# Patent

## Title
Selectively degradable passage restriction and method

## Abstract

An actuation system and method includes a tubular defining a passage, and an assembly disposed with the tubular. The assembly includes a restriction operatively arranged to receive a restrictor for enabling actuation of the assembly. The restriction includes a degradable material with a protective layer thereon, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid.

## Background
BACKGROUND
Plugs, balls, darts, etc. are used in the downhole drilling and completions industry for actuating of a variety of tools and assemblies. Typically, the plugs land in a seat, blocking fluid flow through a passage and enabling a differential pressure to be created thereacross for actuating a tool or assembly. After actuation of the tool or assembly, it is often desirable to remove the resulting obstruction. Advances in selectively removable plugs and plug seats are accordingly well received by the industry.
BRIEF DESCRIPTION
An actuation system and method, the system including a tubular defining a passage, and an assembly disposed with the tubular, the assembly including a restriction operatively arranged to receive a restrictor for enabling actuation of the assembly, the restriction including a degradable material with a protective layer thereon, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid.
An actuation system including a tubular defining a passage, and an assembly disposed with the tubular, the assembly having a restriction operatively arranged for receiving a restrictor, the restrictor enabling actuation of the assembly, the restriction at least partially formed from a degradable material responsive to a fluid in the passage, wherein actuating the assembly performs a primary function and also exposes the degradable material to the fluid.
A method of operating a downhole system, including launching a restrictor through a passage in a tubular, receiving the restrictor at a restriction of an assembly, the restriction formed from a degradable material with a protective layer thereon, actuating the assembly with the restrictor for performing a primary function of the assembly, wherein actuation of the assembly also exposes the degradable material to the fluid.



BRIEF DESCRIPTION OF THE DRAWINGS
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
FIG. 1 is a cross-sectional view of a downhole system having an actuatable plug assembly with a degradable seat in an initial position;
FIG. 2 is a cross-sectional view of the system of FIG. 1 with the plug assembly in an actuated position for exposing a degradable core of the seat to a downhole fluid;
FIG. 3 is a quarter-sectional view of another downhole system having an actuatable plug assembly with a degradable seat;
FIG. 4 is a quarter-sectional view of the system of FIG. 3 with a pressure applied to the plug assembly for exposing a degradable core of the seat to a downhole fluid;
FIG. 5 is an enlarged view of the area generally encircled in FIG. 4 showing a protective layer penetrated in order to expose the core to the downhole fluid;
FIG. 6 is a quarter-sectional view of a downhole assembly having an extension for delaying degradation of a restriction; and
FIG. 7 is a view of the assembly taken generally along line 7-7 in FIG. 6.



DETAILED DESCRIPTION
A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
Referring now to FIG. 1, a system 10 is shown including a tubular 12 having a plurality of ports 14. The ports 14 are selectively openable by use of an assembly 16, which includes a sleeve 18 actuatable by a restrictor 20. That is, by landing the restrictor 20 at a restriction 22 disposed with the sleeve 18, the restrictor 20 blocks fluid flow through a passage 24. In the illustrated embodiments, the restrictor 20 takes the form of a ball and the restriction 22 takes the form of a seat, although these are not to be considered limiting as discussed below. Blockage of the passage 24 enables a pressure differential to be formed across the restrictor 20 for urging the sleeve 18 from an initial or run-in position in which the ports 14 are closed, as shown in FIG. 1, to an actuated position in which the ports 14 are open, as shown in FIG. 2.
The assembly 16 could be used in fracturing operations or the like. The restrictor 20 could be any type of ball, dart, plug, etc. that lands at the restriction 22 for blocking fluid flow and enabling creation of a differential pressure. The restrictor 20 could alternatively be some other element that at least partially blocks fluid flow through the passage 24 and is received at least temporarily fleetingly by the restriction 22 for applying a force on the restriction 22 as it passes through or by the restriction 22, such as a collet, dart, etc. Similarly, the restriction 22 or any other restriction discussed herein could be a full or partial ring, sleeve, cup, etc., or any other member capable of at least partially restricting its corresponding passage, e.g., the passage 24. Likewise, the assembly 16 could be substituted with any other tool or assembly that is triggered, actuated, shifted, moved, opened, closed, etc. (generally, “actuated”) by use of a restrictor. It is thus to be appreciated that the current invention is not limited to merely port control assemblies or fracturing operations. A release member such as a collet, shear screw, etc., could be used to hold the sleeve 18 in the initial position until a differential pressure is created across the restrictor 20 to overcome the release member.
After actuation of the sleeve 18, the restriction 22 is intended to be removed. That is, the restriction 22 includes a core 26 that is degradable upon exposure to a downhole fluid. “Degradable” is intended to mean that the core 26 is disintegratable, dissolvable, weakenable, corrodible, consumable, or otherwise removable. It is to be understood that use herein of the term “degrade”, or any of its forms, incorporates the stated meaning. For example, the core 26 could be made from magnesium, aluminum, controlled electrolytic metallic materials, described in more detail below, etc. and degradable upon exposure to one or more fluids available or deliverable downhole, such as water, brine, acid, oil, etc. By exposing the core 26 to a specified downhole fluid, the restriction 22 can be removed without an intrusive, costly, or time-consuming operation such as milling. Furthermore, by degrading the core 26, the restrictor 20 will be released from the restriction 22 and pass further down the passage 24. For example, a single restrictor is thus usable to successively actuate a plurality of seats, sleeves, assemblies, tools etc. (generally, “assemblies”) down the length of the tubular 12 or a string in which the tubular 12 is installed. For example, a single restrictor could be used to actuate multiple port assemblies in a fracturing operation.
It is expected that the restriction 22 will be subjected to various downhole fluids well before the restrictor 20 has encountered the restriction 22 for actuating the assembly 16. Exposure to the downhole fluids prior to actuation of the assembly 16 would disable actuation of the assembly 16. That is, without the restriction 22, the restrictor 20 would not land or otherwise be interfered with, and a pressure would not be able to be applied across or to the restrictor 20 for actuating the assembly 16. Accordingly, the degradable core 26 includes a protective layer 28. For example, by manufacturing the protective layer 28 from a material that is resistant, inert, passive, inactive, etc. with respect to the downhole fluids, the protective layer 28 will temporarily protect the degradable core 26. The protective layer 28 could be made from, for example, cladding, polymers, thermosets, thermoplastics, elastomers, resins, epoxies, etc. In addition to chemical protection, the layer 28 could also lend additional mechanical strength or durability to the core 26 to protect the core 26 from impact or erosion. The layer 28 could be any thickness, e.g., based on the material used, properties desired to be imparted to the core 26, etc.
In the embodiment of FIGS. 1 and 2, the protective layer 28 does not fully enclose or encapsulate the core 26. That is, the core 26 includes an unprotected area 30 that is not coated by the protective layer 28. A channel 32 extends from the unprotected area 30 through the sleeve 18. When the sleeve 18 is in the initial position of FIG. 1, the channel 32 and the unprotected area 30 of the core 26 are isolated from the downhole fluids via a first pair of seals 34 located between the sleeve 18 and the tubular 12 and a second pair of seals 36 located between the sleeve 18 and the restriction 22. The seals 34 and 36 are, for example, o-rings, bonded seals, or any other suitable sealing element and can be manufactured from any suitable material known in the art. The seals 34 and 36 also isolate the sides of the passage 24 on opposite sides of the restrictor 20 from each other such that a differential pressure can be formed thereacross.
After actuation of the assembly 16, the differential pressure across the restrictor 20 is no longer needed and the restriction 22 and/or the restrictor 20 can be removed. In order to expose the core 26 to the downhole fluid, the protective layer 28 can be penetrated. For example, in the embodiment of FIGS. 1 and 2, actuation of the sleeve 18 not only performs a primary function of the assembly, e.g., selectively opening the ports 14, but also causes the restriction 22 to be exposed to the downhole fluids. Specifically, the passage 24 in the tubular 12 widens downhole for forming a cavity 38 between the sleeve 18 and the tubular 12 when the sleeve 18 is in its open position. Together with the channel 32, the cavity 38 enables fluid communication between the passage 24 and the unprotected area 30 of the core 26. Thus, by providing the proper fluid in the passage 24, degradation of the core 26 can commence immediately after actuation of the sleeve 18.
A system 40 is shown in FIGS. 3 and 4 having an assembly 42 in an initial position and after a pressure is applied thereto, respectively. The assembly 42 generally resembles the assembly 16 in that it includes a sleeve 44 and a restriction 46, with the restriction 46 formed from a degradable core 48 and a protective layer 50. However, unlike the system 10, the protective layer 50 fully encloses the core 48. Instead of channeling fluid into an unprotected area of the core, actuation of the assembly 42 causes the layer 50 to be penetrated.
For example, in addition to performing some primary task or operation (e.g., opening ports, triggering a tool, etc.), actuation of the assembly 42 also drives the restriction 46 into a plurality of penetrating elements 52 on the sleeve 44. The penetrating elements 52 could be any features that penetrate, puncture, pierce, enter, or otherwise provide fluid access through the layer 50 to the core 48. The penetration of the layer 50 is shown in more detail in FIG. 5. The penetrating elements could take the form of sharp points, teeth, spikes, etc. The penetrating elements 52 could also include fins, blades, points, protrusions, abrasive or rough textures, etc., arranged on the circumferential surface of the sleeve 44 or the exterior of the restrictor 20, particularly if the restrictor 20 takes the form of an element that passes through or by the restriction instead of landing at the restriction, for scouring, etching, or abrading the layer 50 as the restriction 46 is actuated. Once the layer 50 is penetrated, the core 48 is exposable to downhole fluids for effecting removal of the restriction 46. In view of this embodiment it is to be appreciated that by positioning ports or the like radially outwardly from the restriction, making the restriction slidable directly against the tubular, and including the penetrating elements on the tubular, sleeves such as the sleeve 44 can be avoided, with the ports opening upon degradation of the restriction.
Another embodiment is shown in FIGS. 6 and 7, namely including an assembly 54. The assembly 54 generally resembles the assemblies discussed above, having a sleeve 56 and a restriction or seat 58. Also similar to the above, the restriction 58 comprises a degradable core 60 and a protective layer 62. In the assembly 54, however, the restriction 58 has an extension 64 protruding axially therefrom. The extension 64 is coated by the layer 62 except for an uncovered area 66 at an end thereof. By distancing the uncovered area 66 from the main body of the restriction 58, the extension 64 acts as a “fuse” for delaying degradation of the restriction 58 until the extension 64 has fully degraded upon exposure of the uncovered area 66 to the downhole fluid. In this way, the length of the extension 64 can be set to delay degradation of the restriction 58 long enough for the restriction 58 to be first used for its primary purpose, e.g., receiving the restrictor 20 or some other plug for opening ports, etc., and then degrading thereafter.
Materials appropriate for the purpose of degradable restriction cores include magnesium, aluminum, controlled electrolytic metallic materials, etc. The controlled electrolytic materials as described herein are lightweight, high-strength metallic materials. Examples of suitable materials and their methods of manufacture are given in United States Patent Publication No. 2011/0135953 (Xu, et al.), which Patent Publication is hereby incorporated by reference in its entirety. These lightweight, high-strength and selectably and controllably degradable materials include fully-dense, sintered powder compacts formed from coated powder materials that include various lightweight particle cores and core materials having various single layer and multilayer nanoscale coatings. These powder compacts are made from coated metallic powders that include various electrochemically-active (e.g., having relatively higher standard oxidation potentials) lightweight, high-strength particle cores and core materials, such as electrochemically active metals, that are dispersed within a cellular nanomatrix formed from the various nanoscale metallic coating layers of metallic coating materials, and are particularly useful in borehole applications. Suitable core materials include electrochemically active metals having a standard oxidation potential greater than or equal to that of Zn, including as Mg, Al, Mn or Zn or alloys or combinations thereof. For example, tertiary Mg—Al—X alloys may include, by weight, up to about 85% Mg, up to about 15% Al and up to about 5% X, where X is another material. The core material may also include a rare earth element such as Sc, Y, La, Ce, Pr, Nd or Er, or a combination of rare earth elements. In other embodiments, the materials could include other metals having a standard oxidation potential less than that of Zn. Also, suitable non-metallic materials include ceramics, glasses (e.g., hollow glass microspheres), carbon, or a combination thereof. In one embodiment, the material has a substantially uniform average thickness between dispersed particles of about 50 nm to about 5000 nm. In one embodiment, the coating layers are formed from Al, Ni, W or Al2O3, or combinations thereof. In one embodiment, the coating is a multi-layer coating, for example, comprising a first Al layer, an Al2O3 layer, and a second Al layer. In some embodiments, the coating may have a thickness of about 25 nm to about 2500 nm.
These powder compacts provide a unique and advantageous combination of mechanical strength properties, such as compression and shear strength, low density and selectable and controllable corrosion properties, particularly rapid and controlled dissolution in various borehole fluids. The fluids may include any number of ionic fluids or highly polar fluids, such as those that contain various chlorides. Examples include fluids comprising potassium chloride (KCl), hydrochloric acid (HCl), calcium chloride (CaCl2), calcium bromide (CaBr2) or zinc bromide (ZnBr2). For example, the particle core and coating layers of these powders may be selected to provide sintered powder compacts suitable for use as high strength engineered materials having a compressive strength and shear strength comparable to various other engineered materials, including carbon, stainless and alloy steels, but which also have a low density comparable to various polymers, elastomers, low-density porous ceramics and composite materials.
While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

## Claims

1. An actuation system comprising:
a tubular defining a passage; and
an assembly disposed with the tubular, the assembly including a restriction operatively arranged to receive a restrictor for enabling actuation of the assembly, the restriction including a degradable material with a protective layer thereon, the degradable material degrading upon exposure to a fluid in the passage and the protective layer isolating the degradable material from the fluid, the degradable material including an uncovered area with respect to the protective layer;
wherein the restrictor blocks fluid flow through the passage, the assembly is actuated by creating a pressure differential across the restrictor, and actuation of the assembly establishes fluid communication between the uncovered area and the passage.

2. The system of claim 1, wherein at least one seal element is included to isolate the uncovered area from the fluid.

3. The system of claim 1, wherein fluid communication between the uncovered area and the passage is enabled by a cavity in the tubular, the cavity misaligned with the uncovered area before actuation.

4. The system of claim 1, wherein actuation of the assembly opens at least one port in the tubular.

5. The system of claim 4, wherein the assembly includes a sleeve disposed between the restriction and the tubular and actuation of the assembly shifts the sleeve to open the at least one port.

6. The system of claim 1, wherein the degradable material is a controlled electrolytic metallic material.

7. An actuation system, comprising:
a tubular defining a passage; and
an assembly disposed with the tubular, the assembly having a restriction operatively arranged for receiving a restrictor, the restrictor enabling actuation of the assembly, the restriction at least partially formed from a degradable material responsive to a fluid in the passage, wherein actuating the assembly performs a primary function and also exposes the degradable material to the fluid;
wherein the degradable material is at least partially encapsulated by a protective layer, and wherein actuating the assembly aligns an uncovered area of the degradable material with a cavity in the tubular, the cavity establishing fluid communication between the uncovered area and the passage.

8. The system of claim 7, wherein the primary function of the assembly is to selectively open at least one port in the tubular.

9. A method of operating the system of claim 1, comprising:
launching the restrictor through the passage in the tubular;
receiving the restrictor at the restriction of the assembly;
actuating the assembly with the restrictor for performing a primary function of the assembly, wherein actuation of the assembly also exposes the degradable material to the fluid.

10. The method of claim 9, wherein the primary function of the assembly is to selectively open at least one port in the tubular.

11. The method of claim 9, wherein actuating the assembly aligns an uncovered area of the degradable material with a cavity in the tubular, the cavity establishing fluid communication between the uncovered area and the passage.