Peripheral sealing system for pre-tensioned screens

A system including a first screen having a first frame and a first sealing element attached to an outer perimeter of the first frame, and a second screen disposed adjacent the first screen, the second screen having a second frame and a second sealing element attached to an outer perimeter of the second frame, wherein the first sealing element and the second sealing element provide a seal between the first screen and the second screen is disclosed. Further, a method of forming a screen frame including forming a frame and attaching a sealing element to an outer perimeter of the frame is disclosed. Additionally, a shaker screen including a frame and a sealing element attached to an outer perimeter of the frame, wherein the sealing element is attached by one selected from thermal bonding and co-molding is disclosed.

BACKGROUND

1. Field of the Disclosure

Embodiments disclosed herein relate generally to oilfield shale shakers. More particularly, embodiments disclosed herein relate to screen frames for oilfield shale shakers.

2. Background Art

Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drillstring. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.

Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures thereby preventing fluids from blowing out if pressurized deposits in the formation are breeched. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Generally, increasing the amount of weighting agent solute dissolved in the mud base will create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use.

Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit acts to stir-up and carry the solid particles of rock and formation to the surface within the annulus between the drillstring and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud. Before the mud can be recycled and re-pumped down through nozzles of the drill bit, the cutting particulates must be removed.

One type of apparatus in use to remove cuttings and other solid particulates from drilling mud is commonly referred to in the industry as a “shale shaker.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning used drilling mud is deposited and through which substantially cleaner drilling mud emerges. Typically, the shale shaker is an angled table with a generally perforated filter screen bottom. Returning drilling mud is deposited at the top of the shale shaker. As the drilling mud travels down the incline toward the lower end, the fluid falls through the perforations to a reservoir below, thereby leaving the solid particulate material behind. The combination of the angle of inclination with the vibrating action of the shale shaker table enables the solid particles left behind to flow until they fall off the lower end of the shaker table. Preferably, the amount of vibration and the angle of inclination of the shale shaker table are adjustable to accommodate various drilling mud flow rates and particulate percentages in the drilling mud. After the fluid passes through the perforated bottom of the shale shaker, it may either return to service in the borehole immediately, be stored for measurement and evaluation, or pass through an additional piece of equipment (e.g., a drying shaker, a centrifuge, or a smaller sized shale shaker) to remove smaller cuttings and/or particulate matter.

Because shale shakers are typically in continuous use, repair operations, and associated downtimes, need to be minimized as much as possible. Often, the filter screens of shale shakers, through which the solids are separated from the drilling mud, wear out over time and subsequently require replacement. Therefore, shale shaker filter screens are typically constructed to be easily removable and quickly replaceable. Generally, through the loosening of several bolts, the filter screen may be lifted out of the shaker assembly and replaced within a matter of minutes. While there are numerous styles and sizes of filter screens, they generally follow similar design. Typically, filter screens include a perforated plate base upon which a wire mesh, or other perforated filter overlay, is positioned. The perforated plate base generally provides structural support and allows the passage of fluids therethrough, while the wire mesh overlay defines the largest solid particle capable of passing therethrough. While many perforated plate bases are flat or slightly arched, it should be understood that perforated plate bases having a plurality of corrugated or pyramid-shaped channels extending thereacross may be used instead. The pyramid-shaped channels may provide additional surface area for the fluid-solid separation process to take place while acting to guide solids along their length toward the end of the shale shaker from where they are disposed.

A typical shale shaker filter screen includes a plurality of hold-down apertures at opposite ends of the filter screen. These apertures, preferably located at the ends of the filter screen that will abut walls of the shale shaker, allow hold down retainers of the shale shaker to grip and secure the filter screens in place. However, because of their proximity to the working surface of the filter screen, the hold-down apertures must be covered to prevent solids in the returning drilling fluid from bypassing the filter mesh through the hold-down apertures. To prevent such bypass, an end cap assembly is placed over each end of the filter screen to cover the hold-down apertures. Presently, these caps are constructed by extending a metal cover over the hold down apertures and attaching a wiper seal thereto to contact an adjacent wall of the shale shaker. Furthermore, epoxy plugs are set in each end of the end cap to prevent fluids from communicating with the hold-down apertures through the sides of the end cap.

Typically, screens used with shale shakers are placed in a generally horizontal fashion on a substantially horizontal bed or support structure located within a basket in the shaker. The screens themselves may be flat, nearly flat, corrugated, depressed, and/or contain raised surfaces. The basket in which the screens are mounted may be inclined towards a discharge end of the shale shaker. The shale shaker imparts a rapidly reciprocating motion to the basket and the screens. Drilling mud, from which particles are to be separated, is poured onto a back end of the vibrating screen. The drilling mud generally flows toward the discharge end of the basket. Large particles that are unable to pass through the screen remain on top of the screen, and move toward the discharge end of the basket where they are collected. Smaller particles and fluid pass through the screen and collect in a bed, receptacle, or pan therebeneath.

In some shale shakers, a fine screen cloth is used with the vibrating screen. The screen may have two or more overlying layers of screen cloth or mesh. Layers of cloth or mesh may be bonded together and placed over a support, multiple supports, a perforated plate, or an apertured plate. The frame of the vibrating screen is resiliently suspended or mounted upon a support, and is caused to vibrate by a vibrating mechanism (e.g., an unbalanced weight on a rotating shaft connected to the frame). Each screen may be vibrated to create a flow of trapped solids on top surfaces of the screen for removal and disposal thereof. The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.

As shown inFIG. 1, a typical shaker screen10may include a plurality of screens12secured in a shaker basket14by various methods, as known in the art. Such an arrangement with multiple screens may be advantageous because it allows for rapid disassembly for routine maintenance and replacement of parts when necessary. However, if the shaker screen is moved off its sealing surface or if neighboring screens are moved slightly apart from one another, the resulting gap may allow cutting particulates to bypass the screen.

Accordingly, there exists a need for a screen frame assembly that may be securely positioned within a shale shaker while effectively reducing the amount of cutting particulates that may bypass the screen. Further, there exists a need for forming a seal against a wall of the shaker and neighboring screens, thereby minimizing the passage of unfiltered drilling mud therethrough.

SUMMARY OF THE DISCLOSURE

In one aspect, embodiments disclosed herein relate to a system of sealing shaker screens, the system including a first screen having a first frame and a first sealing element attached to an outer perimeter of the first frame, and a second screen disposed adjacent the first screen, the second screen having a second frame and a second sealing element attached to an outer perimeter of the second frame, wherein the first sealing element and the second sealing element provide a seal between the first screen and the second screen.

In another aspect, embodiments disclosed herein relate to a method of forming a screen frame including forming a frame and attaching a sealing element to an outer perimeter of the frame.

In another aspect, embodiments disclosed herein related to a shaker screen including a frame and a sealing element attached to an outer perimeter of the frame, wherein the sealing element is attached by one selected from thermal bonding and co-molding.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a screen frame assembly for an oilfield shale shaker. Specifically, embodiments disclosed herein relate to a screen frame assembly that may provide efficient sealing of a screen frame within a shale shaker. Further, embodiments disclosed herein relate to methods of forming screen frame assemblies.

Referring toFIG. 2, in one embodiment, screen frame assembly220may be installed into a shale shaker250on a vibratory screen mounting apparatus or “basket”254. The screen frame assembly220may be any screen frame assembly disclosed herein or have any combination of any feature or features of any screen or screen parts disclosed herein. In one embodiment, screen frame assembly220includes a plurality of screens240. As shown inFIG. 2, the screen frame assembly220may include multiple screens240. These multiple screens may be arranged in various configurations, some of which are illustrated inFIGS. 3A-3C.

With reference toFIGS. 3A-3Cscreen frame assemblies320a-cmay include two screens340a, four screens340bor340c, or any number of screens. One of ordinary skill in the art will appreciate that any number of screens may be disposed in shaker basket354. Additionally, the screens340b,340cmay be oriented in a columnar arrangement or in a grid-like arrangement as shown inFIGS. 3B and 3C, respectively. Each individual screen may have a number of features designed to provide a secure fit within the shaker basket as shown inFIG. 4.

With reference toFIG. 4, a screen440, in one embodiment, comprises a frame426, a filtering element428, and a sealing element430attached to the frame. Frame426may be formed from any material known in the art, for example, stainless steel, metal alloys, or plastics. Additionally, in one embodiment, frame426may be formed from a composite material. The composite material may include high-strength plastic, mixtures of high-strength plastic and glass, high-strength plastic reinforced with high-tensile-strength steel rods, and any combination thereof. Composite screen frames may provide more consistent manufacturing of the frame and may more evenly distribute mechanical stresses throughout the screen frame during operation. In another embodiment, frame426may include composite material formed around a steel or wire frame. Frame426may be formed, for example, by injection molding. A method of forming a screen frame by injection molding is disclosed in, U.S. Pat. No. 6,759,000 issued to Cook, et al., which is incorporated herein by reference in its entirety. A filtering element428may be integrated within frame426during the molding process, in one embodiment.

As shown inFIG. 4, filtering element428may be disposed on frame426. The filtering element428may be a fine screen cloth or any other filtering mesh known in the art. Such filtering meshes may be made of, for example, plastics, metals, alloys, fiberglass, composites, and polytetrafluorethylene (PTFE). The filtering element428may have two or more layers of the same or different filtering mesh and may be layered in any combination. Layers of filtering meshes may be bonded together and placed over a support, supports, or a perforated or apertured plate.

A sealing element430may be disposed on an outer perimeter of frame426. In one embodiment, the sealing element430may be disposed along the entire outer perimeter, along an edge of frame426. In another embodiment, the sealing element430may be disposed along a portion or portions of the outer perimeter, along the edge of frame426. Sealing element430may provide a structural element to secure each screen440within an assembly, and may contact or compress against other sealing elements other sealing elements of neighboring screens or neighboring screen frames as shown inFIGS. 5A-5Dand discussed in greater detail below.

With reference toFIGS. 5A-5D, embodiments relating to the configuration of a frame and sealing element, are shown.FIG. 5Ashows a partial cross-sectional view of one embodiment in which a first screen540ais disposed adjacent a second screen540b. A first sealing element530aand a second sealing element530b, disposed along an outer perimeter of screens540aand540b, respectively, contact each other compressively. Note that the sealing elements530aand530bare attached to frames526aand526b, respectively, and may traverse the entire outer perimeter of each frame or select portions thereof. Thus, there may be contact, for example, between the first sealing element530aand a plurality of other screens (depending on the configuration of the screen frame assembly) or the wall of the shaker basket.

In an alternate embodiment, shown inFIG. 5B, stops560aand560bmay be disposed along one or more edges of frames526aand526b, respectively, and may extend substantially over sealing elements530a,530b. Stops560aand560bmay provide a seal between first frame526aand second frame526b. Accordingly, stops560aand560bmay reduce or minimize the amount of particulates that bypass the screen frame assembly. Furthermore, stops560aand560bmay provide protection of sealing elements530aand530bfrom wear and extend the life of sealing elements530aand530bby reducing the amount of mud and particulates directly contacting the sealing elements. Sealing elements530aand530bmay act as a secondary seal to stops560aand560b. The stops560aand560bmay be formed uniformly around the entire outer perimeter of frames526aand526b, respectively.

Alternatively, stops may be formed along selected portions or lengths of the frame. In one embodiment, stops560aand560bmay include portions along a screen that may be adjacent or may contact the wall of the shaker. Sealing element530aand530bmay be disposed below the stops560aand560b, respectively. The stops560aand560bmay be co-molded from the same material as frames526aand526b, respectively, as a single element or it may be formed from a different material. Additionally, stops560aand560bmay be attached to the frame526aand526b, respectively, by any method known in the art. For example, stops560aand560bmay be thermally bonded, welded, or adhesively attached.

In another embodiment, as shown inFIG. 5C, a seal may be formed by a seal contacting a neighboring stop. The sealing element530aof a first screen540amay contact the stop560bof a second screen540bas shown in the partial cross sectional view ofFIG. 5C. In this arrangement, the first sealing element530a, disposed along at least a portion of an edge of first frame526a, may compress against the second stop560b. Likewise, second sealing element530b, disposed along at least a portion of an edge of second frame526b, compressively contacts first stop560a.

As a result of this arrangement, a dual layer sealing effect may occur with second sealing element530bdisposed above first sealing element530a. Second sealing element530bmay be formed from a material different from first seal530a, for example, a more durable or more wear resistant material, to take into account its direct exposure to the drilling mud. The seal formed between first stop560aand second seal530bmay reduce or minimize drilling particulates from bypassing the screen.

In another embodiment, as shown inFIG. 5D, a first sealing element530aof a first screen540amay contact a second frame526bof a second screen540b, as shown inFIG. 5D. Similarly, a second sealing element530bof second screen540bmay contact a first frame526aof first screen540a. In this embodiment, first sealing element530a, disposed on outer perimeter of first frame526a, compressively contacts second frame526band may compressively contact second sealing element530bdisposed below it. Likewise, second sealing element530b, disposed on an outer perimeter of second frame526b, compressively contacts first frame526aand may compressively contact first sealing element530aabove it. In another embodiment, the seating elements530aand530bmay be placed further apart from each other, such that no contact is made between them.

FIG. 6shows a partial cross sectional area of a sealing element630in accordance with an embodiment disclosed herein. As shown inFIG. 6, sealing element630may include a shell632and a core634. The cross-sectional area of the sealing element in some embodiments, may have a substantially rounded face. In one embodiment, the cross-sectional area of sealing element630is a D-shape. The configuration of sealing element630, along with the composition of shell632and core634, may be chosen to provide an effective seal.

Shell632of sealing element630may be formed from any material for sealing known to one of ordinary skill in the art including, but not limited to, rubbers, thermoplastic elastomers (“TPE”), foams, polychloroprene, polypropylene, and/or any combinations thereof. Shell632, formed from TPE, may include, for example, polyurethanes, copolyesters, styrene copolymers, olefins, elastomeric alloys, polyamides, or combinations of the above. The sealing element630may include properties that allow high durability and elongation, as well as solvent and abrasion resistance. In certain embodiments, sealing element630may preferably include the properties of increased flexibility, slip resistance, shock absorption, and vibration resistance.

In one embodiment, core634may include a gas, foam, and/or other material including the same material as shell632. The material for the sealing element630may be resistant to a variety of chemical conditioners used in mud formulations as known in the art. Sealing element630of different material compositions may be used on different screens in different sections of a single screen as determined by the location of the screen with respect to the assembly and relative to the position in the shaker. For example, for sections of sealing element630that may contact the wall of the shaker it may be beneficial to have that section of the sealing element630formed from a material different than the material used for sealing elements630disposed between neighboring screens.

Sealing element630may be attached to frames626by any method known in the art. In one embodiment, sealing element630may be attached to frame626by thermal bonding. For example, the sealing element630may be formed of a thermoplastic material that may be thermally bonded to the frame626. One skilled in the art will recognize that any thermal bonding process may be used to attach the sealing element630to the frame626, including for example, heat staking or ultrasonic welding. Sealing element630may be thermally bonded to frame626along the entire interface622between sealing element630and frame626or at specific predetermined locations645.

In another embodiment, sealing element630may be integrally molded with frame626. Sealing element630and frame626may be formed contemporaneously. One such method of forming and attaching sealing element630and frame626may include co-molding, using, for example, injection molding and/or gas injection molding, as known to those of ordinary skill in the art of molding plastics.

One method of co-molding sealing element630and frame626may include integrally molding sealing element630with frame626. In this embodiment, sealing element630may be positioned within an injection mold for composite frame626. Once the mold is sealed, a sealing element material (e.g., TPE) may be injected into the mold. The sealing element material is allowed to cure, and then the frame626including an integrally molded sealing element630may be removed. One of ordinary skill in the art will realize that alternative methods of attaching a sealing element630to a frame626exist, for example, using an adhesive resin, and as such, are within the scope of the present disclosure.

In certain embodiments of the present disclosure, the frame and the sealing element may be formed at substantially the same time. In such an embodiment, the frame and the sealing element may be formed via co-extrusion. Generally, co-extrusion includes the process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before cooling. However, in other embodiments, co-extrusion may include the injection of more than two materials extruded into two or more dies. Those of ordinary skill in the art will appreciate that co-extrusion may be used to form both a frame and a sealing element in accordance with the embodiments disclosed herein.

In one aspect of the present disclosure, a first material is extruded into a first orifice (molded into a desired geometry for a frame) of a die while a second material is extruded into a second or orifice (molded into a desired geometry of a sealing element) of the die. Both materials are allowed to cure, and then removed from the die. Because the materials were co-extruded, their interfacing profiles will substantially correspond. Thus, when the frame and the sealing element are aligned, their profiles will correspond such that they may be attached. By having a sealing element with a profile that substantially matches a corresponding frame, the attachment of the two components may be more secure.

In certain embodiments, the aligning of the co-extruded frame and seal may benefit from additional attachment means. Exemplary methods of additional attachment may include mechanical fasteners (e.g., screws, bolts, and rivets), welding, heat staking, thermal bonding, and/or chemical adhesion. One such example is shown inFIG. 7, wherein a sealing element comprising a first portion770and a second portion772are mechanically attached to a screen frame774with a screw776. First and second portions770,772of the sealing element may be formed from a single material or, alternatively, from different materials. For example, the first portion770may be formed from polypropylene, while the second portion772may be formed from TPE.

Referring now toFIG. 8, to help ensure proper alignment between a frame880and a co-extruded sealing element882, the frame may be formed to include a first mating surface884, while the co-extruded sealing element882is formed to include a second mating surface886configured to correspond to the first mating surface884of the screen frame880. In one embodiment, the second mating surface886of the co-extruded sealing element882may include a groove888configured to align with an extension890of the first mating surface884of the screen. In alternate embodiments, the first mating surface884may include a groove (not shown), while an extension (not shown) of the second mating surface886is configured to align with the groove (not shown).

In some embodiments, co-extruded sealing element882may include a first portion892and a second portion894. In this embodiment, the groove888is formed in the first portion892, such that the first portion892is configured to couple with the extension890of the screen frame880. The second portion894is configured to contact a second frame, an extension of a second screen frame894, or a sidewall (not shown), and thus provide a seal. In one embodiment, first and second portions892,894of co-extruded sealing element882may be formed from a single material. Alternatively, first and second portions892,894of co-extruded sealing element882may be formed from different materials. For example, in one embodiment, the first portion892may be formed from polypropylene, and the second portion894may be formed from TPE.

Those of ordinary skill in the art will appreciate that in certain embodiments having a first and second mating surface, the extension portion may be designed with a slightly larger profile than the corresponding groove. As such, when the extension is aligned within the groove, a compression fit may be achieved. Such a compression fit may enhance the sealing characteristics of the seal, while preventing the sealing element from becoming disconnected from the screen during operation of the shaker.

Those of ordinary skill in the art will appreciate that multiple configurations of first and second mating surface may be used when forming frames and sealing elements in accordance with embodiments disclosed herein. For example, combinations of male/female connections, press-fit connections, and dovetails may also be used. Furthermore, those of ordinary skill in the art will appreciate that any of the above methods of forming corresponding frames and sealing elements may be used without co-extrusion.

In other embodiments, as described above, a sealing element of a screen may be configured to interact with a surface of a shaker. In such an embodiment, a screen may be designed to include a first mating surface that is configured to align with a second mating surface on the shaker. For example, the first mating surface of the screen may be configured to interface with the second mating surface of a feed end of a shaker basket. Such a configuration may prevent drilling fluid and solid particles from bypassing the shaker, thereby increasing the efficiency of the operation. In other embodiments, at least a portion of a sealing element of a screen may be configured to align with or interface with at least a portion of a shaker to prevent the loss of drilling fluid and solid particles therefrom.

Advantageously, embodiments disclosed herein may provide an efficient seal for a screen frame assembly within a shale shaker. Some embodiments may facilitate the disassembly, cleaning, maintenance, and repair of the screens used in a shale shaker. Further, embodiments disclosed herein may prevent fluids and drilling particulates from bypassing screen frames disposed in a shale shaker.