WO2012166234A1

WO2012166234A1 - High temperature crosslinked polysulfones used for downhole devices

Info

Publication number: WO2012166234A1
Application number: PCT/US2012/031151
Authority: WO
Inventors: Ping Duan; Gaurav Agrawal; Casey WALLS
Original assignee: Baker Hughes Incorporated
Priority date: 2011-05-31
Filing date: 2012-03-29
Publication date: 2012-12-06
Also published as: US20120305238A1

Abstract

Thermally crosslinked polysulfone may be made from linear polysulfone, such as polyethersulfone, in powder form blended with a powdered inorganic peroxide such as magnesium peroxide or another oxygen source, to form a mixture followed by compression inside a mold. The mixture is cured at a an elevated temperature, for instance above 325C, for an effective period of time to form a dense object. The object is then boiled in water, optionally under pressure, to remove the salt to give a structure that is open and porous which may be used as a filtration device on a downhole tool for hydrocarbon recovery. If a powdered salt is not used, a thermally crosslinked, solid, void-free polysulfone is made which may be strong and rigid at ambient, surface temperatures, but is an elastomer at elevated downhole temperatures, and is thus suitable for use as a packer or an O-ring.

Description

HIGH TEMPERATURE CROSSLINKED

POLYSULFONES USED FOR DOWNHOLE DEVICES

TECHNICAL FIELD

[0001] The present invention relates to a new class of sulfone polymers and their applications such as in filtration devices used in oil and gas wellbores to prevent the production of undesirable solids from the formation, and sealing devices which may be used to seal flow paths to prevent fluid from passing at all. More particularly the invention relates to thermally crosslinked sulfone polymers which are strong and rigid at low temperature below glass transition temperature, which materials are also elastically rubbery at high temperature above glass transition temperature.

TECHNICAL BACKGROUND

[0002] Sulfone polymers are linear amorphous thermoplastics commercially available from companies such as Solvay Plastics. They are widely used as adhesives, composites, or moldings for use in automobiles, household appliances, and other applications. As linear amorphous thermoplastics, they tend to creep under load especially at elevated temperature. Furthermore, they are sensitive to various solvents resulting in their limits of applications. Attempts to improve sulfone polymers have included crosslinking it. For example, U.S. Pat. No. 4431761 disclosed a method to chemically replace the end groups of hydroxyl-terminated polyethersulfone to give ethynyl-terminated polyethersul- fone. U.S. Pat. No. 4414269 disclosed a method to have the functional groups of polysulfones be derived from condensation products of amino-phenols and acid anhydrides, which are thermally cross-linkable. However, these methods require additional chemical reaction steps involving expensive chemicals and solvents. Furthermore, these methods are limited to those commercially available polysulfones having functional end group such as hydroxyl-ended polyethersulfone. It is known that polyethersulfone is not as good as other sulfone polymers, such as polyphenylsulfone, in terms of chemical compatibilities. Polyethersulfone tends to degrade in various fluids at elevated temperature. [0003] In contrast to amorphous thermoplastics, other types of polymers are semi-crystalline thermoplastics such as polyetheretherketone (PEEK). These polymers can withstand high heat and exposure to caustic chemicals. However, these polymers lack elasticity and they are not desirable to be used as sealing materials. Usually, these materials are used as sealing backup rings.

[0004] Fluoroelastomers especially perfluoroelastomers have good thermal stability and excellent chemical resistance. They show rubbery elasticity at a wide range of temperature. Perfluoroelastomers such as KALREZ^® made by DuPont are very expensive. Certain grades are claimed to have a maximum continuous service temperature of 327°C. However, this has not been verified in practice in downhole applications at high temperature and high pressure for well life duration. Some of the perfluoroelastomers tend to have cracks during a sudden drop of pressure.

[0005] It would thus be desirable to discover new materials and devices made from these materials such as screens to prevent the undesirable production of solids and such as seals on downhole packers and the like.

SUMMARY

[0006] There is provided, in one form, thermally crosslinked polysulfone made by heating polysulfone powder in the presence of oxygen to a high temperature, such as at or above 325°C inside an oven for at least 8 hours. The polysulfone is found to be crosslinked via an oxidization process. The oxygen may come from the air, a pure or impure oxygen source and/or a powdered inorganic peroxide.

[0007] Problems have been found when attempting to make a molded part: the surface is found to be crosslinked, but the internal portion of the materials is not crosslinked, resulting in non-uniformity within the material. It has been discovered herein that a small amount of an oxidant such as magnesium peroxide will result in crosslinking for molded polysulfone parts. Unlike other organic or inorganic peroxides such as dicumyl peroxide, benzoyl peroxide, zinc peroxide, calcium peroxide, etc., magnesium peroxide decomposes at much higher temperature at 350°C, and releases oxygen upon decomposition. [0008] There is provided, in another form, thermally crosslinked polysulfone made by a process that involves mixing a polyphenylsulfone (PPSU) powder obtained from company Solvay Plastics under the commercial name RADEL^® R and inorganic peroxide powder such as magnesium peroxide at the percent from about 0.5% to about 5% of the total polysulfone powder by weight. The mixture containing two powders, polysulfone and peroxide powders, may be heated to 375°C for at least 8 hours. Whether or not the resultant polysulfone is crosslinked may be determined by examining a piece of material placed in the solvents such as N-methyl-2-pyrrolidone (NMP) or N.N-dimethyl- formamide (DMF). If material is cross-linked, it does not dissolve in the solvent. Dynamic Mechanical Analysis (DMA) may also be used to examine whether or not the resultant polysulfone is crosslinked. The crosslinked polysulfone will maintain a relatively high modulus at a wide temperature range above its glass transition temperature while the linear non-crosslinked polysulfone will quickly drop its modulus as the temperature is raised higher than its glass transition temperature.

[0009] In another non-limiting embodiment there is provided a method of making thermally crosslinked polysulfone that involves mixing a polysulfone powder, where the polysulfone is selected from the group consisting of poly- ethersulfone, polyphenylsulfone, polysulfone and mixtures thereof, with a powdered magnesium peroxide and a powdered salt selected from the group consisting of NaCI and/or KCI. The method further concerns optionally preheating the mixture to a temperature in the range of about 140 to about 160°C; and curing the mixture at a temperature in the range of from about 365 to about 385°C to crosslink the polysulfone as well as to fuse polysulfone powder together with salt particles forming a solid part.

[0010] Further there is provided in a different, non-restrictive version wellbore seal that includes a substrate and a thermally crosslinked polysulfone on the substrate, where the thermally crosslinked polysulfone is made by the method described in the previous paragraphs. The thermally crosslinked polysulfone may not necessarily be an elastomer at surface ambient temperature, but is an elastomer at an elevated temperature in the wellbore. [0011] Additionally, there may be provided in another non-limiting embodiment a wellbore filtration device that includes a shape-memory porous poly- sulfone material, where the shape-memory porous polysulfone material has a compressed position and an expanded position. The shape-memory porous polysulfone material is maintained in the compressed position at a temperature below its glass transition temperature. The shape-memory porous polysulfone material expands from its compressed position to its expanded position when it is heated to a temperature above its glass transition temperature. The shape- memory porous polysulfone material is a thermally crosslinked polysulfone made by the process involving mixing a polysulfone powder, where the polysulfone is selected from the group consisting of polyethersulfone, polyphenylsul- fone, polysulfone and mixtures thereof, with a powdered magnesium peroxide and a powdered salt selected from the group consisting of NaCI and/or KCI. The process further includes compressing the mixture into a mold. The mixture is preheated to a temperature in the range of about 114 to about 160°C. Subsequently, the mixture is cured at a temperature in the range of from about 290 to about 310°C when sulfur is optionally used as a cross-linker or the mixture is cured at a temperature in the range of from about 365 to about 385°C when magnesium peroxide us used as an oxygen source as a cross-linker to crosslink the polysulfone chains to give a thermally crosslinked polysulfone. Finally, the cured crosslinked polysulfone may be boiled in water and the salt is removed therefrom, optionally in a pressurized environment, to recover the shape-memory porous polysulfone material.

[0012] Additionally, there may be provided in another non-limiting embodiment a wellbore sealing device that includes a void-free solid polysulfone material, the polysulfone material having a thermally crosslinked polysulfone may not necessarily be an elastomer or may be a rigid plastic at surface ambient temperature, but is an elastomer at an elevated temperature in the wellbore. The thermally crosslinked polysulfone may be manufactured as a tubular shape similar to the packers widely used on downhole tools to isolate different zones of downhole. When hydraulic force is applied at the end of the shape, the tubular rubbery cross-linked polysulfone is expanded in diameter and contact with borehole wall to seal the gap between inner borehole wall surface and outside surface of packer.

[0013] Additionally, there may be provided in another non-limiting embodiment a wellbore sealing device that includes a void-free solid polysulfone material. The polysulfone material having a thermally crosslinked polysulfone may not necessarily be an elastomer or may be a rigid plastic at surface ambient temperature, but is an elastomer at an elevated temperature above glass transition temperature. When the thermally crosslinked polysulfone is made as a tubular shape and a center core is placed inside tubular polysulfone material, and also when tubular polysulfone material is pulled from two ends at an elevated temperature above the glass transition temperature (T_g) at which material becomes soft and elastic, the length of tubular material becomes much longer and the outside diameter of tubular material becomes much smaller and the inside diameter of tubular material remains the same. This stressed shape is able to freeze when temperature is quickly cooled down to ambient temperature well below glass transition temperature, and the stressed shape is also able to remain unchanged even outside pulling force is removed because the material becomes rigid plastic at ambient temperature. When the stressed tubular shape of thermally crosslinked polysulfone is installed on the downhole tools, and run in downhole, and contacted with fluids at a given temperature near or above its glass transition temperature, the stressed tubular shape will recovery to its original manufactured shape, i.e., the length will be reduced and the outside diameter will be increased. The expansion of the outside diameter creates a seal between inner wall of downhole and the outside surface of sealing element without additional operations from well surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a graphic image of a thermally crosslinked polysulfone foam made in accordance with a method described herein which appearance suggests a porous rock. DETAILED DESCRIPTION

[0015] Polysulfone is one of the high temperature engineering plastics widely used as adhesives, composites, or moldings, for use in automobiles, household appliances, and other applications, because it displays a variety of desirable characteristics including durability, thermal, hydrolytic and dimensional stability, low coefficient of thermal expansion, retention of modulus to temperatures approaching T_g and radiation resistance. Polysulfone is a linear amorphous thermoplastic. Thus, it is sensitive to various organic solvents. Many attempts have been made to induce molecular crosslinks, but previous attempts required chemical synthesis handling various solvents and monomers. Polysulfone is also made as a porous film or membrane and widely used in the liquid filtration and separation industries.

[0016] Described herein is a new method, making high temperature elastomers or rubbery materials from linear amorphous high temperature thermal plastics such as polyphenylsulfone. These linear amorphous thermal plastics have no functional end groups such as hydroxyl groups, and there is thus no need to chemically convert the hydroxyl end groups into thermally cross-linkable groups such as ethynyl groups. Furthermore, the method described herein may make cross-linked polysulfones as porous materials to be used as sand control media to prevent undesirable production of solids from the formation downhole. These porous tubular materials made from cross- linked polysulfones are able to expand to contact borehole wall when they are contacted with downhole fluids at a given temperature and for a period of time. Furthermore, this method may make a solid or void-free cross-linked polysulfone as a sealing element, such as a packer to isolate different zones of the well bore to prevent flow from passing through. This sealing element in a generally tubular shape is rigid at surface temperature below the material's glass transition temperature, but is rubbery (elastomeric) at the downhole temperature above its glass transition temperature. When hydraulic force is applied at the end, the tubular rubbery cross-linked polysulfones is expanded in diameter and contacts the borehole wall to seal the gap between inner bore- hole wall surface and the outside surface of packer. Furthermore, the method may be used to make a solid or void-free cross-linked polysulfone as a sealing element having a shape memory characteristic. This sealing element in tubular shape is able to run in at diameter smaller than borehole diameter. It is able to expand its diameter at downhole at given temperature and at a period of time when it contacts downhole fluids to recover its original expanded position to seal the gap between the inner wall surface and the outside surface of sealing element without any operational intervention such as hydraulic force.

[0017] Cross-linked sulfone polymers may be obtained from linear amorphous polysulfones blended with a small amount of cross-linkers, such as oxygen or oxidant, such as from an inorganic peroxide. Alternatively, cross- linked sulfone polymers are obtained through oxygen in the air. Cross-linked sulfone polymers may be made as open structure porous materials. When the temperature reaches near or higher than glass transition temperature, these rubbery porous sulfone polymers may be mechanically compressed and the volume can be substantially reduced. The stressed shape can be fixed into a compressed position and maintained, even after the applied mechanic force is removed. The stressed shape may also be recovered to its original manufactured shape (i.e. expanded position) when it is heated to near or above glass transition temperature. Applications may be found for these materials, such as a reactive filtration device used downhole to prevent the production of undesirable solids from the formation. The crosslinked sulfone polymers can also be made as void-free solid materials. Applications may also be found for these materials as a sealing element such as an O-ring or a packer to seal flow paths.

[0018] In more detail, thermally crosslinkable polysulfones and methods without the need for additional chemical reaction steps have been discovered. The starting sulfone polymers are not required to have functional groups such as hydroxyl groups. Any sulfone polymers may be used, including, but not necessarily limited to, polysulfone, polyethersulfone, or polyphenylsulfone, which polysulfones undergo a process of oxidation when the polymer contacts with oxygen in the air at temperature at least 325°C or above. Some inorganic peroxides such as magnesium peroxide have been found to participate in oxygen crosslinking with sulfone polymers. When a small amount of powdered magnesium peroxide is added into powdered sulfone polymers, thermal crosslinks occurs even without contacting oxygen in the air. Many inorganic or organic peroxides such as dicumyl peroxide, benzoyl peroxide, zinc peroxide, calcium peroxide, etc., are thermally decomposed at a relative low temperatures ranging from 105°C for benzoyl peroxide to 275°C for calcium peroxide in comparison with the molding temperature at least 350°C or above for sulfone polymers. Magnesium peroxide decomposes at much higher temperature, for instance at around 350°C, which is comparable to the molding temperature of sulfone polymers. Therefore, it may be very desirable to use magnesium peroxide as a crosslinker for sulfone polymers. In one non-limiting embodiment, the amount of magnesium peroxide mixed with the polysulfone is from about 0.5 wt% independently to about 5 wt%, based on the total amount. Alternatively, the amount of magnesium peroxide of total sulfone polymer powder is from 2% independently to 3%.

[0019] High temperature crosslinked porous polysulfone foams and methods for making them have been discovered. These polysulfones have improved solvent resistance and will find utility at elevated temperatures, such as those encountered downhole. For instance, in one non-limiting embodiment the glass transition temperature was measured as 190°C by Dynamic Mechanical Analysis. The open cell structure allows fluid to flow through the material quickly. These materials may be used on downhole tools as sand control screens, as will be described in detail below.

[0020] As noted, a three-dimensional open cell cross-linked polysulfone has been discovered. Fluid such as water or oil is able to flow through the porous thermally crosslinked polysulfone quickly. The material is strong and tough. In one non-limiting embodiment, the glass transition temperature is measured as about 190°C using Dynamic Mechanical Analysis (DMA). The material is not dissolved in the strong solvents such as N-methyl-2-pyrrolidone (NMP), or Ν,Ν-dimethylformamide (DMF), which lack of sensitivity confirms the cross-linked molecular structure. EXAMPLE 1

[0021] One version of the process involves using commercially available fine polysulfone powders such as UDEL^® P-1800 from Solvay Chemicals, Inc. In one non-limiting embodiment, these polysulfone powders were mixed with liquid one-component thermally degradable polyether polyurethane prepolymer such as DESMODUR™ E-28 from Bayer Corporation. A small amount of water was added and the mixture started to foam. The water was functioning as a blowing agent. The mixture was then transferred into a mold of cylinder shape, followed by curing overnight at 110°C (pre-heating). After being de-molded, the material was sliced into discs, followed by high temperature treatment (curing) at 250°C for two days.

[0022] At high temperature, at least 350°C or above, the polysulfone powders are fused on polyurethane foam cells forming porous materials while the polyurethane itself is decomposed. In one non-restrictive version the combination between polysulfone powder and polyurethane resin was close to 40:60 by weight to have the best openness. A graphic image of the resulting porous polysulfone is shown in FIG. 1. Another non-limiting example included adding a blowing agent such as ENOVATE™ 3000 from Honeywell to increase openness of porous polysulfone.

[0023] Originally it was thought that the polyurethane adhesive would be needed to help the material hold its shape. However, it was discovered that the polyurethane decomposes to give ash which creates an interface that weakens the material.

[0024] There is provided, in one non-restrictive form, thermally cross- linked polysulfone made by a process that involves mixing a polyphenylsulfone powder obtained from company Solvay Plastics under commercial name as RADEL^® R and magnesium peroxide at the percent from 0.5 to 5% of the total polysulfone powder by weight. The equipment for mixing these two powders, polysulfone and magnesium peroxide, be a single- or double-bladed KITCHEN- AID mixer or RESODYN type mixer from company Resodyn Corporation. The mixture containing the polysulfone and magnesium powders was poured into a mold containing a bottom plate and a center ring, and then placed inside an oven to heat to 150°C for two hours; followed by 250°C for 2 hours and finally heated to 375°C for 20 hours. The mixture, including the mold, was taken out of the oven, and a center rod, which was pre-heated to 375°C was placed inside the center ring, followed by compressing via a hydraulic press. The material made by compression was a void-free solid. It was rigid at ambient temperature, but showed rubbery (elastomeric) properties at high temperature above its glass transition temperature, i.e. above 220°C. Alternatively, the mixture containing the polysulfone and magnesium powders is poured into an extruder such as a RINGEXTRUDER from Century, Inc. Inside the extruder, materials are melted and mixed between screws rotating in opposite directions from each other at temperature at or above 375°C. Materials may be squeezed out through a die and molded into sheets for testing, or, alternatively through a die and then cut into individual pellets. The pellets may be molded into sheets or desired parts for evaluation or finished products.

EXAMPLE 2

[0025] In another non-limiting embodiment, thermal cross-linkable sulfone polymer was made from the commercially available polyphenylsulfone powder obtained from company Solvay Plastics under commercial name as RADEL^® R and magnesium peroxide at the percent from 0.5 to 5% of the total polysulfone powder by weight. This material in powder form was blended with a powdered salt, in one case sodium chloride, followed by compression inside tubular mold.

[0026] The mixture or material was pre-heated at 120°C and then cured at 375°C to form a dense disc. This material was then boiled in water in the pressurized or compressed container. The salt was removed by boiling it off. While it is not necessary that the salt removal be conducted under pressure, it speeds up the salt removal process. After all the salt was removed, the material was very open and porous. Differential pressure through open flow test was measured as 0.06 psi (0.4 kPa). This cross-linked porous polyethersulfone showed good elasticity at a temperature above its glass transition temperature (T_g) 232.2°C, as measured by DMA.

[0027] Once the disc was compressed at high temperature above T_g, the volume was greatly reduced. This changed shape at high temperature above T_g can be frozen when temperature is quickly cooled down well below its T_g. Also, this changed shape can be retained sufficiently long enough even when the outside compressive force is removed. When materials are heated to high temperature above T_g, the shape can be fully recovered to its original shape. Thus, the thermally crosslinked polysulfone may function as a shape-memory porous polysulfone material. The cross-linked porous sulfone polymer has very good hydrolytic resistance and is well-compatible with various downhole fluids at high temperature.

[0028] Molecular cross-linking occurs at temperature 325°C or higher. The resulting cross-linked sulfone polymer is not dissolved in the solvents such as NMP or DMA. Materials show good elasticity at temperature above glass transition temperature 232.2°C, measured by DMA in one non-limiting example.

[0029] More specifically, suitable powdered polysulfones include, but are not necessarily limited to polyethersulfone, polyphenylsulfone, polysulfone itself, and mixtures thereof.

[0030] In one non-limiting optional embodiment, oxygen in the air may participate as a crosslinker without any chemical modification (that is, without conversion of the hydroxyl termination to ethynyl termination) if the curing is conducted in a range of from about 325°C to about 400°C. Alternatively the temperature may be 350°C or above, or in another non-restrictive embodiment 375°C or above. This crosslinking begins at the surface of the material does not penetrate into the interior unless the material is mixed so that air or oxygen reaches the interior. The use of oxygen or oxidants as a crosslinker is particularly useful for sulfone polymers.

[0031] The powdered salt employed may include, but is not necessarily limited to NaCI, KCI, and combinations thereof.

[0032] In one non-limiting embodiment the weight ratio of powdered salt to polysulfone powder ranges from about 80:20 independently to about 50:50, alternatively from about 70:30 independently to about 60:40, where by "independently" it is meant that any upper threshold may be combined with any lower threshold to obtain a valid alternative range.

[0033] The compressing of the mixture into a mold and the boiling of the material in the mold may be conducted at a pressure above atmospheric in the range of from about 0 independently to about 0.1 MPa, alternatively from about 0.07 independently to about 0.1 MPa. The boiling may be conducted at a temperature in the range of from about 100 independently to about 121°C, alternatively from about 113 independently to about 121°C. As noted, boiling to remove the salt is optionally done under pressure because the removal process is faster.

[0034] Alternatively, in the mixing of the polysulfone powder with a salt powder, a liquid polyurethane adhesive may be optionally included in the mixing in an amount ranging from about 1 independently to about 10% of total polysulfone powder weight based on the total mixture; alternatively from about 2 independently to about 5 wt% of total polysulfone powder weight based on the total mixture.

[0035] In one non-limiting embodiment, the thermally crosslinked polysul- fones which are not porous or blown with a blowing agent may be used as seals, in a non-restrictive instance as high temperature wellbore seals. Interestingly, at ambient temperatures on the surface, the thermally crosslinked polysulfone may not necessarily be elastomers, but they are elastomers at the relatively high temperatures downhole where they need to function as an elastomeric seal; for instance from about 220 to about 350°C. Thermally crosslinked polysulfones may be used as sealing materials, including but not necessarily limited to packers or O-rings, for any downhole temperature ranging from 220°C or above at the temperature above the material's glass transition temperature. Alternatively, thermally crosslinked polysulfones may be used as sealing materials, including but not necessarily limited to, backup rings or structural parts, below 220°C at the temperature below material's glass transition temperature. Typically, the thermally crosslinked polysulfone would be formed or placed on a substrate, such as a tubular good or downhole tool and located in place where the seal is needed.

[0036] Downhole tools and, in particular, filtration devices for downhole sand control using the thermally crosslinked, porous polysulfones, are disclosed herein. The filtration devices include the thermally crosslinked, porous as one or more shape-memory materials that are run into the wellbore in a compressed shape or position. The shape-memory polysulfone material remains in the compressed shape induced on it after manufacture at ambient surface temperature or at wellbore temperature during run-in. After the filtration device having the shape-memory polysulfone material is placed at the desired location within the well, the shape-memory polysulfone material is allowed to expand to its p re-compressed shape, i.e., its original, manufactured shape, at downhole temperature at a given amount of time. The expanded shape or set position, therefore, is the shape of the shape-memory polysulfone material after it is manufactured and before it is compressed. In other words, the shape- memory material possesses hibernated shape-memory that provides a shape to which the shape-memory polysulfone material naturally takes after its manufacturing when it is deployed downhole.

[0037] As a result of the shape-memory polysulfone material being expanded to its set position, the completely

[0038] More specifically, the shape-memory polysulfone foam material is capable of being mechanically compressed substantially, e.g., from about 20 to about 30% of its original volume, at temperatures above its glass transition temperature (T_g) at which the material becomes soft. While still being compressed, the material is cooled down well below its T_g, or cooled down to room or ambient temperature, and it is able to remain at a compressed state even after the applied compressive force is removed. When the material is heated near or above its T_g, it is capable of recovery to its original un-compressed state or shape. In other words, the shape-memory material possesses hibernated shape-memory that provides a shape to which the shape-memory material naturally takes after its manufacturing. The compositions of polysulfone foam are able to be formulated to achieve desired glass transition tem- peratures which are suitable for the downhole applications, where deployment can be controlled for temperatures below T_g of filtration devices at the depth at which the assembly will be used.

[0039] It has been discovered herein that the thermal stability and solvent resistance are significantly improved when the polysulfone are thermally crosslinked as previously discussed. The compositions of polysulfone foam are able to be formulated to achieve different glass transition temperatures within the range from 190°C to 240°C, which is especially suitable to meet most downhole application temperature requirements. This range is higher than that of some other shape-memory foams, such as certain types of polyurethane foams. It is useful to have different foams with different T_gs to give the design engineer more options.

[0040] In one specific non-limiting embodiment, the shape-memory material is a polysulfone foam material that is extremely tough and strong and that is capable of being compressed and returned to substantially its original expanded shape. The T_g of the shape-memory polysulfone foam in one non- limiting embodiment may be about 232.2°C and it may be compressed by mechanical force at 250°C, in another non-limiting embodiment. While still in compressed state, the material is cooled down to room temperature. The shape-memory polysulfone foam is able to remain in the compressed state even after applied mechanical force is removed. When material is heated to about 250°C, it is able to return to its original shape within 20 minutes. However, when the same material is heated to a lower temperature such as 200°C for about 40 hours, it remains in the compressed state and does not change its shape.

[0041] Factors affecting the T_g of the crosslinked polysulfone, whether or not it is a foam, include the molecular weight of the crosslinked polysulfone. By formulating shape-memory porous polysulfone material using these different factors, different glass transition temperatures of shape-memory polysulfone foam may be achieved. Compositions of a shape-memory polysulfone foam material having a specific T_g may be formulated based on actual downhole deployment/application temperature. Usually, the T_g of a shape-memory poly- sulfone foam is designed about 20°C higher than actual downhole deployment/application temperature. Because the application temperature is lower than T_g, the material retains good mechanical properties.

[0042] Further, when it is described herein that the filtration device "totally conforms" to the borehole, what is meant is that the shape-memory porous material expands or deploys to fill the available space up to the borehole wall. The borehole wall will limit the final, expanded shape of the shape-memory polysulfone porous material and in fact not permit it to expand to its original, expanded position or shape. In this way however, the expanded or deployed shape-memory material, being porous, will permit hydrocarbons to be produced from a subterranean formation through the wellbore, but will prevent or inhibit small or fine solids from being produced since they will generally be too large to pass through the open cells of the porous material.

[0043] It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. Further, the specification is to be regarded in an illustrative rather than a restrictive sense. For example, specific combinations of polysulfone powders, inorganic peroxides, salts and other components and heating steps to make the thermally crosslinked polysulfone, specific downhole tool configurations and other compositions, components and structures falling within the claimed parameters, but not specifically identified or tried in a particular method or apparatus, are anticipated to be within the scope of this invention.

[0044] The terms "comprises" and "comprising" in the claims should be interpreted to mean including, but not limited to, the recited elements.

[0045] The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. For instance, the thermally crosslinked polysulfone may be made by a process consisting of or consisting essentially of mixing a polysulfone powder, where the polysulfone is as defined in the claims, with powdered inorganic peroxide and optionally a powdered salt as described in the claims; optionally preheating the mixture to a temperature in the range of about 1 10 to about 130°C and curing the mixture at a temperature above about 325°C to crosslink the polysulfone to give a crosslinked polysulfone. The process for making thermally crosslinked polysulfone may consist of or consist essentially of these steps. Furthermore, the process for making the shape- memory porous polysulfone material may consist of or consist essentially of the above steps, but also further consist of or consist essentially of boiling the cured crosslinked polysulfone in water and removing the salt therefrom to recover a porous crosslinked polysulfone, with or without pressure.

Claims

CLAIMS What is claimed is:

1. Thermally crosslinked polysulfone made by a process comprising:

mixing a polysulfone powder, where the polysulfone powder is selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone and mixtures thereof, with oxygen from a source selected from the group consisting of air, oxygen and a powdered inorganic peroxide; and

heating the mixture at a temperature above 325°C for a time period effective to crosslink the polysulfone with oxygen to give a thermally crosslinked polysulfone.

2. The thermally crosslinked polysulfone of claim 1 where the time period is at least eight hours.

3. The thermally crosslinked polysulfone of claim 1 where the inorganic peroxide is magnesium peroxide.

4. The thermally crosslinked polysulfone of claim 1 where heating the mixture is at a temperature above 350°C.

5. The thermally crosslinked polysulfone of claim 1 , 2 or 3 where the process further comprises compressing the mixture into a mold after mixing and prior to heating.

6. The thermally crosslinked polysulfone of claim 5 where the process further comprises mixing the polysulfone powder and the powdered inorganic peroxide with a powdered salt selected from the group consisting of NaCI, KCI, and combinations thereof, and after heating to give the thermally crosslinked polysulfone, boiling the cured crosslinked polysulfone in water and removing the salt therefrom to recover a porous crosslinked polysulfone.

7. The thermally crosslinked polysulfone of claim 6 where the boiling is conducted at a temperature in the range of from 100 to 121 °C and the pressure ranges from 0 to 0.1 MPa.

8. The thermally crosslinked polysulfone of claim 6 where the porous crosslinked polysulfone can pass fluids therethrough at a differential pressure of 0.1 psi or less.

9. The thermally crosslinked polysulfone of claim 6 where the weight ratio of powdered salt to polysulfone powder ranges from 80:20 to 50:50.

10. The thermally crosslinked polysulfone of claim 1 , 2 or 3 where in the mixing of the polysulfone powder with a salt powder, a liquid polyurethane adhesive is included in the mixing in an amount ranging from 1 to 10 wt% based on the total polysulfone powder weight.

1 1. A wellbore seal comprising:

a substrate; and

a thermally crosslinked polysulfone on the substrate, where the thermally crosslinked polysulfone is that of claim 1 , 2 or 3.

12. A wellbore filtration device comprising a shape-memory porous polysulfone material comprising the porous crosslinked polysulfone of claim 6.

13. A process for making thermally crosslinked polysulfone comprising: mixing a polysulfone powder, where the polysulfone powder is selected from the group consisting of polyethersulfone, polyphenylsulfone, polysulfone and mixtures thereof, with oxygen from a source selected from the group consisting of air, oxygen and a powdered inorganic peroxide; and

heating the mixture at a temperature above 325°C to crosslink the

polysulfone with oxygen to give a thermally crosslinked polysulfone.

14. The process of claim 13 where the time period is at least eight hours.

15. The process of claim 13 where the inorganic peroxide is magnesium peroxide.

16. The process of claim 13 where heating the mixture is at a temperature above 350°C.

17. The process of claim 13, 14 or 15 further comprising compressing the mixture into a mold after mixing and prior to heating.

18. The process of claim 17 further comprising mixing the polysulfone powder and the powdered inorganic peroxide with a powdered salt selected from the group consisting of NaCI, KCI, and combinations thereof, and after heating to give the thermally crosslinked polysulfone, boiling the cured crosslinked polysulfone in water and removing the salt therefrom to recover a porous crosslinked polysulfone.

19. The process of claim 18 where the boiling is conducted at a temperature in the range of from 100 to 121 °C and the pressure ranges from 0 to 0.1 MPa.

20. The process of claim 18 where the weight ratio of powdered salt to polysulfone powder ranges from 80:20 to 50:50.

21. The process of claim 13, 14 or 15 where in the mixing of the polysulfone powder with a salt powder, a liquid polyurethane adhesive is included in the mixing in an amount ranging from 1 to 10 wt% based on the total polysulfone powder weight.