Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-02-13
2002-03-19
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S209000, C507S211000
Reexamination Certificate
active
06358889
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the in-situ modification of chitosan to produce viscosifiers (thickeners, gellants) for aqueous liquids, and to viscosified aqueous well drilling and servicing fluids containing such modified chitosans dispersed therein, and to methods of drilling a well utilizing such fluids.
BACKGROUND OF THE INVENTION
Many viscosifiers for, and methods of, increasing the viscosity of aqueous liquids are known. Such viscosifiers may be so-called water-soluble polymers such as biopolymers, gums, cellulose derivatives, alginates, and other polysaccharides or polysaccharide derivatives, and various synthetic polymers. Representative polymers are set forth in the book “Handbook of Water Soluble Gums and Resins,” Robert L. Davidson, Ed., 1980.
Noticeably absent from this book is any mention of chitosan or derivatives thereof.
Viscoelastic fluids are characterized as having a rheological profile which is shear thinning, having a high viscosity at extremely low shear rates and a low viscosity at high shear rates. Thus such fluids are pseudoplastic having a high yield stress.
This type of rheology is produced by hydrating in the fluid certain water soluble polymers. These polymers presently known are biopolymers, i.e., microbially produced polysaccharides or heteropolysaccharides, and are well known in the art.
There is a need for fluids which exhibit a high low shear rate viscosity which are shear thinning.
Chitosan is a partially or fully deacetylated form of chitin, a naturally occurring polysaccharide. Structurally, chitin is a polysaccharide consisting of beta-(1→4)2-acetamido-2-deoxy-D-glucose units, some of which are deacetylated. The degree of deacetylation usually varies between 8 and 15 percent, but depends on the species from which the chitin is obtained, and the method used for isolation and purification.
Chitin is not one polymer with a fixed stoichiometry, but a class of polymers of N-acetylglucosamine with different crystal structures and degrees of deacetylation, and with fairly large variability from species to species. The polysaccharide obtained by more extensive deacetylation of chitin is chitosan.
Like chitin, chitosan is a generic term for a group of polymers of acetylglucosamine, but with a degree of deactylation of between 50 and 100 percent. Chitosan is the beta-(1-4)-polysaccharide of D-glucosanine, and is structurally similar to cellulose, except that the C-2 hydroxyl group in cellulose is substituted with a primary amine group in chitosan. The large number of free amine groups (pKa=6.3) makes chitosan a polymeric weak base. Both chitin and chitosan are insoluble in water, dilute aqueous bases, and most organic solvents. However, unlike chitin, chitosan is soluble in dilute aqueous acids, usually carboxylic acids, as the chitosonium salt. Solubility in dilute aqueous acid is therefore a simple way to distinguish chitin from chitosan.
Chitosan is unique in that it is a polysaccharide containing primary amine groups. Chitosan forms water-soluble salts with many organic and inorganic acids.
It is known to prepare chitosan derivatives by attaching various groups to one or more hydroxyl groups of the chitosan, as in various cellulose derivatives, and/or in attaching various groups to the primary amino group of chitosan. Thus it is disclosed in Hall and Yalpani U.S. Pat. No. 4,424,346 that chitosan can be reacted with various aldehydes by Schiff base formation with the primary amino group. The reaction is conducted in the presence of a reducing agent, specifically sodium cyanoborohydride, to reduce the imino group formed to a secondary amino group, i.e., the chitosan undergoes reductive alkylation. The aldehyde reactants include aldose or ketose sugars, or sugars oxidizable or hydrolyzable to aldoses or ketoses, for example, glucose, galactose, arabinose, xylose, N-acetylglucosamine, lactose, cellobiose, maltose, and melibiose, and aromatic aldehydes containing at least one hydroxyl or carboxyl group. Example 5 specifically discloses the reductive alkylation of chitosan with lactose at weight ratios of lactose/chitosan of 2.4 (Product A), 3.0 (Product B, Product C), and 6.0 (Product D), to form products having the group—NHR′ therein, where R′ is an aldose or ketose residue. When the reaction was carried out in the absence of the sodium cyanoborohydride reducing agent at a weight ratio of lactose/chitosan of 8.0, the resulting product was minimally reacted with a degree of substitution of only 0.1. The reactions were carried out at room temperature. A paper which discusses the preparation and characteristics of the chitosan derivatives set forth in the Hall et al. U.S. Pat. No. 4,424,346 is “Some Chemical and Analytical Aspects of Polysaccharide Modifications. 3. Formation of Branched-Chain, Soluble Chitosan Derivatives,” M. Yalpani and L. D. Hall, MACROMOLECULES 1984, 17, 272-281. These chitosan derivatives are disclosed to offer a wide range of solubility, gelling and compatibility properties.
A paper entitled “Chitosan Derivatives Bearing C
10
-Alkyl Glycoside Branches: A Temperature-Induced Gelling Polysaccharide,” K. R. Holme and L. D. Hall, Macromolecules 1991, 24, 3828-3833, discloses chitosan derivatives having mixed hydrophobic/hydrophilic branches.
U.S. Pat. No. 3,879,376, incorporated herein by reference, discloses chitosan derivatives formed by acylation of chitosan with a saturated or unsaturated organic diacid anhydride and their use as a skin-moisturizing agent in cosmetic compositions.
The following papers disclose the reaction of chitosan with various anhydrides, each incorporated herein by reference: (1) “Formation and Characterization of a Physical Chitin Gel,” L. Vachoud et al., Carbohydrate Research 302 (1977), 169-177; (2) “Chitosan Film Acylation and Effects on Biodegradability,” Jin Xu et al., Macromolecules 1996, 29, 3436-3440; (3) “N-Acetylchitosan Gel: A Polyhydrate of Chitin,” Shigehero Hirans et al., Biopolymers 15 (1976), 1685-1691.
There is disclosed in co-pending U.S. patent application Ser. No. 09/222,293 filed Dec. 28, 1998, well drilling fluids containing chitosan and aldose or ketose sugars, and/or oligosaccharides of such sugars.
SUMMARY OF THE INVENTION
We have now determined that aqueous alkaline fluids useful in oil and gas well operations, such as drilling, fracturing, sand control, lost circulation control, completion, workover and the like can be formulated to contain chitosan and an anhydride modifier. The chitosan and anhydride react to increase the viscosity of the fluid. Optionally, the fluids can contain an aldehyde modifier to increase the viscosity or enhance the stability of the fluids.
Thus, it is an object of the invention to provide aqueous alkaline well drilling and servicing fluids containing chitosan and an anhydride modifier.
It is another object of the invention to provide aqueous well drilling and servicing fluids containing chitosan, an anhydride modifier, and a modifier selected from the group consisting of an aldehyde, pyruvic acid, and mixtures thereof.
Another object of the invention is to provide a method of drilling a well comprising circulating in a wellbore during drilling an aqueous alkaline fluid containing chitosan and an anhydride modifier therefore.
Still another object of the invention is to provide a method of drilling a well comprising circulating in a wellbore during drilling an aqueous alkaline fluid containing chitosan, an anhydride modifier, and a modifier selected from the group consisting of an aldehyde, pyruvic acid, and mixtures thereof
Yet another object of the invention is to provide aqueous alkaline fluids useful in oil and gas well operations comprising an aqueous liquid having incorporated therein chitosan, an anhydride modifier, optionally an aldehyde modifier, optionally pyruvic acid, and an alkalizing additive.
These and other objects of this invention will be apparent to one skilled in the art upon reading this specification and the appended claims.
While the invention is susceptible of various modifications and al
House Roy F.
Pitre Kimely P.
Waggenspack John H.
House Roy F.
Tucker Philip
Venture Innovations, Inc.
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