Boring or penetrating the earth – Cutter element laterally shiftable below ground – Cutter element shifted by longitudinally relatively movable...
Reexamination Certificate
2001-05-19
2003-09-09
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Cutter element laterally shiftable below ground
Cutter element shifted by longitudinally relatively movable...
C175S267000, C166S055800
Reexamination Certificate
active
06615933
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a downhole tool, and in particular to a tool having radially extendable members, such as an underreamer or an expandable stabiliser.
BACKGROUND OF THE INVENTION
In drilling operations, such as the drilling of bores to access subterranean hydrocarbon deposits, the drilled bores are lined with steel tubing, known as casing, which is cemented in place by pumping cement into an annulus between the casing and the bore wall. Once a length of casing is in place, this places restrictions on the diameter of any subsequent sections of bore, as drill bite and any further bore-lining casing must be able to pass through the existing casing. Clearly, reductions in bore diameter are undesirable as, for example, this limits the production flowrate of hydrocarbons through the bore.
It is known to underream beneath a section of casing to increase the bore diameter beyond the internal diameter of the casing in order to, for example, create a bore of sufficient diameter to allow a caning of outer diameter only slightly smaller than the inner diameter of the existing casing to be cemented in the underreamed bore. This is achieved by an underreaming tool which features radially extendable cutters which are initially retracted to permit the tool to be run into the bore on a drill string, and are then extended once the tool has passed beyond the end of the casing, so that drilling and underreaming may commence.
Underreamers of various forms are currently in use, though a number of existing tools have encountered some significant problems. For example, in certain situations underreamer blades have jammed in the extended configuration, such that the underreamer cannot be withdrawn through the existing casing. Of course, this prevents the drill string on which the underreamer is mounted from being withdrawn from the bore; rectifying this situation involves considerable inconvenience and expense.
It is among the objectives of embodiments of aspects of the present invention to obviate or mitigate this problem.
SUMMARY OF THE INVENTION
According to the present invention there is provided a downhole tool for mounting on a drill string, the tool comprising:
a mandrel;
a body axially movably mounted on the mandrel; and
a radially extendable member mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induced radial movement of the member, application of axial tension to the tool producing axial movement of the body relative to the mandrel tending to retract the member from an extended configuration.
The tool may take the form of an underreamer or an expandable stabiliser. For brevity, reference will be made primarily to underreamers, in which the radially extendable member will he a cutter.
This aspect of the invention facilitates retraction of the member on removal of the tool from a bore through a restriction; if the member is extended when the tool encounters a bore restriction, the member will engage the restriction and by applying tension to the string the mandrel may be lifted relative to the body and member, or vice versa, thus allowing retraction of the member.
According to another aspect of the present invention there is provided a downhole tool for coupling to a drill string, the tool comprising:
a mandrel;
a body movably mounted on the mandrel; and
a radially extendable member mounted in the body and being operatively associated with the mandrel such that relative movement of the mandrel and the body induces radial movement of the member, the mandrel including means for drawing the member inwardly to permit positive retraction of the member from an extended configuration.
This aspect of the invention overcomes the difficulties associated with existing underreamers, in which the cutters may be extended by interaction between a cutter and a spring-loaded mandrel, the mandrel being movable to extend the cutter under the influence of fluid flow through the tool. In the event that the spring force, for whatever reason, is insufficient to retract the mandrel, the blades cannot be retracted.
Preferably, said means for drawing the member inwardly is in the form of an undercut groove on one of the mandrel and member and a corresponding profile on the other, which groove and profile may be of a T-slot or dovetail configuration.
According to a further aspect of the present invention there is provided a downhole tool for coupling to a drill string, the tool comprising:
a mandrel;
a body movably mounted on the mandrel and defining an channel;
a radially extendable member mounted in the body channel and being operatively associated with the mandrel such that relative movement of the mandrel and body induces radial movement of the member; and
the mandrel and the member including means for maintaining a desired orientation of the member relative to the body channel.
This aspect of the present invention avoids the difficulties associated with extendable members such as underreamer cutters “cocking” or jamming in body channels or apertures from application of axial or circumferential forces to the outer parts of the cutters producing a moment on the cutter and tending to rotate the cutter in the channel; it the cutter is maintained at a desired orientation to the body such rotation is avoided or at least minimised.
Preferably, said means for maintaining a desired orientation is in the form of a groove and cooperating profile, and moat preferably an undercut groove and corresponding profile, such as a dovetail configuration.
Preferably also, the body defines an aperture to accommodate the member.
According to a still further aspect of the present invention there is provided a downhole tool for mounting between first and second sections of a drill string, the tool comprising:
a mandrel for coupling to a first section of drill string;
a body axially movably mounted on the mandrel and for coupling to a second section of drill string whereby application of weight to the string induces axial movement of the body relative to the mandrel;
fluid pressure responsive means for moving the body axially relative to the mandrel on application of a fluid pressure force between the body and mandrel; and
a radially extendable member mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induces radial movement of the member.
This aspect of the invention allows the member to be extended by one or both of weight applied to the string and by application of fluid pressure, for example by application of elevated pressure to the tool bore. Thus, using an underreamer in accordance with the invention, it is possible to ream in circumstances where an underreamer actuated only by applied weight will encounter difficulties; when drilling and reaming soft formations it may not be possible to apply sufficient weight to actuate the extendable cutters, and when “re-reaming” a section of bore it is not possible to apply weight to the string to compress an intermediate section of the string.
The first or second drill string section may take the form of a drill bit, that is the tool may be mounted on the end of a drill string and the drill bit mounted directly to the tool.
These various aspects of the present invention may be combined as desired, and a preferred embodiment of the present invention will incorporate all of the different aspects of the invention. Some preferred features of the various aspects of the invention are set out below.
Preferably, a plurality of members are provided, and most preferably the tool is provided with three members which retract and expand in unison.
Preferably also, the mandrel and body define a throughbore to permit drilling fluid to pass therethrough, and where the member is a cutter a conduit may extend from the throughbore to permit fluid to be directed towards the cutter. The conduit may be provided with a nozzle. Preferably, the throughbore is initially closed, and is opened by relative movement of the mandrel and bod
Alston & Bird LLP
Andergauge Limited
Bagnell David
Walker Zakiya
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