Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1998-12-28
2001-07-10
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S141000, C507S145000, C536S020000, C536S055300
Reexamination Certificate
active
06258755
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to viscosified fluids, particularly fluids used in the drilling and/or servicing of oil and/or gas wells, and particularly drilling fluids, drill-in fluids, workover fluids, completion fluids, perforating fluids, fracturing fluids, acidizing fluids, spotting fluids, filter cake removal fluids, various pills, and the like. The invention provides chitosan viscosified fluids and methods of enhancing the thermal stability of such fluids.
BACKGROUND OF THE INVENTION
It is known to produce viscoelastic fluids for use in oil well drilling and servicing, especially for the so called “drill-in” fluids used in horizontal drilling within a hydrocarbon-bearing formation. See for example the following references: “Drill-In Fluids Improve High Angle Well Production,” p. 5-11, Supplemental to the Petroleum Engineer International, March, 1995; and “Soluble Bridging Particle Drilling System Generates Successful Completions In Unconsolidated Sand Reservoirs,” Jay Dobson and Delton Kayga, presented at the 5th International Conference On Horizontal Well Technology, Amsterdam, The Netherlands, Jul. 14-16, 1993.
Such 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-glucosamine, 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 generally 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. Among the aldehyde reactants are 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. These chitosan derivatives are disclosed to offer a wide range of solubility, gelling and compatibility properties.
It is also known to incorporate certain water soluble chitin derivatives into clay-containing aqueous drilling muds for controlling the viscosity, gel strength, and fluid loss of the drilling mud. See Jones U.S. Pat. No. 2,670,329.
It is well known that polysaccharides are degraded by heat as the temperature of the fluid containing them is increased. The thermal degradation of the polysaccharides decreases the viscosity of the fluid, most especially the low shear rate viscosity which provides the fluid with its desirable characteristics as many other water soluble polymers and other materials can provide the high shear rate viscosity required. Thus there is a need for enhancing the thermal stability of polysaccharide-containing aqueous fluids.
SUMMARY OF THE INVENTION
We have now determined that viscous fluids suitable for use as well drilling and servicing fluids can be prepared by solublizing chitosan in aqueous acidic solutions and thereafter raising the pH of the solution to an alkaline pH whereby fluids having an enhanced low shear rate viscosity (hereinafter sometimes referred to as ELSRV) and which are extremely shear thinning are obtained.
We have further determined that the thermal stability of alkaline aqueous fluids viscosified with chitosan is enhanced by incorporating into the fluids certain aldose or ketose sugars and/or oligosaccharides of such sugars as set forth hereinafter, optionally together with a water soluble bisulfite compound.
The preferred oligosaccharide is lactose, dextrose or a mixture comprised primarily of pentosans and hexosans containing from two to ten combined sugar units selected from the group consisting of arabinose, mannose, galactose, glucose, and xylose sugar units, and mixtures thereof, the mixture most preferably comprising the water soluble portion of thermally hydrolyzed lignocellulose.
It is an object of this invention to provide a process for enhancing the thermal stability of aqueous chitosan-containing fluids as evidenced by the viscosity of the fluids, and the fluids prepared thereof.
It is another object of this invention to provide a process for preparing a well drilling and servicing fluid which comprises forming an acidic chitosan solution and thereafter adding a basic compound to raise the pH to above about 7.0, wherein the concentration of chitosan is sufficient to provide the fluid with a low shear rate viscosity of at least 1,000 centipoise and a shear thinning index greater than about 10, preferbaly a low shear rate viscosity at least about 5,000 centipoise, most preferably at least about 10,000 centipoise.
It is also an object of the invention to provide a rotary process for drilling a well wherein there is circulated in the wellbore during drilling an alkaline aqueous drilling fluid having a low shear rate viscosity of at least 1,000 centipoise and a shear thinning index greater than about 10 comprising forming an acidic chitosan solution, thereafter adding a basic compound to raise the pH to above about 7.0, and circulating the resulting fluid in the wellbore during drilling.
Still another object of the invention is to provide chitosan-containing well drilling and servicing fluids as disclosed herein.
These and other objects of the invention will be apparent to one skilled in the art upon reading the specification and claims hereof.
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
Cowan Jack C.
House Roy F.
House Roy F.
Tucker Philip
Venture Innovations, Inc.
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