Source: https://patents.google.com/patent/WO2008124080A1/en
Timestamp: 2018-11-21 17:18:39
Document Index: 181122652

Matched Legal Cases: ['Application No. 11', 'Application No. 60', 'Application No. 11', 'Application No. 1', 'Application No. 11', 'Application No. 20040043906', 'Application No. 20060078682', 'Application No. 20050154083', 'Application No. 20050154221', 'Application No. 20030083450', 'art 2', 'art 5', 'art.\n18']

WO2008124080A1 - A method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified thermoset polymer nanocomposite particles as proppants - Google Patents
A method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified thermoset polymer nanocomposite particles as proppants Download PDF
WO2008124080A1
WO2008124080A1 PCT/US2008/004428 US2008004428W WO2008124080A1 WO 2008124080 A1 WO2008124080 A1 WO 2008124080A1 US 2008004428 W US2008004428 W US 2008004428W WO 2008124080 A1 WO2008124080 A1 WO 2008124080A1
PCT/US2008/004428
A METHOD FOR THE FRACTURE STIMULATION OF A SUBTERRANEAN
FORMATION HAVING A WELLBORE BY USING IMPACT-MODIFIED THERMOSET
POLYMER NANOCOMPOSITE PARTICLES AS PROPPANTS CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of U.S. Patent Application No. 11/323,031
entitled "Thermoset Nanocomposite Particles, Processing For Their Production, And Their Use In Oil And Natural Gas Drilling Applications", filed December 30, 2005, which claims priority to U.S. Provisional Application No. 60/640,965 filed December 30, 2004. This
application is also a continuation-in-part of U.S. Patent Application No. 11/451,697 entitled
"Thermoset Particles With Enhanced Crosslinking, Processing For Their Production, And Their Use In Oil And Natural Gas Drilling Applications", filed June 13, 2006. The contents of prior application nos. 11/323,031, 11/451,697 and 60/640,965 are fully incorporated herein by reference. FIELD OF THE INVENTION
The present invention relates to a method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified ultralightweight thermoset polymer nanocomposite particles as proppants. Without reducing the generality of the invention, in its currently preferred embodiments, the thermoset polymer matrix of said particles comprises a terpolymer of styrene, ethyvinylbenzene and divinylbenzene; carbon
black is used as the nanofiller, suspension polymerization in the rapid rate polymerization mode is performed to prepare said particles, and post-polymerization heat treatment is performed in an unreactive gas environment to further advance the curing of the thermoset polymer matrix. One main benefit of the incorporation of impact modifier(s) is to enable the use of larger quantities of crosslinker, nanofiller, or combinations thereof, in the formulation from which the particles are prepared; thus achieving higher maximum use temperatures, higher fracture conductivities throughout the use temperature range, or combinations thereof, without inducing brittleness in the particles. The fracture stimulation method of the invention can be implemented by placing said particles in the fracture either as a packed mass or as a partial monolayer. Without reducing the generality of the invention, said particles are placed as a partial monolayer in its preferred embodiments. BACKGROUND 1. Introduction
U.S. Patent No. 6,248,838, "Chain entanglement crosslinked proppants and related uses"; the background section of U.S. Patent Application No. 1 1/323,031 entitled "Thermoset nanocomposite particles, processing for their production, and their use in oil and natural gas drilling applications"; and the background section of U.S. Patent Application No. 11/451,697 entitled "Thermoset particles with enhanced crosslinking, processing for their production, and their use in oil and natural gas drilling applications", provide background information related to the present invention and are fully incorporated herein by reference. The background discussion below is intended to supplement the background discussions in these three prior filings, and focuses entirely on impact modification.
Impact modification has only been given limited and cursory consideration in prior art on fracture stimulation. U.S. Patent Application No. 20040043906 cited impact modifiers among the types of additives that can be incorporated into polymeric proppants in order to control their mechanical properties. U.S. Patent Application No. 20060078682 disclosed particles for use as proppants, where the particles comprise a substrate comprising an inorganic material, and an organic coating (disposed upon the substrate) which may optionally contain impact modifiers intended mainly to impart elastic properties to the organic coating. U.S. Patent Nos. 5597784 and 6372678, and U.S. Patent Application Nos. 20050194141 and 20070036977, disclosed fracture stimulation technologies utilizing coated proppants comprising more than one coating layer, where a "reinforcing agent" may be interspersed at the boundary between different layers of the coating, and impact modifiers may serve as reinforcing agents.
Applicant has, however, found no prior art in the patent literature, and no publications in the general scientific literature, that disclose a method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified ultralightweight thermoset polymer nanocomposite particles as proppants. The discussion below is hence intended to be mainly of a pedagogical nature, by providing background information that will help those in the field understand the invention better by familiarizing them with key information related to impact modification. Since the preferred embodiments of the invention involve the use of thermoset nanocomposite particles having styrenic polymer matrices, this description of information related to impact modification will be done in the context of the impact modification of styrenic polymers. 2. Types of Impact-Modified Styrenic Polymers
High-impact polystyrene (HIPS) is the most commonly used impact-modified styrenic polymer. Copolymers of styrene with other suitable vinylic monomers (such as other styrenic monomers, acrylic monomers, nitrile monomers, monomers containing ion exchange capable functional groups, etc.) have also been toughened. Crosslinked versions of many of these styrenic polymers, with divinylbenzene being the most commonly used crosslinking agent, have also been toughened. Macroporous styrenic beads of various compositions (sometimes crosslinked with divinylbenzene) have also been toughened. See Conway et al. (1997) for the toughening of porous aminated crosslinked poly(vinylbenzyl chloride - divinylbenzene) beads. See Coelho et al. (2000) and World Patent No. WO9607675 for the toughening of copolymers that have been crosslinked with divinylbenzene. U.S. Patent No. 5,847,054 teaches a method for the preparation of crosslinked styrenic polymer particles containing an impact modifier, for use as additives intended to increase the "dullness" (reduce the glossiness, make more matte) and/or enhance the impact strengths of thermoplastic and thermoset polymers when incorporated into them. U.S. Application No. 20050154083 teaches styrenic particle compositions (possibly crosslinked to a slight extent by using a small amount of a comonomer such as divinylbenzene, and possibly also containing an impact modifier) encapsulating high aspect ratio particles; and intended to be used as pigments which, when incorporated into any of a very wide variety of matrix polymers, will impart attractive optical properties to those matrix polymers.
Syndiotactic polystyrene (a highly crystalline form of polystyrene that has especially high stiffness and heat resistance, but that is even more brittle than ordinary general-purpose polystyrene) has also been toughened (U.S. Patent No. 5,352,727 and U.S. Patent No. 5,436,397) by incorporating impact modifiers.
While impact-modified styrenic polymers have been used in many industrial applications, applicant does not believe that these applications include the use of impact- modified styrenic polymers as proppants in the fracture stimulation of a subterranean formation having a wellbore. Nor is applicant aware of any patented or reported methods for the fracture stimulation of a subterranean formation having a wellbore by using impact- modified ultralightweight thermoset polymer nanocomposite particles based on any other type of polymeric matrix material as proppants.
Rubber modification is the most common method for the impact modification of styrenic polymers. It has provided up to several times higher notched Izod impact strength and much higher ductility (as quantified by the ultimate tensile elongation); without large losses in the stiffness (elastic moduli), strength, gloss, or heat distortion temperature.
Increasing effectiveness of impact modification in improving the mechanical properties has been shown to correlate with increasing energy dissipation by the deformation of the rubbery phase (as quantified by its "tan δ" peak) during dynamic mechanical analysis under cyclic deformation. See Turley and Keskkula (1980), Choi et al. (2000), Coelho et al. (2000), Aiamsen et al. (2003), Qiao-long et al. (2005), Rivera et al. (2006), U.S. Patent No. 5,352,727, U.S. Patent No. 5,436,397 and European Patent No. EP0475461 for some examples of the effects of rubber modification on the mechanical properties. Toyoshima et al. (1997) provide an example of the optimization of the balance between the impact strength and gloss by means of the choice of impact modifier. U.S. Patent No. 5,475,053 teaches impact-resistant thermoplastic (including HIPS) molding compositions having a matte surface. Cho et al. (1997) show that the environmental stress cracking resistance in the simultaneous presence of a hostile chemical environment along with a mechanical load can also be improved by rubber modification. 4. Rubbers Used as Impact Modifiers for Styrenic Polymers Many types of rubbers can be and have been used as tougheners for styrenic polymers, with varying levels of effectiveness in improving the properties, practicality of manufacturing, and economic viability in terms of the balance between improved properties and increased cost. Polybutadiene (dissolved in the reactive monomer mixture after being placed there in a solid particulate form) is the rubbery phase that is most often incorporated as a toughener into polystyrene in order to manufacture HIPS.
The effects of using polybutadienes of different chain microstructure (different cis- 1,4, trans- 1,4, and vinyl- 1,2 isomer contents) have also been investigated. For example, it has been shown by Rivera et al. (2006) that some polybutadiene microstructures provide noticeably more favorable balances between impact modification and the other mechanical properties.
Natural rubber, poly(alkyl acrylate) rubbers, partially or completely hydrogenated diene rubbers, and olefinic rubbers, are some other examples of rubbers that have been used as impact modifiers. For example, see Aiamsen et al. (2003) for the use of radiation- crosslinked natural rubber, Qiao-long et al. (2005) for the use of nanosilica-containing poly(butadiene styrene) rubber, European Patent No. EP0475461 for the use of a selectively partially hydrogenated polybutadiene, and U.S. Patent No. 5,847,054 for the use of olefinic rubbers.
It is also worth noting that some of the terms that may be used for the different types of rubbers overlap. Sometimes, they may refer to the same type of molecular structure obtained in different ways. For example, a completely hydrogenated polybutadiene or a completely hydrogenated polyisoprene has the same general type of molecular structure as a polyolefϊn. Both are fully saturated aliphatic hydrocarbons. The difference is that one is obtained by polymerizing butadiene or isoprene and hydrogenating the resulting polymer; while the other is obtained directly by reacting olefinic monomers such as ethylene, propylene and/or 1 -butene.
Various block copolymers (such as styrene-butadiene or styrene-isoprene diblock and styrene-butadiene-styrene or styrene-isoprene-styrene triblock copolymers and their partially hydrogenated versions) have been used either as impact modifiers on their own or as compatibilizers between polystyrene and an impact modifier such as polybutadiene. For some examples, see Conway et al. (1997), Cho et al. (1997), Toyoshima et al. (1997) and Aiamsen et al. (2003). A method using block copolymers as impact modifiers incorporated into crosslinked styrenic polymer particles is taught in U.S. Patent No. 5,847,054. Impact- modified syndiotactic polystyrene compositions containing block copolymers are taught by U.S. Patent No. 5,352,727 and U.S. Patent No. 5,436,397; while U.S. Patent No. 5,380,798, U.S. Patent No. 5,475,053 and World Patent No. WO9607675 teach some other examples of the use of block copolymers as impact modifiers for styrenic polymers.
The rubbers used in the impact modification of styrenic polymers include both thermoset elastomers and thermoplastic elastomers. Thermoset elastomers (usually more simply referred to as "rubbers"), such as crosslinked polybutadiene and crosslinked polyisoprene, have a covalently crosslinked three-dimensional network structure, but possess a low glass transition temperature [below "room temperature" (25 0C)]. Thermoplastic elastomers, such as styrene-butadiene diblock copolymers and styrene-butadiene-styrene triblock copolymers, contain soft domains that are "physically crosslinked" by hard domains, while they lack a covalently crosslinked three-dimensional network structure. Both thermoset elastomers and thermoplastic elastomers are used simultaneously in some formulations for the impact modification of styrenic polymers. An example is the use of a crosslinked polybutadiene as the main component of the impact modifier, along with some thermoplastic styrene-butadiene diblock copolymer that serves mainly as a compatibilizer between the styrenic phase domains and the polybutadiene phase domains. If there is a significant reactivity difference between the styrenic monomer(s) and the other type(s) of monomer(s) present in a reactive mixture, then there is a tendency towards the formation of a heterogeneous morphology [with domains rich in the styrenic polymer and domains rich in the product(s) of the polymerization of the other type(s) of monomer(s)] even when the reaction is started with a mixture of monomers rather than incorporating the non- styrenic component in an oligomeric or polymeric form. See, for example, Lu and Larock (2006). This article also illustrates the utilization of a renewable resource (corn oil) as a source of monomers for use in the preparation of polymer composites. The growing use of renewable resources as feedstocks will be discussed further in the next paragraph.
A background paper on biopolymers, published by the U. S. Congress, Office of Technology Assessment (September 1993), suggested that the use of biologically derived polymers could emerge as an important component of a new paradigm of sustainable economic systems that rely on renewable sources of energy and materials. This concept has, indeed, gained increasing acceptance in the years that followed the publication of the background paper. The utilization of monomers obtained from biological starting materials (such as amino acids, nucleotides, sugars, phenols, natural fats, oils, and fatty acids) in the chemical synthesis of polymers is an important component of this paradigm of sustainable development. This is an area of intense research and development activity because of the global drive to reduce the dependence of the world economy on petrochemical feedstocks. Such renewable feedstocks can be obtained from a wide variety of microorganism-based, plant-based, or animal-based resources. The utilization of monomers, oligomers and polymers obtained from renewable resources as components of polymer composites is, therefore, anticipated to continue to increase in the future. Among renewable feedstocks for the synthesis of polymeric products, natural fats and oils extracted from some common types of plants [such as soybean, sunflower, canola, castor, olive, peanut, cashew nut, pumpkin seed, rapeseed, corn, rice, sesame, cottonseed, palm, coconut, safflower, linseed (also known as flaxseed), hemp, castor bean, tall oil, and similar natural fats and oils; and especially soybean, sunflower, canola and linseed oils] appear to be very promising as potential sources of inexpensive monomers. Some animal-based natural fats and oils, such as fish oil, lard, neatsfoot oil and tallow oil, may also hold promise as potential sources of inexpensive monomers. U.S. Patent Application No. 20050154221 teaches integrated chemical processes for the industrial utilization of seed oil feedstock compositions. An article by Pillai (2000) discusses the wealth of high value polymers that can be produced by using constituents extracted from cashew nut shell liquid. Belcher et al. (2002) show that the blending of functionalized soybean oil with petrochemical-based resins can increase the toughness of a petroleum-based thermoset resin without compromising stiffness, while also improving its environmental friendliness. 5. Methods for Manufacturing Impact-Modified Styrenic Polymers
In toughening styrenic polymers by incorporating polybutadiene, the most common preparation method is bulk-suspension copolymerization. In applying this method, a prepolymer is first prepared by using bulk polymerization. The preparation of HIPS in the form of beads (or pellets) is then completed via suspension polymerization. It is, however, also possible to use bulk polymerization by itself, or (as taught, for example, in U.S. Patent No. 4,730,027) suspension polymerization by itself from the beginning to the end to prepare HIPS. Batch polymerization is most commonly used, but methods (such as the one taught in U.S. Patent Application No. 20030083450) are available for continuous polymerization.
When suspension polymerization is used (either by itself or after bulk polymerization), substantially spherical polymer beads of a wide variety of desired diameters can be produced by varying the process parameters (and especially the stirring rate). The details of the formulation and processing conditions play crucial roles in determining the extent of grafting, as well as the size distribution and morphology of the rubbery domains. For example, the stirring (shear) rate is a process variable that has been used to control the dispersed rubbery domain size. Faster stirring normally results in smaller rubbery domain sizes. The effects of processing conditions on the morphologies of heterophasic polymeric materials (including toughened polymers and toughened polymeric composites) have been discussed by Bicerano (2002) in terms of the interplay between thermodynamic and kinetic factors.
The use of 5% to 15% by weight of polybutadiene (with 7% by weight being viewed as an optimum value by some experts) is the most common approach. However, the rubbery phase volume fraction in HIPS is typically much higher than the weight fraction of the rubber since the rubbery phase domains also normally contain a lot of occluded polystyrene. For further discussions of the optimum rubber weight fraction and/or rubbery phase volume fraction, see Turley and Keskkula (1980), Cho et al. (1997), Choi et al. (2000) and Aiamsen et al. (2003). In general, much better impact modification is obtained if the rubbery material becomes covalently bonded to (grafted onto) the styrenic polymer chains during preparation rather than just being physically blended into the polymer. See Cho et al. (1997), Choi et al. (2000), Qiao-long et al. (2005) and Rivera et al. (2006) for examples of this effect. This is why suspension polymerization techniques, which lead to the grafting of an impact modifier containing one or more reactive functionalities onto the matrix polymer, are normally preferred to approaches such as the melt blending of a rubber into polystyrene.
A reactive impact modifier can be incorporated into the formulation as a monomer, as an oligomer, or as a polymer. The use of a reactive oligomer or polymer as the impact modifier can cause the mixing of the impact modifier into the formulation to become more difficult than the use of a monomeric impact modifier of similar chemical structure, especially if the reactive oligomer or polymer is a solid. However, once a reactive oligomer or polymer impact modifier is mixed adequately with the other components of the formulation, this approach may offer the advantage of the more facile attainment of a heterophasic morphology where the impact modifier is present in phase-separated domains that provide an optimum toughening effect with the least possible reductions of other important properties such as stiffness (modulus) and strength. SUMMARY OF THE INVENTION 1. Introduction
The particles are manufactured by suspension polymerization (Section 5) and postcured by heat treatment (Section 6) before being used in fracture stimulation (Section 7). 2. Matrix Polymer
Any rigid thermoset polymer may be used as the matrix polymer. Rigid thermoset polymers are, in general, amorphous polymers where covalent crosslinks provide a three- dimensional network. However, unlike thermoset elastomers (often referred to as "rubbers") which also possess a three-dimensional network of covalent crosslinks, the rigid thermosets are, by definition, "stiff. In other words, they have high elastic moduli at "room temperature" (25 0C), and often up to much higher temperatures, because their combinations of chain segment stiffness and crosslink density result in a high glass transition temperature.
For the purposes of this disclosure, a rigid thermoset polymer is defined as a thermoset polymer whose glass transition temperature, as measured by differential scanning calorimetry at a heating rate of 10 °C/minute, equals or exceeds 45 0C. The gradual softening of an amorphous polymer with increasing temperature accelerates as the temperature approaches the glass transition temperature. As discussed by Bicerano (2002), the rapid decline of the stiffness of an amorphous polymer (as quantified by its elastic moduli) with a further increase in temperature normally begins at roughly 20 0C below its glass transition temperature. Consequently, at 25 0C, an amorphous polymer whose glass transition temperarature equals or exceeds 45 0C will be below the temperature range at which its elastic moduli begin a rapid decline with a further increase in temperature, so that it will be rigid.
Commonly used rigid thermoset polymers include, but are not limited to, crosslinked epoxies, epoxy vinyl esters, polyesters, phenolics, melamine-based resins, polyurethanes, and polyureas. Rigid thermoset polymers that are used less often because of their high cost despite their exceptional performance include, but are not limited to, crosslinked polyimides. For use in proppant particles suitable for different embodiments of the fracture stimulation method of the invention, these various types of polymers can be prepared by starting from their monomers, from oligomers that are often referred to as "prepolymers", or from combinations thereof.
Many additional types of rigid thermoset polymers can also be used. Such polymers include, but are not limited to, various families of crosslinked copolymers prepared most often by the polymerization of vinylic monomers, of vinylidene monomers, or of mixtures thereof. The "vinyl fragment" is commonly defined as the CH2=CH- fragment. So a "vinylic monomer" is a monomer of the general structure CH2=CHR where R can be any one of a vast variety of molecular fragments or atoms (other than hydrogen). When a vinylic monomer CH2=CHR reacts, it is incorporated into the polymer as the -CH2-CHR- repeat unit. Among rigid thermosets built from vinylic monomers, the crosslinked styrenics and crosslinked acrylics are especially familiar to workers in the field. Some other familiar types of vinylic monomers (among others) include the olefins, vinyl alcohols, vinyl esters, and vinyl halides.
The "vinylidene fragment" is commonly defined as the CH2=CR"- fragment. So a "vinylidene monomer" is a monomer of the general structure CH2=CR5R" where R' and R" can each be any one of a vast variety of molecular fragments or atoms (other than hydrogen). When a vinylidene monomer CH2=CR5R" reacts, it is incorporated into a polymer as the - CH2-CR5R"- repeat unit. Among rigid thermosets built from vinylidene polymers, the crosslinked alkyl acrylics [such as crosslinked poly(methyl methacrylate)] are especially familiar to workers in the field. However, vinylidene monomers similar to each type of vinyl monomer (such as the styrenics, acrylates, olefins, vinyl alcohols, vinyl esters and vinyl halides, among others) can be prepared. One example of particular interest in the context of styrenic monomers is alpha-methyl styrene, a vinylidene-type monomer that differs from styrene (a vinyl-type monomer) by having a methyl (-CH3) group serving as the R55 fragment replacing the hydrogen atom attached to the alpha-carbon. Thermosets based on vinylic monomers, vinylidene monomers, or mixtures thereof, are typically prepared by the reaction of a mixture containing one or more non-crosslinking (difunctional) monomer(s) and one or more crosslinking (three or higher functional) monomer(s).
The following are some specific but non-limiting examples of crosslinking monomers that can be used: Divinylbenzene, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimethylolpropane dimethacrylate, trimethylolpropane diacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, pentaerythritol dimethacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, pentaerythritol diacrylate, bisphenol- A diglycidyl methacrylate, ethyleneglycol dimethacrylate, ethyleneglycol diacrylate, diethyleneglycol dimethacrylate, diethyleneglycol diacrylate, triethyleneglycol dimethacrylate, and triethyleneglycol diacrylate, a bis(methacrylamide) having the formula:
CH2=C C N (CH2);; N C C=CH2
CH2=CH-C N I1 (CH2); N I2 C CH=CH2
CH2=CH C O — CH2-CH, — (O — CH2-CH2J; — O CH2-CH2-O ϊ C — CH=CII2
O a molecule or a macromolecule containing at least three isocyanate (-N=C=O) groups, a molecule or a macromolecule containing at least three alcohol (-OH) groups, a molecule or a macromolecule containing at least three reactive amine functionalities where a primary amine (-NH2) contributes two to the total number of reactive functionalities while a secondary amine (-NHR-, where R can be any aliphatic or aromatic organic fragment) contributes one to the total number of reactive functionalities; and a molecule or a macromolecule where the total number of reactive functionalities arising from any combination of isocyanate (- N=C=O), alcohol (-OH), primary amine (-NH2) and secondary amine (-NHR-, where R can be any aliphatic or aromatic organic fragment) adds up to at least three, 1 ,4-divinyloxybutane, divinylsulfone, diallyl phthalate, diallyl acrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate or mixtures thereof.
The following are some specific but non-limiting examples of non-crosslinking monomers that can be used: Styrenic monomers, styrene, methylstyrene, ethylstyrene (ethylvinylbenzene), chlorostyrene, chloromethylstyrene, styrenesulfonic acid, t- butoxystyrene, t-butylstyrene, pentylstyrene, alpha-methylstyrene, alpha-methyl-p- pentylstyrene; acrylic and methacrylic monomers, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, glycidyl acrylate, glycidyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, di ethylene glycol acrylate, diethylene glycol methacrylate, glycerol monoacrylate, glycerol monomethacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, butanediol monoacrylate, butanediol monomethacrylate; unsaturated carboxylic acid monomers, acrylic acid, methacrylic acid; alkyl vinyl ether monomers, methyl vinyl ether, ethyl vinyl ether; vinyl ester monomers, vinyl acetate, vinyl propionate, vinyl butyrate; N-alkyl substituted acrylamides and methacrylamides, N- methylacrylamide, N-methylmethacrylamide, N- ethyl acrylamide, N-ethyl methacrylamide; nitrile monomers, acrylonitrile, methacrylonitrile; olefinic monomers, ethylene (H2C=CH2) and the alpha-olefins (H2C=CHR) where R is any saturated hydrocarbon fragment; vinylic alcohols, vinyl alcohol; vinyl halides, vinyl chloride; vinylidene halides, vinylidene chloride, or mixtures thereof. 3. Nanofiller
Without reducing the generality of the invention, to facilitate the teaching of the invention, we note that nanoscale carbon black, fumed silica, fumed alumina, carbon nanotubes, carbon nanofibers, cellulosic nanofibers, natural and synthetic nanoclays, very finely divided grades of fly ash, the polyhedral oligomeric silsesquioxanes; and clusters of different types of metals, metal alloys, and metal oxides, are some examples of nanofillers that can be incorporated into the nanocomposite particles used as proppants in implementing the fracture stimulation method of the invention. Since the development of nanofillers is an area that is at the frontiers of materials research and development, the future emergence of yet additional types of nanofillers that are not currently known may also be readily anticipated. 4. Impact Modifier
The impact modifier enables the use of larger quantities of crosslinker, nanofiller, or combinations thereof, in the formulation from which the particles are prepared; to achieve higher maximum use temperatures, higher fracture conductivities throughout the use temperature range, or combinations thereof, without inducing brittleness in the particles. Any mixture of two or more different types of impact modifiers may also be used as the impact modifier. The impact modifier is present in an amount ranging from 0.1 to 65 weight percent in the mixture of the impact modifier, plus the monomer, oligomer, or combinations thereof that react to form the matrix polymer. It comprises at least one of a monomer, an oligomer or a polymer; obtained or derived from a petrochemical feedstock, a renewable feedstock, or a combination thereof. Some examples will now be provided without reducing the generality of the invention.
The impact modifier may comprise at least one of a monomer, oligomer or polymer selected from the group consisting of polybutadiene (including its solid and liquid forms, and any of its variants comprising different cis-1 ,4, trans- 1,4, and vinyl- 1 ,2 isomer contents), natural rubber, synthetic polyisoprene, polychloroprene, nitrile rubbers, other diene rubbers, partially or completely hydrogenated versions of any of the diene rubbers, acrylic rubbers, olefinic rubbers, epichlorohydrin rubbers, fluorocarbon rubbers, fluorosilicon rubbers, block and/or graft copolymers prepared from formulations comprising styrenic monomers and diene monomers, partially or completely hydrogenated versions of block and/or graft copolymers prepared from formulations comprising styrenic monomers and diene monomers, silicone rubbers, rubbers containing aliphatic or partially aromatic polyether chain segments, rubbers containing aliphatic or partially aromatic polyester chain segments, rubbers containing aliphatic or partially aromatic polyurethane chain segments, rubbers containing aliphatic or partially aromatic polyurea chain segments, rubbers containing aliphatic or partially aromatic polyamide chain segments, ionomer resins which may be partially or wholly be neutralized with counterions; other rubbery homopolymers, copolymers containing random, block, graft, star, or core-shell morphologies, and mixtures thereof; and the monomeric or oligomeric precursors of any of the cited types of rubbery polymers.
Some illustrative examples will now be provided without reducing the generality of the invention. The impact modifier may be polybutadiene. It may be polybutadiene plus a styrene-butadiene diblock copolymer. It may contain an aliphatic polyester component synthesized by using monomers obtained from soybean oil in addition to containing a polybutadiene component. It may consist entirely of an aliphatic polyester that has been synthesized by using monomers obtained from petrochemical feedstocks or from soybean oil. With any of these examples, and the many other embodiments that can be readily imagined by workers skilled in the art, the impact modifier may be added into the formulation as an oligomer, as a polymer, or as a monomer which will react with the other components of the reactive mixture during the manufacture of the particles. It may also be added as any suitable combination of monomers, oligomers and/or polymers. 5. Suspension Polymerization Any method for the fabrication of thermoset polymer nanocomposite particles known to those skilled in the art may be used to prepare the particles which are utilized as proppants in implementing the fracture stimulation method of the invention.
Without reducing the generality of the invention, it is especially practical to use methods that can produce the particles directly in the desired (usually substantially spherical) shape during polymerization from the starting monomers. A substantially spherical particle is defined as a particle having a roundness of at least 0.7 and a sphericity of at least 0.7, as measured by the use of a Krumbien/Sloss chart using the experimental procedure recommended in International Standard ISO 13503-2, "Petroleum and natural gas industries - Completion fluids and materials - Part 2: Measurement of properties of proppants used in hydraulic fracturing and gravel-packing operations" (first edition, 2006), Section 7, for the purposes of this disclosure.
Without reducing the generality of the invention, suspension (droplet) polymerization, where the polymer precursor mixture is dispersed in a suitable liquid medium prior to being polymerized, is currently the most powerful manufacturing method available for accomplishing this objective. In pursuing this approach, it is especially important for the nanofiller particles to be well-dispersed within the liquid medium so that they can become intimately incorporated into the thermoset nanocomposite particles that will be formed upon polymerization. 6. Heat Treatment
Processes that may be used to enhance the degree of curing of a thermoset polymer include, but are not limited to, heat treatment (which may be combined with stirring, flow and/or sonication to enhance its effectiveness), electron beam irradiation, and ultraviolet irradiation. Without reducing the generality of the invention, we focused mainly on the use of heat treatment as a post-polymerization process step during the manufacturing of the particles. Such heat treatment can be performed in many types of media; including a vacuum, a non-oxidizing gas, a mixture of non-oxidizing gases, a liquid, or a mixture of liquids. It is possible, in some instances, to postcure the "as polymerized" particles adequately as a result of the elevated temperature of a downhole environment of a hydrocarbon reservoir during the application of the fracture stimulation method of the invention. However, since it does not allow nearly the same level of consistency and control of particle quality, this "in situ" approach to heat treatment is generally less preferred than the application of heat treatment as a manufacturing process step before using the particles in fracture stimulation. 7. Fracture Stimulation
The optimum mode of particle placement is determined by the details of the specific fracture that needs to be propped. In practice, the use of ultralightweight particles as proppant particles in implementing the fracture stimulation method of the invention provides its greatest advantages in situations where a proppant partial monolayer is the optimum mode of placement. Furthermore, the development of the fracture stimulation method of the invention has resulted in partial monolayers becoming the optimum proppant placement method in many situations where the use of partial monolayers was either impossible or impractical with previous technologies. In any case, the method for fracture stimulation comprises (a) forming a slurry comprising a fluid and a proppant, (b) injecting this slurry into the wellbore at sufficiently high rates and pressures such that the formation fails and fractures to accept the slurry, and (c) thus emplacing the proppant in the formation so that it can prop open the fracture network (thereby allowing produced gases, fluids, or mixtures thereof, to flow towards the wellbore). The most commonly used measure of proppant performance is the conductivity of liquids and/or gases (depending on the type of hydrocarbon reservoir) through packings of the particles. A minimum liquid conductivity of 100 mDft is often considered as a practical threshold for considering a packing to be useful in propping a fracture that possesses a given closure stress at a given temperature. In order for a fracture stimulation method to have significant practical utility, a static conductivity of at least 100 mDft must be retained for at least 200 hours at a temperature greater than 80 0F. It is a common practice in the industry to use the simulated environment of a hydrocarbon reservoir in evaluating the conductivities of packings of particles. The API RP 61 method, described by a publication of the American Petroleum Institute titled "Recommended Practices for Evaluating Short Term Proppant Pack Conductivity" (first edition, October 1, 1989), is currently the commonly accepted testing standard for conductivity testing in the simulated environment of a hydrocarbon reservoir. As of the date of this filing, however, work is underway to develop alternative testing standards, such as International Standard ISO 13503-5, "Petroleum and natural gas industries - Completion fluids and materials - Part 5: Procedures for measuring the long-term conductivity of proppants" (final draft, 2006).
The fracture stimulation method of the invention is preferably implemented by placing the ultralightweight thermoset polymer nanocomposite particles in the fracture as a partial monolayer. We have found, under standard laboratory test conditions, that the use of particles of narrow size distribution such as 14/16 U.S. mesh size ((diameters in the range of 1.19 to 1.41 millimeters) is more effective than the use of broad particle size distributions.
We have also found, under standard laboratory test conditions, that 0.02 lb/ft2 is an especially preferred level of coverage of the fracture area with a partial monolayer of thermoset nanocomposite particles of sufficient stiffness and strength that possess an absolute density of 1.054. However, real-life downhole conditions in an oilfield may differ significantly from those used under laboratory test conditions. Consequently, in the practical application of the fracture stimulation method of the invention, the use of other particle size distributions, other coverage levels, or combinations thereof, may be more appropriate, depending on the conditions prevailing in the specific downhole environment where the fracture stimulation method of the invention will be applied. The thermoset polymer matrix consists of a terpolymer of styrene (S), ethyvinylbenzene (EVB) and divinylbenzene (DVB). The current preference for the use of such terpolymers instead of copolymers of S and DVB is a result of economic considerations related to monomer costs. DVB, which functions as a crosslinker, is present in an amount ranging from 3% to 35% by weight of the reactive monomer mixture of the preferred embodiments.
An impact modifier that has one or more reactive functionalities capable of causing the impact modifier to become grafted onto the thermoset polymer matrix is preferred. The impact modifier is incorporated in an amount ranging from 3 to 35 percent by weight in the mixture of the impact modifier, plus the S, EVB and DVB monomers that react to form the matrix polymer. A polymer additive grade of polybutadiene, sold as a solid, is dissolved in the organic phase of the suspension used in the suspension polymerization process, and becomes grafted onto the thermoset polymer matrix as a rubbery phase when polymerization forms the S-EVB-DVB terpolymer matrix. A block copolymer may also be used in some embodiments, usually mainly serving as a compatibilizer between the styrenic matrix and the polybutadiene-rich rubbery domains but sometimes also providing additional impact modification of its own. Suspension polymerization in its "rapid rate polymerization" mode is performed to prepare the particles. The most important additional formulation ingredient (besides the reactive monomers and the impact modifier) that is used during polymerization is the initiator. The initiator may consist of one type molecule or a mixture of two or more types of molecules that have the ability to function as initiators. We have found with experience that the "dual initiator" approach, involving the use of two initiators which begin to manifest significant activity at different temperatures, often provides the best results.
Post-polymerization heat treatment in an unreactive gas environment is performed as a manufacturing process step to further advance the curing of the thermoset polymer matrix. This approach works especially well (without adverse effects such as degradation that could occur if an oxidative gaseous environment such as air were used and/or swelling that could occur if a liquid environment were used) in enhancing the curing of the particles. The particles undergo a total exposure to temperatures in the range of 150 0C to 200 0C for a duration of 10 minutes to 90 minutes, inclusive, in an unreactive gas environment. The specific selection of an optimum temperature and duration of heat treatment within these ranges depends on the formulation from which the particles were prepared. Nitrogen is used as the unreactive gas environment.
Some theoretical examples of preferred embodiments of the fracture stimulation method of the invention will now be given, without reducing the generality of the invention, to provide a better understanding of some of the ways in which the invention may be practiced. Workers skilled in the art can readily imagine many other embodiments of the invention with the benefit of this disclosure. Some comparative examples will also be given of embodiments that do not meet a key requirement of the invention and hence are not expected to perform adequately. Example 1
The thermoset polymer matrix of the nanocomposite particles used in this example consists of a terpolymer of styrene (S), ethyvinylbenzene (EVB) and divinylbenzene (DVB). The quantities of these three monomers in the reactive monomer mixture are 68.73% S, 1 1.27% EVB and 20% DVB by weight. However, the complete polymer also contains 10% of an "impact modifier" grade of polybutadiene by weight in the mixture of the total amount of impact modifier and styrenic monomers. Relative to this total amount, the quantities of the main ingredients of the polymer are 61.86% S, 10.14% EVB, 18% DVB and 10% polybutadiene. In addition, the particle contains 1% by volume of carbon black as a nanofiller. The particles are prepared by rapid rate suspension polymerization. They are then postcured in a nitrogen environment for 20 minutes at a temperature of 185 0C. Example 2
The same types of particles are used as in Example 1. However, detailed consideration of the downhole environment shows that an the use of the full available 14/40 U.S. mesh size range of the particles will be optimal. Particles in this size range are placed into the fracture by using slickwater as the carrier fluid. Example 3
It is also determined that, since this particular hydrocarbon reservoir is deeper than the one considered in Example 1 , the proppant pack will need to be able to withstand both a significantly higher closure stress and a significantly higher temperature than in Example 1. These factors result in the need to use thermoset polymer nanocomposite particles prepared from a formulation containing both a larger amount of crosslinker and a larger amount of nanofiller. The use of a larger total amount of impact modifier, including a compatibilizer, overcomes the increased tendency towards embrittlement resulting from the use of larger quantities of crosslinker and nanofiller. The post-polymerization heat treatment is also
L I applied in a more vigorous manner in order to approach full cure with the formulation used in these particles.
More specifically, the quantities of the three monomers in the reactive monomer mixture are 53.09% S, 16.91% EVB and 30% DVB by weight. However, the complete polymer also contains 10% of an "impact modifier" grade of polybutadiene plus 3% of a styrene-butadiene diblock copolymer by weight in the mixture of the total amount of impact modifier and the styrenic monomers. The total of the two components of the impact modifier thus amounts to 13% of the total amount of impact modifier and styrenic monomers. Relative to this total amount, the quantities of the main ingredients of the polymer are 46.19% S, 14.71 % EVB, 26.10% DVB, 10% polybutadiene, and 3% styrene-butadiene diblock copolymer. In addition, the particle contains 1.5% by volume of carbon black as a nanofiller. The particles are prepared by rapid rate suspension polymerization. They are then postcured in a nitrogen environment for 30 minutes at a temperature of 195 0C. Comparative Example 1 As in Example 1 , except that an impact modifier is not included. The particles are stiff and strong, but brittle. Their brittleness causes them to be inadequate for use in a proppant pack in the implementation of the fracture stimulation method of the invention. Comparative Example 2
1. A method for fracture stimulation of a subterranean formation having a wellbore, comprising: providing a thermoset polymer nanocomposite particle precursor composition comprising a polymer precursor mixture, dispersed within a liquid medium, containing at least one of an initiator; at least one of a monomer, an oligomer or combinations thereof, said monomer and oligomer having three or more reactive functionalities capable of creating crosslinks between polymer chains; at least one of an impact modifier, said impact modifier comprising from 0.1 to 65 weight percent of the impact modifier, plus the monomer, oligomer, or combinations thereof; and from 0.001 to 60 volume percent of nanofiller particles possessing a length that is less than 0.5 microns in at least one principal axis direction; said nanofiller particles comprising at least one of dispersed fine particulate material, fibrous material, discoidal material, or a combination of such materials, wherein said nanofiller particles are substantially dispersed within the liquid medium; subjecting the nanocomposite particle precursor composition to suspension polymerizing conditions to form the polymeric nanocomposite particle, whereby said nanofiller particles are substantially incorporated into a polymer; subjecting the resulting nanocomposite particles to heat treatment as a post- polymerizing process; forming a slurry comprising a fluid and a proppant, wherein said proppant comprises the heat-treated nanocomposite particles, said heat-treated nanocomposite particles being formed from a rigid thermoset polymer matrix; injecting into the wellbore said slurry at sufficiently high rates and pressures such that said formation fails and fractures to accept said slurry; and emplacing said proppant within a fracture network in said formation in a packed mass or a partial monolayer of particles, which packed mass or partial monolayer props open the fracture network; thereby allowing produced gases, fluids, or mixtures thereof, to flow towards the wellbore.
CH3 R1 R2 CH3 CH2=C-C N (CH2)- N C-C=CH2
CH2=CH C — O — CH2-CH2 — (O — CH2-CH2), — O — CHj-Ql2-O — f C — CH=CH2 O a molecule or a macromolecule containing at least three isocyanate (-N=C=O) groups, a molecule or a macromolecule containing at least three alcohol (-OH) groups, a molecule or a macromolecule containing at least three reactive amine functionalities where a primary amine (-NH2) contributes two to the total number of reactive functionalities while a secondary amine (-NHR-, where R can be any aliphatic or aromatic organic fragment) contributes one to the total number of reactive functionalities; and a molecule or a macromolecule where the total number of reactive functionalities arising from any combination of isocyanate (- N=C=O), alcohol (-OH), primary amine (-NH2) and secondary amine (-NHR-, where R can be any aliphatic or aromatic organic fragment) adds up to at least three, 1 ,4-divinyloxybutane, divinylsulfone, diallyl phthalate, diallyl acrylamide, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate or mixtures thereof.
4. The method of claim 1, wherein said polymer precursor mixture comprises a non- crosslinking monomer selected from the group consisting of: Styrenic monomers, styrene, methylstyrene, ethylstyrene (ethyl vinylbenzene), chlorostyrene, chloromethyl styrene, styrenesulfonic acid, t-butoxystyrene, t-butylstyrene, pentylstyrene, alpha-methylstyrene, alpha-methyl-p-pentylstyrene; acrylic and methacrylic monomers, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, lauryl acrylate, lauryl methacrylate, glycidyl acrylate, glycidyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, diethylene glycol acrylate, diethylene glycol methacrylate, glycerol monoacrylate, glycerol monomethacrylate, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, butanediol monoacrylate, butanediol monomethacrylate; unsaturated carboxylic acid monomers, acrylic acid, methacrylic acid; alkyl vinyl ether monomers, methyl vinyl ether, ethyl vinyl ether; vinyl ester monomers, vinyl acetate, vinyl propionate, vinyl butyrate; N-alkyl substituted acrylamides and methacrylamides, N-methylacrylamide, N-methylmethacrylamide, N- ethyl acrylamide, N- ethyl methacrylamide; nitrile monomers, acrylonitrile, methacrylonitrile; olefinic monomers, ethylene (H2C=CH2) and the alpha-olefins (H2C=CHR) where R is any saturated hydrocarbon fragment; vinylic alcohols, vinyl alcohol; vinyl halides, vinyl chloride; vinylidene halides, vinylidene chloride, or mixtures thereof.
5. The method of claim 1, wherein said thermoset polymer matrix comprises a styrene- divinylbenzene copolymer or a styrene-ethylvinylbenzene-divinylbenzene terpolymer.
7. The method of claim 1 , wherein said nanofiller is selected from the group of nanofillers consisting of carbon black, fumed silica, fumed alumina, carbon nanotubes, carbon nanofibers, cellulosic nanofibers, natural clays, synthetic clays, fly ash, polyhedral oligomeric silsesquioxanes, metal clusters, metal alloy clusters, metal oxide clusters, or mixtures thereof.
8. The method of claim 1, wherein said nanofiller comprises carbon black, possessing a length that is less than 0.5 microns in at least one principal axis direction and an amount from 0.1 % to 15% of said particle by volume.
11. The method of claim 1 , wherein said impact modifier comprises at least one of a monomer, an oligomer or a polymer having one or more reactive functionalities; obtained or derived from a petrochemical feedstock, a renewable feedstock, or a combination thereof.
12. The method of claim 1, wherein said impact modifier comprises at least one of a monomer, oligomer or polymer, having one or more reactive functionalities; selected from the group consisting of: Polybutadiene (including its solid and liquid forms, and any of its variants comprising different cis-1,4, trans- 1,4, and vinyl- 1,2 isomer contents), natural rubber, synthetic polyisoprene, polychloroprene, nitrile rubbers, other diene rubbers, partially or completely hydrogenated versions of any of the diene rubbers, acrylic rubbers, olefinic rubbers, epichlorohydrin rubbers, fluorocarbon rubbers, fluorosilicon rubbers, block and/or graft copolymers prepared from formulations comprising styrenic monomers and diene monomers, partially or completely hydrogenated versions of block and/or graft copolymers prepared from formulations comprising styrenic monomers and diene monomers, silicone rubbers, rubbers containing aliphatic or partially aromatic polyether chain segments, rubbers containing aliphatic or partially aromatic polyester chain segments, rubbers containing aliphatic or partially aromatic polyurethane chain segments, rubbers containing aliphatic or partially aromatic polyurea chain segments, rubbers containing aliphatic or partially aromatic polyamide chain segments, ionomer resins which may be partially or wholly be neutralized with counterions; other rubbery homopolymers, copolymers containing random, block, graft, star, or core-shell morphologies, and mixtures thereof; and the monomeric or oligomeric precursors of any of the cited types of rubbery polymers.
14. The method of claim 1, wherein said polymer precursor mixture further comprises additional formulation ingredients selected from the group of ingredients consisting of:
Initiators, catalysts, inhibitors, dispersants, stabilizers, rheology modifiers, buffers, antioxidants, defoamers, plasticizers, pigments, flame retardants, smoke retardants, or mixtures thereof.
16. The method of claim 1 , wherein said heat treatment is performed in a medium including a vacuum, a non-oxidizing gas, a mixture of non-oxidizing gases, a liquid, or a mixture of liquids; or in a downhole environment of a hydrocarbon reservoir.
17. The method of claim 1, wherein said particle is a bead having an average roundness of at least 0.7 and an average sphericity of at least 0.7 as measured by the use of a
Krumbien/Sloss chart.
18. The method of claim 1 , wherein said particle has an average diameter that ranges from 0.1 mm to 4 mm.
19. The method of claim 1, wherein said packed mass or said partial monolayer exhibits a static conductivity of at least 100 mDft after 200 hours at a temperature greater than 80 0F.
PCT/US2008/004428 2004-12-30 2008-04-03 A method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified thermoset polymer nanocomposite particles as proppants WO2008124080A1 (en)
US11/695,745 2007-04-03
WO2008124080A1 true true WO2008124080A1 (en) 2008-10-16
PCT/US2008/004428 WO2008124080A1 (en) 2004-12-30 2008-04-03 A method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified thermoset polymer nanocomposite particles as proppants
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