GB2147033A - Improved drilling tools - Google Patents

Abstract

An oil drilling tool having a plurality of stabiliser blades 13 and with each blade housing an undercut groove containing an inlay 14 of a wear resistant material, is characterised in that each groove runs substantially transverse to its blade. This makes it possible to cut the grooves by a simple tool such as a lathe. The grooves could be formed by removing material in a series of adjacent but axially spaced circular cuts. Alternatively they could be part of a continuous left-hand or right-hand helix. Preferably a single respective backing strip 15 extends the length of each blade and all the wear resistant strips of that blade abut it. <IMAGE>

Description

SPECIFICATION Improved drilling tools The invention relates to improved drilling tools.

The invention is particularly applicable to tools for use in drilling for oil or for natural gas, and is especially concerned with the stabilisation of directional drilling in varying formations, particularly when drilling through hard rock.

The quality and face design of the stabiliser blades is a major factor in deciding the quality and ease of directional drilling when using such tools. Hitherto it has been conventional to braze the wear surfaces to the tool blades.

UK Patent Specification No 1 372 181 (Groom) shows an oil drilling tool whose blades run lengthwise of the tool body and are straight. UK Patent Specification No 1 293 905 (Lion Oil Tool Holdings) shows a tool in which the blades again run lengthwise of the tool body but are skewed. In each case, the wear surfaces are brazed to the tool blades.

This conventional brazing is a highly skilled manual operation, and the quality of the finished tool relies very heavily on the skill and consistency of the brazing operator. This overreliance on individual manual skill and concentration is undesirable.

It is also known to provide the blade of an oil drilling tool with a wear surface using a method which comprises the steps of inserting a tungsten carbide inlay into an undercut groove running lengthwise of the blade and heating the mass until the inlay bonds to the groove.

The tungsten carbide inlays may be replaced by ceramic wear surfaces.

These known tools suffer from the disadvantage that during manufacture it is extremely difficult to machine the undercut grooves. It is necessary to use a milling machine, whereby the manufacturing process is lengthy and the finished article consequently more expensive.

It is an object of the present invention to overcome the above machining difficulty, and to provide a tool having undercut grooves which may be cut by a simple tool which is a lathe.

According to the present invention, there is provided an oil drilling tool having a plurality of stabiliser blades, each blade housing an undercut groove running substantially transverse to the blade and containing an inlay of a wear resistant material.

The wear resistant material is preferably tungsten carbide.

Hitherto, as exemplified in the two UK patent specifications listed above, it has been conventional to use fragmented tungsten carbides bonded into a matrix of brass. If the inlay itself is solid tungsten carbide strip, the wear properties are greatly improved.

There are preferably a plurality of grooves in each blade, generally running substantially parallel one to the other.

The grooves could be formed by removing material in a series of adjacent but axially spaced circular cuts. Alternatively, the grooves could be part of a continuous left-hand or right-hand helix, formed by a thread cutting lathe.

Since the major forces acting on the wear resistant strips tend generally to push them along their respective grooves, there may also be provided a backing strip so dimensioned and located as to abut the end of each wear resistant strip and prevent it from being pushed out of its groove by frictional contact with the bore hole walls.

There may be provided a backing strip which extends the length of each blade. It may be a bright steel bar and be welded along the length of the blade.

An oil drilling tool faced in a manner embodying the invention may be characterised in that some or all of its blades exhibit faced portions separated by an unfaced portion.

Such a tool, correctly designed, can then be reversible end-for-end and will have a longer life than an irreversible tool.

A tool of the kind just outlined may exhibit blades of herring-bone pattern with the arms of each herringbone faced in a manner embodying the invention and separated by an unfaced portion in the region where the arms meet. This enables the advantageous herringbone-pattern faced blade to be readily produced and renewed.

One oil drilling tool embodying the invention is shown, by way of example only, in the accompanying drawings. The tool, and the method of facing its blades, will now be described with reference to those drawings, in which: Figure 1 shows the tool in side elevation; and Figure 2, drawn to a much larger scale, shows in cross-section along the line ll-ll, the inlays and its backing strip.

Referring initially to Fig. 1, a "near-bit" stabiliser consists essentially of a hollow elongate linear circular-cylindrical body 11 enlarged in diameter about its mid-length region to provide an externally-faced upset 1 2. The stabiliser is "double-boxed", ie. bored and internally threaded at each of its opposite ends as indicated in broken line in Fig. 1. The precise details of the double-box connections can be settled without inventive thought by the intended skilled addressee of this specification, and need not be pursued here.

Blades 1 3 are formed lengthwise of the tool body by machining channels 1 3a out of it.

Each thus-defined blade 1 3 is elongate and linear, and although it runs lengthwise of the tool body it runs at an angle to the tool axis.

Each channel 1 3a is of identical width, and the blades 1 3 are equally circumferentially spaced about the periphery of the upset 1 2.

Each blade 1 3 is trapezoidal in cross-section, and is provided with a plurality of undercut grooves each of which is also trapezoidal in section. All the grooves are linear and elongate, and of constant depth throughout their length; and all run from one to the other of the flanks of the blades. Similarly elongate linear tungsten carbide or other ceramic inlays 14 are pressed, machined, and sintered and are each inserted into the undercut trapezoidal-section grooves running across the blades 1 3. The flanks and base of each inlay, and of each groove, are coated with a low melting point flux and alloy paste, and the inlays are pushed along their grooves until they occupy the positions illustrated in Fig. 1.

There are a number of inlays 14 which continue along the length of the blade 13, which are not shown for clarity. The grooves shown in Fig. 1 form a helix, separated of course by the channel 1 3a, which continues around the periphery of the upset 1 2. However, the grooves could form a plurality of axially spaced annularly extending around the upset 1 2. A backing strip 1 5 is welded along one edge of each blade to hold the inlays 14 from being forced out of the groove by friction with the bore hole wall. The backing strip is preferably a bright steel bar with dimensions half inch by quarter inch.

The tool body is so machined that the inlays 14 can be inserted into either end of their undercut receiving grooves and then advanced along grooves to their desired final positions.

The inlaid tool is then put into an oven and heated, and the oven temperature is monitored by thermocouples. The temperature of the tool body, especially in the groove region, is similarly carefully monitored. The body is heated by gas, electric inducation coils, or any other suitable means until the flux melts and bonds each inlay into its groove. As soon as that occurs, heating stops, and the tool is allowed then to cool progressively before being taken out of the oven.

The skilled reader will of course determine the temperatures to which different tool body and tungsten carbide inlay combinations need to be heated, but very accurate means of monitoring the tool body temperature have been available for many years and this accuracy of control and termination of the process is a major advantage of the invention.

A suitable flux paste can similarly be selected by the reader from known alternatives.

A further advantage of the trapezoidal inlays is that, the more wear takes place, the larger is the wear resistant surface.

Claims (9)

1. An oil drilling tool having a plurality of stabiliser blades, each blade housing an undercut groove containing an inlay of a wear resistant material, and characterised in that each groove runs substantially transverse to its blade.

2. A tool according to Claim 1 and in which the inlay is a solid tungsten carbide strip.

3. A tool according to Claim 1 or Claim 2 and in which there are a plurality of grooves in each blade, generally running substantially parallel one to the other.

4. A tool according to any of Claims 1 to 3 and in which the grooves have been formed by removing material in a series of adjacent but axially spaced circular cuts.

5. A tool according to any of Claims 1 to 3 and in which the grooves are part of a continuous left-hand or right-hand helix.

6. A tool according to any of the preceding Claims and with a backing strip so dimensioned and located as to abut the end of each wear resistant strip and, in use, resist the tendency of that strip to be pushed out of its groove by frictional contact with the bore hole walls.

7. A tool according to Claim 6 and in which a single respective backing strip extends the length of each blade and all the wear resistant strips of that blade abut it.

8. A tool according to any of the preceding Claims and characterised in that some or all of its blades exhibit faced portions separated by an unfaced portion.

9. A tool according to Claim 8 and having blades of herring-bone pattern with the arms of each herringbone faced in a manner according to any of the preceding Claims and separated by an unfaced portion in the region where the arms meet.

1 0. An oil drilling tool substantially as described with reference to and as illustrated in the accompanying drawings.