GB2273160A

GB2273160A - A sound source for a drill string

Info

Publication number: GB2273160A
Application number: GB9324137A
Authority: GB
Inventors: Norbert Froelich
Original assignee: TARGET DRILLING SERV AS
Current assignee: TARGET DRILLING SERV AS
Priority date: 1992-12-03
Filing date: 1993-11-24
Publication date: 1994-06-08
Also published as: GB9324137D0; NO924654L; NO924654D0

Abstract

A downhole sound source, especially for the oil industry, uses the flowing drilling liquid (mud) to move a sound generating member to generate sound by mechanical contact. In one embodiment a rotor 4 having paddle blades 5 is adapted to be rotated in a direction marked by an arrow 7 by drill mud flowing in a direction marked by an arrow 6. The rotor rests against an annular dolly 2, which is attached internally to a drill string 1. The dolly is provided with notches 3 adjusted to corresponding notches 3' on one end of the rotor 4. When the rotor 4 is rotated, the notches 3, 3' will generate sound waves which are transferred to the drill string 1 and further to the formation wherein drilling is taking place. In other embodiments, a rod-shaped spring (10, Figs.3, and 4, not shown) attached to a plumb (11) is oscillated by flowing drilling mud to strike a sleeve (5), and a motor (14, Figs. 5 and 6, not shown) is driven by the drilling mud to rotate a resilient arm (16) engaging a toothed rim (13). <IMAGE>

Description

A SOUND SOURCE FOR A DRILL- STRING The invention relates to a downhole sound source for a drill string, especially but not exclusively for the oil industry.

When drilling for oil and gas, it is an advantage to know the geological formations, and these may to a certain extent be chartered beforehand by means of seismic surveys. More accurate information about the oil well's location, extent and ground conditions is provided afterwards by lowering probes down into the well. However, it is desirable to have a better knowledge of geological formations and the location of the bit within the formation during the drilling operation itself.

It is known to chart geological formations by means of seismic analyses based on sound generated by the bit when it is working. Upon comparison of sound waves picked up by geophones placed at the surface with sound waves within the drill string, it is possible to chart geological formations and to determine the position of the bit. A disadvantage of this known technique is that it can only be used for bits having rotary cutting wheels, because bits having fixed shares do not produce recognisable sound waves of sufficient sound intensity.

An object of the invention is to provide a downhole sound source which may be used with seismic charting of the ground and for determining the position of a bit within the formation, independently of the type of bit.

According to one aspect of the invention there is provided a sound source for a drill string comprising sound generating means arranged to be mounted in a drill string and arranged to be operated by liquid flowing through the drill string to generate sound.

According to another aspect of the invention there is provided a drill string including a sound source according to the first aspect of the invention.

According to a further aspect of the invention there is provided downhole sound source, especially for the oil industry, characterised by an object adapted to be put into motion by flowing liquid and thereby generating sound waves e.g. through rolling, impact or friction against a drill string or a wearing surface placed into the drill string.

In one embodiment the sound source comprises a rotor adapted to be rotated by flowing liquid and provided with notches which, when the rotor is turned, hammer against corresponding notches on a dolly placed internally in the drill string and being attached thereto.

In another embodiment the sound source comprises a spring and a plumb forming an oscillatory circuit adapted to be put into oscillations by flowing liquid, and where the plumb is adapted to beat against the drill string or a sleeve placed internally in the drill string and being attached thereto, when the plumb is put into oscillations.

In a further embodiment the sound source comprises a motor driven by flowing drill mud, and adapted to drive a resilient arm around a toothed rim or other rough surface, whereby the arm produces sound waves which, directly or indirectly, are transferred to the drill string.

Three embodiments of the invention are described in the following by way of example and with reference being made to the attached drawings, wherein: Fig. 1 shows a portion of a drill string equipped with a sound source in a first embodiment, seen in side elevational view and partly in section; Fig. 2 shows the same as Fig. 1, seen from above; Fig. 3 shows a portion of a drill string equipped with a sound source in a second embodiment comprising a swinging plumb placed on a rod-shaped spring, seen in side elevational view and in section; Fig. 4 shows the same as Fig. 3, seen from above; Fig. 5 shows a portion of a drill string equipped with a sound source in a third embodiment comprising a motor driving a resilient arm over a toothed wheel rim, seen in side elevational view and partly in section;; Fig. 6 shows the same as Fig. 5, seen from above and in a section along the line A-A.

In Figs. 1 and 2, reference numeral 1 denotes a drill string wherein is provided an annular dolly 2 attached to the drill string 1 by means of a fastener, not shown. In the upwardly facing end face of the dolly 2, one or more notches 3 have been formed, said .notches 3 fitting into corresponding notches 3' on the downwardly facing end face of a cylindrically tubular rotor 4. The rotor 4 includes a number of turbine blades 5 adapted to be driven from the drill mud flowing within the drill string, whereby the rotor 4 rotates about the longitudinal axis thereof. Drill mud flows in the direction as indicated by an arrow ó, and the rotor 4 turns in the direction as indicated by an arrow 6, and the rotor 4 turns in the direction as indicated by an arrow 7. When the rotor 4 is rotated, it ratchets against the dolly 2.The notches 3, 3' give the rotor 4 a hammering motion against the dolly 2, generating sound waves within the drill string 1.

The sound waves follow the drill string 1 partly downward towards the bit, partly upward towards the surface and pass partly into the drill mud within and outside the drill string. The sound propagates from bit and drill mud to well wall, and may be recorded by geophones at the surface in known manner.

Irregular sound waves or sound waves which are repeated with a pattern or a signature, are easier to distinguish from noise than periodic knocking sounds.

Therefore, it is an advantage to have more than one notch 3, 3', and for some of the notches 3, 3' to have different shapes. If the rotor 4 is rotated with a smooth speed, the sound will then occur as an uneven knocking having an easily recognisable pattern or signature.

Figs. 3 and 4 show a portion of a drill string 1 wherein is provided a sleeve 8. On a fastener 9 within the sleeve 8 is provided a rod-shaped spring 10 which itself is attached to a plumb 11. The spring 10 and the plumb 11 form a mechanical oscillatory circuit. When drill mud flows through the sleeve 8, energy is transferred from the mud flow to the oscillatory circuit, so that the spring 10 carrying the plumb 11 swings to and fro. The spring 10 and the plumb 11 are shown by dotted lines in two extreme positions as 10', 11' and 10", 11". The plumb 11 beats against the inner surface of the sleeve 8, whereby the desired sound waves are generated. In order to stimulate the oscillatory circuit and the movement of the plumb 11, baffles may be installed within the sleeve 8, so that flowing drill mud receives irregular movements adjacent to the plumb 11.

Figs. 5 and 6 shows a portion of a drill string 1 wherein is provided a sleeve 12 provided with an internal toothed rim 13. Further, a motor 14 driven by flowing drill mud is placed within the sleeve 12.

To the outgoing shaft 15 of the motor, a resilient arm 16 is attached, said arm engaging the toothed rim 13.

When the motor 14 drives the resilient arm 16 around the toothed rim 13, the desired sound waves are produced. By varying the tooth shape around the circumference of the toothed rim 13, a characteristic sound pattern may be generated.

Instead of the toothed rim 13, another rough wearing surface may be used.

Claims

1. A sound source for a drill string comprising sound generating means arranged to be mounted in a drill string and arranged to be operated by liquid flowing through the drill string to generate sound.

2. A sound source as claimed in claim 1, wherein the sound generating means comprises a sound generating member which is arranged to be moved by flowing liquid to generate sound by mechanical contact.

3. A sound source as claimed in claim 2, wherein the sound generating means is arranged to generate sound by rolling, impact or friction.

4. A sound source as claimed in claim 2 or claim 3, wherein the sound generating means is arranged to mechanically contact a drill string in which it is mounted to generate the sound.

5. A sound source as claimed in claim 4, wherein the sound generating member comprises a flexible element which has a free end and can be moved by fluid flow in a drill string so that the free end contacts the drill string.

6. A sound source as claimed in claim 2 or claim 3, wherein the sound source further includes a reaction surface and the sound generating member is arranged to mechanically contact the reaction surface to generate the sound.

7. A sound source as claimed in claim 6, wherein the reaction surface is defined by a sleeve.

8. A sound source as claimed in claim 6 or claim 7, wherein the sound generating member comprises a flexible element which has a free end and can be moved by fluid flow in the drill string so that the free end contacts the reaction surface.

9. A sound source as claimed in claim 5 or claim 8, wherein the flexible element has a plumb at the free end.

10. A sound source as claimed in claim 5, 7 or 8, wherein the flexible element is a spring and the arrangement is such that the spring and plumb form an oscillatory circuit arranged to be put into oscillation by flowing liquid.

11. A sound source as claimed in claim 4, wherein the sound generating means comprises two sound generating members which are arranged to be rotated relative to one another by liquid flowing through a drill string and thereby hit each other repeatedly.

12. A sound source as claimed in claim 11, wherein one of the sound generating members comprises a resilient arm.

13. A sound source as claimed in claim 12, wherein the other sound generating member comprises a rough surface.

14. A sound source as claimed in claim 12, wherein the other sound generating member comprises at least one tooth.

15. A sound source as claimed in claim 14, wherein the other sound generating member comprises a toothed rim.

16. A sound source as claimed in claim 11, wherein the sound generating members form a ratchet arrangement and move relatively over one another.

17. A sound source as claimed in claim 11, wherein the sound source includes a sound generatingmember which is provided with notches which, when the member is turned in use hammer against corresponding notches on a dolly.

18. A sound source as claimed in claim 17, wherein the dolly is arranged to be attached internally in a drill string.

19. A sound source as claimed in any of claims 11 to 18, wherein one of the sound generating members is mounted on a: rotor which is arranged to be rotated by flowing liquid.

20. A sound source as claimed in any of claims 10 to 14, wherein one of the members is mounted on a motor which is arranged to be driven by flowing liquid.

21. A sound source for a drill string substantially as described herein with reference to Figs. 1 and 2, Figs. 3 and 4 or Fig. 5 and 6 of the accompanying drawings.

22. A drill string including therein a sound source as claimed in any preceding claim.

23. A drill string as claimed in claim 22, wherein the drill string is for use in oil drilling.