BACKGROUND

In oil and gas wells, an annular region exists around the production tubing. It is often desirable to isolate some portions of this annular region from other portions, e.g., to prevent fluid flow between different zones of a formation, or to force formation fluids from a completion zone to enter ports in the production tubing en route to the surface. Tools that isolate different annular regions by creating a seal around the production tubing are known as "packers."

The fluids leaving a formation in a completion zone may be transporting sand, grit, and other solids that can accumulate inside the production tubing and create barriers to further fluid flow. To prevent such solids from entering the production tubing, engineers routinely equip the ports of the production tubing with screens, and pack the annular region outside the screen with gravel (i.e., a "gravel pack") or similar materials that are transported into place by fluid flow from the surface. To facilitate this transport, one of the packers used to define the completion zone (i.e., the "gravel-pack packer") is equipped with crossover, or "shunt", tubes that, when open, enable fluid-transported gravel to flow from the annulus between the casing and screen or blank pipe into the shunt tubes to exit at a point lower in the screen interval.

Because the shunt tubes provide a bypass from one screen to another screen section, they must be closed during normal production operations to force all fluid flow through the screens. Mechanical valves, such as check valves, ball valves, and sliding sleeves, are often used. However, such valves are subject to sticking, erosion, and incomplete sealing in sandy environments such as those encountered in gravel pack operations.

BRIEF DESCRIPTION OF THE DRAWINGS

Accordingly, systems and methods for preventing flow through shunt tubes using magnetically responsive particles are disclosed herein. In the following detailed description of the various disclosed embodiments, reference will be made to the accompanying drawings in which:

Figure 1 is a contextual view of an illustrative drilling environment;

Figure 2 is a cross-sectional view of an illustrative casing and cementing operation; Figure 3 is a cross-sectional view of an illustrative perforated borehole;

Figure 4A is downhole view of an illustrative gravel-packing assembly;

Figure 4B is a detail view of an illustrative configuration of shunt tubes on the screen assembly; Figures 5 and 6 are cross-sectional views of illustrative fluid chambers and release assemblies for the magnetically responsive particles;

Figures 7 is a cross-sectional view of an illustrative system for plugging shunt tubes using magnetically responsive particles; and

Figure 8 is a flow diagram of an illustrative shunt tube plugging method using magnetically responsive particles.

It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claims to refer to particular system components and configurations. As one of ordinary skill will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function.

In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to...". Also, the term "couple" or "couples" is intended to mean either an indirect or a direct electrical or physical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through a direct physical connection, or through an indirect physical connection via other devices and connections in various embodiments.

DETAILED DESCRIPTION

The issues identified in the background are at least partly addressed by systems and methods for plugging shunt tubes using magnetically responsive particles. Shunt tubes are flow paths that enable gravel slurry to flow from inside the production tubing to the annular region outside the sand screens, bypassing the screens. Multiple shunt tubes may be disposed on the same gravel-pack assembly, and the tubes may have various lengths, diameters, and cross-sectional shapes. Larger tubes have relatively low friction, and therefore support higher flow rates. The shunt tubes may need to be plugged after use, and the disclosed systems and methods for plugging the shunt tubes enable a variety of sizes of shunt tubes to be plugged using the same equipment. Additionally, at least some of the disclosed systems and methods enable the shunt tubes to be easily unplugged and re-plugged.

Figure 1 illustrates how a well may be formed. Specifically, a drilling platform 2 is equipped with a derrick 4 that supports a hoist 6. In at least some embodiments, the platform 2 is located offshore for subsea drilling. Drilling of oil and gas wells is carried out by a string of drill pipes connected together by "tool" joints 7 so as to form a drill string 8. The hoist 6 suspends a kelly 10 that lowers the drill string 8 through a rotary table 12. Connected to the lower end of the drill string 8 is a drill bit 14. The bit 14 is rotated and drilling of the borehole 20 is accomplished by rotating the drill string 8, by use of a downhole motor near the drill bit, or by both methods.

Drilling fluid, termed mud, is pumped by mud recirculation equipment 16 through a supply pipe 18, through the kelly 10, and down through the drill string 8 at high pressures and volumes to emerge through nozzles or jets in the drill bit 14. The mud then travels back up the hole via the annulus formed between the exterior of the drill string 8 and the borehole wall 20, through a blowout preventer, and into a mud pit 24 on the surface. On the surface, the drilling mud is cleaned and then recirculated by recirculation equipment 16.

Figure 2 shows an illustrative borehole 202 that has been drilled into the earth. Such boreholes are routinely drilled to ten thousand feet or more in depth and can be steered horizontally for twice that distance. During the drilling process, the driller circulates a drilling fluid to clean cuttings from the bit and carry them out of the borehole. In addition, the drilling fluid is normally formulated to have a desired density and weight to approximately balance the pressure of native fluids in the formation. Thus the drilling fluid itself can at least temporarily stabilize the borehole and prevent blowouts. To provide a more permanent solution, the driller inserts a casing string 204 into the borehole 202. The casing string 204 is normally formed from lengths of tubing joined by threaded tubing joints 206. The driller connects the tubing lengths together as the casing string 204 is lowered into the borehole 202.

The casing string 204 may be coupled to a measurement unit 214 that senses one or more parameters of the casing 204 including temperature, pressure, strain, acoustic (noise) spectra, acoustic coupling, chemical (e.g., hydrogen or hydroxyl) concentration, and the like. The measurement unit 214 may process each measurement and combine it with other measurements to obtain a high-resolution measurement of that parameter. Though Figure 2 shows a cable as the sensing element, alternative embodiments of the system variously employ an array of spaced-apart sensors that communicate measurement data via wired or wireless channels to the measurement unit 214. A data processing system 216 may periodically retrieve the measurements as a function of position and establish a time record of those measurements. Software, represented by information storage media 218, runs on the data processing system 216 to collect the measurement data and organize it in a file or database. The software further responds to user input via a keyboard or other input mechanism 222 to display the measurement data as an image or movie on a monitor or other output mechanism 220. Some software embodiments may provide audible and/or visual alerts to the user.

To cement the casing 204, the drilling crew injects a cement slurry 225 into the annular space (typically by pumping the slurry 225 through the casing 204 to the bottom of the borehole 202, which then forces the slurry 225 to flow back up through the annular space around the casing 204). It is expected that the software and/or the crew will be able to monitor the measurement data in real time or near real time to observe the profile of the selected parameter (i.e., the value of the parameter as a function of depth) and to observe the evolution of the profile (i.e., the manner in which the profile changes as a function of time).

Figure 3 is a cross-sectional view of an illustrative, perforated borehole 302. The illustrative borehole 302 has been fully drilled, all drilling equipment has been removed, and the borehole 302 has been cased with casing 304 and cemented to sustain the structural integrity and stability of the borehole 302. The borehole 302 is formed within the earth and, more precisely, through target formation 300, which extends beyond the limited scope with which it is represented in Figure 3. The target formation 300 may include multiple layers, each layer with a different type of rock formation, including the hydrocarbon-containing target formation within which the borehole may extend horizontally for some distance. The casing 304 contains multiple perforations 306, which may be formed by a perforation gun. The perforation gun may be transported downhole on a perforation tool using a wireline. When the gun is aligned with the desired perforation location, the gun may emit a high energy charge in order to perforate the surrounding casing 304 and formation 300. For example, the perforation tool may be aligned a certain distance 314 from the bottom of the borehole 302, and the perforation gun may create perforations having a certain spacing 312.

Once the borehole has been formed, cased, and cemented, the sump packer is run downhole using an electric line tool that locates the sump packer at the correct position in the well. The packer is set using a setting tool, after which the setting tool and electric line tool are retrieved. The borehole may then be equipped with a gravel-packing assembly. Figure 4A is downhole view of an illustrative gravel-packing assembly 400 suitable for use in a cased- hole environment. A sump packer 402 may be used as a base on which the screen 404 rests. In addition to support, the sump packer 402 may be used to accurately place the screen 404 next to the perforations 406. The sump packer 402 may be run into the well on an electric wireline before perforation, and may be set a specified distance (e.g., 5 to 10 ft.) below the lowest planned perforation.

On top of the sump packer 402, the screen 404 creates an annulus between the screen 404 and the production casing 416, and the screen 404 holds the gravel 410 in place during production. Near the top of the gravel-pack assembly is a gravel-pack packer 414 that creates a hydraulic seal against the production casing 416 in order to isolate the annulus below the gravel-pack packer 414. For example, an expandable elastomeric element may be used to form the seal between the gravel-pack assembly 400 and the production casing 416. The gravel-pack packer 414 may be permanent or retrievable.

The annulus is packed with natural or synthetic gravel 410 of a specific size designed to prevent the passage of formation sand but not the passage of hydrocarbons into the production tubing 418 for transport to the surface. A slurry of gravel and carrier fluid is pumped into the perforations 406 and the annulus between the screen 404 and the perforated casing. The gravel 410 is deposited as the carrier fluid is squeezed into the formation or as it circulates back to surface through the screen 404. As such, the gravel 410 should be large enough to be held in place by the screen 404.

The gravel-pack assembly 400 includes one or more shunt tubes 408, internal or external to the outer pipe, that create a secondary path for slurry. Multiple shunt tubes 408 may be used in the same gravel packing operation and the shunt tubes 408 may be various sizes. Larger shunt tubes 408 have relatively low friction, and therefore support higher flow rates. The shunt tubes 408 may be mounted external to the screen 404 as illustrated in detail in Figure 4B.

Figure 4B is a detail view of one shunt tube configuration on the gravel-pack assembly 400. Specifically, two shunt tubes 404 are external and parallel to the screen base pipe 401 and screen base jacket 403. The shunt tubes 404 may be made of steel or a similar rigid material. Here, the shunt tubes 04 are of similar size, but in other embodiments the shunt tubes are different lengths and have different cross-sectional diameters. A shunt tube bulkhead 409 provides fluid communication between the tubes and the inside of the production tubing.

The gravel-pack assembly 400 also includes one or more magnetic field generators, which generate one or more magnetic fields. For example, the one or more magnetic fields may be generated by one or more magnets 405, as shown here, positioned on the outer diameter of the screen base pipe 401. In other embodiments, the magnets 405 are positioned on the inner diameter of the screen base pipe 401, embedded in the screen base pipe 401, run down on a separate tool, and the like. The magnets 405 may be attached or otherwise secured to the screen base pipe 401 via adhesives, welding, mechanical attachments, embedding the magnets within the tubing, and the like. Additionally, although one magnet 405 is shown for ease of reference, it should be understood that multiple magnets 405 may be used, and each may be ring-shaped and positioned around the circumference of tubing. The magnet 405 generates a magnetic field that arrests released fluid, including magnetically responsive particles, within the shunt tube 404 thus creating plugs 407 that may extend farther than the end of the shunt tubes 404 as shown. The fluid may be stored and released as shown in Figures 5 and 6, the description of which also describes the fluid in detail. The description of Figure 7 describes the arresting process in detail.

Figure 5 is a cross-sectional view of a release assembly 501 including a fluid chamber 510. The fluid chamber 510 stores fluid 507 including magnetically responsive particles 505. For example, the fluid 507 may be a magnetorheological fluid, ferrofluid, and the like. The fluid 507 may additionally include a polymer precursor material or similar material that forms cross-links such as plastics, adhesives, thermoplastics, thermosetting resins, elastomeric materials, polymers, epoxies, silicones, sealants, oils, gels, glues, acids, thixotropic fluids, dilatant fluids, epoxies, and the like. If the polymer precursor is an epoxy, the epoxy may be a one-part epoxy (e.g., a silicone sealant) or a multi-part epoxy.

The polymer precursor may be a material that can carry the magnetically responsive particles 505 and cure or otherwise set given appropriate forces, environmental conditions, or time. The polymer precursor may also return to a flowing state given appropriate forces, environmental conditions, or time for ease of unplugging. The polymer precursor may be a material that can create a seal in order to plug the shunt tube entrances and exits, and the polymer precursor may be capable of being stored downhole without having to be activated for immediate use. Any other type of polymer precursor or other material that may act as a carrier for magnetically responsive particles, and that can cure to form a seal or otherwise act as a sealant, may also be used.

The magnetically responsive particles 505 (which may also be referred to herein as particles 505) may be units of a ferromagnetic material, such as iron, nickel, cobalt, any ferromagnetic, diamagnetic, or paramagnetic particles, any combination thereof, or any other particles that can respond to a magnetic field. The particles 505 may not be easily visible in the fluid 507 due to their size, and they have thus been exaggerated in the figures for ease of viewing. However, any suitable particle size can be used for the particles 505. For example, the particles 505 may range from the nanometer size up to the micrometer size. In one example, the particles 505 are in the size range of about 100 nanometers to about 1000 nanometers. In another example, the particles 505 range into the micrometer size, e.g., up to about 100 microns. The particles 505 may also be any shape, non-limiting examples of which include spheres, spheroids, tubulars, corpusculars, fibers, oblate spheroids, or any other appropriate shape. Multiple shapes and multiple sizes may be combined in a single group of particles 505 in the fluid 507.

The fluid chamber 510 includes a release assembly 501 that releases fluid 507 stored in the fluid chamber 510 into a line 502 coupled to the shunt tube (not shown). The release assembly 501 may include a piston 508 that forces the fluid 507 out of the fluid chamber 510 during release when pressure is applied to the fluid 507 via the piston 508. The piston 508 may have a spring engagement 506 that causes movement of the piston 508 when activated. Alternatively, the piston 508 may be driven by hydraulic fluid or a motor-driven threaded rod. The spring is used to provide pressure by keeping the piston 508 in contact with the fluid 507. The pressure is maintained by creating a seal between the fluid chamber 510 wall and the piston 508. This may also prevent the fluid 507 from prematurely hardening by preventing air from contacting the fluid 507 within the fluid chamber 510.

A burstable disk 504 may be provided to prevent premature injection of the fluid 507 into the line 502 and shunt tube. Pressure, when applied, may cause the fluid 507 to rupture or burst the burstable disk 504 and exit the fluid chamber 510 into the line 502 through the resultant opening. Specifically, the spring engagement 506 may exert a force on the piston 508 in the direction of the fluid 507. The force exerted on the piston 508 may cause the piston 508 to exert a force on the fluid 507 in the direction of the burstable disk 504. The burstable disk 504 may remain closed and exert a force on the fluid 507 in a direction opposite to the direction of the force exerted by the piston 508. Once the force exerted on the fluid 507 by the piston 508 exceeds the force able to be exerted by the burstable disk 504, the burstable disk 504 bursts. Such bursting removes the force exerted by the burstable disk 504 on the fluid 507. This allows the fluid 507 to flow into the line 502 and shunt tube in response to the force exerted by the piston 508.

The burstable disk 504 may be a piece of foil, metal, or other material. The burstable disk may also be implemented as a dissolvable barrier that dissolves upon a certain pH exposure, environmental exposure, or other pre-selected trigger. For example, the burstable disk 504 may be formed as a temperature- sensitive material or shape-memory material that dissolves upon a certain temperature, shrinks or enlarges at a certain environmental condition, or otherwise ceases to contain the fluid 507 in the fluid chamber 510 in response to a preselected trigger.

The release assembly 501 may include a sensor to sense a remotely-generated signal, the signal initiating release of the fluid when received by the sensor. For example, the burstable disk 504 may be coupled to an electronic circuit housed within the gravel-packer or system 500 to create electronic activation of the burstable disk 504 when desired. A wireless signal may be generated remotely, sent to the circuit, and received by the circuit. The signal may be based on the pressure rise from screen out of the gravel pack, tubing movement, pressure cycles, temperature changes, or any other activating event. Another implementation of the release assembly is shown in Figure 6.

Figures 6 is a cross-sectional view of a release assembly 606 including a fluid chamber 604. The release assembly 606 may include a collapsible tube 603 that forces the fluid 605 out of the fluid chamber 604 (and the collapsible tube 603 itself) during release in response to pressure external to the collapsible tube 603 that collapses the collapsible tube 603. For example, a hydraulic pump may generate the pressure within the fluid chamber 604 through a pressure line 602. The release assembly 606 may also include a check valve 610 coupled to the fluid exit line 608 that enables the fluid 605 to exit the fluid chamber 604 (and collapsible tube 603). The check valve 610 may also prevent the fluid 605 from flowing back into the fluid chamber 510 or collapsible tube 603.

In addition to containing magnetically responsive particles 607, the fluid 605 may be viscous. The fluid 605 may have a minimum yield stress before it flows, such as Bingham plastic, and it may behave as a thixotropic material, such as a gel. The fluid 605 may remain in a moveable form until a magnetic field arrests the magnetically responsive particles 607 as described with respect to Figure 7.

Figure 5 and 6 show an active deployment; specifically, the fluid is forced to exit the release assemblies. However, a passive deployment is also possible. For example, the fluid may be attracted toward the magnetic fields to allow the fluid to enter the shunt tube.

Figures 7 is a top-view of an illustrative system 700 for plugging a shunt tube 706 using magnetically responsive particles. A magnetic field 714 is generated by a magnetic field generator, shown here as a magnet 708. The magnet 708 may be a disk magnet, ring- shaped magnet, block magnet, or the like. Another type of magnetic field generator may include a sensor to sense a remotely-generated signal, the signal initiating generation of and/or extinguishing the magnetic field when received by the sensor. As shown, the magnet 708 is embedded in the screen jacket 712, which is surrounding the screen base pipe 710. However, the magnet 708 may be disposed radially outside of the screen jacket 712 or radially inside of the screen base pipe 710. Also, multiple magnets 708 may be disposed on the gravel packer in various such configurations to produce a magnetic fields with a particular shape to optimize shunt tube plugging for multiple shunt tubes and multiple fluid chambers.

Fluid containing magnetically responsive particles flows from the fluid chamber 702, through the line 704, and into the shunt tube 706. In the shunt tube 706, passage of the fluid through the magnetic field 714 causes the magnetically responsive particles to align with the magnetic field 714. Alignment of the particles with the magnetic field 714 causes the particles to hold the fluid in place, thereby plugging the shunt tube 706. Subsequent movement of the fluid is limited due to arrangement of the particles. Specifically, the arrangement of the particles changes the shear strength of the fluid, decreasing its viscosity.

Once formed, the fluid may be allowed to cure, harden, or otherwise create a seal. Any polymer precursor material may begin to cross-link. For example, the passage of time, applied heat, and/or exposure to certain fluids or environments may cause the fluid to set to form a plug within the shunt tube 706, thereby preventing any material from passing through the shunt tube 706. In this way, the formation fluid is forced to pass into the production tubing via the screens. Plugging the shunt tubes provides a way to isolate sections at the producing interval from one another. Without isolation, the different zone layers may communicate, allowing water zones or gas zones to flow thus preventing preferable oil flow.

Figure 8 is a flow diagram of an illustrative shunt tube plugging method using magnetically responsive particles. At 802, a shunt tube diverts the gravel slurry to bypass blockages or bridges. For example, field operators pump a slurry of gravel and carrier fluid into the perforations and the annulus between the screen and the perforated casing. The pressure from blockages diverts the slurry into shunt tubes of different sizes and cross- sectional diameters disposed on the gravel packer. The gravel is deposited as the carrier fluid enters the formation or circulates back to surface through the screen.

At 804, a sensor receives a signal generated by a remote source. The signal may be generated remotely, wirelessly sent to a circuit including the sensor on the gravel packer, and wirelessly received by the circuit. The signal may be based on the pressure rise from screen out of the gravel pack, tubing movement, pressure cycles, temperature changes, or any other activating event.

At 806, in response to the received signal, fluid chambers release fluid, including magnetically responsive particles, into the shunt tubes. Multiple fluid chambers may be coupled to multiple shunt tubes in various configurations. For example, multiple fluid chambers may release fluid into a single shunt tube, one fluid chamber may release fluid into multiple shunt tubes, and the like. Burstable disks or check valves may be coupled to electronic circuits housed within the gravel packer to create electronic activation of the burstable disks or check valves when desired. The disks may burst and the check valves may open in response to the electronic activation.

At 808, magnetic field generators generate magnetic fields to activate the magnetically responsive particles. Once activated, the fluids released into the shunt tubes are arrested, thereby plugging the shunt tubes. Specifically, passage of the fluids through the magnetic fields cause the magnetically responsive particles to align with the magnetic fields. Alignment of the particles with the magnetic fields causes the particles to hold the fluids in place because the arrangement of the particles changes the shear strength of the fluids, decreasing the viscosity. Once formed, the fluids may be allowed to cure, harden, or otherwise create a seal. Any polymer precursor material may begin to cross-link. For example, the passage of time, applied heat, and/or exposure to certain fluids or environments may cause the fluids to form plugs within the shunt tubes, thereby preventing any material from passing through the shunt tubes. In this way, the gravel packer may isolate a zone of the annulus without open shunt tubes.

In at least one embodiment, the gravel slurry may include a second set of magnetically responsive particles, and the method 800 may include arresting the gravel slurry by activating the second set of magnetically responsive particles using the one or more magnetic fields.

In at least one embodiment, a borehole packer includes a shunt tube and a fluid chamber coupled to the shunt tube. The fluid chamber includes a release assembly that releases fluid stored in the fluid chamber into the shunt tube. The fluid includes magnetically responsive particles. The packer also includes one or more magnetic field generators that generate one or more magnetic fields that arrest released fluid within the shunt tube by activating the magnetically responsive particles, thereby plugging the shunt tube.

In another embodiment, a method of performing a gravel packing operation within a borehole includes releasing fluid including magnetically responsive particles into a shunt tube. The method further includes plugging the shunt tube by activating the magnetically responsive particles to arrest the fluid released into the shunt tube.

The following features may be incorporated into the various embodiments described above, such features incorporated either individually in or conjunction with one or more of the other features. The one or more magnetic fields may be generated by one or more magnets. The release assembly may include a sensor to sense a remotely-generated signal, the signal initiating release of the fluid when received by the sensor. The one or more magnetic field generators may include a sensor to sense a remotely-generated signal, the signal initiating generation of the one or more magnetic fields when received by the sensor. The gravel slurry may include a second set of magnetically responsive particles, and the one or more magnetic fields may arrest the gravel slurry by activating the second set of magnetically responsive particles. The packer may also include a gravel screen, and the fluid chamber may be external to the screen. The release assembly may include a check valve that enables the fluid to exit the fluid chamber and prevents the fluid from entering the fluid chamber. The release assembly may include a piston that forces the fluid out of the fluid chamber during release. The release assembly may include a collapsible tube that forces the fluid out of the fluid chamber during release in response to pressure external to the collapsible tube that collapses the tube. A hydraulic pump may generate the pressure. The release assembly may include a burstable disk responsive to pressure within the fluid chamber that bursts the disk and enables fluid to exit the fluid chamber. The packer may include a second shunt tube. The fluid chamber may be coupled to the second shunt tube, and the release assembly may release the fluid into the second shunt tube. The one or more magnetic fields may arrest released fluid within the second shunt tube by activating the magnetically responsive particles, thereby plugging the second shunt tube. The packer may include a second fluid chamber sharing the release assembly with the fluid chamber. Releasing the fluid may include releasing the fluid after gravel transported by a gravel slurry is placed. Releasing the fluid may include releasing the fluid as a result of receiving a signal generated from a remote source. Plugging the shunt tube may include isolating a zone of an annulus of the borehole. Plugging the shunt tube may include generating one or more magnetic fields to activate the magnetically responsive particles. Generating the one or more magnetic fields may include generating the one or more magnetic fields as a result of receiving a signal generated from a remote source. The gravel slurry may include a second set of magnetically responsive particles, and the method may include arresting the gravel slurry by activating the second set of magnetically responsive particles using the one or more magnetic fields.

While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations.