U.S. patent application number 11/123431 was filed with the patent office on 2006-11-09 for whipstock kick off radius.
Invention is credited to Gregory L. Hern, Calvin J. Stowe.
Application Number | 20060249310 11/123431 |
Document ID | / |
Family ID | 37393084 |
Filed Date | 2006-11-09 |
United States Patent
Application |
20060249310 |
Kind Code |
A1 |
Stowe; Calvin J. ; et
al. |
November 9, 2006 |
Whipstock kick off radius
Abstract
An improved whipstock design features a ramp having a lower
terminus at the location of the expected window bottom. The lower
end of the whipstock ramp transitions gradually from a preferably
flat guide surface to a more drastic exit orientation that is
preferably obtained by going to an arcuate exit of a rather large
radius to present a smooth transition from the flat guide surface
to an orientation that allows kick-out to occur by the end of the
ramp. This in turn allows the ramp end to closely approximate the
window bottom to reduce the risk of creation of a pocket near the
window bottom that could trap or damage equipment delivered in
subsequent runs.
Inventors: |
Stowe; Calvin J.; (West
University Place, TX) ; Hern; Gregory L.; (Huffman,
TX) |
Correspondence
Address: |
DUANE, MORRIS, LLP
3200 SOUTHWEST FREEWAY
SUITE 3150
HOUSTON
TX
77027
US
|
Family ID: |
37393084 |
Appl. No.: |
11/123431 |
Filed: |
May 6, 2005 |
Current U.S.
Class: |
175/80 ;
166/117.6; 175/81 |
Current CPC
Class: |
E21B 7/061 20130101 |
Class at
Publication: |
175/080 ;
166/117.6; 175/081 |
International
Class: |
E21B 7/08 20060101
E21B007/08 |
Claims
1. A whipstock, comprising: an elongated body having a longitudinal
axis and a ramp surface having an upper and a lower end; said ramp
surface comprising a lowermost segment and an adjacent segment,
said lowermost segment having an arcuate portion.
2. The whipstock of claim 1, wherein: said lowermost segment
comprising no more than 20% of the length of said ramp.
3. The whipstock of claim 1, wherein: said lowermost segment
providing a continuation of said adjacent segment initially in the
same plane.
4. The whipstock of claim 1, wherein: said elongated body further
comprises a cylindrical segment at its lower end and said lowermost
segment reaching said cylindrical segment at an angle of at least
10 degrees with said longitudinal axis.
5. The whipstock of claim 1, wherein: said arcuate portion
comprises more than one radius.
6. The whipstock of claim 5, wherein: said radii decrease in length
on said lowermost segment in a direction toward said lower end of
said ramp.
7. The whipstock of claim 1, wherein: said lowermost segment
providing a continuation of said adjacent segment initially within
5 degrees of the plane of said adjacent segment.
8. The whipstock of claim 2, wherein: said lowermost segment
providing a continuation of said adjacent segment initially within
5 degrees of the plane of said adjacent segment.
9. The whipstock of claim 8, wherein: said lowermost segment
providing a continuation of said adjacent segment initially in the
same plane.
10. The whipstock of claim 8, wherein: said elongated body further
comprises a cylindrical segment at its lower end and said lowermost
segment reaching said cylindrical segment at an angle of at least
10 degrees with said longitudinal axis.
11. The whipstock of claim 10, wherein: said arcuate portion
comprises more than one radius.
12. The whipstock of claim 11, wherein: said radii decrease in
length on said lowermost segment in a direction toward said lower
end of said ramp.
13. The whipstock of claim 12, wherein: said lowermost segment
providing a continuation of said adjacent segment initially in the
same plane.
Description
FIELD OF THE INVENTION
[0001] The field of this invention is whipstock design for making
windows in tubulars downhole for the purpose of extending a lateral
bore from a main bore.
BACKGROUND OF THE INVENTION
[0002] Whipstocks are devices that have long been in use to deflect
a mill system through casing to create an opening known as a
window. Whipstocks tend to be very long so that an inclined face on
them can gradually nudge a mill system into the casing wall to
start the window and to further guide the milling system until it
makes an exit though the window. As a result the window shape is
long and thin and narrows at the upper and lower ends. The slope on
the whipstock guide surface is generally a small angle or series of
angles.
[0003] Window milling with whipstocks has several unique issues
that can affect the performance of the milling equipment. One
concern has been when the center of the mill comes even with the
casing wall and there is a tendency for the mill to bog down in
that position so some designs have featured a steeply inclined
surface on the whipstock guide face to engage the mill just as its
center is in line with the casing wall. This kick-out surface
occurs part way down the guide surface to address one specific
problem.
[0004] Other approaches to whipstock design concern themselves with
avoiding the milling of the whipstock at the onset of milling and
configuring the contact angle between the mill and the whipstock
guide surface at its upper end to be closer to parallel to decrease
contact stress of the mill on the whipstock ramp at the top. The
idea was to increase contact stress against the casing so that the
casing would be milled rather than the top of the whipstock as the
window is initiated.
[0005] There have been other approaches to insure getting a long
enough window which have mostly been dealt with by making the ramp
on the whipstock longer than the needed window length. The thinking
here was that the longer ramp was insurance that the window length
would not fall below a minimum desired dimension. In these designs,
it was anticipated that the window mill will completely leave the
ramp well before its lower end and this would insure the window was
long enough and that the mill would safely enter the lateral. Even
if this concept worked to give a window of a desired length, it
created subsequent problems when downhole equipment needed to get
through the window. FIG. 1 illustrates the problem. The whipstock
face 10 extends downhole below the bottom of the window 12 in
wellbore 14. In subsequent trips to get into lateral 16 and
complete drilling and completion of it, a pocket trap 18 is
created. If the later runs had mills or bits with blades, the
blades would hang in the pocket 18 and the equipment would stall.
The rig crew would sense this and have to stop rotation and pick up
and then resume rotation and hope that on a subsequent attempt they
would not direct a blade into the very same pocket trap. On the
other hand if the equipment run subsequently had peripheral soft
components like rubber seals or packer seals, the edge 20 of casing
22 acted as a razor sharp surface that could easily shred the
softer components and render them unserviceable.
[0006] FIG. 2 shows another problem with whipstocks in the past.
Here the mill fails to make an exit at the ramp end and simply
continues to mill the whipstock base 24 and an anchor 26 below as
indicated by the dashed line 28.
[0007] Over the years different ideas have been tried in whipstock
designs but these problems have persisted. Several designs have
tried gradual slopes and arcuate guide surfaces over the length of
the whipstock all in the name of better mill guidance but none of
these designs have eliminated the conditions depicted in FIGS. 1
and 2. Some examples of such designs are U.S. Pat. Nos. 4,420,049;
3,116,799; 6,401,821; 2,699,920; 6,105,675; and 6,209, 645. The
last patent actually puts a radial surface 300 for the mill to
catch on to hopefully define the lower end of the window.
[0008] One attempt to solve the above described problems has been
to include an end surface on the guide face of the whipstock that
is a sharper angle than the long gradual guide surface that is
normally in the range of about 3 degrees. In soft formations the
increase in angle at the ramp bottom puts a greater lateral load on
the mill to help keep it against the whipstock surface as opposed
to kicking out too early. In the hard formations the steeper end
face directs the mill away from the whipstock to try to avoid
having it continue down misdirecting the lateral and potentially
damaging the whipstock or underlying anchor. While this approach it
was hoped to eliminate the problems described above and left
unresolved by the prior art but such was not the case.
[0009] Accordingly what is provided by this invention is
recognition of the solution to these problems in the form of a
gradual transition at the lower end of a guide ramp from a low
degree taper angle to a larger exit angle along a preferably
arcuate surface. In another aspect of the invention the final
surface is positioned in the vicinity of the expected window lower
end to eliminate the effect of pocket 18, described above. These
and other features of the present invention will be more readily
appreciated by those skilled in the art from a review of the
description of the preferred embodiment and the claims that appear
below.
SUMMARY OF THE INVENTION
[0010] An improved whipstock design features a ramp having a lower
terminus at the location of the expected window bottom. The lower
end of the whipstock ramp transitions gradually from a preferably
flat guide surface to a more drastic exit orientation that is
preferably obtained by going to an arcuate exit of a rather large
radius to present a smooth transition from the flat guide surface
to an orientation that allows kick-out to occur by the end of the
ramp. This in turn allows the ramp end to closely approximate the
window bottom to reduce the risk of creation of a pocket near the
window bottom that could trap or damage equipment delivered in
subsequent runs.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is section view of a prior art design with the ramp
longer than the intended window and the formation of a pocket as a
result;
[0012] FIG. 2 is a section view of a prior art design that shows
milling the whipstock and the anchor instead of licking out when
needed to make the window bottom;
[0013] FIG. 3 is a section view of the present invention show after
the window is milled and the mills are removed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Referring to FIG. 3, the casing 10 is cemented at 12 and has
the whipstock 14 in position for milling the window 16, in a known
manner. The whipstock 14 is supported by a known anchor 18 and the
orientation of the ramp 20 has been previously accomplished by
known orientation equipment. Ramp 20 has a top end 22 and a bottom
end 24 and in the preferred embodiment has a transition location
26. Segment 28 lies between top end 22 and transition 26. It can be
a single sloping surface at about 3 degrees to longitudinal axis
30. It can be a single flat sloping surface or it can have multiple
faces at different or similar slopes. There can be an alternative
sloping surface next to a non sloping surface followed by another
sloping surface at the same or a different slope as had been
located higher up the ramp 20. Preferably segment 28 regardless of
its configuration should be about 80% of the length of ramp 20
measured along its faces 28 and 32.
[0015] Preferably, face 32 should be arcuate with a preferably
gradual transition from the adjacent flat face 28 and gradually
going into an arcuate turn using a fairly large radius. This can
start as a surface continuation in essentially the same plane or it
can be within about 5 degrees of face 28 at the transition. The
radius to the lower end 24 need not be constant and it is preferred
to decrease the radius on the way to lower end 24. It can also be
possible to have segment 32 reach outer cylindrical surface 34 at
close to a 60 degree angle, with an angle of at least 10 degrees
preferred. The objective is to slowly transition the window mill
(not shown) into the formation in the lower 20% of the ramp 20 so
as to avoid the problem in prior designs described above.
[0016] While a kick out surface near the lower end of the ramp has
been tried as a flat surface at a more drastic angle to the
longitudinal axis that the adjacent ramp surface, the problem has
been that the severe angle transition accounted for an early exit
of the window mill right at the transition of the two angles so as
to make the window to short or to direct the direction of the
subsequent lateral at a steeper angle than was intended. The
gradual transition from segment 28 to the lowest point 24 insures
that the mill go down along the ramp 20 to as close as possible to
the depth of point 24 if not right to it. Thus the present
invention allows the ramp 20 to terminate within inches or right at
the intended bottom of window 16 and early termination of the
window 16 or having a lateral come out at an unintended angle is a
possibility that is reduced if not eliminated.
[0017] Segment 32 may have a flat section or sections along with
the arcuate guide surface.
[0018] It is to be understood that this disclosure is merely
illustrative of the presently preferred embodiments of the
invention and that no limitations are intended other than as
described in the appended claims.
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