The present invention is directed to dry, stable, storable compositions which are capable of readily dispersing in water and causing the resultant aqueous system to exhibit a high degree of pseudoplastic properties. Such compositions are useful for on-site formation of improved water-based drilling fluids as well as imparting pseudoplasticity to other water-based systems.
Various compositions have been used to impart viscosity to the aqueous system. These materials include organic materials as, for example, xanthan gums such as described in U.S. Pat. Nos. 3,198,268; 3,208,526; 3,251,147; 3,243,000; 3,307,016 and 3,319,715. Although such materials can be formed into a dry product suitable for shipment, readily disperse in water to produce an aqueous system having good pseudoplastic properties at varying low shear rates, these materials have the distinct drawback of being expensive to produce and being unstable when subjected to elevated temperatures.
Aluminum containing compositions have been used to form aqueous gels or cements. For example, U.S. Pat. No. 1,871,781 discloses that when the aluminum salt of the organic acid, acetic acid, is combined with hydrated lime they form a cement composition having good waterproofing properties. U.S. Pat. No. 3,395,221 is directed to the formation of hydrous aluminum oxide gels by separately introducing an aluminum cloride or sulfate, and an alkali metal hydroxide, such as sodium hydroxide, into an aqueous solution. U.S. Pat. No. 3,815,681 discusses aqueous solutions containing an aluminum salt with a time delay pH increasing reactant such as ammonium carbamates, carbamic acid, or halide salts of cyanic acid. Such systems eventually form rigid, immobile gels capable of plugging voids in subterranean earth formations. U.S. Pat. No. 3,860,070 discloses aqueous compositions containing a water soluble amphoteric metal salt and a small quantity of a water soluble base in a ratio such that the aqueous composition has an acidic pH of about 2 to 3. This patent teaches that at such a ratio and resultant pH composition exhibits a high degree of desired properties.
Each of the above aqueous systems are unsuitable for the presently intended purpose of providing a dry, stable composition which is readily dispersible in water and causes the water to exhibit pseudoplastic properties over a wide range of varying low shear rates.
Compositions which are suitable for the intended purpose must be stable under storage conditions and must be readily dispersible in aqueous medium. The ability to readily disperse and form a pseudoplastic system is critical in the area of oil well drilling fluids. Field conditions do not permit the utilization of elaborate equipment nor the luxury of long periods of time to form the desired aqueous fluid. The American Petroleum Institute Specification 13A is directed to a testing procedure to determine suitable materials for forming drilling fluids. Such a test has equivalent meaning in the case of formation of other aqueous systems.
The term "pseudoplastic" as used in the subject application and claims refers to aqueous systems which exhibit non-Newtonian properties, that is to say that the viscosity of the aqueous system varies inversely with respect to the shear rate imposed on the fluid. The relationship of the shear stress with respect to shear rate can be defined by the rheological power law model relationship of EQU .tau.=K(.gamma.).sup.n
in which .tau. represents the shear stress exerted on the aqueous system of the drilling fluid in units such as pounds per 100 ft.sup.2 or dynes/cm.sup.2 ; .gamma. is the shear rate in units of reciprocal time such as sec.sup.-1 ; K is a constant having the value of the shear stress of the particular system at a shear rate of 1 sec.sup.-1 ; and n is a numerical value of from 0 to 1 or more. Fluids which exhibit a high degree of non-Newtonian, pseudoplastic properties can be defined by the above power law model relationship wherein n has a numerical value of less than about 0.4. Compositions capable of imparting such properties to fluid systems, especially aqueous systems, are highly desired. Such aqueous systems when utilized as water-based drilling fluids cause substantial increase in the efficiency of a drilling operation.