Wells – Means for guiding insertable element laterally of well axis – Secured in operative position by movable means engaging well...
Patent
1998-01-07
2000-04-18
Dang, Hoang
Wells
Means for guiding insertable element laterally of well axis
Secured in operative position by movable means engaging well...
175 80, 175 82, E21B 708
Patent
active
060503343
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a single trip whipstock assembly, that is to say a whipstock assembly which can be run complete into a wellbore, set, and operated to mill a window in the casing of the wellbore and open up a lateral in the surrounding formation in a single trip.
2. The Prior Art
In the drilling of oil and gas wells it is sometimes necessary to form a branch extending off an existing bore. Such branches (generally known as "laterals") are in general formed by locating a tapering deflector device (known as a "whipstock") in the existing bore, and then using the whipstock to deflect a milling tool laterally of the axis of the existing bore to mill a window in the surrounding casing. Once the window has been milled, drilling of the surrounding formation can continue using the milling tool or the milling tool can be withdrawn from the well and replaced by an appropriate formation drilling assembly.
Heretofore, the initiation of a lateral using a whipstock system has necessitated a number of separate trips into the well. Typically, a packer is first run into the well and, using appropriate equipment, is located at the correct depth and orientation and is set. The packer string is then removed from the well, leaving the packer in position, and the whipstock, possibly in association with one or more mills, is run into the well to mate with the packer prior to commencement of the milling operation.
Various attempts have been made to increase the efficiency of the formation of a lateral using a whipstock system, and in particular U.S. Pat. No. 5,109,924 illustrates a window milling assembly to make the cut out and mill the window in one run, and U.S. Pat. No. 5,425,419 illustrates a system in which a deflector head at the top of the whipstock is used to locate the milling tool. All prior art systems, however, require some form of anchor or packer to locate the whipstock at the correct depth and orientation. Such anchors or packers must be run into the well on a separate trip from the whipstock proper necessitating at least two trips in any whipstock milling operation.
SUMMARY OF THE INVENTION
The present invention aims to improve the known techniques for forming a lateral using a whipstock system by providing a whipstock assembly which incorporates a packer or anchor and which can be run into a well, set, and operated in a single trip.
According to one aspect of the present invention a single trip whipstock assembly includes a whipstock having a milling tool attached to the upper end thereof and a packer or anchor attached to the lower end thereof, the packer or anchor being settable to fix the depth of the whipstock prior to, but during the same trip as, operation of the milling tool to form a window in the casing of the wellbore.
In general, the lateral will have a required heading and accordingly the connection between the whipstock and the packer or anchor will prevent relative rotation therebetween so that, after the assembly has been run into the wellbore to the required depth, the assembly can be orientated by appropriate means (for example using signals derived from a measuring while drilling tool which may optionally form part of the assembly) prior to setting of the packer or anchor. Once the packer or anchor has been set, the orientation of the face of the whipstock relative to ground co-ordinates, which will determine the heading of the lateral, will be fixed by virtue of the non-rotatable connection between the whipstock and the packer or anchor.
In a particularly preferred embodiment of the invention the milling tool is secured directly to the top end of the whipstock by releasable fastening means, for example shear bolts. Accordingly, after the packer or anchor has been set and the setting verified by appropriate loading of the drillstring, an upward or downward load can be applied to the drillstring sufficient to release the releasable fastenings, whereafter milling can commence.
Preferably, the upper end of the whipstock is formed w
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McGarian Bruce
Steinkamp Manfred
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