling;

(c) altering the flow rate of fluid to move the body members to the aligned configuration to permit circulation;
and;

(d) repeating steps (b) and (c) as required.

28. A method according to claim 27, wherein the drill string also includes a fluid operated motor, such as a positive displacement motor, and/or a reamer.

29. A method according to claims 27 or 28, wherein the fluid is a drilling fluid.

30. A method according to claims 27 or 28, wherein the fluid may be nitrogen gas.