Abstract:
This invention relates to compositions and methods A method of treating a subterranean formation including forming a fluid comprising zein, and introducing the fluid to a subterranean formation. A method of treating a subterranean formation comprising a wellbore, including introducing a tubular to the wellbore wherein the tubular comprises zein.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to methods and fluids used in treating a subterranean formation. In particular, the invention relates to the preparation and use of fluid delivery systems comprising a biodegradable material. 
         [0003]    2. Description of the Related Art 
         [0004]    The demand for degradable materials specifically for oilfield applications has become increasingly important over the years as cost, formation conditions, and environmental regulations often limit the use of common polymeric materials. 
         [0005]    There is a broad range of degradable polymers that may be used in the oil field services industry such as polysaccharides (e.g. starch, guar, chitosan, hydroxypropyl guar, hydroxymethyl guar, xanthan, hydroxyethyl cellulose) and proteins (e.g. collagen, fibrin, and gelatin). Synthetic degradable polymers derived from polyesters, polyanhydride and polyamide have also been developed to target specific applications. Starch is currently used in oilfield applications such as fracturing, drilling and diversion. In fracturing application starch is mainly used as a fluid loss additive. Starch is also used as a viscosifier and as a fluid loss additive in drilling fluids. In these applications the starch is not fully solubilized and is deposited onto the fracture surface or formation wall as part of the filtercake. Considerable effort is placed in the cleanup of filter cakes e.g. prior to gravel packing to ensure minimum impairment to flow of formation fluids. The mode of degrading the polymers is through hydrolysis, oxidation or exposure to heat. Some biopolymers may be degraded through the use of enzymes however, it has temperature limitations. In any event, a low cost, reliable, readily available material is desirable for use in the oil field services industry. 
       SUMMARY 
       [0006]    Embodiments of this invention relate to compositions and methods of treating a subterranean formation including forming a fluid comprising zein, and introducing the fluid to a subterranean formation. Embodiments of this invention relate to compositions and methods of treating a subterranean formation comprising a wellbore, including introducing a tubular to the wellbore wherein the tubular comprises zein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a plot of viscosity as a function of shear rate of an embodiment of the invention. 
           [0008]      FIG. 2  is a schematic view of a tubular comprising an embodiment of the invention. 
           [0009]      FIG. 3  is a schematic view of a tubular comprising an additional embodiment of the invention. 
           [0010]      FIG. 4  is a schematic view of a tubular comprising an additional embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The description and examples are presented solely for the purpose of illustrating the preferred embodiments of the invention and should not be construed as a limitation to the scope and applicability of the invention. While the compositions of the present invention are described herein as comprising certain materials, it should be understood that the composition could optionally comprise two or more chemically different materials. In addition, the composition can also comprise some components other than the ones already cited. 
         [0012]    In the summary of the invention and this description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors have disclosed and enabled the entire range and all points within the range. 
         [0013]    Generally, zein may be selected for a variety of oil field services applications. Furthermore, the material properties can be adjusted to target a wide range of specific oilfield applications. The degradability of the material can be controlled by using different chemistries. The applications that can be targeted ranges from swelling packers, degradable completion hardware, degradable canister, screenless completions, degradable bridge or temporary plugs, degradable piping, degradable fluid loss additive, surface modification of proppants, coatings on breakers, coated additives, coating as barriers to oil or water, coating for controlled release of materials with controlled delivery, reactive coating on proppants that become sticky, diversion, lost circulation, conformance, water control, drilling, cementing, gravel packing, wormhole, etc. Shapes and sizes of zein particles or particles coated with zein may be selected to control fluid loss and diversion. 
         [0014]    Some embodiments may benefit from using zein to coat the proppant to change its wettability profile. Likewise, some embodiments may benefit from using zein to change the wettability profile of the subterranean formation. 
         [0015]    Zein is 45-50 percent of the protein present in corn. It is a group of alcohol soluble proteins (prolamins) found in corn endosperm. Centrifugal separation of starch from the endosperm leaves protein rich mass (corn gluten) from which zein is extracted. It is rich in glutamic acid, leucine, alanine and proline that gives it high hydrophobicity. Zein is an alcohol soluble protein and exhibits hydrophobic properties and low water uptake. Zein has alpha, beta, and gamma protein fractions. Alpha accounts from 75-85 percent of the total protein and is dominated by Z19 and Z22 protein corresponding to 19 kDa and 22 kDa molecular weight. Zein is commercially available from Sigma-Aldrich of Houston, Tex., Showa Sangyo Co Ltd of Japan and Freeman Industries of Tuckahoe, N.Y. 
         [0016]    Zein can form tough greaseproof coatings, with flexibility and compressibility. Zein is commercially utilized due to its film formation capability in the food and pharmaceutical industries. The thin films of zein are formed that may be edible or may be utilized in biodegradable packaging. 
         [0017]    Zein films on its own are generally brittle but when the films are plasticized they are flexible. Addition of different plasticizers and cross linkers will give films of different mechanical and barrier properties that could be utilized accordingly for specific applications. Plasticization and crosslinking affects its mechanical and barrier properties. Polyethylene glycol and glycerol are effective plasticizer for zein dispersion. Zein dissolves in ethyl alcohol/water 90/10 w/w mixture. Stability of the aqueous zein dispersion is dependent on pH and electrolyte content. The dispersion is stable at pH of 3-4. Glass transition temperature of pure zein powder is 170.8 C. Zein dissolves in ethanol and is hydrophobic. Water resistance of zein can be achieved by modifying the hydrophilic side groups such NH 2 , OH, COOH, and SH by hydrophobic groups. 
         [0018]    Common plasticizers for zein include glycerol, glyceryl monoesters, PEG and fatty acids. Zein is also plasticized by water although it is not soluble in water. Additional plasticizers include glycols such as triethylene glycol, propylene glycol, ethylene glycol, polyethylene glycol, and polypropylene glycol; sulfonamides such as benzene sulfonamide, N-ethyl benzene sulfonamide, p-toluene sulfonamide, and N-ethyl p-toluene sulfonamide; fatty acids such as oleic acid, palmitic acid, myristic acid, and stearic acid; amides such as acetamide, acetanilide, and urea; amides such as triethanolamine and diethanolamine; glyceryl esters such as glyceryl monooleate, glyceryl monopalmitate, and glyceryl monostearate; glycol esters such as glycol monooleate, glycol monopalmitate, and glycol monostearate; esters such as dibutyl tartrate, monobutyl phthalate, monomethyl azelate, and monomethyl sebacate; ethylene glycol monophenyl ether, tricresyl phosphate, tall oil, glycerol, sorbitol, diphenylamine, dibutyl phthalate, dibutyl sebacate, and triphenyl phosphate. 
         [0019]    Zein on its own has a glass transition temperature of 139° C. and its glass transition temperature decreases rapidly with moisture content. Zein may be utilized in the oilfield applications as a tunable glass transition temperature material e.g. in forming a plug of zein that is later removed due to absorption of water and lowering of glass transition temperature. 
         [0020]    Biodegradable fibers of zein on its own or its blend with other polymers such as chitosan may also be used as additives in drilling fluid, fracturing fluids or cement. These fibres could be used to generate diversion during fracturing operations, in the form of plugs, in the form of near wellbore screenouts, or in the form of far field diversion pills. The fibers could be also used as proppant suspension additives or as lost circulation material. Fibers of zein could also be used as strengthening fillers for materials requiring improved compressive, tensile or shear properties, such as cement, plugs, darts for applications such as treat and produce completions, etc. 
         [0021]    Zein could be used to generate thermoplastic parts and pieces, such as plugs for low temperature applications where the material is to be insoluble in water and oil, but might be solubilized and thus removed by injection of alcohol blends of specific composition. 
         [0022]    Zein can be also used in order to prepare melt composites with polyester materials, to alter the mechanical properties and the dissolution and degradation rate of said polyesters to acid, base and alcohol initiated hydrolysis alcoholysis. Zein would be used to alter the Tg and Tm (glass transition temperature, melting temperature) of the blend resulting typically in plasticized polymers, or polymers which would more easily swell, resulting in materials with enhanced degradation rates. This would be used for low temperature fiber applications. 
         [0023]    Zein may be adsorbed preferentially on hydrophobic or hydrophilic surfaces. Such surface modification with zein may be used on proppant coating or targeting specific sites in the subterranean formation. Zein may be used as binding agent e.g. in proppant and preventing proppant flowback. 
         [0024]    Zein may be used for some parts of conventional completions that will eventually degrade. Zein articles are degradable with temperature, time, and solvents. Zein articles may be made of different size and shape including fibers, particulates, tubulars, rods, and containers. In some embodiments, the material may be used for casing, cementing, or general completions operations. In some embodiments, perforating steps may benefit from using materials comprising zein. 
         [0025]    Zein may be used as a viscosifier. Zein may be x-linked to give unique material properties for oilfield applications. Crosslinkers such as borates, zirconium, or other crosslinkers often used in fracturing fluids may also be desirable for fluids comprising zein. Some zein compositions may benefit from further comprising other polymers such as guar or modified guar. Some compositions comprising zein may be used to form energized fluids and/or foams. 
         [0026]    In some embodiments, the material may be especially desirable as a coating to protect from brine-based degradation. In some embodiments, small particles and/or chemicals may be encapsulated with the material for process steps that include the presence of brine. 
         [0027]    Generally, zein may be used to encapsulate acids or oils for controlled release. Biodegradable nanospherical particles may be formed using zein to encapsulate solids such as breakers and liquids such as acids and alkalis. Zein may be used as an oxygen barrier e.g. in sensors since zein has excellent resistance to oxygen permeation. Zein may be used to protect encapsulated material from oxidation due to its pronounced oxygen barrier property. Zein may be used individually or blended with other resins such as rosin or neutral resins for coating proppants. The coated proppant may aid proppant transport during fracturing. Zein may be used to coat tubulars to prevent corrosion. Zein coating on tubulars to give improved cement bonding. 
         [0028]    Zein and fatty acid resin may be used for preparing semi solid resin plugs in oilfield applications. Zein may also be used as a barrier to oil and grease e.g. temporary plugs made from zein are dissolved using specific solvent such as methanol, ethylene glycol, DEG, ethyl ether, furfuryl alcohol, ethyl alcohol/water 90/10 w/w, acetic acid, lactic acid, citric acid, phenol+alcohol+water, ionic liquids (e.g. 1-butyl-3-methylimidazolium chloride), benzene, toluene, xylene and acetone. Examples of solvents include acetamide, acetic acid, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1-propanol, 2-amino-2-methyl-1,3-propanediol, o-aminophenol, m-aminophenol, aniline, benzyl alcohol, benzyl cellosolve, butylamine, butyl tartrate, 1,3-butylene glycol, o-cyclohexylphenol, 1,3-diaminopropanol, di[-β-hydroxyethyl]janiline, diethanolamine, diethylene glycol, diethylene glycol monoethyl ether (carbitol), diethylene glycol monomethyl ether (methyl carbitol), diethylenetriamine, diglycol chlorohydrins, diisopropanolamine, diphenylquanidine, a-diphenylthiourea, dipropylene glycol, ethyl ether tripropylene glycol, ethyl lactate, ethylphenylethanolamine, ethylene chlorohydrins, ethylene glycol, ethylene glycol monoethyl ether (cellosolve), ethylene glycol monomethyl ether (methyl cellosolve), ethylenediamine, formic acid, furfuryl alcohol, glycerol, glycerol furfural, glyceryl-α-γ-dichlorohydrin, glyceryl-α-γ-dimethyl ether, glyceryl-α-monochlorohydrin, glyceryl-α-methyl ether, glyceryl-α-phenyl ether, β-hydroxyethylaniline, hydroxyethylethylenediamine, 2-hydroxymethyl-1.3-dioxolane, lactic acid, methyl alcohol, methyl lactate, monoethanolamine, monoisopropanolamine, morpholine, morpholine ethanol, phenol, phenyl cellosolve, phenyldiethanolamine, phenylethanolamine, propionic acid, propylene chlorohydrins, propylenediamine, propylene glycol, pyridine, resorcinol monoacetate, triethanolamine, triethylenetetramine, tetrahydrofurfuryl alcohol, triethylene glycol, triisopropanolamine, and trimethylaminomethane. Additional solvents include water with acetone, acetonyl acetone, n-butanol, t-butanol, s-butanol, dioxalane, dioxane, ethanol, isobutanol, isopropanol, methanol, or n-propanol. More examples of solvents include a lower aliphatic alcohol with acetaldehyde, acetone, benzene, butyl lactate, chloroform, dichloromethane, diethylene glycol monoethyl ether, ethyl lactate, ethylene, dichloride, ethylene glycol, ethylene glycol monoethyl ether, furfural, methyl ethyl ketone, methylene chloride, nitroethane, nitromethane, propylene glycol, 1,1,2,2-tetrachloroethane, 1,2,3-trichloroethane, or toluene. 
         [0029]    The use of ionic liquids may therefore be considered for not only the cleanup of filtercakes containing starch but also filtercakes containing zein or other biopolymers. 1-ethyl-3-methylimidazolium ethylsulfate (EMIMEtOSO3) ionic liquid may also be used to dissolve polymers such as guar, starch and zein. The ionic liquid may also be used as a pre flush and post flush fluid in gravel pack operations. Additional examples of ionic liquids include 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium methanesulfonate, 1-ethyl-2,3-di-methylimidazolium ethylsulfate, methylimidazolium chloride, methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazolium hydrogensulfate, 1-ethyl-3-methylimidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium tetrachloroaluminate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium thiocyanate, choline acetate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. 
         [0030]    Finally, zein may be used to suppress scaling especially with calcium or magnesium in either high or low temperature wells. 
       EXAMPLES 
       [0031]    The following examples are presented to illustrate the preparation and properties of fluid systems, and should not be construed to limit the scope of the invention, unless otherwise expressly indicated in the appended claims. All percentages, concentrations, ratios, parts, etc. are by weight unless otherwise noted or apparent from the context of their use. 
         [0032]    The following Examples, unless described differently, used a commodity grade sample of zein that is commercially available from Sigma Aldrich with a standard moisture content. 
       Example 1 
       [0033]    This example uses ionic liquid such as 1-butyl-3-methylimidazolium chloride (BMIM Cl) for filtercake cleanup containing biopolymers such as starch and zein. 
         [0034]    Biopolymers such as starch and zein are soluble in ionic liquids up to 10% w/w concentration at 80° C. 1-Butyl-3-methylimidazolium chloride (BMIM Cl) ionic liquid is effective in solubilizing such biopolymers. Photographs show that 5% w/w of zein and starch that are insoluble in water and are soluble in 20% BMIMCl/80% water mixture at 80 C. 
       Example 2 
       [0035]    Zein may be used to form solid plugs e.g. degradable plugs or it may be used as zonal isolation plugs. Photographs show that zein is progressively more soluble as the concentration of zein increases at 1, 5, and 10 percent zein. This shows that plugs made from zein and utilized downhole may be dissolved using ethylene glycol. 
       Example 3 
       [0036]    Zein may be used as a viscosifier for fluids used in subterranean formation.  FIG. 1  is a plot of viscosity as a function of shear rate of an embodiment of the invention.  FIG. 1  shows the effect of zein concentration on viscosity, as zein concentration increases, viscosity increases. Ethylene glycol was used as a base fluid to solubilize zein. 
       Example 4 
       [0037]    Using different ratio mixtures of methanol and water zein plugs were formed having different properties. Photographs show that a swollen and compressible plug was formed using 10% methanol and 90% water. In contrast a mixture with 50% methanol and 50% water formed a competent plug. 20, 30, and 40 percent methanol mixtures formed plugs with progressively more compact properties. 
       Example 5 
       [0038]    Photographs show that zein particles are insoluble in ethylene glycol at 25 C however at 60 C they are completely soluble. This property indicates that diversion and cleanup applications may benefit from using this composition. 
       Example 6 
       [0039]    A composite casing or tubular may be considered.  FIG. 2  illustrates an embodiment of a tubular. Such tubular will allow logging through casing of formation fluids. The composite tubulars/casings have the distinct advantage over the metallic tubular/casings since their non conductive properties makes them electrically transparent. In additions such tubulars are also transparent to NMR logging and/or resistivity measurements. In some embodiments, the material may be degradable, also. In some embodiments, the casing or tubular may comprise a canister. 
       Example 7 
       [0040]      FIG. 3  is a schematic view of a tubular comprising an additional embodiment of the invention. A metallic tubular that includes degradable material in a specific formatted array such that the degradable material disappears with time and creates perforations in the tubular. This concept may be used also to form a screen for sand control purposes. The shape and size of the degradable material may be varied. 
       Example 8 
       [0041]      FIG. 4  is a schematic view of a tubular comprising an additional embodiment of the invention. Varying the striations may be desirable for perforating process steps. Some embodiments of the invention may benefit from a non conductive, electrically transparent tubular. 
       ADVANTAGES 
       [0042]    The use of ionic liquids for the cleanup of biopolymers in the oil industry has immense economic implications on well services business including stimulation, fracturing, diversion, cementing and gravel packing. 
         [0043]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.