U.S. patent application number 15/469821 was filed with the patent office on 2018-09-27 for pressure perforated well casing systems.
The applicant listed for this patent is Lloyd Murray Dallas. Invention is credited to Lloyd Murray Dallas.
Application Number | 20180274341 15/469821 |
Document ID | / |
Family ID | 63582270 |
Filed Date | 2018-09-27 |
United States Patent
Application |
20180274341 |
Kind Code |
A1 |
Dallas; Lloyd Murray |
September 27, 2018 |
PRESSURE PERFORATED WELL CASING SYSTEMS
Abstract
Pressure perforated casing system has a plurality of grooves cut
to an equal depth in an outer surface of a casing joint or a casing
collar. Each groove has a bottom spaced from and internal surface
of the casing joint or the casing collar. Sidewall bottom material
in the groove ruptures at a predetermined fluid pressure below the
burst pressure rating of the casing joint or casing collar.
Inventors: |
Dallas; Lloyd Murray;
(Streetman, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dallas; Lloyd Murray |
Streetman |
TX |
US |
|
|
Family ID: |
63582270 |
Appl. No.: |
15/469821 |
Filed: |
March 27, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 43/114 20130101;
E21B 34/063 20130101; E21B 43/261 20130101; E21B 17/00
20130101 |
International
Class: |
E21B 43/08 20060101
E21B043/08; E21B 17/042 20060101 E21B017/042 |
Claims
1. (canceled)
2. The pressure perforated well casing joint as claimed in claim 4,
wherein the grooves are arranged in at least one cluster, a total
area of the at least one cluster being less than a total area of
the outer surface between the external threads on the first and
second ends of the pipe.
3. (canceled)
4. A pressure perforated well casing joint, comprising: a pipe
having a sidewall with a first end, a second end, an inner surface,
an outer surface and a burst pressure rating; an external thread on
each of the first and second ends adapted to threadedly engage a
casing collar; and a plurality of spaced apart grooves cut in the
outer surface, each groove extending inwardly from the outer
surface to an extent less than a thickness of the sidewall, so
there remains sidewall bottom material in each groove and the
grooves are cuts having ends that overlap; whereby fluid pressure
applied within the pressure perforated well casing will cause the
sidewall bottom material in the grooves to rupture before the burst
pressure rating of the pipe is reached, thereby opening a slot
through the sidewall at each of the plurality of grooves subjected
to the fluid pressure.
5. The pressure perforated well casing joint as claimed in claim 4,
wherein the grooves surround a narrow column of sidewall material
designed to facilitate cement penetration when the sidewall bottom
material in the grooves rupture.
6. The pressure perforated well casing joint as claimed in claim 4,
wherein the grooves are filled with a coating material to protect
machined surfaces while the casing joint is in storage and while
the casing joint is being run into a recently drilled well
bore.
7. The pressure perforated well casing joint as claimed in claim 4,
wherein the grooves are grouped in at least two spaced apart
clusters between the external thread on the respective first and
second ends.
8. The pressure perforated well casing joint as claimed in claim 4,
wherein the grooves are grouped in three equally spaced apart
clusters between the external thread on the respective first and
second ends.
9. The pressure perforated well casing joint as claimed in claim 4,
further comprising a groove cut on the inside surface of each of
the respective first and second ends to positively identify the
perforated well casing joint in a well casing string comprising
perforated well casing joints and plain casing joints connected
together.
10. A pressure perforated well casing collar, comprising: a pipe
having a sidewall with a first end, a second end, an inner surface,
an outer surface and a burst pressure rating; an internal thread on
each of the first and second ends adapted to threadedly engage an
external thread on a casing joint; a plurality of spaced apart
grooves respectively having overlapping ends cut in the outer
surface, each groove extending inwardly from the outer surface to
an extent less than a thickness of the sidewall, so there remains
sidewall bottom material in each groove; whereby fluid pressure
applied within the pressure perforated well casing collar will
cause the sidewall bottom material in the grooves to rupture before
the burst pressure rating of the casing collar is reached, thereby
opening a slot through the sidewall at each of the plurality of
grooves.
11. The pressure perforated well casing collar as claimed in claim
10, wherein the plurality of grooves are filled with a coating
material to protect machined surfaces while the casing collar is in
storage and while a casing string including the casing collar is
being run into a recently drilled well bore.
12. (canceled)
13. The pressure perforated well casing system as claimed in claim
16 further comprising an interval on an outer surface of the well
casing joint or the well casing collar without grooves.
14. The pressure perforated well casing system as claimed in claim
16 wherein the well casing joint comprises at least two clusters of
grooves, each cluster of grooves being separated from the ends of
the well casing joint and any other cluster of grooves by an outer
surface of the well casing joint without grooves.
15. (canceled)
16. A pressure perforated well casing system, comprising: a well
casing joint and a well casing collar respectively having a
plurality of spaced apart if grooves cut in an outer surface
thereof, the grooves being cut to an equal depth in the outer
surface, each groove having sidewall bottom material remaining in a
bottom of the groove the respective grooves having ends that
overlap; whereby sufficient fluid pressure applied to the grooves
cause the sidewall bottom material in the respective grooves to
rupture before a burst pressure rating of the well casing joint or
the well casing collar is reached, thereby opening slots through
the sidewalls at each of the respective grooves under sufficient
fluid pressure.
17. The pressure perforated well casing system as claimed in claim
16 wherein the grooves respectively surround a sidewall material
designed to facilitate cement penetration when the sidewall bottom
material in the grooves rupture.
18. The pressure perforated well casing system as claimed in claim
16, wherein the grooves are filled with a coating material to
protect machined surfaces while the casing joint or the casing
collar is in storage and while the casing joint or the casing
collar is in a casing string being run into a recently drilled well
bore.
19. A well casing string comprising the pressure perforated well
casing joints claimed in claim 16.
20. A well casing string comprising the pressure perforated well
casing collars claimed in claim 16.
Description
FIELD OF THE INVENTION
[0001] This invention relates in general to hydrocarbon well casing
systems and, in particular, to a novel well casing system that is
pressure perforated after a casing string is assembled, inserted
and cemented into a section of a recently drilled wellbore.
BACKGROUND OF THE INVENTION
[0002] Well casing is made up of casing joints and casing collars
for connecting the casing joints together to assemble a casing
string. Well casing is well known in the art and used to line
recently drilled hydrocarbon wellbores to prevent borehole collapse
and provide a smooth conduit for inserting tools required to
complete the well for production and to produce hydrocarbon from
the well. Most hydrocarbon wells drilled today are vertical bores
extending down to proximity of a production zone and horizontal
bores within the production zone. There are two ways commonly used
to complete a horizontal bore, plug-and-perf (PNP) and openhole
multistage (OHMS).
[0003] The openhole multistage system has external casing packers
that provide a seal between a production casing and the horizontal
bore. The production casing has dropped-ball actuated sliding
sleeves. The sliding sleeves open ports through the production
casing. The sliding sleeves are opened in succession from the toe
to the heel of the horizontal bore. The dropped balls are graduated
in size to pass through each sliding sleeve until they reach the
sliding sleeve to be opened next. When a ball is caught by a
sliding sleeve the fracture fluid pressure opens the sliding sleeve
exposing the ports, and the ball provides a seal to prevent frac
fluid from going downhole past the opened sliding sleeve. The
permits OHMS systems to perform multiple fracture stimulations
without the need to rig up wireline or set plugs to perforate new
intervals. Casing perforation is unnecessary because communication
between the cased borehole and the productive formation is afforded
by each set of ports opened by the balls dropped to open the
respective sliding sleeves. When the entire horizontal bore has
been fractured the balls are captured at the surface during flow
back of the fracturing fluid.
[0004] With plug-and-perf, after assembly and insertion of the
casing in the open borehole, the casing is "cemented in" by
circulating a cement slurry through the inside of the casing and
out into the annulus through a casing shoe at the bottom of the
casing string. The cement fills the annulus around the casing and
hardens to prevent the migration of fluids between zones in the
wellbore. Once cemented in, the casing is perforated in sections
from toe to heel using a perforating gun system that is run into
the well with wireline or completion tubing. The perforating guns
are triggered from the surface to fire steel projectiles that
penetrate the casing to let the hydrocarbon flow into the casing.
After a section of casing has been perforated, the spent
perforating guns are withdrawn and fracturing fluid is pumped down
the casing to fracture the formation behind the perforations. When
fracturing of that section is completed, a fiber plug is run into
the well with the next perforating gun system. The fiber plug is
set in the casing up hole from the fractured section, before the
perforating guns are fired to perforate a new section of the
casing. This process is repeated until the entire horizontal bore
has been plugged, perforated and fractured. Thereafter, the fiber
plugs are milled out to put the horizontal bore into
production.
[0005] OHMS and PNP each have their advantages and disadvantages.
OHMS is more expensive to install, but fracturing proceeds more
quickly because the sliding sleeves are opened in succession and
fracturing can be performed with virtually no interruptions.
However, OHMS is much less flexible in that once installed it
cannot be reconfigured or changed. OHMS also has shorter reach
because the reach is restricted by the number of sliding sleeves
that can be opened using a series of different sized balls that are
pumped into the well. OHMS also severely restricts fracture fluid
flow rates at the toe of the lateral well bore because of the ball
seat size through which fracturing fluid must be pumped. OHMS bores
are likewise more difficult to re-complete, and the service life of
the sliding sleeves is known to be limited. A further hazard is
that sliding sleeves are sometimes skipped because a wrong sized
ball is dropped, a ball shatters before it can seat in the sliding
sleeve, or one or more of the openhole packers provide an
incomplete seal.
[0006] PNP offers complete flexibility because casing perforations
can be located at any desired interval and the location can be
dynamically determined as the production zone is being fractured.
PNP also offers unlimited reach because newly available completion
tubing can be pushed to the furthest extent that a horizontal bore
can be drilled and cased. PNP is also secure because the casing is
cemented in, so fracture fluid has no place to migrate except into
the formation. PNP can also provide much more drainage area than
OHMS, which can be advantageous. The disadvantage of PNP is the
time required to run the perforating gun strings and to set the
plugs in the cased well bore. While each run is being performed the
fracturing crews sit idle. This adds significantly to expense.
[0007] A disadvantage of both systems is the fracturing pump
horsepower required to complete the well. The interval fractured in
OHMS systems is necessarily long even though the fracture fluid
ports are concentrated in a very small area opened by the sliding
sleeve, and the interval fractured in PNP is preferably long in
order to minimize idle time. Consequently, both OHMS and PNP
require a large number of high powered pump trucks, about 25,000
total horsepower, each with attendant crew. Those trucks must be
scheduled, congregated and maintained onsite throughout the well
completion. This requires long term planning, complex scheduling
and significant expense.
[0008] Perforated casing is also known and is used for openhole
completions in certain heavy oil reservoirs. However, perforated
casing does not permit cementing or well stimulation and its use is
therefore limited.
[0009] There therefore exists a need for a novel well casing system
that is pressure perforated after it is assembled, inserted and
cemented into a section of a recently drilled wellbore.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the invention to overcome the
disadvantages of prior art hydrocarbon well casing systems and
provide a novel well casing system that is pressure perforated
after it is assembled, inserted and cemented into a section of a
recently drilled wellbore.
[0011] The invention therefore provides a pressure perforated well
casing joint, comprising: a pipe having a sidewall with a first
end, a second end, an inner surface, an outer surface and a burst
pressure rating; an external tread on each of the first and second
ends adapted to threadedly engage a casing collar, and a plurality
of grooves cut in the outer surface, each groove extending inwardly
from the outer surface to an extent less than a thickness of the
sidewall, so there remains sidewall bottom material in each groove;
whereby fluid pressure applied within the pressure perforated well
casing will cause the sidewall bottom material in the grooves to
rupture before the burst pressure rating of the pipe is reached,
thereby opening a slot through the sidewall at each of the
plurality of grooves subjected to the fluid pressure.
[0012] The invention further provides a pressure perforated well
casing collar, comprising: a pipe having a sidewall with a first
end, a second end, an inner surface, an outer surface and a burst
pressure rating; an internal tread on each of the first and second
ends adapted to threadedly engage an external thread on a casing
joint; a plurality of grooves cut in the outer surface, each groove
extending inwardly from the outer surface to an extent less than a
thickness of the sidewall, so there remains sidewall bottom
material in each groove; whereby fluid pressure applied within the
pressure perforated well casing collar will cause the sidewall
bottom material in the grooves to rupture before the burst pressure
rating of the casing collar is reached, thereby opening a slot
through the sidewall at each of the plurality of grooves.
[0013] The invention yet further provides a pressure perforated
well casing system, comprising: a well casing joint and a well
casing collar respectively having a plurality of grooves cut in an
outer surface thereof, the grooves being cut to an equal depth in
the outer surface, each groove having sidewall bottom material
remaining in a bottom of the groove; whereby sufficient fluid
pressure applied to the grooves cause the sidewall bottom material
in the respective grooves to rupture before a burst pressure rating
of the well casing joint or the well casing collar is reached,
thereby opening slots through the sidewalls at each of the
respective grooves under sufficient fluid pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Having thus generally described the nature of the invention,
reference will now be made to the accompanying drawings, in
which:
[0015] FIG. 1 is a schematic view of an embodiment of a pressure
perforated casing joint of the well casing system in accordance
with the invention;
[0016] FIG. 2 is a schematic view of another embodiment of a
pressure perforated casing joint of the well casing system in
accordance with the invention;
[0017] FIG. 3 is a schematic view of yet another embodiment of a
pressure perforated casing joint of the well casing system in
accordance with the invention;
[0018] FIG. 4 is a schematic view of yet a further embodiment of a
pressure perforated casing joint of the well casing system in
accordance with the invention;
[0019] FIG. 5 is a schematic view of a pressure perforated casing
collar in accordance with the invention;
[0020] FIG. 6 is a schematic cross sectional view of a groove cut
in a sidewall of the casing joint or the casing collar in
accordance with the invention;
[0021] FIG. 7a is a schematic cross sectional view of other grooves
cut in the sidewall of a casing joint or the casing collar in
accordance with the invention;
[0022] FIG. 7b is a top plan view of one embodiment of another
groove cut in the sidewall of a casing joint or the casing collar
in accordance with the invention;
[0023] FIG. 7c is a longitudinal cross sectional view taken along
lines 5c-5c of the groove shown in FIG. 7b;
[0024] FIG. 7d is a cross sectional view taken along lines 5d-5d of
the groove shown in FIG. 7b;
[0025] FIG. 7e is a top plan view of yet another embodiment of a
groove cut in the sidewall of a casing joint or the casing collar
in accordance with the invention;
[0026] FIG. 7f is a cross sectional view taken along lines 5f-5f of
FIG. 7e;
[0027] FIG. 8a is a schematic cross sectional view in longitudinal
section of a further embodiment of a groove cut in the sidewall of
a casing joint or the casing collar in accordance with the
invention;
[0028] FIG. 8b is a schematic cross sectional view in longitudinal
section of the groove shown in FIG. 8a after the casing joint or
the casing collar has been pressure perforated and a formation in
which the casing is cemented has been fractured;
[0029] FIG. 9 is a schematic diagram of one embodiment of a casing
string in accordance with the invention; and
[0030] FIG. 10 is a schematic diagram of another embodiment of a
casing string in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The invention provides a pressure perforated well bore
casing system that permits hydrocarbon wells to be completed and
fractured with greater efficiency and at less expense than prior
art casing and completion systems. The casing system in accordance
with the invention eliminates the need for sliding sleeves,
openhole packers, wirelines, perforating gun systems, plugs and
plug mills. In one embodiment the casing system in accordance with
the invention also reduces the pump horsepower requirement for
completing a well by up to 60%, thus significantly reducing
completion cost and simplifying job scheduling. The well casing
system in accordance with invention also significantly reduces
fracturing crew idle time while providing fracture location
flexibility. The well casing system in accordance with invention
may be used in vertical or horizontal well bores and is equally
effective and efficient in either a vertical or a horizontal well
bore.
[0032] FIG. 1 is a schematic view of an embodiment of a pressure
perforated casing joint 10 of the well casing system in accordance
with the invention. The casing joint 10 has a first end 12, a
second end 14 and a sidewall 16. An external thread 18 cut on each
of the first end 12 and the second end 14 is adapted to threadedly
engage a casing collar (not shown but well known in the art) for
connecting one casing joint 10 to another. The casing joint 10 has
a length "L" and an outside diameter "OD". The outside diameter is
typically 4.5'' (11.4 cm), 5.5'' (13.97 cm), 7.5'' (19.05 cm) or
7.625'' (19.37 cm), although 3'' (7.62 cm), and other diameters of
casing are occasionally used. The length "L" Is a matter of design
choice selected by a well consultant or operator. The length "L"
may be as short as 3' (91.4 cm) or as long as a drill rig can
handle, typically 40' (12.19 m). A plurality of grooves 20 are cut
into the sidewall 16. The grooves 20 in this embodiment are shown
to be straight axial grooves, but the shape of the grooves 20 is a
matter of design choice. It is only important that the grooves 20
are spaced far enough apart that any potential erosion (known in
the art as "wash") from fracturing operations will not join two or
more grooves 20, which could compromise the strength of the casing
joint 10.
[0033] In one embodiment, each groove 20 is about 0.375''-0.5''
(1-1.27 cm) wide and 1''-3'' (2.5-7.6 cm) long. As will be
explained below with reference to FIGS. 6 and 7, the grooves 20 are
not cut through the sidewall 16. Rather, a predetermined thickness
of sidewall bottom material is left between a bottom of each groove
20 and an inner wall 22 of the casing joint 10. The thickness of
the sidewall bottom material is calculated to have a rupture
pressure (yield strength) that is less than a burst pressure rating
of the casing joint 16, yet greater than the fluid pressure
normally required to cement the casing in the well bore, which is
typically about 3,000 psi (20,648 KPa). At the predetermined
rupture pressure the sidewall bottom material will rupture, opening
a slot though the casing sidewall. The rupture pressure is also far
below the fluid pressure potential of modern fracturing pumps and
completion tubing, which is at least 15,000 psi (103,421 KPa).
Consequently, the casing joint 10 can be run into a recently bored
well bore without hazard of well bore material intrusion, and it
can be cemented in without danger of cement intrusion into the
casing string. Once the casing 10 is installed in a recently
drilled well bore and cemented in, it can be selectively perforated
using a downhole fracturing tool, the description of which is
beyond the scope of this disclosure. In one embodiment, a shallow
groove 24 is cut in the interior wall 22 of each end 12, 14 of the
casing joint 10 when the exterior threads 18 are being cut. The
groove 24 is detectable by a collar locator to provide a positive
identification of any casing joint 10 in an assembled casing
string, which will be described below in more detail with reference
to FIG. 9.
[0034] FIG. 2 is a schematic view of another embodiment of a
pressure perforated casing joint 30 of the well casing system in
accordance with the invention. The casing joint 30 has a first end
32, a second end 34, a sidewall 36 and an external thread 38 cut on
each end of the sidewall 36. The casing joint 30 is identical to
the casing joint 10 described above with an exception that the
grooves 40 cut in the sidewall 36 are radial rather than axial
grooves. It should be noted that although the grooves 40 are shown
to be straight radial grooves, that is a matter of design choice.
It is only important that the grooves 40 are spaced far enough
apart that any potential erosion from fracturing operations will
not join two or more grooves 40, which could compromise the
strength of the casing joint 30.
[0035] FIG. 3 is a schematic view of yet another embodiment of a
pressure perforated casing joint 50 of the well casing system in
accordance with the invention. The casing joint 50 has a first end
52, a second end 54, a sidewall 56 and an external thread 58 cut on
each end of the sidewall 56. The casing joint 50 is identical to
the casing joint 10 described above with an exception that the
grooves 60 cut in the sidewall 56 are circular trepans rather than
axial grooves. It should be noted that although the grooves 60 are
shown to be circular, they may be any shape in which the beginning
and ending of the groove overlap. Consequently, the grooves 60 may
be oval, square, rectangular, triangular, oblong, obround or
irregular in shape. It is only important that the grooves 60 are
spaced far enough apart that any potential erosion from fracturing
operations will not join two or more grooves 60, which could
compromise the strength of the casing joint 50.
[0036] FIG. 4 is a schematic view of yet a further embodiment of a
pressure perforated casing joint 72 of the well casing system in
accordance with the invention. The casing joint 72 has a first end
74, a second end 76 and an external thread 78 on each of the first
and second ends adapted to threadedly engage a casing collar. In
this embodiment, grooves 80 in the casing joint 72 are arranged in
clusters (cluster-1-cluster-n). A total area of the clusters is
less than a total area of the sidewall 72. The shape and the number
of grooves in each cluster 1-n is a matter of design choice, as is
the number of clusters on the pressure perforated casing joint 72.
The pressure perforated casing joint 72 may have 1 cluster or
several clusters. Typically, each pressure perforated casing joint
has 1-3 clusters. If there is more than one cluster, the clusters
1-n are spaced apart. The shape of the grooves in any cluster need
not be the same, as shown in cluster 2. In this example, cluster 1
is spaced from the first end 74 by an interval u-1 without grooves.
Cluster n is spaced from the second end 76 by an interval u-n
without grooves. Each cluster 1-n is spaced from any other cluster
2-(n-1) by an interval u-2, u-3, etc. without grooves. The
intervals without grooves u-1-u-n may be the same length or of
different lengths. The purpose of the intervals u-1-u-n is to
provide an area for landing packers of the downhole fracturing tool
(not shown or described). In one embodiment, the casing joint 72
has a length "L" of 40' (12.19 m) and 3 clusters (cluster 1-3).
Each cluster 1-3 is about 2'-3' (0.61-0.91 m) in length and each
interval without grooves (u-1-u-4) is about 7.75'-8.5' (2.29-2.59
m) in length.
[0037] In one embodiment the number of grooves and the size of each
of the grooves in each cluster 1-n opens slots through the sidewall
72 having a predetermined total area when the grooves in that
cluster are ruptured using frac fluid pressure, that predetermined
total area being an area through which fracturing fluid can be
pumped at a constant rate by about 10,000 horsepower of pump
capacity. This reduces the pump horsepower requirement for
completing a well bore by about 60%, thus significantly reducing
completion cost and simplifying job scheduling.
[0038] FIG. 5 is a schematic view of a pressure perforated casing
collar 82 in accordance with the invention. The casing collar 82
has a length "L" that is longer than a standard casing collar to
accommodate pressure perforated grooves that open slots as
described above when the casing collar 82 is pressure perforated.
The length of the casing collar 82 is typically 2'-4' (0.61-1.22
m), though the length is a matter of design choice. The casing
collar 82 has a first end 83, a second end 84, a sidewall 85 and an
internal thread 86 cut inside of each end of the sidewall 85. The
internal threads 86 mate with the external threads of a
corresponding size of casing joint, in a manner well understood in
the art. Consequently, the outside diameter "O.D." of the casing
collar 82 is the same as the outside diameter of any casing collar
of a corresponding weight and grade of casing. A plurality of
grooves 88 are cut in the sidewall 85, between the internal threads
on the first end 83 and the second end 84. The number of grooves 88
cut in the sidewall 85 is a matter of design choice. The grooves 88
may also be grouped into clusters as described above with reference
to FIG. 4, also as a matter of design choice. In one embodiment
when the collar 82 is pressure perforated, the grooves 88 cut in
the sidewall 85 open slots through the sidewall 85 having a
predetermined total area through which fracturing fluid can be
pumped at a constant rate by about 10,000 horsepower of pump
capacity. The shape and size of the grooves 88 is also a matter of
design choice. It is only important that the grooves 88 are spaced
far enough apart that any potential erosion from fracturing
operations will not join two or more grooves 88, which could
compromise the strength of the casing collar 82.
[0039] The casing collar 82 provides further flexibility to a well
operator, who can assemble casing strings with plain casing joints
and the pressure perforated casing collars 82, pressure perforated
casing joints 10, 30, 50, 70 and plain casing collars, or pressure
perforated casing joints 10, 30, 50, 70 and pressure perforated
casing collars 82, in any combination, as will be described below
in more detail with reference to FIGS. 9 and 10.
[0040] FIG. 6 is a schematic cross sectional view of a groove 60
cut in the sidewall 56 of the casing joint 50 shown in FIG. 3. The
sidewall 56 has a thickness "A". The thickness "A" is dependent on
the outside diameter and the grade of the casing joint. The groove
60 is cut to a depth that leaves sidewall bottom material 61
between the bottom of the groove and the inner wall of the casing
joint 56. The sidewall bottom material 61 has a thickness "B". The
thickness "B" of the sidewall bottom material is computed using
methods described below to rupture at a desired rupture pressure
(yield strength). Fluid pressure within the casing sidewall that
exceeds the rupture pressure causes the sidewall bottom material to
burst, opening a slot through the casing sidewall 56. Any material
62 surrounded by the groove 60 need not be removed. The material 62
may be machined to a point or a wedge to facilitate well cement
perforation, as will be explained below with reference to FIGS. 5e
and 5f.
[0041] The thickness "B" may be calculated, for example, using a
formula (Formula 1) described on page 16 and 17 of American
Petroleum Institute Bulletin 5C3, Fifth Edition, July, 1989,
incorporated herein by reference. The formula is:
P.sub.y=0.7854(D.sup.z-d.sup.z)Y.sub.p (Formula 1)
[0042] where: [0043] P.sub.y=pipe body yield strength in pounds
rounded to nearest 1000; [0044] Y.sub.p=Specified minimum yield
strength for pipe, psi; [0045] D=specified outside diameter,
inches; [0046] d=specified inside diameter, inches.
[0047] Table 1 shows examples of commonly used sizes and grades of
well casing, and the sidewall bottom material thickness (SBT) for
each to achieve a perforation rupture pressure of 4,000 psi (27,579
KPa) and 7,000 psi (48,263 KPa).
TABLE-US-00001 TABLE 1 Outside Inside Burst Pipe Grade Diameter
Diameter Pressure SBT SBT Lb/FT (inches) (inches) PSI (4,000 psi)
(7,500 psi) N80 4.5 4.0 7,778 0.122'' 0.240'' 11.60 P110 4.5 4.0
10,694 0.087'' 0.169'' 11.60 N80 5.5 4.5 12,727 0.137'' 0.270''
26.30 P110 5.5 4.5 17,500 0.098'' 0.191'' 26.30 4140 5.5 4.00
28,636 0.079'' 0.154'' 38.03
[0048] FIG. 7a is a schematic cross sectional view of other grooves
40a, 40b and 40c cut in the sidewall 36 of the casing joint 30
described above with reference to FIG. 2. As seen, the grooves may
be V-shaped as shown at 40a, keystone shaped as shown at 40b or
U-shaped as shown at 40c. If the groove is U-shaped, the bottom of
the U is used as the measure of the thickness "B" of the sidewall
bottom material described above with reference to FIG. 6. As
understood by those skilled in the art, if the casing joints 10,
30, 50, 70 or the casing collars 82 are to be run into
high-temperature, high-pressure production zones where they will be
subject to considerable hoop stress, U-shaped grooves or grooves
without right angle cuts, i.e. cuts having corners with a radius,
may be preferable. In general, square or U-shaped grooves are
faster to cut as they require only one machining pass, and bits for
generally square grooves can be ground at the corners to provide a
radius to corners in the groove. However, the shape of the groove
is not material to the practice of the invention provided that all
grooves 20, 40, 60, 80 are cut to the same, consistent depth so the
sidewall bottom material always has about the same thickness for
any particular diameter and grade of casing pipe, provided that
excessive hoop stress is not a significant factor.
[0049] FIG. 7b is a top plan view of one embodiment of a groove 20a
cut in the sidewall of a casing joint 10, 30, 50, 70 or a casing
collar in accordance with the invention. In this embodiment, a
narrow groove 43 is cut in a substantially rectangular or obround
pattern to leave a sidewall bottom material thickness, computed as
described above with reference to Formula 1. A cross-wise groove 45
is then optionally cut to form two narrow columns 44a, 44b of the
sidewall material, as best visualized with reference to FIG. 7c,
which is a longitudinal cross sectional view taken along lines
5c-5c of the groove 20a shown in FIG. 7b, and FIG. 7d, which is a
cross sectional view taken along lines 5d-5d of the groove 20a
shown in FIG. 7b. The narrow columns 44a, 44b function to break up
cement surrounding a casing 10, 30, 50 when the casing is pressure
perforated and the groove 20a ruptures under fracturing fluid
pressure. In one embodiment the grooves 43, 45 are filled with a
coating compound 47 designed to protect the machined surfaces while
the casing 10, 30, 50, 70 is in storage and while it is being run
into a recently drilled well bore. The coating compound also
prevents the intrusion of cement into the grooves 20, 40, 60, 80,
20a, etc., and remains soft to facilitate rupture of the sidewall
bottom material under fluid pressure. Such coating compounds are
available, for example, from Masterbond, Hackensack, N.J.,
U.S.A.
[0050] FIG. 7e is a top plan view of another embodiment 20b of a
groove cut in the sidewall of a casing joint 10, 30, 50, 70 or
casing collar 82 in accordance with the invention. The groove 20b
is similar to the groove 20a described above with reference to
FIGS. 5b-5d, except that the narrow columns are further machined to
form pointed wedges 48a, 48b. The pointed wedges 48a, 48b, best
seen in FIG. 7f, which is a cross sectional view taken along lines
5f-5f of FIG. 7e. The pointed wedges 48a, 48b slice through well
cement surrounding the casing joints 10, 30, 50, 70 described above
when the well casing is pressure perforated. In this embodiment the
grooves 43, 45 are likewise filled with a coating compound 47
designed to protect the machined surfaces while the casing 10, 30,
50, 70 is in storage and while it is being run into a recently
drilled well bore.
[0051] FIG. 8a is a schematic cross sectional view in longitudinal
section of one of the grooves cut in the sidewall 16 of the casing
joint 10 described above with reference to FIG. 1, or the sidewall
85 of the casing collar 82 described above with reference to FIG.
5. As will be understood by those skilled in the art, the groove 20
has been cut with a wheel-type slotting cutter well known in the
art. Consequently, the ends 26 are concave, reflecting the diameter
of the slotting cutter. This is one fast and convenient way of
cutting the grooves 20. The same type of tool can be used to cut
the grooves 40 seen in FIG. 2. In this embodiment, the casing joint
is 4140 heat-treated steel casing pipe, having an outside diameter
of 4.5'' (11.43 cm) and the thickness "B" of the sidewall bottom
material 28 of the groove 20 is about 0.15'' (3.81 mm), which will
rupture at about 7,500 psi (51,711 KPa) of fluid pressure, opening
a slot through the sidewall 16 (see Table 1). In one embodiment,
the groove 20 is filed with a coating compound 47 designed to
protect the machined surfaces while the casing 10 is in storage and
while it is being run into a recently drilled well bore.
[0052] FIG. 8b is a schematic cross sectional view in longitudinal
section of the groove 20 shown in FIG. 8a after the casing has been
pressure perforated to open a slot through the casing 10 sidewall
16 or collar 82 sidewall 85, and fracturing has been completed in a
formation 150 in which the casing 10 or collar 82 is cemented by
cement slurry 148. As seen, fragments 28a of the sidewall bottom
material 28 (see FIG. 8) of the casing 10 have been driven to
varying degrees into the formation 150. The coating compound and
the hardened cement slurry 148 were disintegrated by the force of
the impact when the casing 10 was pressure perforated, and ground
into particles by the sand-laden fracturing fluid. Fractures 152
have propagated deeply into the formation 150 and filled with sand
carried by the fracturing fluid, in a manner well known in the art.
The ends of the groove 26a, 26b have been eroded to some extent by
the fracturing fluid pumped into the formation 150. The amount of
erosion is dependent on the concentration of sand in the fracturing
fluid, and other factors well understood in the art.
[0053] FIG. 9 is a schematic diagram of a casing string 90
assembled in accordance with the invention as it is inserted into a
recently bored well bore. In this embodiment the casing string 90
is made up of plain casing joints (pc) connected end-to-end between
one or more joints of pressure perforated casing joints 10, 30, 50,
70, or casing collars 82 (pp) made from the same size and grade of
pipe. Plain casing collars that are part of the casing string 90
are not shown. The number of plain casing joints in each plain
casing (pc) interval 92, 96, 100, 104, 108, 112, 116 is a matter of
design choice dependent on formation properties and other factors.
The number of plain casing joints in each plain casing (pc)
interval is typically 1-3 plain casing joints. The number of
pressure perforated casing joints in each pressure perforated
casing (pp) interval 94, 98, 102, 104, 106, 110, 114 is typically
1, though any number of pressure perforated casing (pp) joints may
be used. The number of pressure perforated casing collars 82 in
each pressure perforated casing collar (pp) interval 94, 98, 102,
104, 106, 110, 114 is 1. The length of each pressure perforated
casing joint (pp) is also a matter of design choice, as is the
length of each pressure perforated casing collar. Each pressure
perforated casing joint (pp) may be as short as 3' (0.91 m) or as
long as 40' (12.19 m). Each pressure perforated casing collar (pp)
is typically about 2'-3' (0.61-0.91 m). Each pressure perforated
casing joint or casing collar (pp) may have grooves of any size,
any shape, and any number of clusters, as a matter of design choice
and operative constraints described above and understood in the
art.
[0054] FIG. 10 is a schematic diagram of another casing string 120
in accordance with the invention. The casing collars required in
the casing string 120 may be plain casing collars or pressure
perforated casing collars 82. The casing string 120 is entirely
made up of the pressure perforated (pp) casing joints 10, 30, 50,
70 and plain casing collars or pressure perforated (pp) casing
collars 82 in accordance with the invention. Each pressure
perforated casing joint (pp) in the casing string 120 may be a
casing joint 10, 30, 50 or 70, or any combination of same. In one
embodiment all of the casing joints in the casing string 120 are
the same but this is also a matter of design choice. The casing
string 120 offers more flexibility in terms of locating fracture
zones during well completion.
[0055] The explicit embodiments of the invention described above
have been presented by way of example only. The scope of the
invention is therefore intended to be limited solely by the scope
of the appended claims.
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