Compositions – Leather or fur treating
Patent
1985-08-09
1986-10-28
Guynn, Herbert B.
Compositions
Leather or fur treating
166308, 2523153, E21B 4326
Patent
active
046197761
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to viscous aqueous fluids, such as hydraulic fracturing fluids for oil and gas wells, containing a galactomannan polymer crosslinked with boron.
BACKGROUND OF THE INVENTION
It is well known that organic polyhydroxy compounds having hydroxyl groups positioned in the cis-form on adjacent carbon atoms or on carbon atoms in a 1,3-relationship react with borates to form five or six member ring complexes. At alkaline pH above about 8.0 these complexes form didiol crosslinked complexes, i.e., ##STR1##
This leads to a valuable reaction with dissociated borate ions in the presence of polymers having the required hydroxyl groups in a cis-relationship. The reaction is fully reversible with changes in pH. An aqueous solution of the polymer will gel in the presence of borate when the solution is made alkaline, and will liquify again when the pH is lowered below about 8. If the dry powdered polymer is added to an alkaline borate solution, it will not hydrate and thicken until the pH is dropped below about 8. The critical pH at which gelation occurs is modified by the concentration of dissolved salts. The effect of the dissolved salts is to change the pH at which a sufficient quantity of dissociated borate ions exists in solution to cause gelation. The addition of an alkali metal base such as sodium hydroxide enhances the effect of condensed borates such as borax by converting the borax to the dissociated metaborate.
Known polymers which contain an appreciable content of cis-hydroxyl groups are exemplified by guar gum, locust bean gum, dextrin, polyvinyl alcohol, and derivatives of these polymers. Derivatives tend to react less with borate ions as the amount of substituting groups in the molecule increases. This results because the shear bulk of substituting groups changes the regular, alternating, and single-member branched, linear configuration of the molecule and prevents adjacent chains from approaching as closely as before, and the substitution of secondary cis-hydroxyl positions decreases the number of such unsubstituted positions available for complexing with the borate ion.
Strong reactions of such polymers are also obtained with solutions of certain inorganic cations. The addition of a high concentration of calcium salt, for example, will cause a polymer gel to form under alkaline conditions. If dry powdered polymer is added to the salt solution, the polymer will not generally hydrate and thicken. In general, the polymer will react with polyvalent cations much as it does with borate anions.
Depending on the relative concentration of polymer, and borate anion or polyvalent cation, the crosslinking reaction may produce useful gels, or may lead to insolubilization, precipitation, or unstable, non-useful gels. The viscosity of the hydrated polymer solution increases with an increase in the concentration of borate anion until a maximum is obtained. Thereafter the viscosity decreases and the gel becomes unstable as evidenced by a lumpy, inhomogeneous appearance and syneresis. As the temperature of the solution increases, the concentration of borate required to maintain the maximum degree of crosslinking, and thus maximum viscosity increases. Derivatization with non-ionic hydroxyalkyl groups greatly improves the compatibility of the polymer with most salts.
Hydraulic fracturing is a widely used method for stimulating petroleum producing subterranean formations and is commonly performed by contacting the formation with a viscous fracturing fluid having particulated solids, widely known as propping agents, suspended therein, applying sufficient pressure to the fracturing fluid to open a fracture in the subterranean formation, and maintaining this pressure while injecting the fracturing fluid into the fracture at a sufficient rate to extend the fracture into the formation. When the pressure is reduced, the propping agent within the fracture prevents the complete closure of the fracture.
The properties that a fracturing fluid should possess, are amongst others, low leakoff r
REFERENCES:
patent: 2779735 (1957-01-01), Brown et al.
patent: 3058909 (1962-10-01), Kern
patent: 3215634 (1965-11-01), Walker
patent: 3562176 (1971-02-01), Stancioff et al.
patent: 3974077 (1976-10-01), Free
patent: 4250044 (1981-02-01), Hinkel
patent: 4369124 (1983-01-01), Elphingstone et al.
Chatterji et al., "Applications of Water Soluble Polymers in the Oil Field", J. Pet. Tech., Nov., 1981, pp. 2042-2056.
Conway et al., "Chemical Model for the Rheological Behavior of Cross Linked Fluid Systems", Soc. Pet. Eng. Paper No. 9334, Sep. 21-24, 1980.
Guynn Herbert B.
House Roy F.
Texas United Chemical Corp.
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