Milling method for liners extending into deviated wellbores

An apparatus and method of milling a liner extending from a deviated wellbore into a main wellbore is disclosed. The liner is inserted through a window and cemented in place with the cement extending back into the main wellbore. Mechanisms are provided on the liner to keep it away from the main wellbore casing wall to facilitate the proper operation of the washover tool. A top end taper is provided to help the washover tool reorient over the tubular liner if milling requires more than one trip into the well. A diverter is insertable prior to installation of the liner to assist in getting the liner to extend through a window. Upon milling through the liner, the washover tool straddles the diverter and latches into it to facilitate not only the removal of the diverter but also the entrapment of any debris created by the milling operation. Suitable sealing is provided with the diverter to keep the cement away from the latching mechanism during the cementing operation.

FIELD OF THE INVENTION 
The field of this invention relates to the milling of tubulars extending 
through a main wellbore into a deviated wellbore after cementing in place. 
BACKGROUND OF THE INVENTION 
In the past, whipstocks have been used to create a window in a casing in a 
main wellbore for the initiation of a deviated wellbore which diverges 
from the original wellbore. After milling the window and drilling the 
deviated wellbore, a tubular is inserted through the window into the 
deviated wellbore. Prior completions have generally involved the absence 
of any cementing of the liner extending into the deviated wellbore or if 
cementing were done, it was terminated short of the window milled in the 
casing in the main wellbore. In those earlier techniques, since cement 
would not be allowed to come back from the deviated wellbore into the main 
wellbore, milling out the tubing from the main wellbore which extended 
into the deviated wellbore was not necessary if further production was 
required from the main wellbore. Completion techniques have evolved to the 
point where after milling the window and creating the deviated wellbore, 
the liner is placed through the window into the deviated wellbore and 
cemented. Thereafter, a milling operation is necessary to remove that 
portion of the liner in the main wellbore and to retrieve the whipstock, 
if it has not already been earlier retrieved. 
FIGS. 1 and 2 indicate these procedures that had been previously required 
in view of the use of existing equipment, as just described. FIG. 1 
illustrates a main wellbore 10 which has a deviated wellbore 12 already 
drilled through it. Inside of the main wellbore 10 is casing 14, which has 
already been milled through the use of a whipstock 16 and a milling tool 
(not shown). At the conclusion of the milling of the "window" 18 in the 
casing 14, a liner 20 is inserted into casing 14 and is diverted into 
window 18 into deviated wellbore 12, as shown in FIG. 1. In order to make 
the turn into deviated wellbore 12, the liner 20 winds up being wedged 
against one side of the casing 14, as shown in FIG. 1. Similarly, that 
same liner 20 in the deviated wellbore 12 also can become wedged against 
the uncased bore making up wellbore 12, as shown in FIG. 1. 
After placement of the liner 20 into deviated wellbore 12, the deviated 
wellbore is cemented around the liner 20 up into the main wellbore 10. 
Thereafter, a milling tool 22 is employed to mill out the portion of the 
liner 20 that extends in wellbore 10. Thereafter, the whipstock 16 is 
removed. This procedure is illustrated in more detail in U.S. Pat. No. 
5,301,760. FIG. 2 reflects the use of centralizers 24 in the deviated 
wellbore 12 to centralize the liner 20 therein. While the centralizers 
located in the deviated wellbore 12 help to centralize the liner 20, that 
portion of the liner 20 that extends into the wellbore 10 is still wedged 
firmly against the casing 14 within wellbore 10 due to the angular 
deflection of the liner 20. 
There are many practical problems disclosed by the method in U.S. Pat. No. 
5,301,760 that are not revealed in the patent. The biggest problem occurs 
when a milling tool such as 22 is employed to begin the milling operation. 
Typically, a "washover"-type milling tool is used which has cutting 
elements on the bottom and on the inside. This type of tool is called a 
washover tool because its purpose is to straddle the tubular object to be 
milled. This type of milling tool generally has no cutting elements on its 
exterior. Cutting elements on the exterior of the milling tool 22 would be 
undesirable since it would result in milling away of the wall of casing 14 
in wellbore 10. The problem arises in the sense that with the liner 20 
wedged up against the casing 14 in wellbore 10, the washover milling tool 
22 cannot fully get around the upper end of the liner 20. Instead, as 
shown in FIG. 1, some milling goes on on the inboard side 26 of liner 20, 
while more complete milling takes place on the outboard side 28. The 
result of this uneven milling is that slivers are formed because segments 
of the inboard side 26 are not fully milled. Since segments of the inboard 
side are not fully milled, they retain additional structural strength 
which ultimately results in directing the milling tool 22 in a deviated 
path toward window 18. This is undesirable since continued milling with 
the milling tool 22 in a skewed or deviated position can result in 
unwanted milling of segment 30 of the casing 14, which is located below 
the window. FIG. 2 is intended to illustrate the formation of slivers and 
the skewing of the milling tool 22 when an attempt is made to use a 
washover tool over a liner 20 when the liner 20 is pressed rigidly against 
the casing 14. As a result of the milling process illustrated in FIG. 2, 
segment 32 while shown in the drawing is, in effect, fully milled away 
while only portions of segment 34 on the inboard side 26 is effectively 
milled due to the inability of the washover tool 22 to fully wash over the 
inboard side 26. Accordingly, as a result of the milling operation 
illustrated in the U.S. Pat. No. 5,301,760, slivers 36 are formed which 
subsequently must be fished out or further ground up before the whipstock 
16 can be removed. 
Accordingly, one of the several objectives of the method of the present 
invention is to facilitate the milling operation by providing mechanisms 
to keep the liner 20 away from the wall of the casing 14 to facilitate the 
washover milling operation. Additionally, it is a further object of the 
invention to facilitate the insertion of the liner through the use of a 
diverter. It is another object to employ a diverter of suitable dimensions 
to allow the washover mill to straddle it and ultimately latch into it so 
that any segments of cement or similar material or metal slivers which may 
be formed are caught within the washover tool when it is latched to the 
diverter. Ultimately, it is another object of the invention to be able to 
remove the diverter and thus provide a clear access to a packer which is 
further downhole in the main wellbore. 
SUMMARY OF THE INVENTION 
An apparatus and method of milling a liner extending from a deviated 
wellbore into a main wellbore is disclosed. The liner is inserted through 
a window and cemented in place with the cement extending back into the 
main wellbore. Mechanisms are provided on the liner to keep it away from 
the main wellbore casing wall to facilitate the proper operation of the 
washover tool. A top end taper is provided to help the washover tool 
reorient over the tubular liner if milling requires more than one trip 
into the well. A diverter is insertable prior to installation of the liner 
to assist in getting the liner to extend through a window. Upon milling 
through the liner, the washover tool straddles the diverter and latches 
into it to facilitate not only the removal of the diverter but also the 
entrapment of any debris created by the milling operation. Suitable 
sealing is provided with the diverter to keep the cement away from the 
latching mechanism during the cementing operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 3 schematically indicates the tubular liner 40, extending from the 
main wellbore 42 into the deviated wellbore 44. The main wellbore 42 has a 
casing 46 into which a window 48 has already been milled. A diverter 50, 
and generally indicated in the drawing as D, is located in the main 
wellbore 42 and supported by a packer 52, also referred to as P in the 
drawing of FIG. 3. The diverter 50 is inserted into the main wellbore 42 
after removal of the whipstock at the conclusion of the milling of the 
window 48 in a manner well-known in the art. The diverter 50 is used in 
the position shown in FIG. 6 to deflect the liner 40 as it is inserted in 
the main wellbore 42 to orient its leading edge into the deviated wellbore 
44, as shown in FIGS. 6 and 7. 
One of the features of the present invention is the use of exterior 
spacers, such as ribs 54. As shown in the cross-section of FIG. 4, one 
embodiment is the use of longitudinal ribs disposed at 90.degree. 
intervals continuously or discontinuously on the outer periphery of the 
liner 40 such that they extend into the main wellbore 42, thus keeping the 
liner 40 away from the casing 46, as shown in FIG. 3. Ribs 54 may be also 
circumferentially extending in the main wellbore 42 and can be of a 
construction shown in item 24 of FIG. 2. The ribs need not be continuous 
and can be at different spacing than 90.degree.. Any type of spacer 
located so as to keep the upper segment of liner 40 away from the casing 
46, as shown in FIG. 3, is within the scope of the invention. The liner 40 
is encased in a sealer such as a cementitious material 56. Material 56 
fills the voids around any spacer, such as ribs 54. The cementitious 
material extends into the main wellbore 42. As shown in FIG. 7, the 
cementitious material 56 is placed in the main and deviated wellbores 42 
and 46, respectively, with the diverter 50 in position. Diverter 50 has a 
seal or seals 58 which retain the cementitious material 56 above a 
centralizer 60. The outside diameter of the diverter 50 is smaller than 
the diameter of the casing 46 within the mail wellbore 42. 
Referring now to FIG. 5, an alternative embodiment to the ribbed structure 
illustrated in FIG. 4 is shown. In FIG. 5, a series of protrusions which 
can be orderly or randomly arranged are placed on the outer periphery of 
the liner 40, particularly in the zone extending into the main wellbore 42 
to, again, keep the upper end 62 away from the casing 46. A known running 
tool (not shown) can be used to facilitate the lowering and insertion of 
the liner 40 into the position shown in FIG. 3. Such a known running tool 
can leave a segment behind after release from the liner 40 which includes 
a taper 64. The significance of this taper 64 at the upper end 62 of the 
liner 40 will be explained below. It should be noted that it is within the 
purview of the invention to use a wide variety of spacing mechanisms on 
the outer periphery of the liner 40 in the portion that extends into the 
main wellbore 42 to keep that portion away from the casing 46. Thus, many 
types of mechanisms can be employed as a spacing mechanism to accomplish 
the objective without departing from the spirit of the invention; for 
example, apart from the longitudinal ribs and random or orderly 
protrusions, other devices can be used such as a helix, discrete rods, 
spaced transverse rings, as long as the objective of keeping the upper end 
62 away from the rigid contact with casing 46 is accomplished. Whatever 
mechanism is employed, it should not interfere with the free flow of the 
cementitious material 56 which must be placed around the outer periphery 
of the liner 40 in the deviated wellbore 44 and on up to the upper end 62 
of the liner 40, disposed within the main wellbore 42. 
By employment of the spacing mechanism such as ribs 54 or other protrusions 
66, illustrated in FIG. 5, the washover tool 68 (see FIG. 8) can easily 
straddle the liner as it properly needs to do so that cutting can be 
accomplished with minimal creation of slivers which had occurred employing 
the washover tool in the methods revealed in U.S. Pat. No. 5,301,760, as 
illustrated in FIGS. 1 and 2. By moving the upper end 62 away from the 
wall, the internal cutters 70 (see FIG. 8) can evenly cut away the 
protrusion and then that portion of the liner 40 within the main wellbore 
42. Since the washover tool 68 is not eccentrically disposed with respect 
to the liner 40 adjacent the upper end 62 as was the case in FIGS. 1 and 
2, slivers are not a problem. In effect, the washover tool 68 cleanly 
mills away the ribs, such as 54. Eventually, the washover tool 68 begins 
to cut through the wall of the liner 40. However, by then it has cleanly 
encircled the upper end 62 of liner 40 and can then make meaningful 
progress in a direction straight ahead toward a position where the 
diverter 50 is fully straddled, as shown in FIG. 8. Since the upper end 62 
serves as a guide for the washover tool 68 because milling is cleanly 
going on around the periphery of the upper end 62, the tendency of the 
liner 40 to misdirect the washover tool 68 toward window 48, which was 
present in the milling techniques illustrated in FIGS. 1 and 2, is 
removed. Even if the washover tool 68 must be replaced prior to the 
conclusion of the entire milling operation, the same results can be 
obtained without risk of inadvertent milling of any portion of the casing 
46 in the region 72 below the window 48. What occurs if the washover tool 
68 must be removed before the conclusion of the milling is that the 
spacing mechanism, such as ribs 54 or protrusions 66, have been milled 
from a portion of the upper end 62. Upon initial removal of the washover 
tool 68 before the conclusion of the milling operation, the upper end 62 
of the liner 40 will flex toward the casing 46 in the main wellbore 42. 
However, because of the taper 64 which has been deposited at the upper end 
62 when the release has occurred from the running tool (not shown), the 
newly inserted washover tool 68 can readily get behind the upper end 62 of 
the liner 40 to once again resume the milling operation with the upper end 
62 fully enclosed within the washover tool 68 as the milling continues. 
Again, the presence of the liner 40 acts as a guide to keep the initial 
progress of the washover tool 68 oriented in the direction of main 
wellbore 42 until actual cutting through the liner wall is accomplished, 
as shown in FIG. 8. Thereafter, the washover tool 68 progresses to the 
point where an internal recess 74 passes over and beyond a latch mechanism 
such as spring-loaded dogs 76. As shown in FIG. 8, the trimmed section of 
liner 78 is effectively trapped within the washover tool 68 above the 
diverter 50. A comparison of FIGS. 7 and 8 reveals that the use of the 
washover tool 68 has resulted in the milling away of the seal 58 as well 
as the centralizer 60. Although only the liner section 78 is shown to be 
within the washover tool 68 in FIG. 8, those skilled in the art can 
appreciate that other metal fragments or portions of the cementitious 
material 56 can also be disposed within the washover tool 68 above the 
diverter 50. For example, the ribs 54 (see FIG. 4) or protrusions 66 (see 
FIG. 5) are also milled by the cutters 70 and captured within the body of 
the washover tool 68. 
At the conclusion of the milling operation, the washover tool 68 is pulled 
up, bringing up recess 74 until dogs 76 come into alignment with recess 
74, thereby facilitating the release of the diverter tool 50 from the 
packer 80 (see FIGS. 8 and 9). What remains is a deviated wellbore 44 that 
is lined with a cementitious material or equivalent 56 disposed around the 
cut-off liner 40 which terminates at window 48. In the main wellbore 42, 
the casing 46 has a clear path down to packer 80. This facilitates 
subsequent operations in the main wellbore 42 below packer 80, if 
necessary, or removal of packer 80. Simultaneously, production can proceed 
from the deviated wellbore 44. This process can be repeated many times to 
create multiple deviated wellbores, such as 44, using the equipment above 
described. 
Those skilled in the art can appreciate that the method as above described 
offers unique advantages over prior techniques. Since the liner is held, 
at least initially, away from the wall of the casing 46 at the onset of 
milling with the washover tool 68, proper operation of the washover tool 
68 minimizes the formation of slivers of the liner 40 during the milling 
operation. Also, the tendency of the liner 40 to pull the washover tool 68 
laterally toward the window 48, due to the uneven milling which occurred 
with the prior designs, is eliminated. Instead, the washover tool 68 
proceeds to initially grind the cementitious material 56, as well as any 
projections or protrusions, such as 54 or 66, and ultimately slices 
cleanly through the liner 40 as it approaches the area of window 48. Other 
types of mills may be used without departing from the spirit of the 
invention. 
The diverter 50 is installed after removal of the whipstock. Generally, to 
withstand the forces applied during the milling of the window 48, the 
whipstock (not shown) must be full-size or close thereto. The diverter 50, 
which does not need to withstand loads comparable to those delivered 
during the milling of a window 48, can be substantially smaller than a 
whipstock. The function of the diverter is to direct the liner 40 into the 
window 48 on initial insertion. This minimizes the need to twist or turn 
the liner 40 to get it to advance into the window 48. Twisting or turning 
the liner 40 can be disadvantageous, particularly if the spacing devices, 
such as ribs 54 or protrusions 66, are used. The possibility can exist for 
sticking the liner 40 in an attempt to guide it into the lateral wellbore 
44. Accordingly, the use of the diverter 50, which is sufficiently 
undersized when compared to the inside diameter of the casing 46 in the 
main wellbore 42, accomplishes not only the objective of easily guiding 
the liner 40 into the window 48, but also presents a profile for the 
diverter 50 which will allow the washover tool 68 to advance over it, as 
shown in FIG. 8, for ultimate capture of the milling byproducts and the 
removal of such byproducts in conjunction with the removal of the diverter 
50 from the wellbore. The packer 80 can remain in the wellbore for further 
future downhole operations. Additionally, even if multiple trips with one 
or more washover tools 68 become necessary and the upper end 62 flexes 
back toward the casing 46 because some of the ribs 54 or protrusions 66 
have been milled away, on a second or subsequent trip, the washover tool 
68 can easily seek the taper 64 and move the upper end 62 away from the 
wall so that milling can then resume with the washover tool 68 comfortably 
straddling the upper end 62 of the liner 40. 
The foregoing disclosure and description of the invention are illustrative 
and explanatory thereof, and various changes in the size, shape and 
materials, as well as in the details of the illustrated construction, may 
be made without departing from the spirit of the invention.