Boring or penetrating the earth – Means traveling with tool to constrain tool to bore along...
Reexamination Certificate
1999-10-08
2001-08-28
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
Means traveling with tool to constrain tool to bore along...
C175S065000
Reexamination Certificate
active
06279669
ABSTRACT:
BACKGROUND
This invention relates to an indexing mechanism and to apparatus incorporating the same. In various industries, for example the oil extraction industry, it is necessary to control certain pieces of equipment at a considerable distance from where the operator is positioned. In some industries this can be achieved by the use of radio-controlled apparatus, but this is not practicable with submarine or subterranean drilling exercises. The control apparatus can, in certain technical fields, be actuated by electrical signals passed through conventional electrical conductors but this is not satisfactory in the field of drilling for oil or gas, where severe conditions are encountered.
In the drilling field a drill string, formed of lengths of drill pipe joined in end-to-end relationship, is fed down the wellbore. Whilst it may be desirable to actuate certain apparatus at intermediate regions along the length of the drill string, often the most important apparatus to control is at that part of the drill string furthest from the operator, i.e. near the drill bit. Generally speaking the drill string can be regarded as a hollow duct, through which drilling fluid (also known as drilling mud) is passed under pressure. Under certain circumstances it is desirable to allow the drilling fluid being passed under pressure down the drill string to by-pass the drilling bit, by venting through lateral ports and being allowed to return up the bore hole. Thus, it is desirable to be able to control effectively the opening and closing of such ports or the access to, and shutting off of, such ports.
Furthermore, it may also be desirable to actuate a stabiliser incorporated in the drill string. Such a stabiliser may have a plurality of elements capable of being moved radially outwardly, under suitable actuation, so as to engage the internal surface of the wellbore, such elements and the sleeve with which they are associated then remaining prevented from rotation relative to the wellbore, whereas the mandrel within the sleeve, which mandrel forms part of the main duct of the drill string, is free to continue to rotate.
Moreover, in a three-dimensional steering tool where there is an articulated joint it is necessary to impart some degree of eccentricity to the drill string immediately upstream of the joint, the effect of which is that the drill bit, on the remote side of the articulated joint, is forced out of a rectilinear relationship, thereby enabling the drill string to be “steered”.
SUMMARY
According to a first aspect of the present invention, there is provided, within a longitudinally-extending main housing having a longitudinally-extending duct, an indexing mechanism which comprises:
a mandrel within the duct and capable of longitudinal movement relative to the main housing;
a cam sleeve mounted for rotation on, and with respect to, the mandrel but constrained in terms of longitudinal movement with respect to the mandrel, the cam sleeve having an external surface provided with a groove in the form of a closed loop;
a cam follower mounted relative to the main housing and resiliently urged into the groove of the cam sleeve;
main restoring means tending to urge the mandrel in a first direction along the duct; and
a fluid abutment face, on which, in use, fluid under pressure can act to tend to urge the mandrel in a second direction opposite to the first direction;
wherein the groove has ramps and associated steps thereby restricting relative movement of the cam follower with respect to the groove, to one direction progressively around the closed loop; and
wherein the groove has a plurality of rest positions at which the cam follower can rest, depending on whether the force of the main restoring means dominates the force of the fluid pressure, or vice versa:
the arrangement of the indexing mechanism being such that, with the main restoring means initially dominating the force of the fluid pressure, the mandrel is urged in the first direction and carries the cam sleeve in the first direction until the cam follower has travelled a first leg of the closed loop and comes to a first rest position in the groove; but when the fluid pressure is increased so that the force of the fluid pressure exceeds the force of the main restoring means, the mandrel is moved in the second direction, carrying the cam sleeve with it, the cam follower moving along the next leg of the closed loop of the groove until a second rest position is reached, and remaining there until the fluid pressure is reduced sufficiently such that the force of the main restoring means exceeds again the force of the fluid pressure, whereupon the mandrel moves again in the first direction, carrying the cam sleeve with it, with the cam follower travelling along a third leg of the closed loop to a third rest position, and so on, until a complete cycle of the closed loop is effected.
The groove can be thought of as having a plurality of legs, each comprising a ramp terminating in a step. The cam follower rises along each ramp and, at the end thereof, drops down the step to a rest position. The step is such that the cam follower cannot “climb” back up the step, but can only move forward along the next leg in a progressive manner, i.e. as a positive index.
In one convenient arrangement of the indexing mechanism the closed loop of the groove appears on only part of the circumferential external surface of the cam sleeve such that, in operation, during one complete cycle with the cam follower following the whole of the closed loop, the cam sleeve will rotate in opposite directions about its longitudinal axis.
In an alternative convenient arrangement of the indexing mechanism, the closed loop of the groove extends around the whole circumference of the cam sleeve such that, in operation, during one complete cycle the cam sleeve will undergo one complete revolution about its longitudinal axis.
Preferably the cam follower is a ball urged by resilient means into the groove, with the resilient means preferably being a compression spring. Preferably the ball moves radially in a bore in the main housing, which is radial with respect to the main longitudinal axis of the indexing mechanism. The ball is free to rotate about its own centre; and it rises and falls as it follows the ramps and steps of the groove.
Depending on the mode of operation, it is possible, for example, for the groove to have four steps and four rest positions.
Another convenient arrangement is that wherein the groove has six steps and six rest positions.
The main restoring force is conveniently a major compression spring.
Conveniently the fluid abutment face is a perforated plate on which fluid under pressure moving in the second direction can act so as to tend to cause the mandrel to move in the second direction.
Preferably the indexing mechanism includes bearing assemblies to assist in free rotation of the cam sleeve relative to the mandrel.
Preferably the mandrel is provided with sealing mechanisms for sealing the mandrel with respect to the internal surface of the duct of the main housing.
Depending on what the indexing mechanism is to assist in controlling, the mechanism usually includes actuating means associated with the mandrel and capable of reciprocating longitudinal movement in the first and second directions with the mandrel.
In the oil exploration field, a preferred arrangement is that wherein the mandrel is hollow and the actuating means is also hollow, whereby fluid under pressure moving in the second direction can pass through the hollow bore within the mandrel and through the actuating means.
According to a second aspect of the present invention, there is provided a drill string portion which includes a main housing incorporating an indexing mechanism in accordance with the first-mentioned aspect of the present invention, and an upper housing connection and a lower housing connection connected to opposite end regions of the main housing.
According to a third aspect of the present invention, there is provided a by-pass tool which includes a drill string portion according
Abbott Malcolm Adrian
Swietlik George
Pezzuto Robert E.
Pilot DRilling Control Limited
Seyfarth Shaw
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