GB2439177A

GB2439177A - Dynamic damper

Info

Publication number: GB2439177A
Application number: GB0710892A
Authority: GB
Inventors: Nils Reimers; Per Haughom
Original assignee: Tomax AS
Current assignee: Tomax AS
Priority date: 2006-06-12
Filing date: 2007-06-07
Publication date: 2007-12-19
Also published as: NO325253B1; GB0710892D0; NO20062728L

Abstract

A device for a tool (1) for use in drilling with a rotary drill bit (5), the purpose of the tool being to provide an axial movement (6) of the drill bit when the torque (4) exceeds a value given in advance. The drill bit is raised so that it is not damaged when the string is suddenly released following a jam. The tool is made up of two cylindrical string parts (8) and (16) connected through guide elements and seals (13) and (15). The string parts (8) and (16) are interconnected through spiral gearings (17) and (18). Relative rotation of the string parts (8) and (16) results in axial movement and compression of the spring (9) to a predetermined pre-tensioning.

Description

1 2439177 A DEVICE FOR A TOOL FOR &CIAL DISPLACEMENT OF THE DRILL BIT

OF A DRILL STRING EXPERIENCING VARIBL,E TORQUE This invention relates to a device for a tool of the kind which is utilized at a rotary drill bit, in which the aim is to provide axial movement of the drill bit when, for a shorter or longer time, the torque exceeds a value given in advance.

Devices of various designs, the purpose of which is to dampen vibrations and maximally limit the torque on the drill io string, are known from the 0 ]. industry among others. In a drill string several thousand metres long, vibrations may arise due to varying torque in the string. Such vibrations are most often caused by the drill bit hitting different rock formations, causing varying torque loads to be applied to the is drill string. When the torque is applied to the drill string from the drilling machine, large amounts of energy are stared, which are released when the drill bit suddenly breaks loose. Uncontrolled release of energy causes extreme strain on the drill string and drill bit. Today's controllable drilling systems are provided with lot of electromechanical equipment, which may be damaged by extreme shocks and vibra-tions.

In the present invention the object is to provide a suitable arid reliable embodiment of a tool which gives the drill bit an axial movement of retraction when the torque in the drill P25NDE-3i.O2OO7 string exceeds a predetermined value. Such a device is par- ticularly well suited for modern drill bits with fixed cut- ters, in which industrially produced diamonds of high hard-ness are used, but in which the structure is brittle and s sensitive to impacts.

Within the oil industry problems associated with overloading of the drill string are well known, and there has been can-tinuous work on different solutions to remedy the problems.

In this connection reference is made to the following pat-io ents: NO 315209 GB 5,083,623 US 4,281,726 EP 065 601 Al US 4,443,206 In principle the present invention has the seine functionality as that of NO 315209, but the technical design is substan-tially different.

Relative to the state of the art, the object of the invention is to provide a device which gives the tool sufficient strength and robustness to withstand the extreme strain to which it is subjected. The tool is designed in such a way that in the event of torque overload it contracts so as to 2 reduce the axial load on the drill bit. Relative to the state of the art, the invention has significant advantages while at the same time it is simpler and more robust. Thereby the risk of breakdowns is reduced, which is extremely important in connection with carrying out costly drilling operations. In addition, substantially smaller costs for production and maintenance are achieved.

P526lNDE-3105 2OfJ7 This is achieved in accordance with the invention by two cy-lindrical string parts being concentrically supported in each other and arranged for limited axial and rotational relative movement. The string parts are connected through a helical gearing which translates rotational, torsion into axial move-ment. Additionally, the string parts are supported in guide elements and with seals. The seal surfaces are formed in such a way that a trapped volume of lubricant is constant, even though the axial length of the tool changes. Centrically io within the cylindrical string parts is arranged a spring pro-viding, together with the helical gearing, the desired func-' tion by relative rotation of the helical gearings of the two cylindrical string parts compressing the spring. Through com-binations of rigidity of the spring and pitch angle of the is helical gearing the desired characteristic of the tool is achieved.

To achieve a spring characteristic which increases with axial movement, a restriction of the fluid flow through the tool is arranged. This restriction is arranged in such a manner that it starts to function at particular axial movement. Thereby the pressure increases, affecting a piston area so that there is an additional force in addition to the spring force. This force is proportional to the pressure increase and the area on which the pressure increase acts. This functionality gives an advantageous function in the tool at extreme loads.

Tools of the device described are fitted into the drill string just behind the main components in the bottom-hole as- sembly, for example a drilling-fluid-driven motor, data ac-quisition Unit and control system, or as an integral part of o the drilling head (bottom-hole assembly) when a rotary drill string is used.

In what follows is described a non-limiting example of a pre-P2536NDE -31 052007 ferred embodiment which is visualized in the accompanying drawings, in which: Figure 1 shows a system overview with the tool together with main components; s Figure 2 shows the tool with a section made therein; Figure 3 shows the helical gearing and spring; and Figure 4 shows a detail in the restriction device.

In figure 1, 1 indicates the tool fitted between a drill string 2 and a drilling-fluid-driven motor 3 connected to the io drill bit 5. 3ehind the drill bit are placed pads 1 for di-rectional control.

Figure 2 shows the tool 1 with a section made therein. Two cylindrical string parts 8 and 16 are concentrically sup-ported relative to each other through guide elements and is seals 13 and 15. The seal surfaces have like diameters.

Thereby relative axial movement of the string parts 8 and 16 does not change an intermediate volume. On the string part 16 is arranged an adapter 29 with holes 11 for fluid flow 22.

The string parts are also connected through the helical gear-ings 17 and 18 on, respectively, the inner and outer string part. When external torque 4, above a specific value, is ap-plied, relative rotation of the string parts 8 and 16 arises, generating axial movement 24.

Pre-tensioning of the spring 9 with the nut 14 detennines at what torque 4 axial movement is to begin. The nut 14 will come to rest on the shoulder 26 of the string part 16, so that large axial forces can be transferred through the two cylindrical string parts B and 16 on to the end adapter 29 with connection to the drill string 2.

P23268NtJ-3l OS 2007 The spring 9 comes to rest on the shoulder 28 an the string part 8 and on the shoulder 30 with connection to the outer string part 16 through the adapter 29.

In the neutral position, with no axial movement between the s outer and inner cylindrical string parts 8 and 16, the fluid flow 22 passes through the openings 11 and 21. By axial move-nient a choke effect is achieved between the surfaces 19 arid 20. The pressure build-up affects the area between the pe-ripheries 19 and 23. The pressure build-up thereby generates a force coming in addition to the spring force from the spring 9.

With this device an intended functionality of the tool is achieved by the fact that it provides improved dampening and is able to withstand extreme loads without going to mechani-cal end stroke.

P7S268JTE -31 052007

Claims

Cia ixns 1. A device for a tool (1) for use in drilling with a ro- tary

drill bit (5), the aim of the tool being to pro-vide an axial movement (6) of the drill bit (5) at a predetermined torque (4), c h a r a c t e r I z e d i n that cylindrical string parts (8) and (16) are concentrically supported with seals and guide elements (13) and (15) of like diameters.

2. The device as described in claim 1, c h a r a c -t e r I z e d i. n that the spring (9) is placed concentrically inside the cylindrical string part (8).

3. The device as described in claims 1 and 2, c Ii a -r a c t e r I z e d i n that restriction of the fluid flow 22 is arranged through the surfaces (19) and (20) by axial movement (24).

P25268WOE-il OS 2001