Patent Application
20130068461
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.
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.
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.
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.
a is a cross section view of a well bore;
a is a front view of an embodiment of a sealing body,
a is a transparent isometric view an embodiment of a sealing body,
a is a transparent isometric view an embodiment of a sealing body,
a is a transparent isometric view an embodiment of a sealing body,
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.
a 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
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 20a, 20b, 20c situated down-hole of the perforating guns 16a, 16b, 16c.
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
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
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.
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
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.
a,
3
b,
3
c through
In one embodiment, the sealing body 24, as illustrated in
where:
In one embodiment, the sealing body 24 may be used with a seat 20 comprising a ball seat 26, as illustrated in
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/in3 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.
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
As can be seen, for example, in
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/in3 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.
In the embodiment illustrated in
In the embodiment illustrated in
In the embodiment illustrated in
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2752864 | Sep 2011 | CA | national |
