GB2572218A

GB2572218A - Wellbore drilling tool

Info

Publication number: GB2572218A
Application number: GB1804686.2A
Authority: GB
Inventors: Carlsen Truls
Original assignee: Equinor Energy AS
Current assignee: Equinor Energy AS
Priority date: 2018-03-23
Filing date: 2018-03-23
Publication date: 2019-09-25
Also published as: GB201804686D0

Abstract

A wellbore tool 2, adapted to be positioned behind a drill bit 4 in a wellbore 20, comprises: a body portion adapted to be placed in said wellbore so as to form an annular space 18 between the body and an inner wall of the wellbore; a plurality of plates 12 positioned around the body, the plates hingedly connected 16 to the body portion and are movable between: a closed position (fig. 1) in which drilling fluid is free to pass through said annular space; and an open position in which said plates extend outwardly from said body portion so as to seal, or substantially seal, the annular space, thereby reducing preventing the passage of drilling fluid through the annular space. A drilling arrangement and a method using the tool described above are also claimed. The plates maybe overlapping either both sides above the near side of the adjacent plates or one side above one side of adjacent plate and under the adjacent side of the other adjacent plate.

Description

Technical Field

The invention relates to a wellbore tool for reducing or stopping mud loss.

Background

To produce hydrocarbons from a reservoir, a wellbore is drilled in the Earth’s subsurface to reach the reservoir. The drilling operation includes inserting a drill string with a drill bit at the end into the wellbore. Drilling fluids, normally mud, are circulated down the drill string, through the bit, and back up an annulus between the wellbore and the string. The drilling fluids serve multiple purposes such as cooling the drill bit and carrying cuttings (returns) up and out of the wellbore, and may also drive the bit using a mud motor.

When drilling, the mud weight (i.e. the weight of drilling fluids transmitted to the borehole) must be high enough to prevent the pore pressure of the surrounding formation from moving formation fluids into the borehole in the case of a high permeability formation (e.g. sand), or from breaking down the formation and causing the borehole walls to collapse in the case of a low permeability formation (e.g. shale). However, at the same time, the mud weight must be kept below the fracturing pressure of the formation to avoid the mud weight damaging the surrounding formation and thereby compromising the integrity and/or permeability of the wellbore.

If the pore pressure suddenly decreases, i.e. the drill bit enters a so-called underpressure region, the pressure exerted by the drilling fluids may become too high and fracture/damage the formation. Drilling fluids can then penetrate into the formation, which is known as “mud loss”. The mud loss causes lost circulation and can in severe cases lead to the total absence of fluid flow up the annulus. In such cases, the wellbore may not remain filled even after the pumps have been turned off as the loss zone keeps taking mud.

Mud loss is not an uncommon problem in the drilling industry, and it often takes a long time from the start of a loss situation until the loss situation can be cured. In addition, the first attempt to cure the loss may fail, leading to further losses. After the loss situation has been cured, it may be desirable to continue drilling despite the risk of drilling into a new loss zone.

The long timespan of loss-curing introduces several potential problems:

loss of a well barrier if there are insufficient amounts of adequate mud;

high cost of lost drilling fluids;

reservoir formation damage;

wellbore instability;

delayed production; and loss of target (production zone).

One of the biggest problems is the loss of the drilling fluid column in the annulus between the wellbore and the drill string.

Summary of the Invention

The invention provides a wellbore tool, drilling arrangement and method as set out in the accompanying claims.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a schematic diagram of an embodiment of a tool in a closed position;

Figure 2 is a schematic, cross-sectional diagram of the embodiment of the tool in an open position;

Figure 3 is a schematic, top-view diagram of the embodiment of the tool in the open position;

Figure 4 is a schematic diagram of a section of a plurality of plates of the tool according to an embodiment;

Figure 5 is a schematic diagram of a section of a plurality of plates according to another embodiment; and

Figure 6 is a flow diagram illustrating the steps of a method according to an embodiment.

Description of Preferred Embodiments

We describe embodiments of a wellbore tool that is capable of repeatedly sealing off the annulus of a wellbore from a loss zone to reduce or stop mud loss.

Figure 1 illustrates an embodiment of a wellbore drilling tool 2 (also referred to as a “tool” or “tool sub”) in a closed state. The tool 2 is located on a drill string 3 in front of (below) a measurement-while-drilling (MWD) tool (not shown) and behind (above) a 8 ¹/2” (8.5 inches) diameter drill bit 4. The diameter of the tool sub 2 is 6” (6 inches). Just above and below the tool 2, small, 1/4” (0.25 inch) shoulders 6 and 8 are located, which protect the tool 2 from returns 10 and reduce wear on the tool 2. The shoulder 6 is a projecting region formed around the drill string 3, and the shoulder 8 is a projecting region formed around the drill bit 4.

The tool 2 has a plurality of curved and partially overlapping plates 12 arranged around and covering a tubular body 14 of the tool sub 2. In this embodiment the tool 2 comprises eight plates 12 of which three are shown in Figure 1. Each plate 12 is mechanically connected, at its upper edge, to the tubular body 14 by a hinged connection 16, allowing the other (i.e. lower) end of the plate 12 to move out away from the tubular body 14 (i.e. to move into an open position or state illustrated in Figure 2). In a closed position or state, as illustrated in Figure 1, the plates 12 are folded in against the tubular body 14 such that the tool 2 has an outer cylindrical shape which substantially matches the outer cylindrical shape of the adjacent drill string 3. Hence, in the closed state, drilling fluids can flow past the tool 2 in the annulus 18 between the drill string 3 and the wellbore wall 20. During normal drilling operations, the plurality of plates 12 is in the closed state and drilling fluid is circulated down through the drill string 3, out of the drill bit 4 and back up past the outside of the tool sub 2 in the annulus 18.

As the drill bit 4 enters a loss zone (e.g. an underpressure region) and mud loss starts to occur, circulation of the drilling fluid is stopped and the tool 2 is activated. Figures 2 and 3 illustrate the wellbore drilling tool 2 in the open state (i.e. in a loss situation) in a cross-sectional view and a top view respectively. The plates 12 are pushed out (radially) away from the tubular body 14 by four pins 22. The plates 12 open at the end of the plates 12 closest to the bit 4 (with the hinged connection 16 being located at the top of the tool 2) to avoid the tool becoming jammed as a result of mud and particles falling down towards the bit 4 during a loss situation. The pins 22 forcing the plates 12 out are driven by a hydraulic pump (not shown). There is a load indicator (not shown) which tells the pump when the plates 12 are in contact with the wall 20. The four pins 22 are in contact with four “inner” plates 24, which in turn push the other four “outer” plates 26 due to the partially overlapping edges of the plates. In the open state, the distal end 27 of each plate engages the wellbore wall 20, thereby blocking the annulus 18 completely. Each plate 12 still partially overlaps the adjacent plates 12 so that there is no gap between them. The plates 12 can be pushed out more than 8 Τέ” (e.g. 9”) to accommodate for any wash out (i.e. widening of the wellbore as a result of the movement of drilling fluid) or for a slightly bi-centred bit. The pump driving the pins 22 can communicate and be operated in the same way as the hydraulic pumps operating the pads in Rotary Steerable Systems.

It is important that the plates 12 can move fast, in order to avoid high jet-pressure and wash-out in the closing area as fluids squeeze past the partially opened plates 12. The outer plates 26 are biased (e.g. spring loaded) towards the closed position against the tubular body 14. Hence, when the loss situation has been cured and the pins 22 are retracted, the plates 12 move back to the closed position. The inner plates 24 do not need to be biased, as they will be pushed back into the closed position by the outer plates 26.

In case of a loss situation that cannot be recovered, the tool 2 may comprise a quickrelease mechanism, which can leave the tool 2 and bit 4 behind as a fundament for a cement job (i.e. as a support for cement which can be introduced to close the wellbore). As the upper string 3 is released the bit nozzle is blocked to prevent fluid flow through it.

Figure 4 illustrates a portion of the plurality of plates 12 showing three plates in an open state as seen from the bottom of the wellbore and looking upwards. The inner plate 24 covers part of the adjacent outer plates 26 along the edges. The inner plate 24 has a length 28 which is slightly longer than the length 30 of the outer plates 26, in order to provide a full (unbroken) seal against wellbore wall 20. Each plate 24 and 26 has a proximal end 34 which connects the plate 12 to the tubular body 14 of the tool 2 and a distal end 34 which engages the wellbore wall 20. The distal end 34 is wider than the proximal end 32 so that the plates overlap when the plates 12 are in the open position.

Figure 5 shows an alternative arrangement of the plates 12, in which each plate 12 lies above an adjacent plate 12 along one side but below the adjacent plate 12 on the other side. In this arrangement only one plate 12 has to be pushed in order to actuate all plates 12. That is, in Figure 5, pushing the right-hand plate will in turn push on the middle plate which in turn pushes the left-hand plate (and so on). However, more pins 22 (e.g. at least four pins 22) may still be preferable to provide more structural integrity. In this arrangement each plate 12 has the same length 36, as there are no “inner” and “outer” plates in this arrangement.

The plates 12 are preferably constructed of a strong material (e.g. titanium), which is preferably stronger than steel, in order to allow for a reduced thickness of the plates 12 while avoiding deformation of the plates 12.

Figure 6 illustrates the steps of a method of stopping or reducing the loss of drilling fluid, using a wellbore tool according to any of the embodiments described above. The method comprises detecting a loss of drilling fluid in a wellbore (step S1), and (optionally) stopping any pumping of drilling fluid into said wellbore (step S2). The method then comprises moving said plurality of plates to said open position (step S3), in order to stop or reduce further loss of drilling fluid. .

The skilled person will appreciate that various modification may be made to the above described embodiments without departing from the invention as defined by the accompanying claims.

For example, the size of the plates can be changed to correspond to a borehole diameter produced by a different drill bit.

The number of plates can be greater or smaller than eight, but is preferably in the range of four plates to 32 plates.

Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS:

1. A wellbore tool adapted to be positioned behind a drill bit in a wellbore, said wellbore tool comprising:

a body portion adapted to be placed in said wellbore so as to form an annular space between said body portion and an inner wall of said wellbore;

a plurality of plates positioned around said body portion, said plates being hingedly connected to said body portion so as to be movable between:

a closed position in which drilling fluid is free to pass through said annular space; and an open position in which said plates extend outwardly from said body portion so as to seal, or substantially seal, said annular space, thus reducing or preventing the passage of drilling fluid through said annular space.

2. A wellbore tool as claimed in claim 1, wherein each plate at least partially overlaps with an adjacent plate.

3. A wellbore tool as claimed in claim 2, wherein at least some of said plates have two opposite edges which lie above the edges of adjacent plates, and at least some of said plates have two opposite edges which lie below the edges of adjacent plates.

4. A wellbore tool as claimed in claim 2, wherein each plate has one edge which lies above an edge of an adjacent plate, and has an opposite edge which lies below an edge of an adjacent plate.

5. A wellbore tool as claimed in any preceding claim, wherein said body portion is cylindrical.

6. A wellbore tool as claimed in any preceding claim, wherein in said closed position each of said plates lies substantially in a plane which is substantially parallel with a longitudinal axis of said wellbore.

7. A wellbore tool as claimed in any preceding claim, wherein in said open position each of said plates lies substantially in a plane which lies at an angle relative to a longitudinal axis of said wellbore, and wherein said angle is between 30 and 90 degrees.

8. A wellbore tool according to claim 7, wherein said angle is between 30 and 60 degrees.

9. A wellbore tool as claimed in claim 7 or 8, wherein said angle is substantially 45 degrees.

10. A wellbore tool as claimed in any preceding claim which further comprises at least one pin which is movable between an extended position in which the pin drives at least one of said plates into said open position, and a retracted position in which said at least one of said plates moves into said closed position.

11. A wellbore tool as claimed in claim 10, which comprises at least four of said pins.

12. A drilling arrangement comprising a drill bit, a drill string for driving said drill bit, and a wellbore tool as claimed in any preceding claim.

13. A drilling arrangement as claimed in claim 11, wherein each of said plates has a proximal edge which is hingedly connected to said body portion, and a distal edge which is adapted to engage with said inner wall of said wellbore when said plates are in said open position.

14. A drilling arrangement as claimed in claim 12, wherein, at least in said closed position, said distal edge of each plate is closer to said drill bit than said proximal edge.

15. A drilling arrangement as claimed in any one of claims 12 to 14, wherein said wellbore tool is positioned between said drill bit and a portion of said drill string.

16. A drilling arrangement as claimed in any one of claims 12 to 15, wherein said wellbore tool is attached to, and forms part of, said drill string.

17. A method of reducing or stopping a loss of drilling fluid in a wellbore using a wellbore tool as claimed in any one of claims 1 to 11, or a drilling arrangement as claimed in any one of claims 12 to 16, said method comprising the steps of:

detecting a loss of drilling fluid in said wellbore;

5 in response to detecting said loss of drilling fluid, moving said plurality of plates to said open position.

18. A method as claimed in claim 17, which further comprises:

in response to detecting said loss of drilling fluid, also stopping any pumping of

10 drilling fluid into said wellbore.