DOWNHOLE CIRCULATION APPARATUS

Abstract

A downhole circulation apparatus includes a body defining a longitudinal bore. At least one annular port forms a fluid path from longitudinal bore to the outside of the apparatus. A slidable sleeve is mounted in the longitudinal bore and has a closed position blocking annular port and an open position in which the annular port is open to the longitudinal bore. The slidable sleeve also comprises a ball seat in which a non-deformable ball is sized to fit to block the longitudinal bore. An abutment surface is configured to dislodge the non-deformable ball when the slidable sleeve moves into the open position.

Description

BACKGROUND

The present disclosure relates to a downhole circulation apparatus for use in a drill string. The present disclosure also relates to a method of creating a surge of pressurised fluid in a wellbore in which a drill string is located using such a downhole circulation apparatus.

Downhole circulation tools or bypass tools are used in drill strings for drilling wellbores to retrieve hydrocarbons. Circulation tools have several functions, such as when a loss of pressure of drilling fluid is encountered for example due to fractures in the geological formation being drilled. In such circumstances, the circulation tool can be activated in the drill string to open one or more ports to enable fluid to be pumped through the drill string, and out through the ports into the annulus surrounding the drill string. In the case of a fractured formation, the circulation fluid might include material to block the fractures such as wood chips or the like. Circulation tools may also be used to jet and clean out wellbores.

Circulation tools are often operated using a series of deformable and non-deformable balls dropped along the drill string such as described in U.S. Pat. No. 4,889,199. Operation of such tools can be complicated, because different types of activation and deactivation balls, darts or other implements must be dropped for correct functioning. Such tools also require internal ball catchers which prevent other tools below the ball catcher being activated with balls or darts.

The apparatus of U.S. Pat. No. 4,889,199 and other known circulating tools also suffer from the drawback that care must be taken not to land the balls or darts too fast, particularly if they are deformable, as they can shear through the restrictions prematurely meaning that operators must repeat the activation process. Using deformable balls is also undesirable in pressure sensitive drill strings because pressure surges used to pop deformable balls can lead to incorrect operation or damage to the drill string.

Preferred embodiments of the present disclosure seek to overcome the above disadvantages of the prior art.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, there is provided a downhole circulation apparatus comprising:

• • a body defining a longitudinal bore, the body comprising at least one port defining a fluid path from said longitudinal bore out of the body;
  • a slidable sleeve mounted in said longitudinal bore, said slidable sleeve having a closed position blocking said at least one port and an open position in which said port is open to said longitudinal bore;
  • wherein said slidable sleeve comprises at least one ball seat configured to receive at least one first non-deformable ball to block fluid flow through said slidable sleeve and cause said slidable sleeve to move from the closed to the open position; and
  • an abutment surface configured to dislodge said at least one non-deformable ball in used when said slidable sleeve moves into said open position.

By providing an abutment surface configured to dislodge a non-deformable ball used to move a sliding sleeve to expose an annular port in the circulation apparatus, this provides the advantage of a simplified mechanism for both activating and deactivating a circulation apparatus because only a non-deformable ball is required. Once the non-deformable ball has been expelled through the annular port, close tolerances in the apparatus mean that all is required to keep the port open is a flow of pressurised fluid.

This also provides the advantage of removing the likelihood that the circulation tool fails to operate because a deformable ball or dart blows prematurely through its seat.

Furthermore, this provides the advantage that no ball catcher is required in the drill string in which the circulation apparatus is used because no de-activation ball is used to deactivate the circulation apparatus. This is achieved simply by ceasing pumping at the surface. Ball catchers prevent tools in drill strings below the ball catcher being actuated by droppable implements such as balls or darts. The fact that the non-deformable ball is dislodged and can then be expelled through the annular port means that no ball catcher is required.

Moreover, this provides the advantage that the apparatus is deactivated simply by deactivating pumps at the surface. No pressure surge is required to force a deformable ball through a ball seat. This is advantageous because it means that sensitive drill strings can be used which can be damaged or rendered inoperable by high pressures. Expelling a non-deformable ball into the annulus to deactivate the apparatus removes the requirement for pressure surges from pumps on the surface.

In a preferred embodiment, said abutment surface is disposed on an end of an abutment assembly comprising: a nose portion; and

• • at least one internal port to permit fluid to flow through said abutment assembly when the slidable sleeve is in the closed position, wherein said slidable sleeve blocks said at least one internal port when said slidable sleeve is in the open position.

This provides the advantage of a means to both dislodge and expel said non-deformable ball when the circulation apparatus activates whilst also permitting fluid to flow through the longitudinal bore when the slidable sleeve is in the closed position.

Said abutment surface may be formed by a second ball supported in a second restriction formed in the longitudinal bore.

This provides the advantage that the circulation tool can be used in drill strings which also incorporate other tools operated by balls or darts. The abutment assembly can therefore be left open to enable tools in the drill string below the circulation tool to be operated by balls or darts until such time that the circulation tool is required when a correctly sized ball can be dropped to sit in the second sleeve.

Said slidable sleeve may be biased into the closed position by a biasing structure, such as a spring.

The apparatus may further comprise a plurality of ball seats formed in said slidable sleeve configured to receive a plurality of non-deformable balls.

This provides the advantage that to use the apparatus in smaller diameter wellbores or wellbores where the annulus around the drill string is narrow, a plurality of smaller non-deformable balls can be used rather than a single larger ball. Since the non-deformable ball is expelled into the annulus surrounding the drill string, there must be sufficient room in the annulus for the non-deformable ball to fit when expelled from the apparatus. The apparatus can therefore be designed taking into account the size of the annulus outside of the apparatus in the wellbore to choose whether or not multiple smaller balls are required or a single larger ball.

This also provides the advantage that in large wellbores, the apparatus is likely to have a large internal diameter for longitudinal bore. However, using a large non-deformable ball might not be possible because when expelled through port there may be not enough room for the ball to fit in the wellbore so use of multiple smaller balls solves this problem.

This also enables use of smaller annular ports which provide the advantage of less sleeve travel which makes the apparatus stronger and more straightforward to manufacture.

The apparatus may further comprise two or more ports defining multiple fluid paths from said longitudinal bore out of the body.

This provides the advantage that after actuation of the apparatus to open the annular ports, a single non-deformable ball having a diameter larger than the size of the ports can be dropped into the longitudinal bore. This ball will lodge in one of the ports because it is too large to fit through. The projection of the ball from the port into the longitudinal bore locks the sleeve in the open condition.

The downhole circulation apparatus can then be used for tripping dry pipe, to enable the pipe to be drained through the port or enable reverse circulation in which fluid is pumped down the annulus.

According to another aspect of the present disclosure, there is provided a method of creating a surge of pressurised fluid in a wellbore in which a drill string is located, the method comprising:

• • deploying a downhole circulation apparatus according to any one of the preceding claims in a drill string in a wellbore;
  • operating the downhole circulation apparatus to move said slidable sleeve from the closed to the open position;
  • placing a deformable ball in the longitudinal bore of the downhole circulation apparatus such that the deformable ball locks said at least one port defining a fluid path from the longitudinal bore out of the body; and
  • increasing fluid pressure in the longitudinal bore until the deformable ball is deformed and blows through said port to temporarily increase fluid pressure in the wellbore.

This provides the advantage of a means of creating a shock in a wellbore for example to pressure up and release stuck coiled tubing.

Preferred embodiments of the present disclosure will now be described, by way of example only, and not in any limitative sense, with reference to the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a longitudinal cross section of a downhole circulation apparatus in accordance with a first embodiment of the present disclosure;

FIG. 1b is a longitudinal cross section of the apparatus of

FIG. 1a in which a non-deformable ball is seated in the ball seat in the slidable sleeve;

FIG. 1c is a longitudinal cross section of the apparatus of

FIG. 1a showing the circulation apparatus in the open position;

FIG. 2a is a longitudinal cross section of a downhole circulation apparatus in accordance with a second embodiment of the present disclosure;

FIG. 2b is a longitudinal cross section of the apparatus of

FIG. 2a showing a second ball seated in a second restriction to form an abutment surface;

FIG. 2c is a longitudinal cross section corresponding to

FIG. 2a showing the non-deformable ball seated in the slidable sleeve;

FIG. 2d is a longitudinal cross section corresponding to FIG. 2a showing the apparatus in the open position before the non-deformable ball is expelled;

FIG. 3a is an end view of a downhole circulation apparatus in accordance with a third embodiment of the present disclosure;

FIG. 3b is a longitudinal cross section taken along line A-A of FIG. 3a;

FIG. 3c is an end view of the apparatus of FIG. 3a shown with three non-deformable balls seated in their respective ball seats;

FIG. 3d is a longitudinal cross section taken along line B-B of FIG. 3c;

FIG. 3e is a longitudinal cross section of the apparatus of FIG. 3a shown in the open position;

FIG. 4a is a longitudinal cross section of the apparatus of FIG. 3a in the closed position in which the annular port contains a nozzle;

FIG. 4b is a longitudinal cross section corresponding to FIG. 4a but with three non-deformable balls seated in their respective seats;

FIG. 4c is a longitudinal cross section corresponding to FIG. 4a shown in the open position;

FIG. 5a is an end view of the apparatus of FIG. 4a but having a second annular port and one oversized non-deformable ball seated in a ball seat;

FIG. 5b is a longitudinal cross section taken along line A-A of FIG. 5a;

FIG. 5c is a view corresponding to FIG. 5a with the oversized and regular sized balls seated in their ball seats; and

FIG. 5d is a longitudinal cross section of the apparatus of FIG. 5a shown in the open position.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1a to 1c, a downhole circulation apparatus 2 comprises a body 4 defining a longitudinal bore 6. At least one annular port 8 forms a fluid path from longitudinal bore 6 to the outside of the apparatus 8. A slidable sleeve 10 is mounted in the longitudinal bore. The slidable sleeve 10 has a closed position blocking annular port 8 as shown in FIG. 1a and an open position in which the annular port 8 is open to the longitudinal bore 6 as shown in FIG. 1c. The slidable sleeve 10 also comprises a ball seat 12 which is a restriction in the diameter of the internal aperture of sleeve 10. A non-deformable ball 14 is sized to fit in ball seat 12 to block the longitudinal bore 6 at the position of the ball 14.

It should be understood that the term non-deformable is to be construed as being of a material that would not be able to be deformed under the normal pressures of fluid used in downhole drilling operations. For example, a steel ball could be used which would be understood to be non-deformable by those skilled in the art. Other types of non-deformable ball could also be used, such as those formed from hard plastics and also dissolvable type non-deformable balls.

Apparatus 2 also comprises an abutment surface 16 configured to dislodge non-deformable ball 14 when the slidable sleeve 10 moves into the open position in which annular port 8 is open as shown in FIG. 1c. Abutment surface 16 is part of an abutment assembly 36 having a nose portion 34 below which internal ports 22 are disposed. Internal ports 22 permit fluid to flow through the abutment assembly 36 when the slidable sleeve is in the closed position (FIG. 1a) but slidable sleeve 10 blocks the internal ports 22 when the slidable sleeve 10 is in the open position (FIG. 1c).

Slidable sleeve 10 comprises alignment port 18 which exposes the longitudinal bore 6 to the annular port 8 when the sleeve 10 is in open position as shown in FIG. 1c. Spring 20 forms a biasing structure to bias the sleeve 10 into the closed position of FIG. 1a.

Referring to FIG. 1a, during a drilling operation of a drill string in which the downhole circulation apparatus 2 is disposed, drilling fluid can flow along the full length of longitudinal bore 6 to reach the drill bit (not shown) at the end of the drill string (not shown). The flow path through the apparatus is defined by internal ports 22 formed below nose portion 34. Consequently, drilling fluid can flow through internal ports 22 and down out of the circulation apparatus 2 to the lower drill string.

Referring to FIG. 1b, when it is desired to actuate the downhole circulation apparatus 2, a non-deformable ball 14 is dropped into the drill string and moves through the drill string until it seats in ball seat 12. When non-deformable ball 14 is seated in ball seat 12, the flow of fluid in longitudinal bore 16 is prevented below ball 14 such that the pressure above ball 14 increases. The increase in fluid pressure pumped into bore 16 pushes slidable sleeve 10 downwardly to compress spring 20. Eventually, slidable sleeve 10 reaches its lowermost extent which is defined by edge 24 contacting the lowermost edge 26 of sleeve 10. In this position, ports 18 and 8 are aligned which exposes the longitudinal bore 6 to the annulus outside of the apparatus 2. Furthermore, in this position, non-deformable ball 14 contacts abutment surface 16 to become unseated.

Fluid flow can then expel ball 14 out of annular port 8 into the wellbore annulus meaning that no ball catcher for a deactivation ball is required in the drill string in which apparatus 2 is located. In this position, apparatus 2 can be used to circulate fluid out of annular port 8.

Due to the machining of close tolerances between the outer edges 28 of nose 34 portion and internal surface 30 of sleeve 10, fluid flow is prevented past and therefore into the drill string below the nose 34 such that fluid pressure alone pumped from the surface keeps the assembly in the open condition of FIG. 1c until such time as pumping ceased. Spring 20 then returns the sleeve 10 to the closed position of FIG. 1a to deactivate the apparatus 2. Drilling can then be resumed. The circulation apparatus 2 can be reactivated simply by dropping another non-deformable ball 14.

A downhole circulation apparatus of a second embodiment of the present disclosure is shown in FIGS. 2a to 2d with parts common to the embodiment of FIGS. 1a to 1c shown with like reference numerals but increased by 100.

Referring to FIGS. 2a to 2d, in this embodiment of downhole circulation apparatus 102, abutment assembly comprises a second restriction in the form of a ball seat 142 configured to receive second non-deformable ball 144. In the position of FIG. 2a, fluid can flow along the length of longitudinal bore 106 and through internal posts 122. However, small balls, darts or the like can also be dropped through the length of apparatus 102 because ball seat 142 is open. This enables other tools in the drill string below the circulation apparatus 102 can be operated.

When the operator wishes to activate circulation apparatus 102, a second non-deformable ball 114 is dropped to seat into ball seat 142 which enables the apparatus to be pressured up to push sleeve from the position of FIG. 2c to that of FIG. 2d to align ports 108 and 118 to enable circulation. Second non-deformable ball 144 then acts as abutment surface 116 to push non-deformable ball 114 out of port 108.

Referring to FIGS. 3a to 3e, a downhole circulation apparatus 202 of a third embodiment of the present disclosure is shown with parts common to the embodiment of FIGS. 1a to 1c shown with like reference numerals but increased by 200.

In large wellbores, apparatus 202 is likely to have a large internal diameter for longitudinal bore 206. However, using a large non-deformable ball might not be possible because when expelled through port 208, there may be not enough room for the ball to fit in the wellbore. Furthermore, smaller ports 208 mean less sleeve travel which makes the apparatus stronger and more straightforward to manufacture. For these reasons, the embodiment of FIGS. 3a to 3e comprises three identical abutment assemblies 236 each having an abutment surface 216a, 216b and 216c. Each abutment assembly also has internal ports 222 to enable fluid to flow through the apparatus 202.

To activate apparatus 202, three identical non-deformable balls 214a, 214b and 214c are dropped into longitudinal bore 206 to block three corresponding ball seats 212. Pressurised fluid can then shift sleeve 210 into the position of FIG. 3e to align ports 208 and 218. Non-deformable balls 214a, 214b and 214c are then dislodged by corresponding abutment surfaces 216a, 216b and 216c to be expelled through port 208. As with the previous embodiments, continual pumping of fluid maintains the sleeve 210 in the open condition as a consequence of tight tolerances between the abutment assemblies 236 and sleeve 210.

Referring to FIGS. 4a to 4c, a nozzle 250 can be placed in annular port 208 to enable the apparatus 202 to be used for jetting. The size of balls 214a can be chosen such that they are still able to be expelled out of annular port 208 and its corresponding nozzle 250. This enables the nozzle size to be chosen to control the flow regime of the apparatus whilst still enabling actuation by non-deformable balls 214a.

Referring to FIGS. 5a to 5d, a variant of the apparatus of FIGS. 3a has two opposed annular ports 208a and 208b each having a respective nozzle 250a and 250b disposed therein. It may be desirable to lock the sleeve 210 open (FIG. 5d position) without having to pump fluid. To do this, one large non-deformable ball which is too large to fit through nozzle 250b is dropped into bore 206. Two smaller non-deformable balls 214b and 214c are also dropped to seat in all seats 212 to shift sleeve 210 to the open position in the usual manner. However, when abutment surfaces 216 dislodge balls 215, 214b and 214c, only the smaller balls 214b and 214c can fit through nozzles 250a and 250b to be expelled from the apparatus 202. Ball 215 becomes stuck in one of the nozzles and partially protrudes between ports 208 and 218 to prevent spring from closing sleeve 210. This enables the locked open apparatus 202 to be used for reverse circulation draining the pipe and tripping dry pipe.

In all embodiments, a deformable ball can be dropped into the longitudinal bore 6, 106 or 206 when the apparatus is in the open condition. This deformable ball will become stuck in any open annular port 8, 108 or 208 until such time as a pressure increase pops the deformable ball out of the port. This creates a pressure shock in the wellbore for example to release stuck coiled tubing.

Darts and other implements may be used in the place of balls to provide the same blocking functions.

It will be appreciated by persons skilled in the art that the above embodiments have 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 protection as defined by the appended claims. In particular, the features of all embodiments and variants disclosed are interchangeable.

Claims

1. A downhole circulation apparatus comprising: a body defining a longitudinal bore, the body comprising at least one port defining a fluid path from said longitudinal bore out of the body;a slidable sleeve mounted in said longitudinal bore, said slidable sleeve having a closed position blocking said at least one port and an open position in which said port is open to said longitudinal bore;wherein said slidable sleeve comprises at least one ball seat configured to receive at least one first non-deformable ball to block fluid flow through said slidable sleeve and cause said slidable sleeve to move from the closed to the open position; andan abutment surface configured to dislodge said at least one non-deformable ball in used when said slidable sleeve moves into said open position.

2. An apparatus according to claim 1, wherein said abutment surface is disposed on an end of an abutment assembly comprising: a nose portion; andat least one internal port to permit fluid to flow through said abutment assembly when the slidable sleeve is in the closed position, wherein said slidable sleeve blocks said at least one internal port when said slidable sleeve is in the open position.

3. An apparatus according to claim 1, wherein said abutment surface is formed by a second ball supported in a second restriction formed in the longitudinal bore.

4. An apparatus according to claim 1, wherein said slidable sleeve is biased into the closed position by a biasing structure.

5. An apparatus according to claim 1, further comprising a plurality of ball seats formed in said slidable sleeve configured to receive a plurality of non-deformable balls.

6. An apparatus according to claim 1, further comprising two or more ports defining multiple fluid paths from said longitudinal bore out of the body.

7. An apparatus according to claim 2, wherein said abutment surface is formed by a second ball supported in a second restriction formed in the longitudinal bore.

8. An apparatus according to claim 7, wherein said slidable sleeve is biased into the closed position by a biasing structure.

9. An apparatus according to claim 8, further comprising a plurality of ball seats formed in said slidable sleeve configured to receive a plurality of non-deformable balls.

10. An apparatus according to claim 9, further comprising two or more ports defining multiple fluid paths from said longitudinal bore out of the body.

11. A method of creating a surge of pressurised fluid in a wellbore in which a drill string is located, the method comprising: deploying a downhole circulation apparatus according to any one of the preceding claims in a drill string in a wellbore;operating the downhole circulation apparatus to move said slidable sleeve from the closed to the open position;placing a deformable ball in the longitudinal bore of the downhole circulation apparatus such that the deformable ball locks said at least one port defining a fluid path from the longitudinal bore out of the body; andincreasing fluid pressure in the longitudinal bore until the deformable ball is deformed and blows through said port to temporarily increase fluid pressure in the wellbore.