Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
2001-02-13
2001-09-18
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C536S020000
Reexamination Certificate
active
06291404
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 liquids 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 Theological 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-acetanido-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 deacetylation of between 50 and 100 percent. Chitosan is the beta-(1-4)-polysaccharide of D-glucamine, and is structurally similar to cellulose, except that the C-2 hydroxyl group in celullose 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 polysaccbaride 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 amino 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. 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 Geiling 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.
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 liquids useful where viscous or gelled liquids are needed such as 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, an amine reactive acid, and an aldehyde modifier. The chitosan, amine reactive acid, and aldehyde react to increase the viscosity of the liquid. Optionally, the fluids can contain other chitosan modifiers, such as organic anhydrides and epoxy compounds 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, an amine reactive acid, and an aldehyde modifier.
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 amine reactive acid, and an aldehyde modifier therefore.
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 acid, an amine reactive acid, and an aldehyde modifier, 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 alternative forms, specific embodiments thereof will hereinafter be described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.
The compositions can comprise, consist essentially of, or consist of the stated materials. The method can comprise, consist essentially of, or consist of the stated steps with the stated materials.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The invention particularly provides oil and gas well drilling and servicing fluids containing chitosan which is modified in-situ with one or more amine reactive acids and one or more aldehydes. The fluids are useful in various operations such as drilling, fracturing, sand control, lost circulation control, completion, workover, and the like. The preferred fluids are alkaline aqueous pseudoplastic fluids having a Brookfield 0.5 rpm viscosity (hereinafter sometimes referred to as “low shear rate viscosity” or “LSRV”) of at least 5,000 centipoise and a shear thining index (hereinafter sometimes referred to as “STI”) greater than about 10. The STI is the ratio of the Brookfield viscosity at 0.5 rpm to the Brookfield viscosity at 100 rpm and is an indication of the shear thinning,
House Roy F.
Tucker Philip
Venture Innovations, Inc.
LandOfFree
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