U.S. patent application number 13/623376 was filed with the patent office on 2013-03-21 for sealing body for well perforation operations.
This patent application is currently assigned to 1069416 AB LTD.. The applicant listed for this patent is 1069416 AB LTD.. Invention is credited to Leigh DURLING, Stephen MAERZ, Michael Thomas SUTHERLAND.
Application Number | 20130068461 13/623376 |
Document ID | / |
Family ID | 47879531 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130068461 |
Kind Code |
A1 |
MAERZ; Stephen ; et
al. |
March 21, 2013 |
SEALING BODY FOR WELL PERFORATION OPERATIONS
Abstract
A sealing body is provided for use in well operations such as
oil/gas well perforation operations. The sealing body comprises a
shell defining a closed cavity; the shell is comprised of a metal
alloy. The sealing body has neutral or positive buoyancy. In one
embodiment, the sealing body further comprises a reinforcement
structure in the cavity. The reinforcement structure may comprise
one or more pairs of ribs adjoining an inner surface of the shell
of the sealing body.
Inventors: |
MAERZ; Stephen; (Strathmore,
CA) ; SUTHERLAND; Michael Thomas; (Calgary, CA)
; DURLING; Leigh; (Calgary, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
1069416 AB LTD.; |
Calgary |
|
CA |
|
|
Assignee: |
1069416 AB LTD.
Calgary
CA
|
Family ID: |
47879531 |
Appl. No.: |
13/623376 |
Filed: |
September 20, 2012 |
Current U.S.
Class: |
166/297 ;
277/336 |
Current CPC
Class: |
E21B 33/10 20130101;
E21B 43/119 20130101; E21B 41/00 20130101 |
Class at
Publication: |
166/297 ;
277/336 |
International
Class: |
E21B 33/10 20060101
E21B033/10; E21B 43/119 20060101 E21B043/119 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2011 |
CA |
2752864 |
Claims
1. A sealing body for use in well perforation operations, the
sealing body comprising: a shell defining a closed cavity; wherein
the shell is comprised of a metal alloy; and wherein specific
gravity of the sealing body is less than or equal to 1, where 1 is
the specific gravity of water.
2. A sealing body for use in well perforation operations according
to claim 1 wherein the metal alloy is a titanium alloy.
3. A sealing body for use in well perforation operations according
to claim 2 wherein the titanium alloy is Ti-6Al-4V.
4. A sealing body for use in well perforation operations according
to claim 1, wherein the shell is substantially spherical.
5. A sealing body for use in well perforation operations according
to claim 1, further comprising a reinforcement structure within the
cavity.
6. A sealing body for use in well perforation operations according
to claim 5 wherein the reinforcement structure comprises one or
more pairs of ribs adjoining an inner surface of the shell.
7. A sealing body for use in well perforation operations according
to claim 6 wherein each rib of the one or more pairs of ribs
extends in a circle adjoining the inner surface of the shell and
wherein, for each pair, planes of the circles of the ribs are
orthogonal.
8. A sealing body for use in well perforation operations according
to claim 6 wherein the ribs are spaced evenly within the
cavity.
9. A sealing body for use in well perforation operations according
to claim 6 wherein each rib has a substantially square cross
section.
10. A sealing body for use in well perforation operations according
to claim 9 wherein the cross section of each rib is 2 mm.times.2
mm.
11. A sealing body for use in well perforation operations according
to claim 1, wherein the shell has: an inner surface, an outer
surface and an outside diameter in a range of 2.25 to 3.5 inches; a
thickness between the inner surface and the outer surface in a
range of 0.085 to 0.135 inches; wherein the metal alloy comprises a
titanium alloy; and wherein the specific gravity of the sealing
body is less than 1.
12. A sealing body for use in well perforation operations according
to claim 5, wherein the shell has an inner surface, an outer
surface and an outside diameter in a range of 1.25 to 2.0 inches; a
thickness between the inner surface and the outer surface in a
range of 0.042 to 0.06 inches.
13. A sealing body for use in well perforation operations according
to claim 5, wherein the metal alloy is a titanium alloy.
14. A sealing body for use in well perforation operations according
to claim 7 comprising one pair of ribs wherein the planes of the
circles of the ribs intersect a center of the sealing body.
15. A sealing body for use in well perforation operations according
to claim 7 wherein: the outside diameter is in the range of 1.25 to
1.5 inches; the thickness between the inner surface and the outer
surface is in the range of 0.042 to 0.055 inches; and wherein the
metal alloy comprises a titanium alloy.
16. A sealing body for use in well perforation operations according
to claim 7 comprising two pairs of ribs wherein each of the four
ribs are offset from a center of the sealing body.
17. A sealing body for use in well perforation operations according
to claim 16 comprising wherein: the outside diameter is 1.75
inches; the thickness between the inner surface and the outer
surface is 0.055 inches; and wherein the metal alloy comprises a
titanium alloy.
18. A sealing body for use in well perforation operations according
to claim 7 comprising three pairs of ribs wherein four of the six
ribs are offset from a center of the sealing body and wherein the
planes of the circles of the other two ribs intersect a center of
the sealing body.
19. A sealing body for use in well perforation operation according
to claim 18 comprising wherein: the outside diameter is 2 inches;
the thickness between the inner surface and the outer surface is
0.06 inches; and wherein the metal alloy comprises a titanium
alloy.
20. A sealing body for use in well perforation operations according
to claim 1 wherein the cavity is evacuated of gas or liquid.
21. A sealing body for use in well perforation operation according
to claim 1 wherein the cavity is filled with a gas or a liquid.
22. A sealing body for use in well perforation operations according
to claim 6 wherein the one or more pairs of ribs are comprised of a
titanium alloy.
23. A sealing body for use in well perforation operations according
to claim 21 wherein the titanium alloy comprises a Ti-6Al-4V
titanium.
24. A sealing body for use in well perforation operations according
to claim 1 wherein the outer surface of the sealing body comprises
an irregular surface.
25. A method of performing well perforation operations comprising:
introducing a sealing body into a seat positioned in a well bore,
the sealing body comprising a shell defining a closed cavity,
wherein the shell is comprised of a metal alloy; and wherein
specific gravity of the sealing body is less than or equal to 1,
where 1 is the specific gravity of water; and pressurizing a
portion of the well bore up-hole from the seat to a predetermined
pressure threshold for triggering a perforating gun.
Description
RELATED APPLICATION
[0001] This application claims the benefit under Title 35, U.S.C.,
S.199(e) of Canadian Application No. 2,752,864 filed on Sep. 21,
2011, which is herein incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a sealing body for use in a
perforating gun for well perforation operations such as oil/gas
well perforation operations.
BACKGROUND
[0003] Contemporary well drilling operations in the oil and gas
industry may employ a specialized completion operation that
facilitates the flow of fluids and gasses from a producing
geological formation into a well bore. Typically, this operation
involves the insertion of a metal tubular casing into a bare well
bore, down to the full depth of the drilled hole. This casing
strengthens the bore wall, ensures that no oil or natural gas seeps
out of the well hole as it is brought to the surface and keeps
other fluids or gases from seeping into the formation through the
well. With the metal casing in place, a cement mixture may be
pumped down-hole for added protection and structural integrity of
the well. This mixture fills the annular space formed between the
casing outside diameter and well bore and is left for a period of
time to harden. Before hardening takes place, any cement remnants
within the casing must be cleared so that the internal production
passage is unobstructed. After the cement hardens in the annular
space, a "composite" cement and metal bore wall is formed, and the
completed wall is ready for perforation operations.
[0004] The composite wall section of the well bore is perforated or
pierced to permit the passage of liquid and/or gaseous hydrocarbons
into the well. A tool called a perforating gun may be used to
create an array of perforations at various predetermined locations
in the well. The perforating gun typically is assembled with a
plurality of directionally shaped charges, aligned in such a way
that at least one side of the casing is completely penetrated upon
firing of the gun. The hole penetrations are formed by vaporizing
local casing material by one or more jets of intense heat and
pressure emitted by the gun. The jet continues for some distance
beyond the composite wall. Depending on the type of formation and
strength of the charge, this distance may be twelve inches or
more.
[0005] The perforating gun is triggered at one or more
predetermined locations in the well bore by various techniques. One
type of perforating gun uses a pressurized triggering technique
with pressure zones defined by seats placed at predetermined
locations within the tubular casing of the well. The seats receive
sealing bodies of varying sizes corresponding or complementary to
the seat. A sealing body is pumped down-hole to the corresponding
seat and the well bore pressure above the seat is increased until a
predetermined pressure threshold is met or exceeded in the pressure
zone, causing the perforating gun to be activated and fire
[0006] The sealing bodies that are used in a perforating gun must
be capable of withstanding the high pressures needed to trigger the
gun and may be buoyant in order to be easily recoverable from the
well. Sealing bodies used in perforating guns typically are
spherical in shape and composed of a polymeric solid such as
BAKELITE, Garolite G10, PEEK or TORLON. The specific gravities of
these polymeric bodies are generally in the range of 1.3 to 1.5
relative to water which makes them negatively buoyant and less
likely to be recovered by back-flowing the well, particularly if
there is insufficient well flow to push the polymer sealing body
back to the surface of the well.
[0007] Sealing bodies comprised of polymeric solids are prone to
breakage and failure during the pressurization of the perforating
gun. If the sealing body is damaged or breaks during use, zone
pressure needed to trigger the perforating gun is lost and the
process must be repeated with a new sealing body. The failed
sealing body may need to be drilled out of the seat. Failure of the
polymeric sealing body often occurs when the sealing body shears
off at the seat contact line, with the lower portion of the sealing
body being lost down hole. If a sealing body is recovered after the
perforating gun fires, the sealing body may be broken or damaged,
or stressed at the point of contact between the sealing body and
the seat and thus the sealing body cannot be reused. Because of
these characteristics, sealing bodies comprised of polymeric solids
typically are not re-used for multiple perforation operations.
SUMMARY
[0008] Embodiments of the present invention provide a sealing body
for use in well perforation operations. The sealing body comprises
a shell defining a closed cavity, wherein the shell is comprised of
a metal alloy; and wherein specific gravity of the sealing body is
less than or equal to 1, where 1 is the specific gravity of water.
In one embodiment, the shell is comprised of a titanium alloy, such
as Ti-6Al-4V. In one embodiment, the sealing body further comprises
a reinforcement structure in the cavity. The reinforcement
structure may comprise one or more pairs of ribs adjoining an inner
surface of the shell of the sealing body.
[0009] According to another embodiment of the present invention
there is provided a method of performing well perforation
operations. The method comprises introducing a sealing body into a
seat positioned in a well bore, the sealing body comprising a shell
defining a closed cavity, wherein the shell is comprised of a metal
alloy; and wherein specific gravity of the sealing body is less
than or equal to 1, where 1 is the specific gravity of water; and
pressurizing a portion of the well bore up-hole from the seat to a
predetermined pressure threshold for triggering a perforating
gun.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1a is a cross section view of a well bore; FIG. 1b is a
enlarged view of a portion of the cross-section of FIG. 1a;
[0011] FIG. 2 is a close-up view of an embodiment of a sealing body
seated in a ball seat;
[0012] FIG. 3a is a front view of an embodiment of a sealing body,
FIG. 3b is a perspective cutaway view of the sealing body and FIG.
3c is a cross section of the sealing body;
[0013] FIG. 4a is a transparent isometric view an embodiment of a
sealing body, FIG. 4b is a perspective cutaway view of the sealing
body, FIG. 4c is a side view of the sealing body, FIG. 4d is a
cross-section view of FIG. 4c along the line A-A, FIG. 4e is a side
view of the sealing body, FIG. 4f is a cross-section view of FIG.
4e along the line B-B;
[0014] FIG. 5a is a transparent isometric view an embodiment of a
sealing body, FIG. 5b is a perspective cutaway view of the sealing
body, FIG. 5c is a side view of the sealing body, FIG. 5d is a
cross-section view of FIG. 5c along the line A-A, FIG. 5e is a side
view of the sealing body, FIG. 5f is a cross-section view of FIG.
5e along the line B-B; and
[0015] FIG. 6a is a transparent isometric view an embodiment of a
sealing body, FIG. 6b is a perspective cutaway view of the sealing
body, FIG. 6c is a side view of the sealing body, FIG. 6d is a
cross-section view of FIG. 6c along the line A-A, FIG. 6e is a side
view of the sealing body, FIG. 6f is a cross-section view of FIG.
6e along the line B-B.
[0016] Like reference numerals are used in the drawings to denote
like elements and features.
[0017] While the invention will be described in conjunction with
the illustrated embodiments, it will be understood that it is not
intended to limit the invention to such embodiments. On the
contrary, it is intended to cover all alternatives, modifications
and equivalents as may be included within the spirit and scope of
the invention as defined by the appended claims.
DETAILED DESCRIPTION OF EXAMPLE IMPLEMENTATIONS
[0018] FIGS. 1a and 1b illustrate high level views of a well 10, a
wellbore casing 12 and perforation gun system 14. The perforation
gun system 14, a portion of which is shown in FIGS. 1a and 1b, is
used to perforate predetermined sections of the wellbore casing 12
to permit the passage of liquid and/or gaseous hydrocarbons into
the well 10. The perforation gun system 14 comprises one or more
perforating guns 16a, 16b, 16c. The perforating guns 16a, 16b, 16c
are fired at planned locations within a number of pressure
activation zones 18a, 18b, 18c in the well 10. A sequence of
perforation operations may be performed typically starting with
triggering the perforating gun 16a furthest down-hole, then the
next perforating gun 16b down-hole and so forth, in order to
perforate the wellbore casing 12.
[0019] Triggering the perforating gun 16 may be accomplished by a
number of means. One method involves the use of a pressurized
triggering technique, within a pressure activation zone 18 defined
by a seat 20 installed at a pre-determined location within the
wellbore casing 12 down-hole from the corresponding perforating gun
16. When pressure in the activation zone 18 surrounding the
perforating gun 16 reaches a pre-set level, an internal mechanism
(not shown) in the perforating gun 16 is activated and the
perforating gun 16 fires a plurality of shaped charges through the
wellbore casing 12 and into the geological formation surrounding
the well 10. Each pressure activation zone 18 coincides with a
geological formation planned for perforation and spans the up-hole
and down-hole sides of a perforating gun location. The perforating
gun position is carefully chosen to intersect with the geological
production zone.
[0020] The seat 20 receives a sealing body 24 that corresponds or
is complementary to the seat 20. The seat 20 receives the sealing
body 24 in order to form a temporary tight pressure seal and define
the pressure activation zone 18 in the well 10. The perforating gun
system 14 includes multiple seats 20a, 20b, 20c situated down-hole
of the perforating guns 16a, 16b, 16c.
[0021] In one embodiment, the sealing body 24 is generally
spherical and may be used with existing perforating guns 16 and
seats 20, such as a ball seat 26 illustrated in FIG. 2. The ball
seat 26 has a conical face 28 for receiving a corresponding
generally spherical sealing body 24. In other embodiments, the
sealing body 24 may be oval, oblong or generally egg-shaped or
bullet-shaped. In some embodiments the sealing body 24 has a biased
weight distribution in order to ensure the sealing body 24 is
oriented to contact the seat 20 and create a tight pressure seal
with the seat 20 after the sealing body 24 is introduced into the
well 10. Embodiments of a sealing body 24 according to the present
disclosure are described in greater detail below.
[0022] The operation of the seat 20 and activation of the
perforating gun 16 will be described with respect to the seat 20b
and perforating gun 16b illustrated in FIG. 1b. A sealing body 24b
is dropped or pumped with fluids down the well 10 to the
corresponding seat 20b. In some embodiments, the sealing body 24b
is neutral or slightly buoyant in the well fluids and thus is
pumped down-hole to the corresponding seat 20b. The sealing body
24b is sized to pass through the up-hole seat 20c and to mate and
form a tight pressure seal with seat 20b. In one embodiment, the
sealing body 24b mates and forms a seal with the seat 20b in any
orientation of the sealing body 24b. Using high pressure pumps on
the drilling rig (not shown) the well bore pressure above the seat
20b and sealing body 24b is increased until a predetermined
pressure threshold is met or exceeded in the pressure activation
zone 18b, causing the perforating gun 16b to be activated and fire.
After the perforating gun 16b fires, the sealing body 24b floats
and/or travels with the fluids in the well 10 to the top of the
well 10 to be recovered at the wellhead (not shown).
[0023] If there is more than one zone to produce, a number of
perforation operations are carried out. The smallest sized sealing
body 24a is pumped down the well 10 and travels through seats 20b,
20c to the seat 20a in order to create a high pressure in the
activation zone 18a to trigger the perforating gun 16a furthest
down the well 10. After the perforating gun 16a fires, the sealing
body 24a floats and/or travels to the top of the well 10 and is
recovered. Then, a larger sized sealing body 24b is pumped down the
well 10 and travels through seat 20c to the seat 20b in order to
create a high pressure in the activation zone 18b to trigger the
perforating gun 16b at the next predetermined location furthest
down the well. The larger sealing body 24b similarly is recovered
before activating the next perforating gun 16c. A sealing body 24c,
larger than sealing body 24b, is pumped down the well 10 and
travels to the seat 20c to create high pressure in the activation
zone 18c to trigger the last perforating gun 16c. It will be
appreciated that each perforated zone may be fractured using
specialized chemicals in conjunction with high pressure pumping,
prior to introducing the next sealing body 24 in preparation for a
perforation operation.
[0024] Thus, sealing bodies 24a, 24b, 24c of varying sizes are
provided to mate and form a seal with seats 20a, 20b, 20c. The
sealing body 24 that is used with the seat 20 is capable of
withstanding the high pressures needed to trigger the perforating
gun 16, typically above 10,000 psi. Down-hole pressure loads may
act uniformly or asymmetrically around the sealing body 24. The
sealing body 24 is subject to uniform pressure as it is being
pumped down-hole to the seat 20. The sealing body 24 experiences
asymmetric loading when landed in the seat 20 during pressure-up
operations for triggering the perforating gun 16. The force
asymmetry arises from the leak-tight barrier formed between the
sealing body 24 and seat 20, whereby the pressure imbalance acts to
attempt to push the sealing body 24 through the seat 20. The
sealing body 24 also is subject to local stresses at the point of
contact between the sealing body 24 and the seat 20. For example,
in the embodiment illustrated in FIG. 2, severe localized stress
may occur in the sealing body 24 if only line contact is made with
the internal frustum of the conical ball seat 26.
[0025] The sealing body 24 also preferably has a specific gravity
of less than or equal to 1, where 1 is the specific gravity of
water, and thus positive or neutral buoyancy to aid the recovery of
the sealing body 24 after the perforating gun 16 is fired. Fluids
used for wellbore fracturing and perforation operations generally
have a higher specific gravity than water, ranging from 1.02 to
1.40 or higher. The sealing body 24, with a lower specific gravity,
is pumped down the well 10 to the corresponding seat 20 and during
recovery, floats to more easily travel to the top of the well 10
for recovery. The sealing body 24 typically is recovered at the
surface with the fracturing fluid, or with water which may be
located near the wellbore, ahead of the produced petroleum
products. The sealing body 24 also may be recovered along with
produced petroleum products. Although produced petroleum products
typically are lighter and may have specific gravities of less than
1, the sealing body 24, with a specific gravity of less than or
equal to 1, may be recovered with the flow of the produced
petroleum products.
[0026] FIGS. 3a, 3b, 3c through FIGS. 6a to 6f illustrate a sealing
body 24 according to embodiments of the present invention. In one
embodiment, the sealing body 24 comprises a shell defining a closed
or sealed cavity. The cavity is closed or sealed to provide a
hollow sealing body 24 with positive or neutral buoyancy. The
sealing body 24 is comprised of a metal alloy to provide strength
to withstand down-hole pressures in the well during well
perforation operations. The sealing body 24 is sized with a shell
thickness to provide strength and at the same time maintain a mass
to volume ratio such that the specific gravity of the sealing body
24 is less than or equal to 1, where 1 is the specific gravity of
water, in order to provide a sealing body 24 with positive or
neutral buoyancy.
[0027] In one embodiment, the sealing body 24, as illustrated in
FIGS. 3a, 3b and 3c comprises a shell 52 which is generally
spherical in shape and defines a closed or sealed cavity 54. The
cavity 54 is closed or sealed to provide a hollow sealing body 24
with positive or neutral buoyancy. The shell 52 is comprised of a
metal alloy in some embodiments. The thickness of the shell 52,
between an inner surface 56 and a finished outer surface 58, is
configured based on the size of the sealing body 24 and density of
the metal alloy in order to provide strength and also maintain a
mass to volume ratio resulting in a specific gravity of less than
or equal to 1. In one embodiment, the outer diameter of the shell
52 is defined in relation to the thickness of the shell 52 in
accordance with the formula:
27.7008 .times. ( .rho. metal ) .times. ( 1 - d 3 ) D 3 .ltoreq. 1
##EQU00001##
[0028] where: [0029] .rho..sub.metal=density of the shell material
(lbs/in.sup.3); [0030] D=outer sphere diameter (inches); [0031]
d=inner sphere diameter (inches); [0032] 27.7008=a specific volume
constant for water (equal to the inverse of the density of pure
water, 0.0361 lb/in.sup.3); and [0033] 1=the numerical equivalent
of specific gravity. A metric equivalent is provided by the
formula:
[0033] ( .rho. metal ) .times. ( 1 - d 3 ) D 3 .ltoreq. 1
##EQU00002##
[0034] In one embodiment, the sealing body 24 may be used with a
seat 20 comprising a ball seat 26, as illustrated in FIG. 2. The
sealing body 24 mates with the ball seat 26 which has a conical
face 28 which acts as a receiving surface for the sealing body 24.
A tight pressure seal is formed between the sealing body 24 and the
conical face 28.
[0035] As described above, the sealing body 24 is sized with a
shell thickness to provide strength to withstand downhole
pressures, asymmetric pressure loads and stresses from the contact
of the sealing body 24 and the seat 20 or the ball seat 26. The
loads and stresses on the sealing body 24 may depend on the
geometry and design of the seat 20 or ball seat 26. For example,
for the ball seat 26, the asymmetric loading and contact stresses
experienced by the sealing body 24 vary with the angle of the
conical face 28 of the ball seat 26. This angle affects the
magnitude of the load on the line of contact proportional to (Cos
.phi.).sup.-1, where .phi. represents the angle of the conical face
28 relative to the longitudinal axis 30 of the well 10. As the ball
seat 26 becomes shallower and approaches shape of a cylinder,
contact stresses near infinity and line contact with the sealing
body 24 occurs on increasing diameters or outer dimensions of the
sealing body 24.
[0036] The sealing body 24 may have slight irregularities in the
shape and the outer surface 58 of the spherical shell 52. In use,
once the sealing body 24 is seated in the ball seat 26 and pressure
in the pressure activation zone 18 increases, a seal will still
form as the sealing body 24 starts to deform under pressure loads
and the pressure imbalance acts to attempt to push the sealing body
24 through the ball seat 26. In one embodiment, the spherical shell
52 has a surface variance of not more than +/-0.01 inches in order
to form a tight seal with the ball seat 26.
[0037] The sealing body 24 is comprised of a metal alloy with
suitable strength and density properties, such as a high strength
material having a low density. Suitable light metal alloys include
titanium alloy or alloys of aluminum, magnesium and beryllium. In
one embodiment, the metal alloy comprises a Ti-6Al-4V titanium
alloy. The Ti-6Al-4V titanium alloy has a yield strength of 128,000
psi, and 2) density of 0.168 lbs/in.sup.3 and is composed of the
following elements by percent weight; 1) aluminum 6%, 2) iron 0.25%
(maximum), 3) oxygen 0.2% (maximum), 4) vanadium 4%, and 5)
titanium--balance (90%). Other grades of titanium are available
with similar characteristics, and therefore the material of the
sealing body 24 is not limited to grade Ti-6Al-4V.
[0038] In one embodiment, the sealing body 24 further comprises an
internal reinforcement structure 60. The internal reinforcement
structure 60 provides strength for the sealing body 24 to withstand
pressures and loading during use, including asymmetric loading and
localized stresses experienced by the sealing body 24 when mated
with the seat 20. For a smaller sized sealing body 24, the
thickness of the shell 52 may be limited in order to ensure the
specific gravity of the sealing body 24 is less than or equal to 1
and the internal reinforcement structure 60 provides additional
strength to compensate for a thinner shell 52. A reinforcement
structure 60 may be included in a sealing body 24 in order for the
sealing body 24 to withstand increased stresses related to the
geometry of the seat 20, such as for a ball seat 26 with a shallow
angle of its conical face. The reinforcement structure 60 adds
weight to the sealing body 24 and thus it is configured along with
the thickness of the shell 52 based on the outer diameter of the
sealing body 24 and the density of the metal alloy in order to
provide a sealing body 24 with sufficient strength and at the same
time maintain a mass to volume ratio resulting in a specific
gravity of less than or equal to 1.
[0039] In one embodiment, during use, the sealing body 24 is pumped
down the well 10 and comes to rest in the seat 20 in a randomly
determined orientation and thus the reinforcement structure 60 is
configured to be effective and provide strength to the sealing body
24 in any orientation.
[0040] Example embodiments of a sealing body 24 with an internal
reinforcement structure 60 are illustrated in FIGS. 4a to 4f
through 6a to 6f. In one embodiment, the reinforcement structure
comprises one or more pairs of ribs 70, 72. In some embodiments,
the ribs 70, 72 comprise circular bands adjoining the inner surface
56 of the shell 52 of the sealing body 24. The ribs 70, 72 project
from the inner surface 56 of the shell 52 towards a center of the
sealing body 24. In one embodiment, the one or more pairs of ribs
70, 72 are spaced evenly within the shell 52 and symmetrically
within two half sections of the sealing body 24. The plane of the
circle of each rib 70 may be orthogonal to the plane of the circle
of the other rib 72 in the pair of ribs. The ribs 70, 72 increase
the ability of the sealing body 24 to resist pressures in the well
10, including asymmetric pressure loading from zone pressurization
operations used to trigger a perforation gun 16. Other
configurations of reinforcement structures are contemplated.
[0041] As can be seen, for example, in FIGS. 4a to 4f, in one
embodiment, the ribs 70, 72 have a generally square cross-section
with a width of 2.0 mm, or approximately 0.079 inches, and a
height, from the inner surface of the shell 52, of 2.0 mm, or
approximately 0.079 inches. Outer edges of the ribs 70, 82 may be
slightly rounded. Fillet edges with a radius of 0.02 inches may be
formed where the ribs 70, 72 adjoin the inner surface 56 of the
shell 52. In other embodiments, the ribs 70, 72 have a generally
rectangular cross section or a generally semi-circular cross
section.
[0042] The one or more pairs of ribs 70, 72 are comprised of a
metal alloy with suitable strength and density properties, such as
a high strength material having a low density. Suitable light metal
alloys include titanium alloy or alloys of aluminum, magnesium and
beryllium. In one embodiment, the metal alloy comprises a Ti-6Al-4V
titanium alloy. The Ti-6Al-4V titanium alloy has a yield strength
of 128,000 psi, and 2) density of 0.168 lbs/in.sup.3 and is
composed of the following elements by percent weight; 1) aluminum
6%, 2) iron 0.25% (maximum), 3) oxygen 0.2% (maximum), 4) vanadium
4%, and 5) titanium--balance (90%). Other grades of titanium are
available with similar characteristics, and therefore the material
of the ribs 70, 72 is not limited to grade Ti-6Al-4V. In one
embodiment, the ribs 70, 72 are comprised of the same metal alloy
as the shell 52.
[0043] In the embodiment illustrated in FIGS. 4a to 4f, the
internal reinforcement structure comprises one pair of ribs, 70, 72
in the sealing body 24. The ribs 70, 72 are positioned such that
the planes of the circular ribs are orthogonal and each plane
intersects a centre of the sealing body 24. The ribs 70, 72
intersect at two points on the inner surface 56 of the shell
52.
[0044] In the embodiment illustrated in FIGS. 5a to 5f, the
internal reinforcement structure comprises two pairs of ribs, 80,
82 and 84, 86. The ribs 80, 82 and 84, 86 are spaced evenly and
orthogonally within the sealing body 24. In the orientation shown
in FIG. 5a, one of each pair of ribs, 80, 84 is shown extending
vertically around the inner surface 56 of the sealing body 24 and
the other of each pair of ribs, 82, 86 is shown extending
horizontally around the inner surface 56 of the sealing body 24. In
one embodiment the ribs 80, 82 and 84, 86 are offset an equal
distance from a center of the sealing body 24. In an embodiment of
a sealing body 24 comprised of Ti-6Al-4V titanium alloy and having
an outer diameter of 1.75'', the ribs are spaced 0.613 inches
apart, as measured between the outer surfaces of the ribs.
[0045] In the embodiment illustrated in FIGS. 6a to 6f, the
internal reinforcement structure comprises three pair of ribs 90,
92, 94, 96 and 98, 100. The ribs 90, 92, 94, 96 and 98, 100 are
spaced evenly and orthogonally within the sealing body 24. In the
orientation shown in FIG. 6a, one of each pair of ribs, 90, 94, 98
is shown extending vertically around the inner surface 56 of the
sealing body 24 and the other of each pair of ribs 92, 96, 100 is
shown extending horizontally around the inner surface 56 of the
sealing body 24. In the embodiment illustrated, one pair of ribs
94, 96 is positioned such that the planes of the circular ribs 94,
96 intersects a centre of the sealing body 24 and two of the pairs
the ribs 90, 92 and 98, 100 are offset an equal distance from a
center of the sealing body 24. In an embodiment of a sealing body
24 comprised of Ti-6Al-4V titanium alloy and having an outer
diameter of 2.0'', the ribs 90, 92, 94, 96, 98, 100 are spaced
0.391 inches apart, as measured between the outer surfaces of the
ribs.
[0046] Sealing bodies 24 according to the present disclosure may be
provided in discrete sizes for use in a sequence of perforating
operations as described above. In example discrete sizes of a
sealing body 24 having a generally spherical shell 52 comprised of
Ti-6Al-4V titanium alloy, the sealing body 24 has an outside
diameter in a range of 1.25 to 3.5 inches and the shell 52 has a
thickness, between the inner surface 56 and the outer surface 58 in
a range of 0.042 to 0.135 inches. Specifications of example sizes
of sealing bodies 24 comprised of Ti-6Al-4V titanium alloy are
listed in Table 1 below. Size increments of 1/4'' are used in the
examples in Table 1 in order to provide a series of sealing bodies
24 for use in multi-zone perforation operation. Other fractional
size increments and size ranges may be used. A positive buoyancy
rating in Table 1 refers to a sealing body 24 with a specific
gravity of less than 1 and a neutral buoyancy rating refers to a
sealing body 24 with a specific gravity equal to 1. In the example
embodiments described in Table 1 for Ti-6Al-4V titanium alloy, an
internal reinforcement structure 60 comprising one or more pairs of
ribs 70, 72, is included for a sealing body 24 with an outer
diameter (OD) in the range of 1.25 to 2.0 inches.
TABLE-US-00001 TABLE 1 Example Sealing Body Specifications
Estimated Sealing Spherical Equivalent Sealing Shell Spacing Body
OD Volume H2O Weight Body Weight thickness No. of between Bouyancy
(in) (in.sup.3) (Pure) (lbs) (lbs) (in) Ribs ribs Rating 1.25 1.023
0.037 0.037 0.042 2 -- Neutral 1.50 1.767 0.064 0.064 0.055 2 --
Neutral 1.75 2.806 0.101 0.101 0.055 4 0.613 Neutral 2.0 4.189
0.151 0.151 0.06 6 0.391 Neutral 2.25 5.964 0.215 0.210 0.085 0 n/a
Positive 2.50 8.181 0.295 0.290 0.095 0 n/a Positive 2.75 10.889
0.393 0.388 0.105 0 n/a Positive 3.00 14.137 0.510 0.505 0.115 0
n/a Positive 3.25 17.974 0.649 0.645 0.125 0 n/a Positive 3.50
22.449 0.810 0.807 0.135 0 n/a Positive
[0047] The OD, shell thickness and presence and configuration of an
internal reinforcement structure 60 in the sealing body 24 will
vary for different metal alloys or different titanium alloys.
Further, depending on the environment, pressures and loading the
sealing body 24 is exposed to during use, smaller sizes of sealing
bodies 24 may be provided without an internal reinforcement
structure 60. Similarly, larger sizes of sealing bodies 24 may be
configured to include an internal reinforcement structure 60 to
increase the strength of the sealing body 24.
[0048] The cavity 54 of the sealing body 24 may be substantially
empty and filled with air captured within the cavity 54 as the
sealing body 24 is manufactured. In one embodiment, the cavity 54
of the sealing body 24 comprises a vacuum to provide a slight
increase in buoyancy of the sealing body 24. In another embodiment,
the cavity 54 of the sealing body 24 is filled with liquid or gas
to increase the strength of the sealing body 24. Light gases or
petroleum distillates with specific gravities much less than 1.0,
such as specific gravities around 0.01 to 0.25, may be used as a
filling media to increase the strength of the sealing body 24 while
maintaining a neutral or positive buoyancy. In one embodiment, the
cavity 54 is filled with frozen CO2 or "dry ice" prior to joining
the two halves of the sealing body 24. The dry ice sublimates to
gas as it warms up and creates pressure within the cavity 54 to
increase the strength of the sealing body 24.
[0049] Sealing bodies 24 according to the present disclosures may
be manufactured in two halves and joined at an equatorial seam. The
halves may be geometrically equivalent and can be produced from the
same mold. Different mold types, such as press molds or sand
casting type molds may be used to create the halves of the sealing
body 24. The molds are designed to receive a molten charge of metal
alloy, such as titanium alloy, for sand molds or a near-melted
malleable slug for press molds. The same metal alloy, such as
Ti-6Al-4V titanium, composed of but not limited to the constituent
elements noted above, may be used for both types of molds. For a
sealing body including an internal reinforcement structure 60, in
some embodiments, a sand casting type mold is used and the
reinforcement structure 60 is formed in the mold for each half of
the sealing body using the same material for the sealing body 24
and the reinforcement structure 60. In other embodiments, the
reinforcement structure 60 comprises a different material than the
sealing body 24. The reinforcement structure 60 may be formed
separately and affixed to the inner surface 56 of the sealing body
24.
[0050] The heated alloy hardens into the solid state and is removed
from the sand or press mold when the temperature is suitably low.
The halves thus produced are placed against one another at the wall
face and may be held together by a fixture to assist in joining
operations. Joining the two halves typically is performed by
welding the seam such as with a tungsten inert gas (TIG) electric
welder, which may or may not require the use of suitable filler rod
material at the discretion of the operator. When the equatorial
seam is completely welded, the outer surface of the sealing body is
machined and polished to the desired finished diameter.
[0051] Thus, it is apparent that there has been provided in
accordance with the embodiments of the present disclosure a sealing
body for use in oil and gas well perforation operations that fully
satisfies the objects, aims and advantages set forth above. While
the invention has been described in conjunction with illustrated
embodiments thereof, it is evident that many alternatives,
modifications and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications and
variations as fall within the spirit and broad scope of the
invention.
* * * * *