U.S. patent application number 10/504882 was filed with the patent office on 2006-01-26 for casing reaming assembly.
Invention is credited to Paul McClure, Stephen Webster.
Application Number | 20060016603 10/504882 |
Document ID | / |
Family ID | 9931167 |
Filed Date | 2006-01-26 |
United States Patent
Application |
20060016603 |
Kind Code |
A1 |
Webster; Stephen ; et
al. |
January 26, 2006 |
Casing reaming assembly
Abstract
Apparatus and methods for drilling out from a casing string in a
borehole. A reaming assembly is introduced into the borehole and
fixed at a predetermined location. A drillable collar is interposed
between the reaming assembly and a casing. A drilling assembly
introduced into the casing and is then positioned so as to drill
through the drillable collar at a predetermined angle into a
formation surrounding the borehole.
Inventors: |
Webster; Stephen; (West
Yorkshire, GB) ; McClure; Paul; (Aberdeen,
GB) |
Correspondence
Address: |
DRINKER BIDDLE & REATH;ATTN: INTELLECTUAL PROPERTY GROUP
ONE LOGAN SQUARE
18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Family ID: |
9931167 |
Appl. No.: |
10/504882 |
Filed: |
February 14, 2003 |
PCT Filed: |
February 14, 2003 |
PCT NO: |
PCT/GB03/00666 |
371 Date: |
August 13, 2004 |
Current U.S.
Class: |
166/298 ;
166/55.7 |
Current CPC
Class: |
E21B 7/067 20130101;
E21B 29/06 20130101 |
Class at
Publication: |
166/298 ;
166/055.7 |
International
Class: |
E21B 29/00 20060101
E21B029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2002 |
GB |
0203641.6 |
Claims
1. A method for drilling out from a casing string in a borehole,
the method comprising the steps of: introducing a reaming assembly
into the borehole to a predetermined location; fixing the reaming
assembly in position, wherein a drillable collar is attached
between the reaming assembly and a casing introducing a drilling
assembly into the casing; and positioning the drilling assembly so
as to drill through the drillable collar at a predetermined angle
into the formation surrounding the borehole.
2. A method as claimed in claim 1 wherein the point at which the
drilling assembly enters the formation surrounding the borehole is
at least in part determined by the thickness of the drillable
collar through which the drilling assembly drills.
3. A method as claimed in claim 1 wherein the drilling assembly is
a bent housing motor assembly with a drill bit.
4. A method as claimed in claim 1 wherein the drilling assembly is
a rotary steerable system with a drill bit.
5. A method as claimed in claim 3, wherein the drill bit comprises
a PDC drill bit.
6. A method as claimed in claim 1 wherein the reaming assembly is
fixed in place using cement.
7. Apparatus for drilling out from a casing string in a borehole,
the apparatus comprising a drillable collar attached between a
reaming assembly and a casing string.
8. Apparatus as claimed in claim 5 wherein the drillable collar is
provided with a borehole extending from the reaming assembly to the
casing string.
9. Apparatus as claimed in claim 5 wherein the drillable collar is
made from aluminum.
Description
[0001] The present invention relates to a method for drilling out
of a casing string which has been run and fixed in place with the
use of a sacrificial motor assembly.
[0002] It is known to drill out sections of a casing string in
order to drill side-tracked holes that run off the casing string.
Casing is run after drilling a hole section to close off unstable
and low pressure formations and provide hole stability. Various
known methods are deployed to assist in ensuring that the casing
string reaches the total depth of the drilled section. Typically,
this can be achieved using a reaming assembly connected directly to
the bottom of a casing. These components are then run to the bottom
of a borehole and cemented in place.
[0003] In order to create a hole running off the main borehole, a
whipstock, which is a cylindrical triangular metal device, is
positioned at a point near the bottom of the casing along with a
milling assembly. The whipstock is oriented with a gyro device to
the desired direction of drilling and fixed in place. The milling
assembly is then mechanically detached from the whipstock and
activated so as to mill a section of the casing to create a window
at and around the whipstock. After this has been done the milling
assembly is pulled out of the casing. Depending on the condition of
the window created by the milling assembly, a second run of the
milling assembly may be required. After this, a steerable drilling
assembly is run inside the casing and on passing over the whipstock
is guided to point in a set direction, thereafter, drilling is
initiated and continues to the prescribed target.
[0004] Typically the distance from the surface to the borehole is
around 10,000 to 11,000 feet, this means that it takes around 24
hours to complete one round trip to and from the surface for any of
these components. Clearly, any reduction in the number of round
trips required would produce significant savings of rig time and
therefore cost.
[0005] In accordance with a first aspect of the present invention
there is provided a method for drilling out from a casing string in
a borehole, the method comprising the steps of: [0006] introducing
a reaming assembly into the borehole to a predetermined location;
fixing the reaming assembly in position, wherein a drillable collar
is attached between the reaming assembly and a casing introducing a
drilling assembly into the casing; and positioning the drilling
assembly so as to drill through the drillable collar at a
predetermined angle into the formation surrounding the
borehole.
[0007] Preferably, the point at which the drilling assembly enters
the formation surrounding the borehole is at least in part
determined by the thickness of the drillable collar through which
the drilling assembly drills.
[0008] Preferably, the drilling assembly is a bent housing motor
assembly with a drill bit.
[0009] Optionally, the drilling assembly is a rotary steerable
system combined with a drill bit.
[0010] Preferably, the drill bit used comprises a PDC drill
bit.
[0011] Preferably, the reaming assembly is fixed in place using
cement.
[0012] In accordance with a second aspect of the invention there is
provided an apparatus for drilling out from a casing string in a
borehole, the apparatus comprising a drillable collar attached
between a reaming assembly and a casing string.
[0013] Preferably, the drillable collar is provided with a borehole
extending from the reaming assembly to the casing string.
[0014] Preferably, the drillable collar is made from aluminium, or
other high strength but easily drillable material.
[0015] Aluminium is preferred because it is drillable and
sufficiently robust to retain its integrity in the conditions found
in boreholes. Other materials with similar properties may be used
in place of aluminium.
[0016] The present invention will now be described by way of
example only with reference to the accompanying drawings of
which:
[0017] FIG. 1 shows a casing reaming assembly in accordance with
the present invention;
[0018] FIG. 2 is a cross sectional view of a drillable collar;
and
[0019] FIG. 3 shows the effect of a change in width of the
collar.
[0020] Referring to FIG. 1, the assembly 1 is shown with respect to
the base of an unstable subsea formation 15. The assembly 1
comprises a casing 3 which in this example is of 95/8 inch diameter
connected to a float collar 5 which is in turn connected to a
drillable collar 7. The drillable collar 7 is connected to a
reaming assembly 10 which consists of a mud motor 9 having, on its
end, a 121/4 inch bit 11.
[0021] FIG. 1 also shows a side-tracked hole 13, which is created
by the use of a drilling assembly (not shown) capable of drilling
through the drillable collar 7. In this example a borehole is
drilled to a casing point to provide a 121/4 inch diameter hole.
This drilling assembly is then removed from the borehole.
Thereafter a reaming assembly also known as a sacrificial reaming
assembly is constructed. This consists of a reaming assembly as
shown having a mud motor with a 121/4 inch drill bit connected to
its end. This reaming assembly is connected to the drillable collar
7. In this example, as shown in FIG. 2, the drillable collar is
made from aluminium and has an outer diameter of 9M inch and an
inner diameter of 3 inches. Therefore the annular thickness of the
drill collar is 31/4 inches.
[0022] The collar 7 is connected to a float collar 5, which is in
turn connected to the casing 3. The reaming assembly 10 and casing
3 are then run into the bore hole until the bottom of the casing 3
and the drill collar 7 are set in an appropriate formation.
[0023] Thereafter cement is added in order to complete the casing
and reaming assembly in place and to land the cement plug in the
float collar. In this example, the collar is 40 feet in length.
[0024] In order to create a side tracked hole a steerable drilling
assembly capable of fitting inside the casing is run into the hole.
In this example the drill assembly consists of a 1.5 degree bent
housing steerable motor assembly having a 63/4 inch outside
diameter and a PDC drill bit having an 81/2 inch diameter. This
drilling implement is controllable from the surface in a known
manner. This steerable drill assembly is used to drill through the
drill collar and is aligned remotely so as to drill in a
predetermined direction towards a target position.
[0025] The use of a drillable collar as described above allows the
passage of drilling fluid from the casing string to the reaming
motor which provides hydraulic and mechanical power to and from the
motor for reaming operations.
[0026] In addition, the bore 8 contained in the collar provides a
passage to allow the addition of cement in order to cement the
casing string in place. Furthermore, the collar 7 serves as a hard
plug to enable the steerable motor assembly of the second drill to
deviate in the direction of the next well path into new
formation.
[0027] Whilst the above example shows an aluminium collar, it will
be appreciated that a drill collar may be made of any other
material that is drillable and mechanically robust enough to
perform the functions of the collar described in the conditions
typically found in a bore hole.
[0028] Referring now to FIG. 2, this shows the variation in exit
point of the drill that may be achieved simply by varying the
annual thickness of the collar 7.
[0029] The sideways displacement can be calculated by using the
following equation. Sideways .times. .times. displacement = hole
.times. .times. diameter + collar .times. .times. diameter 2
##EQU1##
[0030] Therefore, if the collar diameter alone is increased, the
sideways displacement will be increased.
[0031] FIG. 2 shows the exit point from the drillable collar where
an 8 inch collar 7 is used in comparison to the exit point where a
91/2 inch collar is used. This clearly shows that the exit point
for the 91/2 inch collar is displaced.
[0032] Whilst the above examples show a borehole of 121/4 inches
with a drillable collar and casing sized appropriately. It will be
appreciated that the present invention is not restricted to
boreholes and casings of these dimensions and that the above is an
illustrative example of the general concept set out in the
statements of invention and claims.
[0033] The present invention contains a number of advantages with
respect to the prior art. In particular: it reduces the number of
round trips from the surface required, therefore reducing the
amount of rig time required; a whipstock is not required, these
cost around 100000 to buy and take a significant time to orient;
and the cost and time of milling a window is removed from the
process.
[0034] Improvements and modifications may be incorporated herein
without deviating from the scope of the invention.
* * * * *