Patent Application
20080006413
The manner in which the objectives of the invention and other desirable characteristics may be obtained is explained in the following description and attached drawings in which:
It is to be noted, however, that the appended drawings are not to scale and illustrate only typical embodiments of this invention, and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it may be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
All phrases, derivations, collocations and multiword expressions used herein, in particular in the claims that follow, are expressly not limited to nouns and verbs. It is apparent that meanings are not just expressed by nouns and verbs or single words. Languages use a variety of ways to express content. The existence of inventive concepts and the ways in which these are expressed varies in language-cultures. For example, many lexicalized compounds in Germanic languages are often expressed as adjective-noun combinations, noun-preposition-noun combinations or derivations in Romanic languages. The possibility to include phrases, derivations and collocations in the claims is essential for high-quality patents, making it possible to reduce expressions to their conceptual content, and all possible conceptual combinations of words that are compatible with such content (either within a language or across languages) are intended to be included in the used phrases.
The invention describes well servicing methods and systems for use in same that may reduce the use of wire-wrap sand screens, and that may be applied at any time in the life cycle of a reservoir or field to enhance the value of oil and gas assets through reduced water handling cost, improved hydrocarbon productivity and/or higher recovery factors. As used herein the term “field” includes land based (surface and sub-surface) and sub-seabed applications. The term “oilfield” as used herein includes hydrocarbon oil and gas reservoirs, and formations or portions of formations where hydrocarbon oil and gas are expected but may ultimately only contain water, brine, or some other composition.
Methods and systems of the invention make use of a wellbore tool comprising (i) a base tubular having a plurality of openings and a longitudinal bore adapted to be fluidly connected to a tubular; (ii) a jacket tubular having a second plurality of openings; and (iii) an open, lofty, three-dimensional, non-fines stopping fibrous filter medium between the base tubular and the jacket tubular. Oilfield tubulars, including so-called perforated tubulars, are well known and required little explanation to the skill oilfield artisan, and are not further discussed except to say that the size, shape and configuration of the perforations or openings may vary within wide limits. Suitable base tubulars include any of those described and illustrated in U.S. Pat. No. 6,749,024, incorporated herein by reference, but the invention is not so limited. The tool may also comprise an outer jacket tubular, also having a plurality of openings. The jacket tubular may include a shroud having alternative flow regions, as described in U.S. Pat. No. 6,681,854, incorporated herein by reference.
Fibrous filter media useful in methods and systems of the invention may comprise any fibrous material having porosity sufficient to pass wellbore fluids and treatment fluids therethrough without significant plugging, that does not stop particle fines, and that is capable of serving as a support or base for a sealant precursor composition, if used. The fibrous material may be woven or nonwoven, and may be comprised of organic fibers, inorganic fibers, mixtures thereof, differing layers thereof, and combinations thereof.
Some embodiments the invention may employ a wellbore tool comprising a combination of base tubular, stainless steel fibrous filter media, and jacket tubular known under the trade designation MeshRite™, available from Schlumberger. Developed after extensive research and field testing, these wellbore screen tools use technology that is fully compatible with all types of sand-control techniques, including open-hole and cased-hole gravel packs, horizontal gravel packs, stand-alone screen deployment, and through-tubing sand-control in oil and gas reservoirs.
The wellbore screen tools known under the trade designation MeshRite™ have heretofore proven useful in the field as cost-effective tools for controlling solids and sand production, and when modified in accordance with the invention to include a sealant precursor composition, are useful as a water shut off device. The screens are rugged and can be handled on the rig site and downhole similarly to tubing and casing. Very low pressure drops and a tortuous flow path though the screen fibers dissipate energy, making these screens erosion resistant. These screens allow high production rates with minimal pressure drop due to their exceptional initial permeability of >700 darcies and a porosity that may range from about 85 percent to about 95 percent. Typical preferabilities of reservoir sands are 0.1-5.0 darcies, while the permeability of screens known under the trade designation is several hundred darcies when no sealant precursor composition is fixed in some of the openings between fibers. The permeability is slightly higher when a sealant precursor composition is present, but not significantly different from the “bare” fiber embodiments. A broad pore-size distribution in the filter media relative to the particle-size distribution of the sand acts to stabilize sand, minimizing pressure drop and reducing screen-face skin. Three-dimensional, substantially triangular spaces formed by the stainless steel fibers create a large open area that allows fluids and gas to easily pass through the fibrous filter media of the screens known under the trade designation MeshRite™. These screens reliably control a wide range of particle sizes and reduce the dependence on accurate particle size analysis and screen sizing. Fibrous filter media useful in the invention may retain sand associated with medium- to fine-grained reservoirs (D50>80 microns) with a medium degree of reservoir nonuniformity (D40/D90<10 microns). Unlike traditional sand-control methods that rely on fixed pore sizes and bridging, fibrous filter media useful in the invention resist failure and plugging, even with extended use. In particular, in fibrous filter media used in wellbore screen tools known under the trade designation MeshRite™, particles of various sizes, initially mobilized with fluid production, enter the outer third of the mesh and become stabilized in the triangular pore spaces, while large flow paths remain unobstructed. The perforated base tubular may be wrapped with the fibrous filter media, although other methods of applying the filter media to the base tubular may be used. The fibers may be compressed to form angular pore spaces from 15 to 600 microns in a three-dimensional structure that maximizes the porosity and permeability within the filter element. A perforated outer jacket protects the filter element and provides significant additional structural strength.
Fibrous filter media known under the trade designation MeshRite™ may have any length, but are typically provided in a variety of lengths ranging from 10 ft (3 m) up to 30 ft (9 m) sections wrapped on range 1, 2, and 3 base tubular. Diameter of the tool may range from about ¾ to 9⅝ in. (19.0 to 244.5 mm). The fibrous filer media may have a variety of compressions in accordance with the type of reservoir they are to be used in. So-called standard compression (SC) media and high compression (HC) designs may be suitable for reservoir sands with a D50>120 microns and a D50>75 microns, respectively. When the fibrous filter media comprises metallic fibers, the metallic fiber metallurgy may vary, usually in accordance with the corrosive nature of the fluids the fibrous filter media is expected to encounter in the wellbore environment. Stainless steels, for example, but not limited to, 316 and 434, may be used, as well as specialty and exotic metals such as platinum, beryllium, titanium, Monel, Inconel, and the like. The base tubular and jacket tubular also may have a variety of lengths, inner and outer diameters, and metallurgies. A list of possible steel nonwovens, base tubulars, and jacket tubulars useful in the present invention known under the trade designation MeshRite™ is provided at Table 1.
Other steel fiber-based nonwovens useful in the invention include those described in U.S. Pat. No. 4,176,420, incorporated by reference herein. This patent describes a continuous narrow strip or ribbon of stainless steel which is wound successively and alternately in random directions relative to a surface of a support piece in a plurality of wraps. The stainless steel strip may be in the form of a ribbon having a helical configuration so as to provide continuous coils extending throughout its length, thereby adding to the sponge-like characteristic of the media, increasing its porosity. A sufficient number of wraps are used to build up a pad of sufficient thickness and thereby form a sponge-like mass of the stainless steel ribbon. In this embodiment, the ribbon is relatively thin, the thickness of the ribbon depending on the specific type of operations for which the pad is to be used. The ribbon is also relatively narrow, preferably within the range of 1/16 to ⅛ of an inch (0.16 to 0.32 cm), the width depending to a degree on the type of operation for which the pad is to be used. In accordance with the effect desired, the coils may be formed in a tight-fitting relationship or spaced-apart, forming either a curled or a semi-curled configuration respectively throughout the continuous length of the ribbon. Another embodiment of the strip or ribbon which may be used to form the pad is a flat ribbon of stainless steel which may have a width and thickness selected in accordance with the considerations which dictate its dimensions. Thus, the ribbon may be of the same dimensions as the ribbon of the first embodiment except that it is provided in a helical configuration to form coils as explained above.
Another type of fibrous filter medium usable in the invention comprises an open, lofty, three-dimensional nonwoven web comprising a plurality of thermoplastic organic fibers, and a binder which adheres the fibers at points of mutual contact. This category of lofty, nonwoven filter media may be made from crimped, staple, thermoplastic organic fibers such as polyamide and polyester fibers, although it is also known to use other fibers such as rayon. Although crimping is not necessary to the invention, crimped, staple fibers can be processed and entangled into nonwoven webs by conventional web-forming machines such as that sold under the tradename “Rando Webber” which is commercially available from the Curlator Corporation. Methods useful for making nonwoven webs suitable for use in the invention from crimped, staple, synthetic fibers are disclosed by Hoover, et al., in U.S. Pat. Nos. 2,958,593 and 3,537,121, which are incorporated herein by reference. Continuous crimped or uncrimped fibers may also be used.
The staple fibers may be stuffer-box crimped, helically crimped as described, for example, in U.S. Pat No. 4,893,439, or a combination of both, and the nonwoven webs useful in the invention may optionally contain up to about 50 weight percent melt-bondable fibers, more preferably from about 20 to about 30 weight percent, to help stabilize the nonwoven web and facilitate the application of the coating resin.
Melt-bondable fibers useful in the present invention can be made of polypropylene or other low-melting polymers such as polyesters as long as the temperature at which the melt-bondable fibers melt and thus adhere to the other fibers in the nonwoven web construction is lower than the temperature at which the staple fibers or melt-bondable fibers degrade in physical properties under wellbore conditions. Suitable and preferable melt-bondable fibers include those described in U.S. Pat. No. 5,082,720, mentioned above. Melt-bondable fibers suitable for use in this invention must be activatable at elevated temperatures below temperatures which would adversely affect the helically crimped fibers. Additionally, these fibers are preferably coprocessable with the helically crimped fibers to form a lofty, open unbonded nonwoven web using conventional web forming equipment. Typically, melt-bondable fibers have a concentric core and a sheath, have been stuffer box crimped with about 6 to about 12 crimps per 25 mm, and have a cut staple length of about 25 to about 100 mm. Composite fibers have a tenacity of about 2-3 g/denier. Alternatively, melt-bondable fibers may be of a side-by-side construction or of eccentric core and sheath construction.
Fibers useful in the invention may be helically crimped polyester staple fibers in combination with a low-melting polyester melt-bondable fiber. Helically crimped polyethylene terephthalate (PET) fibers may be used.
U.S. Pat. No. 3,595,738, incorporated herein by reference, discloses methods for the manufacture of helically crimped bicomponent polyester fibers suitable for use in this invention. The fibers produced by the method of that patent have a reversing helical crimp. U.S. Pat. Nos. 3,868,749, 3,619,874, and 2,931,089, all of which are incorporated herein by reference, disclose various methods of edge crimping synthetic organic fibers to produce helically crimped fibers.
Helically crimped fibers may have from about 1 to about 15 full cycle crimps per 25 mm fiber length, while stuffer box crimped fibers may have about 3 to about 15 full cycle crimps per 25 mm fiber length. As taught in the '439 patent, when helically crimped fibers are used in conjunction with stuffer box crimped fibers, preferably the helically crimped fibers have fewer crimps per specified length than the stuffer box fibers.
Crimp index, a measure of fiber elasticity, may ranges from about 35 to about 70 percent for helically crimped fibers, which is about the same as stuffer box crimped fibers. Crimp index can be determined by measuring fiber length with appropriate “high load” attached, then subtracting fiber length with appropriate “low load” attached, and then dividing the result value by the high load fiber length and multiplying that value by 100. (The values of the appropriate “high load” and “low load” depend on the fiber denier. For fibers of the invention having 50 100 denier, low load is about 0.1-0.2 grams, high load is about 5-10 grams.) The crimp index can also be determined after exposing the test fibers to an elevated temperature, e.g., 135 C to 175 C for 5 to 15 minutes, and this value compared with the index before heat exposure. Crimp index measured after the fiber is exposed for 5 to 15 minutes to an elevate temperature, e.g., 135 C to 175 C, should not significantly change from that measured before the heat exposure. The load can be applied either horizontally or vertically.
The length of the organic fibers employed is dependent on upon the limitations of the processing equipment upon which the nonwoven open web is formed. However, depending on types of equipment, fibers of different lengths, or combinations thereof, very likely can be utilized in forming the lofty open webs of the desired ultimate characteristics specified herein. Fiber lengths suitable for helically crimped fibers preferably range from about 60 mm to about 150 mm, whereas suitable fiber lengths for stuffer box fibers range from about 25 to about 70 mm.
Fiber size suitable for producing lofty, open, low density nonwoven products from organic fibers is an important consideration. The thickness (denier) of organic fibers used in nonwoven articles may range broadly from about 6 to about 400, and may range from about 15 to about 200 denier, and may range from about 50 to about 100 denier. Finer deniers than about 15 may result in increased frictional drag. Fiber deniers larger than about 200 reduce drag.
Nonwoven articles useful in the invention comprising organic fibers, when formed for use as fibrous filter media for use in tools of the invention, may have a non-compressed thickness of at least about 0.5 cm, and may range from about 2 cm to about 10 cm. As mentioned above, the thickness is dependent upon the fiber denier chosen for the particular application. If the fiber denier is too fine, the nonwoven articles may be less lofty and open, and thus thinner, resulting in the article tending to be more easily loaded with particles.
Binders suitable for use in organic fiber nonwovens useful in the invention may comprise any thermoplastic or thermostat resin suitable for manufacture of nonwoven articles, but it will be clear to those skilled in the art of such manufacture that the resin in its final, cured state must be compatible (or capable of being rendered compatible) with the fibers of choice.
Another consideration is that the cured resin should be soft enough to allow the nonwoven articles to be somewhat flexible during use so as to allow the pad to conform to irregularities in the tubulars. However, the cured resin should not be so soft as to cause undue frictional drag between the nonwoven articles of the invention and the tubulars. Suitable resins will not readily undergo unwanted reactions, will be stable over a wide pH and humidity ranges, and will resist moderate oxidation and reduction. The cured resins should be stable at higher temperatures and have a relatively long shelf life.
The resins of the binders suitable for use in organic-fiber containing nonwoven articles useful in the invention, and which may also be used to adhere sealant precursor compositions to organic and/or inorganic fibers, such as in steel wool media, may comprise a wide variety of resins, including synthetic polymers such as styrene-butadiene (SBR) copolymers, carboxylated-SBR copolymers, melamine resins, phenol-aldehyde resins, polyesters, polyamides, polyureas, polyvinylidene chloride, polyvinyl chloride, acrylic acid-methylmethacrylate copolymers, acetal copolymers, polyurethanes, and mixtures and cross-linked versions thereof. In certain embodiments, the sealant precursor composition may adhere itself to the fibers and require no additional binder.
One preferred group of resins useful in the present invention, particularly if a substantial number of the fibers of the nonwoven web are polyester, are terpolymeric latex resins formed by linear or branched copolymerization of a mixture of a non-functionalized monoethylenically unsaturated co-monomer, a functionalized monoethylenically unsaturated co-monomer, and a non-functionalized diethylenically unsaturated co-monomer. (“Functionalized”, as used herein, means a monomer having a reactive moiety such as —OH, NH2, COOH, and the like, wherein “non-functionalized” means a monomer lacking such a reactive moiety.)
Useful terpolymer latex resins, used when the fibers of the nonwoven web are substantially polyester, may be formed by random or block terpolymerization of styrene, butadiene, and a functionalized monoethylenically unsaturated monomer selected from monomers having the general formula R1R2C═CR3COOH and anhydrides thereof, wherein R1 and R2 are independently selected from H and CH3, and R3 is selected from H, CH3 and COOH. In commercially available resins of this type, the amount of functionalized monoethylenically unsaturated monomer is typically proprietary, but is believed to be about 1 to about 10 mole percent of the total monomer. The mole percent of styrene may range from about 50 percent to about 80 percent as mole percentage of styrene and butadiene.
The terpolymer latex resin may be that sold under the trade designation “AMSCO RES 5900”, from Unocal. This aqueous latex resin is a terpolymer of styrene/butadiene/functionalized monoethylenically unsaturated monomer having styreneibutadiene mole ratio of 65/35, 1-10 mole percent of functionalized monoethylenically unsaturated monomer, solids weight percent of 50, pH of 9.0, anionic particle charge, particle size of 0.2 micrometer, and glass transition temperature of −5 C. Higher butadiene mole ratios produce a softer resin, but at the cost of greater drag. Typical and preferred coatable binder precursor solutions containing this latex resin which are useful in forming cured binders are presented in Table A (wet parts by weight).
The above described terpolymers may be used uncross-linked, but they are preferably cross-linked by the reaction of the reactive COOH moiety with a polyfunctionalized monomer, such as a phenolic or melamine resin, as indicated in Table A.
Cross-linking resins, as mentioned in Table A, below, may be used to improve the water and solvent resistance of the nonwoven articles, and to increase their firmness. Melamine-formaldehyde resins, such as the fully methylated melamine-formaldehyde resins having low free methylol content sold under the trade designations “Cymel 301”, 1133, and 1168, “Cymel 303” and “Aerotex M-3” (all currently available from American Cyanamid Company), and the like, are suitable. The former provides slightly higher tensile strength while the latter enhances stiffness and resilience of the nonwoven. Phenolic resins have also been used as cross-linking resins, such as those sold under the trade designations “433” (Monsanto) and “R-7” (Carborundum), and the like.
Latex resins useful in the present invention, if cross-linked, may have greater than 10% cross-linking, usually having in the range from about 15% to 80% cross-linking, more usually having in the range from about 25% to 60% cross-linking, and typically being in the range from about 45% to 55% cross-linking. The cross-linked latex resin particles may act as organic fillers, helping to smooth the coating of the fibers of the nonwoven webs with the linear or branched copolymers. The calculated or theoretical percentage of cross-linking is defined as the weight of polyfu-nctionalized monomer (or monomers) divided by the total weight of monomers.
Non-functionalized monoethylenically unsaturated monomers generally suitable for preparing linear, branched, and cross-linked latex resins useful herein include, styrene, ethylvinylbenzene, and vinyltoluene.
Diethylenically unsaturated monomers useful in the invention include isopropene, butadiene and chloroprene, with butadiene being particularly preferred.
If the nonwoven filter media comprise a substantial amount of polyamide (e.g., nylon 6,6) fibers, other resins may be used as the resin component of the binder. Examples of suitable binders for use when the fibers comprise polyamides include: phenolic resins, aminoplast resins, urethane resins, urea-aldehyde resins, isocyanurate resins, and mixtures thereof. One preferred resin is a thermally curable resole phenolic resin, such as described in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., John Wiley & Sons, 1981, N.Y., Vol. 17, p. 384-399, incorporated by reference herein.
Examples of commercially available phenolic resins include those known by the trade names “Varcum” and “Durez” (from Occidental Chemicals Corp., N. Tonawanda, N.Y.), and “Arofene” (from Ashland Chemical Co.). The resole phenolic resin of choice has about 1.7:1 formaldehyde to phenol weight ratio, 76 weight percent solids.
Methods of making organic fiber-based lofty, three-dimensional webs is known in the art and need not be explained here in detail. In one method, a coatable binder precursor solution, comprising uncured resin, and other ingredients, such as thickeners, depending on the coating procedure, is applied to a nonwoven web using two-roll coating. Then, during further processing, the binder precursor is cured or polymerized to form a cured binder. Other coating methods may of course be employed as are known in the art, such as spray coating, and the like. Binder precursor solutions and cured binders suitable for use in the invention may contain appropriate curing agents, non-abrasive fillers, pigments, and other materials which are desired to alter the final properties of the nonwoven articles. In particular, it may be desired to color the nonwoven articles to characterize the article (for example white being the least porous, darker colors indicating more porous). Thus, the resins, binder precursor solutions, and binders useful in the invention may be compatible or capable of being rendered compatible with pigments.
U.S. Pat. No. 6,450,260, incorporated herein by reference, describes many useful compositions that may be used as sealant precursor compositions and, when triggered by a chemical mechanism, triggering compositions. While the compositions described herein are described as comprising certain materials, it should be understood that the sealant precursor compositions and triggering compositions (when used) may optionally comprise two or more chemically different such materials. For example, a composition could comprise a mixture of two or more gel components, crosslinking agents, or other additives, provided that the compounds chosen for the mixture are compatible with the intended use of the composition as taught herein. The '260 patent describes consolidating fluids based on aqueous solutions. The solution can comprise buffers, pH control agents, and various other additives added to promote the stability or the functionality of the fluid. Sealant precursor compositions useful in the invention may comprise a component that gels (gellable component) upon being triggered. The gel may be flexible or substantially inflexible. A “gellable component,” as the term is used herein, is a compound or compounds that, under at least some downhole conditions, can form a flexible gel. If the gellable component is a polymer, the gel may be formed by cross-linking of the polymer, preferably in a three-dimensional network. Cross-linking may occur by contacting the gellable component with a triggering composition, by heat, light, or some other mechanism or combination of mechanisms. If the gel component is a monomer, the is formed by polymerization, preferably generating a three-dimensional polymer network.
As used herein, a “flexible gel” is a gel that is essentially non-rigid after consolidating the formation. Non-rigidity of a gel can be determined by any one or more techniques described in the '260 patent. A non-rigid gel is one that will substantially return to its starting condition after compression with a linear strain of at least about 10%, preferably at least about 25%, and more preferably greater than about 50%. (Minute permanent deformation may be seen at a sufficiently small scale). The unconfined compressive strength (UCS) of loose sand (40-60 U.S. mesh) consolidated with a flexible gel, as measured according to standard protocols, is typically about 2 psi to about 400 psi, preferably about 2 psi to about 50 psi. (It should be noted a flexible gel by itself typically has a UCS less than about 5 psi). The storage modulus G′ of a flexible gel, as measured according to standard protocols given in U.S. Pat. No. 6,011,075, is typically about 150 dynes/cm to about 500,000 dynes/cm, preferably from about 1000 dynes/cm2 to about 200,000 dynes/cm2, more preferably from about 10,000 dynes/cm to about 150,000 dynes/cm2.
Another feature of the flexible gels described in the '260 patent is that it significantly reduces the permeability of the formation or gravel pack, by which is meant reducing the permeability by at least about 90%, or at least about 95%, or at least about 99%. This also describes the reduction in permeability of the fibrous filer media useful herein.
Gel components capable of forming a gel (including flexible gels) include the following exemplary water-soluble polymers, copolymers, or terpolymers: polyvinyl polymers (such as polyvinyl alcohol or polyvinyl acetate), polyacrylamides, acrylamide copolymers and terpolymers, acrylic acid-methacrylamide copolymers, partially hydrolyzed polyacrylamides, polymethacrylamides, partially hydrolyzed polymethacrylamides, cellulose ethers, polysaccharides, heteropolysaccharides, lignosulfonates, polyalkyleneoxides, carboxycelluloses, carboxyalkylhydroxyethyl celluloses, hydroxyethyicellulose, galactomannans, substituted galactomannans, the ammoniumri salts or alkali metal salts of the foregoing, and alkaline earth salts of lignosulfonates, among others.
Exemplary water-soluble polymerizable monomers that can be used as a gel component include acrylic acid, acrylamide, methacrylic acid, methacrylamide, hydroxyethylacrylate, maleic acid, diallyldimethyl ammonium chloride, methylene bis-acrylamide, urea, vinyl acetic acid, styrene sulfonic acid, salts thereof, or mixtures thereof. Neither list is intended to be exhaustive.
The concentration of a polymeric gel component in the sealant precursor composition may range from about 1 wt % to about 10 wt % gel component, and may range from about 4 wt % to about 8 wt % gel component. The concentration of a monomer gel component may range from about 2 wt % to about 60 wt %, and may range from about 5 wt % to about 45 wt %.
The '260 describes a gel-form-ing agent, and this may coincide with the triggering component used in the present invention. If the sealant precursor composition is a polymer, the triggering component may be a crosslinking agent, i.e. an agent capable of crosslinking polymer molecules to form a three-dimensional network. Exemplary organic crosslinking agents include, but are not limited to, aldehydes, dialdehydes, phenols, substituted phenols, and ethers. Exemplary inorganic crosslinking agents include, but are not limited to, polyvalent metals, chelated polyvalent metals, and compounds capable of yielding polyvalent metals.
If the sealant precursor composition is provided as a monomer, the triggering component may be able to crosslink the monomer or catalyze the polymerization of the monomer to form a three-dimensional network.
The concentration of the triggering component in the triggering composition may range from about 0.001 wt % to about 5 wt %, and may range from about 0.005 wt % to about 2 wt %.
Optionally, if the sealant precursor composition comprises a monomer and the triggering component is chosen to crosslink the monomer, the triggering composition may further comprise a water-soluble initiator to start the crosslinking reaction. Exemplary initiators include oxidizers, such as ammonium persulfate or azo compounds, such as 2,2′-azobis(2-amidinopropane)dihydrochioride, among others. The concentration of the initiator may range from about 0.0001 wt % to about 5 wt %. Optionally, agents to accelerate or delay initiation, such as potassium ferricyanide, may be added as well.
If the triggering mechanism is chemical, the triggering composition may not form a gel until after its injection into the formation. Before that time, it is desirably a flowable solution that may be readily pumped or otherwise handled. In order to prevent gelation until after the triggering composition is injected into the formation, the triggering composition may be formed shortly before injection into the formation. The triggering component may be the last ingredient added to the nascent triggering composition during the latter's formation. Since the sealant precursor composition is located in the fibrous filter element downhole and the triggering component is at the surface until injected, there is physical separation already; however, a gelation inhibitor that readily degrades upon exposure to downhole conditions may be a component of the triggering composition, or a reaction that is temperature initiated may be employed. Whichever approach is used, it is desirable that after injection of the triggering composition, gelation is allowed to readily occur, such as by stripping any emulsifying agent against the formation face or degradation of a gelation inhibitor under downhole temperature. If premature gelation was inhibited by preparing the triggering composition shortly before use, then gelation will typically readily occur after injection.
The triggering composition (if used) and sealant precursor composition may further comprise stabilizing agents, surfactants, diverting agents, or other additives. Stabilizing agents can be added to slow the degradation of the gel after its formation downhole. Typical stabilizing agents include buffering agents, especially agents capable of buffering at pH of about 8.0 or greater (e.g. water-soluble bicarbonate salts, carbonate salts, phosphate salts, or mixtures thereof, among others); and chelating agents (e.g. ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), or diethylenetriaminepentaacetic acid (DTPA), hydroxyethylethylenediaminetriacetic acid (BEDTA), or hydroxyethyliminodiacetic acid (HEIDA), among others). Buffering agents may be added to the triggering composition to at least about 0.05 wt %, or at least about 0.75 wt %. Chelating agents may be added to a triggering composition to at least about 0.75 mole per mole of metal ions expected to be encountered in the downhole environment, or at least about 0.9 mole per mole of metal ions.
Surfactants may be added to promote dispersion or emulsification of components of the triggering composition, or to provide foaming of the gel upon its formation downhole. Usable surfactants include, but are not limited to, alkyl polyethylene oxide sulfates, alkyl alkylolamine sulfates, modified ether alcohol sulfate sodium salts, or sodium lauryl sulfate, among others. A surfactant may be added to the triggering composition in an amount ranging from about 0.01 wt % to about 10 wt %, or from about 0.1 wt % to about 2 wt %. Surfactant may be added to a triggering composition shortly before injection.
After the triggering composition is prepared, it may be injected into a formation to initiate water shut off of at least a portion of the formation. Techniques for injection of fluids are well known in the art. Typically, a triggering composition would be injected through the wellbore, through coiled tubing or other tubular, into the formation at a pressure less than the fracturing pressure of the formation. Formations for which water shut off may be desirable include sand, sandstone, chalk, and limestone, among others. Typically, a triggering composition would be injected below the formation fracturing pressure.
The volume of triggering composition to be injected, if used at all, into the formation is a function of the number and size of wellbore tools comprising open, lofty fibrous filter media. The volume may be readily determined by one of ordinary skill in the art. Packers or similar devices can be used to control flow of the triggering composition into the formation for which water shut off is desired. The minimum and maximum injection rates that can be used are a function of the downhole gelation rate; the maximum pressure that will not lead to fracturing of the formation, if relevant; and limitations of equipment. Preferably, the gelation rate is sufficiently slow to allow complete injection of the desired volume into the formation, but is sufficiently rapid to allow a quick gelation after injection and thus minimize the time spent to perform the water shut off method.
After the triggering mechanism is delivered to the site or sites in the wellbore it is needed, gelation occurs, whereby the gel component is cross-linked or polymerized, as appropriate given the sealant precursor composition. In either case, a gel may be formed in at least some open regions of the lofty, open fibrous filter medium near a surface of the fibrous filter medium.
Other sealant precursor composition and/or triggering composition chemistries may be employed, as long as at least one of the components can adhere or otherwise remain trapped in an inert state by the fibrous filter media during normal operations, but be triggered by another component to form a seal as explained herein. Such other chemistries include compositions known under the trade designation SANDLOCK™ (Schlumberger), which comprise a resin, and optionally a curing agent, a catalyst, and an oil wetting agent, as more thoroughly described in U.S. Pat. No. 6,632,778. When injected into the formation, the resin (acted upon by the curing agent and catalyst, if present) hardens, causing a rigid seal. These systems were designed to maintain sufficient permeability of the formation to allow production, but in a water shut off application, a good seal is desired at the wellbore screen tool, as explained herein=Other useful chemistries and methods for their use are reported in U.S. Pat. Nos. 5,806,593; 5,199,492; 4,669,543; 4,427,069; and 4,291,766. U.S. Pat. No. 5,712,314 discusses the use of a flexible furan resin system for water control. U.S. Pat. Nos. 5,246,073; 5,335,733; 5,486,312; and 5,617,920, assigned to Unocal, describe a fluid comprising a polyvinyl polymer, a polymethacrylamide, a cellulose ether, a polysaccharide, a lignosulfonate, an ammonium salt or alkali metal salt of the foregoing, or an alkaline earth salt of a lignosulfonate; and a crosslinking agent, such as an aldehyde, a dialdehyde, a phenol, a substituted phenol, an ether, a polyvalent metal, a chelated polyvalent metal, or a compound capable of yielding a polyvalent metal. One version of such a fluid is commercially available under the trade name “OrganoSEAL-R.” These references teach the fluid can be used to seal a wellbore to prevent contamination by water from a water-containing formation penetrated by the wellbore. U.S. Pat. Nos. 4,683,949 and 5,947,644, assigned to Marathon Oil Co., describe a fluid comprising polyacrylamide and a chromium III/carboxylate complex crosslinking agent. The fluid is commercially available under the trade name “MARASEAL.” These references also teach the fluid can be used to seal a wellbore to prevent contamination by water from a water-containing formation penetrated by the wellbore. Zeltmann et al., U.S. Pat. No. 6,047,773, assigned to Halliburton Energy Services, Inc., reports the use of viscous fluids, such as fluids comprising hydroxyethyiceilulose, guar, or acrylic, to occupy a wellbore and provide a barrier to entry of stimulation fluids into a formation. The viscous barrier fluid itself is taught to not penetrate the formation. U.S. Pat. No. 6,011,075 discloses flexible gel compositions having increased storage modulus G′ while maintaining flexibility, the compositions or fluids comprising an aqueous liquid, such as water, an effective a mount of a water soluble crosslinkable polymeric gel forming material, and a crosslinking agent; and an effective or gel strengthening amount of an inert colloidal particulate material. The crosslinkable polymeric gel forming composition is preferably selected from water soluble crosslinkable polymers and polymerizable monomers capable of forming a water soluble crosslinkable polymer, and mixtures thereof. As used therein, the term “colloidal” refers not only to the size of the particles but to the capability of the particulate material in forming at least substantially stable dispersions in an aqueous liquid, while the term “inert” indicates that the particulate material retains its identity to at least a substantial extent in the aqueous liquid. The compositions may be foamed. All of the patents mentioned in this paragraph are incorporated by reference herein, once again with the proviso that at least one of the components can adhere or otherwise remain trapped in an inert state by the fibrous filter media during well production and workover operations, but be triggered to form a water shut off seal when desired, as explained herein.
Certain methods of the invention utilize a communication line. The communication line may have one or more than one function. In certain embodiments the communication line may only communicate information, either one way or two-way between the wellbore screen tool location and the surface. In other embodiments the communication line may include one or more sensing devices at or near the distal end of the communication line. Systems of the invention may include a pressurized housing for a reel, a pumping system for conveying the communication line down the wellbore to the tool using one or more well treatment fluids, such as one or more triggering fluids, well stimulation or other fluids, and optionally, depending on the embodiment, means for re-spooling the communication line, means for guiding the communication line down and back out of the wellbore, and a surface data acquisition and/or monitoring system, as described in pending U.S. patent application Ser. No. 11/278,512 filed Apr. 3, 2006, incorporated herein by reference.
The optical fiber may typically be transported to the wellhead on a small drum. It may be introduced into the flow of the fluid by passing the fiber through a stuffing box such as disclosed in U.S. Pat. No. 3,831,676, in which case the reel is not subjected to the wellbore pressure. Alternatively, the fiber may be spooled onto a reel which is enclosed in a housing attached to the wellhead and thus subjected to the wellbore pressure, as described in pending U.S. patent application Ser. No. 11/278,512 filed Apr. 3, 2006, previously incorporated herein by reference. The optical fiber may optionally be encased in a small amount of cladding for protection from abrasion and corrosion. The cladding may also help minimize long term darkening of the fiber caused by exposure to hydrogen ions. Rather than bringing a secondary coiled tubing unit to the location, instead the fiber is passed into the flow-path of the pumped treatment and/or stimulation fluids. The flowing fluid provides sufficient drag on the fiber that it may be conveyed the full length of the wellbore while the fluid is being bull-headed. Miniature sensors may be added to the end of the fiber to provide downhole pressure, flow, or other information. Alternatively, the fiber itself may be modified by the addition of gratings along its length. Surface interrogation of optical fiber gratings may be performed with a laser at the surface as disclosed, for example, in U.S. Pat. No. 5,841,131, incorporated herein by reference.
By “pumping system” we mean a surface apparatus of pumps, which may include an electrical or hydraulic power unit, commonly known as a powerpack. In the case of a multiplicity of pumps, the pumps may be fluidly connected together in series or parallel, and the energy conveying a triggering composition or communication line, or both, may come from one pump or a multiplicity. The pumping system may also include mixing devices to combine different fluids or blend solids into the fluid, and the invention contemplates using downhole and surface data to change the parameters of the fluid being pumped, as well as controlling on-the-fly mixing.
By the phrase “surface acquisition system” is meant one or more computers at the well site, but also allows for the possibility of a networked series of computers, and a networked series of surface sensors. The computers and sensors may exchange information via a wireless network. Some of the computers do not need to be at the well site but may be communicating via a communication system such as that Known under the trade designation InterACT™ or equivalent communication system. In certain embodiments the communication line may terminate at the wellhead at a wireless transmitter, and the downhole data may be transmitted wirelessly. The surface acquisition system may have a mechanism to merge the downhole data with the surface data and then display them on a user's console.
In exemplary embodiments of the invention, advisor software programs may run on the acquisition system that would make recommendations to change the parameters of the operation based upon the downhole data, or upon a combination of the downhole data and the surface data. Such advisor programs may also be run on a remote computer. Indeed, the remote computer may be receiving data from a number of wells simultaneously.
The surface acquisition system may also include apparatus allowing communication to the downhole sensors. For example, in embodiments wherein the communication line includes an optical fiber, laser devices, such as diode lasers, may be used to interrogate the state of downhole optical components. Optionally, the laser devices may transmit a small amount of power to any downhole component on the end of the communication line. The surface acquisition system should be able to control the surface communication apparatus and the user's console would typically display status of those apparatus.
Communication lines useful in the invention may have a length much greater than their diameter, or effective diameter (defined as the average of the largest and smallest dimensions in any cross section). Communication lines may have any cross section including, but not limited to, round, rectangular, triangular, any conical section such as oval, lobed, and the like. The communication line diameter may or may not be uniform over the length of the communication line. The term communication line includes bundles of individual fibers, for example, bundles of optical fibers, bundles of metallic wires, and bundles comprising both metallic wires and optical fibers. Other fibers may be present, such as strength-providing fibers, either in a core or distributed through the cross section, such as polymeric fibers. Aramid fibers are well known for their strength, one aramid fiber-based material being known under the trade designation “Keviar”. In certain embodiments the diameter or effective diameter of the communication line may be 0.125 inch (0.318 cm) or less. In one embodiment, a communication line would include an optical fiber, or a bundle of multiple optical fibers to allow for possible damage to one fiber.
In an alternative embodiment, the communication line may comprise a single optical fiber having a fluoropolymer or other engineered polymeric coating, such as a Parylene coating. The advantage of such a system is the cost is low enough to be disposable after each job. One disadvantage is that it needs to be able to survive being conveyed into the well, and survive the subsequent fluid stages, which may include proppant stages. In these embodiments, a long blast tube or joint comprising a very hard material, or a material coated with known surface hardeners such as carbides and nitrides may be used. The communication line would be fed through this blast tube or joint. The length of blast joint may be chosen so that the fluid passing through the distal end of the joint would be laminar. This length may be dozens of feet or meters, so the blast joint may be deployed into the wellbore itself. In embodiments where the communication line is a single fiber, the sensing apparatus may need to be very small. In these embodiments, nano-machined apparatus that may be attached to the end of the fiber without significantly increasing the diameter of the fiber may be used. Similar devices are marketed for downhole pressure measurement by Sensa, Southampton, United Kingdom. A small sheath may be added to the lowest end of the fiber and cover the sensing portion so that any changes in outer diameter are very gradual.
In one embodiment of the invention the sensing device is the communication line itself. For example, the communication line may include an optical fiber, and the data transmitted may be distributed temperature. Accessing distributed temperature is known in the art, except for the teachings herein, and has been disclosed, for example, by U.S. Pub. Pat. App. No. US20040129418, “Use of distributed temperatures during wellbore treatments” by Jee, et al., incorporated by reference herein. Alternatively, an optical fiber itself may be modified by the addition of doping or gratings along its length. Surface interrogation of these gratings may be done with a laser at the surface as disclosed, for example, in U.S. Pat. No. 5,841,131, incorporated by reference herein.
Referring now to the drawing figures,
In a typical water shut off operation when multiple wire-wrap screens 28 are present, the wire-wrap screens are typically substantially plugged with fines, and water enters the production string through joints in the production string. Wire-wrap sand screens need to be have openings small enough to restrict particulate flow, often having gaps in the 60-120 mesh range, but other sizes may be used. The packer elements 24, 30 are set to ensure a seal between the tubular member 22 and the casing 16. A series of tubular patches may be installed via tubular member 22 at joints between the wire-wrap screens 28 and blank sections 32. Gels or other chemicals may also be injected to prevent water from being produced, however, placing the gel or other sealant composition is not specific in location and maybe wasted, possibly damaging the well, and/or reducing production of hydrocarbons when water is not being produced. Some water may also be produced by way of the sand screen elements 28 and enter the tubular member 22, and flows up through the tubular member 22 until the cross-over 26 places it in the annulus area 36 above the production packer 24 where it can leave the wellbore 10 at the surface.
Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art may readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, no clauses are intended to be in the means-plus-function format allowed by 35 U.S.C. § 112, paragraph 6 unless “means for” is explicitly recited together with an associated function. “Means for” clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.
