WO1999028590A1

WO1999028590A1 - Drilling tools and wear detection methods

Info

Publication number: WO1999028590A1
Application number: PCT/NZ1998/000174
Authority: WO
Inventors: Geoffrey Neil Murray
Original assignee: Weatherford U.S., L.P.
Priority date: 1997-11-27
Filing date: 1998-11-27
Publication date: 1999-06-10
Also published as: AU1696699A

Abstract

A drilling tool (11; 23) having a cavity (8, 21) for containing a detectable substance. A wall (13) of the cavity or a passage (29) extending from the cavity (21) is located adjacent a surface (17; 28) exposed to wear. When the surface (17; 28) is worn down to a certain level the detectable substance is released to the exterior of the tool (11; 23). The detectable substance may then be detected in pumping fluid returned to the surface to indicate that the tool has been worn to a certain extent.

Description

DRILLING TOOLS AND WEAR DETECTION METHODS

Field of the Invention

The present invention relates to methods and apparatus for detecting mechanical wear and/or failure in downhole drilling equipment. More particularly, although not exclusively, the present invention relates to methods and apparatus for detecting wear and/or failure of drilling components used in oil, gas, geothermal or other well drilling environments.

Background to the Invention

Considerations of wear and failure in relation to downhole drilling equipment are essential. Due to the nature of the downhole environment, as well as difficulty in retrieving objects from such an environment, there are various components of downhole equipment which should only be operated up to a certain degree of wear. For example, drilling stabilisers serve to minimise drill string whip and vibration, tool joint wear and reduce the tendency for the drill bit to wander. Excessively worn stabilisers can result in the above mentioned problems either singularly or in combination.

Wear is also an important consideration in relation to roller cone rock bits. Excessive wear can lead to bearing seal failure which is quickly followed by bearing failure and ultimately the loss of a cone. The loss of a cone results in loss of productive drilling time due to the effort and time required to pull out the drill string and fish the lost cone. A further problem arising from drilling with any type of bit which is worn to less than a specified diameter (i.e. below gauge), is that it may be difficult to case the well due to inadequate running clearance between the well casing and the well bore. Further, insufficient annular space between the outside of the casing and the wall of the bore may result in inferior cementing which could result in fluid communication between differentially pressured zones. Loss of gauge is normally considered to be of sufficient importance to justify rectification by means of reaming. Such a remedial step involves considerable time and expense.

To the present time, most drilling contractors decide to pull out a bottom hole assembly based on their experience of drilling in the area coupled with their clients requirements in terms of bore gauge and bore straightness. In most cases, the optimum life of stabilisers or bits would not be realised due to the drilling contractor being either overly conservative or being too optimistic regarding tool life leading to the loss of parts downhole as well as compromising bore gauge and straightness.

It is an object of the present invention to provide a wear detection method and apparatus which may be used to indicate either imminent failure, predetermined wear level or failure of a downhole component and at least ameliorate a number of the above mentioned disadvantages, or to at least provide the public with a useful choice.

Disclosure of the Invention

In one aspect, the invention provides a drilling tool having a cavity for containing a detectable substance wherein one wall of the cavity or a closed passage from the cavity is located proximate a surface of the tool which is exposed to wear in use and which will allow a substance to be released when the surface proximate the wall or passage is worn to a certain extent.

The detectable substance may be such that when a predetermined amount of wear has occurred, the ejection of the detectable substance can be detected in drilling fluid pumped out of a well bore in which the drilling device is inserted.

The detectable substance may be a radioactive isotope, odorant, fluorescent dye or similar. Suitable radioactive isotopes include Cobalt 60, Barium 131, Indium 113/114 or similar. Suitable odorants include ethyl mercaptan and methyl mercaptan, mixtures thereof or similar odorant(s).

There is further provided a method of detecting wear of a drilling tool having a cavity for containing a detectable substance wherein one wall of the cavity or a closed passage from the cavity is located proximate a surface of the tool which is exposed to wear in use and which will allow a substance to be released when the surface proximate the wall or passage is worn to a certain extent comprising: at least partially filling the cavity with a detectable substance; using the drilling tool in a drilling application; and monitoring material exiting a well to determine whether the detectable substance has been released.

Brief Description of the Drawings

The invention will now be described by way of example only and with reference to the drawings in which:

Figure la illustrates a cross-sectional view through a stabiliser;

Figure lb illustrates an enlarged view of the wear detection device shown in figure la; and

Figure 2 illustrates a wear detection embedded device in a drill bit.

Referring to figure la, a cross-sectional view through a drilling stabiliser 10 is shown. The drilling stabiliser provides standoff by means of an annular ring 11. The annular ring includes wear surfaces 12 which are brought into mechanical contact with the interior surface of a well in use.

Referring to figure lb, details of the wear detection device are shown. A reservoir 14 is inserted into a cavity 8 and retained by a retention means 13. The reservoir 14 is biased against the retention means using a bias means 16. In a preferred embodiment, the bias means 16 is a spring. The retention means in the present case, corresponds to a threaded plug 13 which is screwed into a complimentary thread 15 in cavity 8. The exterior surface of the retention means 17 is shaped and adapted so as to smoothly conform with the wear surface 12. In operation, a detectable substance is encapsulated in the reservoir 14. The reservoir is inserted into the cavity 8 and the retention means 13 secured by means of the thread.

During use, the wear surface 12 of the stabiliser is mechanically degraded by contact with the interior surface of the well. As the wear surface 12 is worn down the wear surface 17 of retention means 13 is also degraded. Further wear results in the cavity 8 becoming exposed to the drilling environment. At this point, the bias means 16 ejects the reservoir 14 from the cavity 8 where upon the reservoir is destructively opened thus releasing the detectable substance.

As can be seen from figure lb, the radial dimensions of the cavity, the retention means and the reservoir may be selected so as to provide a highly specific degree of wear which must be encountered before the detectable substance is released. In the example shown in figure lb, the detectable substance will be released while there is still a wear surface 12 left. Once the release of the detectable substance is detected, the drill string can be withdrawn prior to failure or any other deleterious effects such as those discussed above.

An alternative embodiment is shown in figure 2. A reservoir 21 is formed as a cavity inside a drill bit body 23. The reservoir 21 is retained by means of a plug 31 which allows for insertion, servicing and placement of a detectable substance within the reservoir 21. In use, the plug 31 is secured in place.

The reservoir is connected to a passage 22 having a first end 30 and second end

29. The second end 29 positioned so that it is immediately adjacent a wear surface 28. In the present case, this wear surface is chosen so as to be indicative of the point at which failure and/or loss of drilling cone may occur.

The reservoir may be pressurised by means of a piston 25 which moves within of the cavity. The piston is sealed by means of O rings 32a and 32b which retain the detectable substance within the reservoir 21. The piston is forced against the reservoir 21 by means of pressure transmitted thorough a pressure line. The pressure line emerges from the drill bit body in the region indicated by 33 A. In an alternative embodiment, the piston may be biased by a biasing means such as a spring thereby pressurising the reservoir.

A charging passage 34 may be provided to allow charging of the reservoir 21. This may be sealed by a non return valve 24.

In the pre-failure state, the wear surface 28 is sufficiently thick so as to prevent the pressurised ejection of the detectable substance 21 via the passage 22. As the drill bit is used, the wear surface immediately adjacent the second end of passage 29 gets thinner and thinner. Once sufficient wear has occurred, the wear surface 28 exposes the second end of 29 of the first passage 22. Once this occurs, the pressure caused by pumping of drilling fluid exerted through a pressure passage 3 forces the piston along the cavity and into the reservoir 21 thus ejecting the detectable material contained therein. The detectable material returns to the surface via pumping of the drilling fluid and thus a particular degree of wear of the drill bit is indicated and, if necessary, the drill string withdrawn.

The detectable substance may be a powder, liquid, gaseous or other suitable material which is selected so as to provide a suitable degree of indication to a surface observer.

In a preferred example, the detectable substance is a radioactive tracer, which, once the wear surface is sufficiently abraded, provides an unambiguous indication that a predetermined degree of wear has occurred and that the drill string and drill bit should be withdrawn from the well.

Suitable radioactive isotopes include Cobalt 60 which is a gamma-ray emitter. The radioactivity of the drilling fluid may be monitored by means of GeLi detectors located at the surface. Alternatively, Nal detectors may be used to detect the gamma-rays. While the latter type of gamma-ray detector does not exhibit particularly good resolution, it is nevertheless more efficient than the former. This may be of importance where only small quantities of the detectable material are returned to the surface in the pumping fluids.

A variety of suitable radioactive isotopes may be used at one time with the detection electronics adapted or programmed to identify each individual tracer. By using this method, it is envisaged that it will be possible to identify which components have failed. Similarly, if an odorant type tracer is used, a gas chromatograph type detector would be used. Again, the detection electronics may be programmed to allow the differentiation of the various odorants which may be used thus allowing the failure of different downhole components to be distinguished.

Detection electronics (not shown) connected to a radiation detector (not shown) may be configured so that when the radiation exceeds a predetermined threshold and/or of specific signature, a warning or similar notification is provided where upon drilling may be halted and the drill string withdrawn from the well.

It is envisaged that, with suitable selection of a radioactive isotope, the health and safety hazards posed by short lived isotopes may be minimised while at the same time avoiding the necessity to rapidly obtain such isotope from a supplier before its activity reduces to below a useful level. To this end, it is possible that activation methods may be used to sustain the radioactivity of a particular source whereupon the useful life of the source would be only a matter of days once inserted into the detection environment. The selection of a suitable radioactive isotope will also depend on the time delays involved between inserting the isotope into the downhole equipment, the expect time of failure, as well as the viability of obtaining sufficiently intense radioactive sources which meet the required safety standards.

Alternatively, the detectable material may be a fluorescent dye which might be optically detected in a sample of pumping fluid at the surface.

The piston 25 in figure 2 may be replaced by a rupturable membrane or similar type of device. The main function of this component is to transmit the external pressure to the internal reservoir 21 so that upon exposure of the second end 29 to the drilling environment, the detectable material in the reservoir 21 is ejected. Further, the example shown in figure 2 includes only one wear detection point. It is envisaged that the invention may incorporate more than one detectable material ejection passage so that different regions of the drill bit which are susceptible to wear may be monitored simultaneously.

Also, while the present example has been described in the context of a radioactive tracer or dye based detectable material, other substances may suffice so long as their physical characteristics allow them to be detected or measured in a pumping fluid which is recirculated to the surface. Such substances may include coloured dyes or similar substances having a physically detectable presence.

Where in the foregoing description reference has been made to elements or integers having known equivalents, then such equivalents are included as if they were individually set forth.

Although the invention has been described by way of example and with reference to particular embodiments, it is to be understood that modifications and/or improvements may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A drilling tool having a cavity for containing a detectable substance wherein one wall of the cavity or a closed passage from the cavity is located proximate a surface of the tool which is exposed to wear in use and which will allow a substance to be released when the surface proximate the wall or passage is worn to a certain extent.

2. A tool as claimed in claim 1 having a plurality of passages extending from the cavity to locations proximate surfaces of the tool exposed to wear.

3. A tool as claimed in claim 1 or claim 2 including ejection means to force the substance out of the reservoir when the cavity or passage is opened.

4. A tool as claimed in claim 3 wherein the ejection means includes a piston which forces the substance out of the cavity when a cavity wall or passage is opened to the exterior of the tool.

5. A tool as claimed in claim 4 wherein the piston is forced by pressurised fluid.

6. A tool as claimed in claim 4 wherein the piston is forced by a biasing means.

7. A tool as claimed in any one of the preceding claims incorporating a charging passage extending from the exterior of the tool to the cavity to enable the cavity to be filled with a detectable substance.

8. A tool as claimed in claim 7 wherein the charging passage incorporates a non-return valve which prevents the detectable substance from passing from the cavity out via the charging passage.

9. A tool as claimed in claim 1 wherein the cavity contains a breakable reservoir containing a detectable substance.

10. A tool as claimed in claim 9 wherein biasing means are provided between an internal wall of the cavity and the breakable reservoir which biases the breakable reservoir in an outward direction.

11. A tool as claimed in claim 9 or claim 10 wherein the cavity includes a removable plug at one end which, when removed, allows a breakable reservoir to be placed within the cavity.

12. A tool as claimed in any one of the preceding claims wherein the detectable substance is a radioactive isotope.

13. A tool as claimed in claim 12 wherein the radioactive isotope is cobalt 60.

14. A tool as claimed in claim 12 wherein the radioactive isotope is barium 131.

15. A tool as claimed in claim 12 wherein the radioactive isotope is indium 113/114.

16. A tool as claimed in any one of claims 1 to 11 wherein the detectable substance is an odorant.

17. A tool as claimed in claim 16 wherein the odorant is ethyl mercaptan.

18. A tool as claimed in claim 16 wherein the odorant is methyl mercaptan.

19. A tool as claimed in any one of claims 1 to 11 wherein the detectable substance is a fluorescent dye.

20. A method of detecting wear of a drilling tool as claimed in claim 1 comprising: at least partially filling the cavity with a detectable substance; using the drilling tool in a drilling application; and monitoring material exiting a well to determine whether the detectable substance has been released.

21. A method as claimed in claim 20, when dependent upon claim 12, wherein a radiation detector is employed at the well surface to detect whether a radioactive isotope is present in the pumping fluids returned to the surface.

22. A method as claimed in claim 20, when dependent upon claim 19, wherein an optical detector is employed to determine whether a fluorescent dye is present pumping fluid returned to the surface.

23. A method as claimed in any one of claims 20 to 22 substantially as herein described.

24. A tool substantially as herein described with reference to figure 1 or figure 2 of the accompanying drawings.