GB2066332A - Drilling stabiliser - Google Patents

Abstract

A drilling stabiliser of the lock-on type comprises a main sleeve 10 internally threaded at each end 13A, 13B having a centrally disposed internal collar 14 laterally of which are conical surfaces 15A, 15B. A tubular end cap 24A, 24B which is externally threaded 25A, 25B, is provided for attachment to the threaded ends of the sleeve 10 and these end caps 24A, 24B are respectively mechanically interlocked to a split ring 21A, 21B, each of which has an external conical surface 23A, 23B, for engagement with conical surfaces 15A, 15B, of the main sleeve. The interlocking arrangement comprises an annular groove 27A, 27B, on the bore of the end cap and an annular rib 28A, 28B, on the external surface of the pertaining split ring, such that the mechanical interlock is maintained to withdraw the split rings 21A, 21B, during the release procedure. <IMAGE>

Description

SPECIFICATION Drilling stabiliser This invention relates to a drilling stabiliser.

Oil field drilling operations utilizing a rotary drill string and having one or more sections of drill collar above the drill bit require the application of drilling stabilisers in order to minimise the seizure of the drill collars within the drill bore and to stabilise the drill string during drilling operations.

Conventionally drilling stabilisers have been formed integrally with a drill collar section but recently a form of stabiliser has been proposed which clamps externally to the drill collar section and which can therefore be located at any desired position along the length of the drill collar section.

These latter stabilisers are known as the 'lock-on' type and they are described in U.K. Patent Specification No. 2,005,750A.

It is an object of the present invention to provide an improved form of lock-on stabiliser.

According to the present invention a drilling stabiliser comprises: a substantially cylindrical rigid main sleeve the bore of which has threaded portions at each end the intermediste bore portion comprising two radially-inwardly divergent conical surfaces each terminating at a common collar of sufficient size to permit the sleeve to be slidably received over a drill collar section, clamping means positioned internally of the main sleeve and comprising two split rings each with a single split opening and each with a radially-inwardly divergent conical external surface for engagement with one of the conical surfaces of the main sleeve, the rings being of sufficient bore size to be slidably received over a drill collar section, two tubular end caps threadedly received by the main sleeve and respectively mechanically interlocked with the two split rings whereby as the end caps are threadedly received by the main sleeve the conical surfaces of the split rings engage the conical surfaces of the main sleeve to reduce the bore of the split rings for clamping the stabiliser to a drill collar section and each split ring is disengaged axially from the pertaining conical surface of the main sleeve as the pertaining end cap is threadedly removed from the main sleeve.

Preferably the mechanical interlock between the tubular end caps and the split rings comprises an annular groove on the inner surface of each end cap and an annular rib on the outer surface of each split ring, the split rings extending internally of the end caps.

Preferably the half cone angle of the conical surfaces of the main sleeve and of the split rings is about 10 degrees.

Preferably a stop is provided to limit the axial extent to which each end cap can be threaded onto the main sleeve. Conveniently the stop is in the form of an annular shoulder between the threaded portion and the adjoining conical surface of the main sleeve bore against which the end face of the end cap abuts.

Preferably the outer surface of each end cap includes an annular shoulder which is axially spaced from the adjoining end face of the main sleeve when the end cap is fully threadedly received by the main sleeve and the dimensions of the end caps, the split rings and the main sleeve are such that when each end cap annular shoulder is spaced by a predetermined distance from the adjoining end face of the main sleeve the inner surface of the end caps, the split rings and the common collar of the main sleeve bore provides a passageway of substantially constant diameter for receiving a drill collar section.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing which is a longitudinal cross-sectional view of a drilling stabiliser.

The stabiliser illustrated comprises a substantially cylindrical rigid main sleeve 10 made of 4145H steel (U.S. standard specification) having on its external surface a plurality of flanges 11 for effecting stabilised engagement with the drill bore (not shown). The flanges 11 may be axial or helical. The bore 12 of the sleeve 10 is screw threaded at each end 1 3A, 1 3B and axially between the threaded portions 1 3A, 1 3B there is a common collar 14 of sufficient size to permit the sleeve 10 to be slid over a drill collar section (not shown). Axially on either side of collar 14 there is a conical surface 1 5A, 1 5B each of which is radially-inwardly divergent and terminates at the collar 14.At their larger diameter end the surfaces 15A, 15B merge into cylindrical surfaces 1 6A, 1 6B which are each spaced from the adjoining threaded portion 1 3A, 1 3B by an annular recess 1 7A, 1 7B so that between recess 1 7A and surface 1 6A an annular shoulder 1 8A is formed, a corresponding shoulder 1 8B being formed between recess 1 7B and surface 16B. The sleeve 10 has end faces 1 9A, 1 9B. The half cone angle of the surfaces 1 5A, 1 5B is about 100 and the screw threading on portions 1 3A, 1 3B is conveniently of the Acme type but may be Dardelet.

Within the sleeve 10 there is provision for clamping means whereby the sleeve 10 can be clamped to the external surface of a drill collar section, this means taking the form of a pair of split rings 21 A, 21 B each of which has a single split opening 22A, 22B respectively.The outer surface of each ring contains a conical surface 23A, 23B respectively which is radially-inwardly divergent having a half cone angle of about 100 and is arranged for engagement with the respective conical surface 1 SA, 1 SB. The rings 21 A, 21 B are respectively mechanically interlocked as will be explained to tubular end caps 24A, 24B each of which is externally threaded at 25A, 25B respectively for threaded engagement with the screw threaded portions 1 3A, 1 3B of the main sleeve 10.The external surface of the end caps 24A. 24B also incorporates an annular shoulder 26A, 26B respectively which, when the end caps are fully threadedly received by the sleeve 10, are axially spaced from the adjoining end face 1 9A, 1 9B of the sleeve 10. The end faces of the caps 24A, 24B are 29A, 29B respectively.

In order to provide the mechanical interlock between the end cap and the pertaining split ring the inner surface of the end cap has an annular groove 27A, 27B and the external surface of the split ring-has an annular rib 28A, 28B such that rib 28A fits into groove 27A and rib 28B fits into groove 27B. Thus, as the end caps with the split rings interlocked thereto are threaded onto the main sleeve the conical surfaces of the split rings engage the conical surfaces of the sleeve to reduce the bore of the split rings for clamping the stabiliser to a drill collar section and as the end caps are threaded out of the sleeve the split rings are withdrawn with them by virtue of the mechanical interlock.

It will be understood that with the split rings fitted to and interlocked with the end caps, but in the absence of radial compression by the main sleeve the bore of the stabiliser is sufficiently large to be slid over a drill collar section. Furthermore the various components are dimensioned so that when shoulder 26A is brought to a predetermined distance from end face 1 9A (and similarly with shoulder 26B and end face 19B), conveniently by means of a plastics split ring spacer element, the stabiliser provides a through passageway of substantially constant diameter which is free of abutments which might snag the entry of the drill collar section.

When the stabiliser has been correctly positioned axially with respect to the drill collar section the plastic spacer elements can be discarded and the end caps tightened into the sleeve to clamp the stabiliser to the drill collar section, this tightening effect being limited by the abutment of the face 29A with shoulder 1 8A and end face 29B with shoulder 1 SB, the dimensions of the grooves 27A, 27B and the ribs 28A, 28B being such that the mechanical interlock is maintained even at the limit of the tightening procedure. By way of modification it will be appreciated that the stop for preventing overtightening could be achieved by shoulders 26A, 26B of the end caps abutting end faces 1 9A, 1 9B of the sleeve.

Claims (7)

1. A drilling stabiliser comprises: a substantially cylindrical rigid main sleeve the bore of which has threaded portions at each end the intermediate bore portion comprising two radially-inwardly divergent conical surfaces each terminating at a common collar of sufficient size to permit the sleeve to be slidably received over a drill collar section, clamping means positioned internally of the main sleeve and comprising two split rings each with a single split opening and each with a radially-inwardly divergent conical external surface for engagement with one of the conical surfaces of the main sleeve, the rings being of sufficient bore size to be slidably received over a drill collar section, two tubular end caps threadedly received by the main sleeve and respectively mechanically interlocked with the two split rings whereby as the end caps are threadedly received by the main sleeve the conical surfaces of the split rings engage the conical surfaces of the main sleeve to reduce the bore of the split rings for clamping the stabiliser to a drill collar section and each split ring is disengaged axially from the pertaining conical surface of the main sleeve as the pertaining end cap is threadedly removed from the main sleeve.

2. A stabiliser as claimed in claim 1, wherein the mechanical interlock between the tubular end caps and the split rings comprises an annular groove on the inner surface of each end cap and an annular rib on the outer surface of each split ring, the split rings extending-internally of the end caps.

3. A stabiliser as claimed in either preceding claim, wherein the half cone angle of the conical surfaces of the main sleeve and of the split rings is about 10 degrees.

4. A stabiliser as claimed in any preceding claim, wherein a stop is provided to limit the axial extent to which each end cap can be threaded onto the main sleeve.

5. A stabiliser as claimed in claim 4, wherein the stop is in the form of an annular shoulder between the threaded portion and the adjoining conical surface of the main sleeve bore against which the end face of the end cap abuts.

6. A stabiliser as claimed in any preceding claim, wherein the outer surface of each end cap includes an annular shoulder which is axially spaced from the adjoining end face of the main sleeve when the end cap is fully threadedly received by the main sleeve and the dimensions of the end caps, the split rings and the main sleeve are such that when each end cap annular shoulder is spaced by a predetermined distance from the adjoining end face of the main sleeve the inner surface of the end caps, the split rings and the common collar of the main sleeve bore provides a passageway of substantially constant diameter for receiving a drill collar section.

7. A drilling stabiliser substantially as hereinbefore described with reference to the accompanying drawing.