Note: Descriptions are shown in the official language in which they were submitted.
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SEALING BODY FOR WELL PERFORATION OPERATIONS
TECHNICAL FIELD
[0001] 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
[0002] 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.
[0003] 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
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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.
[0004] 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
[0005] 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 BAKELITETm, Garolite G10, PEEK or TORLONTm. 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.
[0006] 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.
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SUMMARY
[0007] 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-6A1-4V. 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.
[0008] 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
[0009] FIGURE la is a cross section view of a well bore; FIGURE lb is a
enlarged view of a portion of the cross-section of Figure la;
[0010] FIGURE 2 is a close-up view of an embodiment of a sealing body
seated in a ball seat;
[0011] FIGURE 3a is a front view of an embodiment of a sealing body,
FIGURE 3b is a perspective cutaway view of the sealing body and FIGURE 3c
is a cross section of the sealing body;
[0012] FIGURE 4a is a transparent isometric view an embodiment of a
sealing body, FIGURE 4b is a perspective cutaway view of the sealing body,
FIGURE 4c is a side view of the sealing body, FIGURE 4d is a cross-section
view of FIGURE 4c along the line A-A, FIGURE 4e is a side view of the sealing
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body, FIGURE 4f is a cross-section view of FIGURE 4e along the line B-B;
[0013] FIGURE 5a is a transparent isometric view an embodiment of a
sealing body, FIGURE 5b is a perspective cutaway view of the sealing body,
FIGURE 5c is a side view of the sealing body, FIGURE 5d is a cross-section
view of FIGURE 5c along the line A-A, FIGURE 5e is a side view of the sealing
body, FIGURE 5f is a cross-section view of FIGURE 5e along the line B-B; and
[0014] FIGURE 6a is a transparent isometric view an embodiment of a
sealing body, FIGURE 6b is a perspective cutaway view of the sealing body,
FIGURE 6c is a side view of the sealing body, FIGURE 6d is a cross-section
view of FIGURE 6c along the line A-A, FIGURE 6e is a side view of the sealing
body, FIGURE 6f is a cross-section view of FIGURE 6e along the line B-B.
[0015] Like reference numerals are used in the drawings to denote like
elements and features.
[0016] 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
[0017] Figures la and lb 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 Figures la and lb, 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.
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[0018]
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.
[0019] 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.
[0020] 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 Figure 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.
[0021] 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 Figure lb. A sealing body 24b is dropped or pumped with fluids
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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).
[0022] 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.
[0023] 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
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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 Figure 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.
[0024] 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.
[0025]
Figures 3a, 3b, 3c through Figures 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
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,
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.
[0026] In one embodiment, the sealing body 24, as illustrated in Figures
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 x in f
,, metal) X (1-d3) 5_ 1
D3
where:
P metal = density of the shell material (lbs/in3);
D = outer sphere diameter (inches);
d = inner sphere diameter (inches);
27.7008 = a specific volume constant for water (equal to the
inverse of the density of pure water, 0.0361 lb/ in3); and
1 = the numerical equivalent of specific gravity.
A metric equivalent is provided by the formula:
(p metal) X (1-d3) 1
D3
[0027] In one embodiment, the sealing body 24 may be used with a seat
20 comprising a ball seat 26, as illustrated in Figure 2. The sealing body 24
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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.
[0028] 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 cD)-1, where (130 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.
[0029] 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.
[0030] 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-6A1-4V titanium alloy. The Ti-6AI-4V titanium alloy has a yield
strength of 128,000psi, and 2) density of .168 lbs/in3 and is composed of the
following elements by percent weight; 1) aluminum 6%, 2) iron .25%
(maximum), 3) oxygen .2% (maximum), 4) vanadium 4%, and 5) titanium -
balance (90%). Other
grades of titanium are available with similar
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characteristics, and therefore the material of the sealing body 24 is not
limited
to grade Ti-6AI-4V.
[0031] 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.
[0032] 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.
[0033] Example embodiments of a sealing body 24 with an internal
reinforcement structure 60 are illustrated in Figures 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
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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.
[0034] As can be seen, for example, in Figures 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.
[0035] 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-6A1-4V titanium alloy. The Ti-6A1-4V titanium alloy
has a yield strength of 128,000psi, and 2) density of .168 lbs/in3 and is
composed of the following elements by percent weight; 1) aluminum 6%, 2)
iron .25% (maximum), 3) oxygen .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-6A1-4V. In one embodiment, the ribs 70, 72 are comprised of the
same metal alloy as the shell 52.
[0036] In the embodiment illustrated in Figures 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.
[0037] In the embodiment illustrated in Figures 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 Figure 5a, one of each pair of ribs, 80,
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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-6AI-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.
[0038] In the embodiment illustrated in Figures 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 Figure 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-6AI-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.
[0039] 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-6A1-4V 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-6A1-4V 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
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= .
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-6A1-4V 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.
Equivalent Estimated
Sealing Shell
Spherical H20 Sealing No. Spacing
Body thick-
Bouyancy
Volume Weight Body of between
OD ness
Rating
(in 3) (Pure) Weight Ribs ribs
(in) (in)
(lbs) (lbs)
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
Table 1: Example Sealing Body Specifications
[0040] 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.
[0041] 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
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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.
[0042] 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-6A1-4V 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.
[0043] 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
14
CA 02752864 2011-09-21
completely welded, the outer surface of the sealing body is machined and
polished to the desired finished diameter.
[0044] 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.
