US20130068461A1

US20130068461A1 - Sealing body for well perforation operations

Info

Publication number: US20130068461A1
Application number: US13/623,376
Authority: US
Inventors: Stephen Maerz; Michael Thomas Sutherland; Leigh DURLING
Original assignee: 1069416 Ltd AB
Current assignee: 1069416 Ltd AB
Priority date: 2011-09-21
Filing date: 2012-09-20
Publication date: 2013-03-21
Also published as: CA2752864A1; CA2752864C

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.

Description

RELATED APPLICATION

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

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

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.
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.
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
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.
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

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.
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

FIG. 1 a is a cross section view of a well bore; FIG. 1 b is a enlarged view of a portion of the cross-section of FIG. 1 a;

FIG. 2 is a close-up view of an embodiment of a sealing body seated in a ball seat;

FIG. 3 a is a front view of an embodiment of a sealing body, FIG. 3 b is a perspective cutaway view of the sealing body and FIG. 3 c is a cross section of the sealing body;

FIG. 4 a is a transparent isometric view an embodiment of a sealing body, FIG. 4 b is a perspective cutaway view of the sealing body, FIG. 4 c is a side view of the sealing body, FIG. 4 d is a cross-section view of FIG. 4 c along the line A-A, FIG. 4 e is a side view of the sealing body, FIG. 4 f is a cross-section view of FIG. 4 e along the line B-B;

FIG. 5 a is a transparent isometric view an embodiment of a sealing body, FIG. 5 b is a perspective cutaway view of the sealing body, FIG. 5 c is a side view of the sealing body, FIG. 5 d is a cross-section view of FIG. 5 c along the line A-A, FIG. 5 e is a side view of the sealing body, FIG. 5 f is a cross-section view of FIG. 5 e along the line B-B; and

FIG. 6 a is a transparent isometric view an embodiment of a sealing body, FIG. 6 b is a perspective cutaway view of the sealing body, FIG. 6 c is a side view of the sealing body, FIG. 6 d is a cross-section view of FIG. 6 c along the line A-A, FIG. 6 e is a side view of the sealing body, FIG. 6 f is a cross-section view of FIG. 6 e along the line B-B.

Like reference numerals are used in the drawings to denote like elements and features.
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

FIGS. 1 a and 1 b 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. 1 a and 1 b, 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 16 a, 16 b, 16 c. The perforating guns 16 a, 16 b, 16 c are fired at planned locations within a number of pressure activation zones 18 a, 18 b, 18 c in the well 10. A sequence of perforation operations may be performed typically starting with triggering the perforating gun 16 a furthest down-hole, then the next perforating gun 16 b down-hole and so forth, in order to perforate the wellbore casing 12.
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.
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 20 a, 20 b, 20 c situated down-hole of the perforating guns 16 a, 16 b, 16 c.
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.
The operation of the seat 20 and activation of the perforating gun 16 will be described with respect to the seat 20 b and perforating gun 16 b illustrated in FIG. 1 b. A sealing body 24 b is dropped or pumped with fluids down the well 10 to the corresponding seat 20 b. In some embodiments, the sealing body 24 b is neutral or slightly buoyant in the well fluids and thus is pumped down-hole to the corresponding seat 20 b. The sealing body 24 b is sized to pass through the up-hole seat 20 c and to mate and form a tight pressure seal with seat 20 b. In one embodiment, the sealing body 24 b mates and forms a seal with the seat 20 b in any orientation of the sealing body 24 b. Using high pressure pumps on the drilling rig (not shown) the well bore pressure above the seat 20 b and sealing body 24 b is increased until a predetermined pressure threshold is met or exceeded in the pressure activation zone 18 b, causing the perforating gun 16 b to be activated and fire. After the perforating gun 16 b fires, the sealing body 24 b 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).
If there is more than one zone to produce, a number of perforation operations are carried out. The smallest sized sealing body 24 a is pumped down the well 10 and travels through seats 20 b, 20 c to the seat 20 a in order to create a high pressure in the activation zone 18 a to trigger the perforating gun 16 a furthest down the well 10. After the perforating gun 16 a fires, the sealing body 24 a floats and/or travels to the top of the well 10 and is recovered. Then, a larger sized sealing body 24 b is pumped down the well 10 and travels through seat 20 c to the seat 20 b in order to create a high pressure in the activation zone 18 b to trigger the perforating gun 16 b at the next predetermined location furthest down the well. The larger sealing body 24 b similarly is recovered before activating the next perforating gun 16 c. A sealing body 24 c, larger than sealing body 24 b, is pumped down the well 10 and travels to the seat 20 c to create high pressure in the activation zone 18 c to trigger the last perforating gun 16 c. 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.
Thus, sealing bodies 24 a, 24 b, 24 c of varying sizes are provided to mate and form a seal with seats 20 a, 20 b, 20 c. 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.
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.
FIGS. 3 a, 3 b, 3 c through FIGS. 6 a to 6 f 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.
In one embodiment, the sealing body 24, as illustrated in FIGS. 3 a, 3 b and 3 c 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:
$27.7008 \times (ρ_{metal}) \times \frac{(1 - d^{3})}{D^{3}} \leq 1$
where:

- ρ_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:

$(ρ_{metal}) \times \frac{(1 - d^{3})}{D^{3}} \leq 1$
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.
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 φ)⁻¹, where φ 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.
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.
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/in³and 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.
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.
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.
Example embodiments of a sealing body 24 with an internal reinforcement structure 60 are illustrated in FIGS. 4 a to 4 f through 6 a to 6 f. 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.
As can be seen, for example, in FIGS. 4 a to 4 f, 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.
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/in³and 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.
In the embodiment illustrated in FIGS. 4 a to 4 f, 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.
In the embodiment illustrated in FIGS. 5 a to 5 f, 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. 5 a, 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.
In the embodiment illustrated in FIGS. 6 a to 6 f, 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. 6 a, 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.
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 ¼″ 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 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)	(in³)	(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

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.
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.
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.
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.
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.

Claims

What is claimed is:

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×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.