Composition and Method for Reducing the Surface Tension of Aqueous Fluids

For various reasons it is often desired to lower the surface tension of aqueous liquids. For example, by lowering the surface tension of aqueous liquids, solid matter can be more easily wet by the liquid. This property is useful, for example, when treating subterranean formations with various aqueous liquids to stimulate the flow of petroleum and/or aqueous fluids therefrom. Thus, it is desirable to, for example, employ acidizing, hydraulic fracturing, and other aqueous treatment liquids having low surface tensions.

Low surface tension values in combination with the water wetting properties of an aqueous liquid reduce the capillary forces in the formation being treated. Reduction of the capillary forces in a reservoir results in a more effective recovery of fluids after the formation has been treated. The present invention concerns the discovery of a composition which, when added to an aqueous liquid, effectively reduces the surface tension thereof and also increases the water wetting properties of the liquid.

Various quaternized perfluoroalkane-sulfona-midopolymethylenealkylamine compounds are known to reduce the surface tension of neutral, acidic and basic aqueous solutions even when present in minute amounts (see U.S. Pat. No. 2,759,019). However, these compounds were found to become ineffective when the aqueous solution in which they were employed came into contact with earthen formations. Thus, the use of such compounds in liquids employed to treat, for example, subterranean formations is limited. The present invention concerns the discovery of how to effectively make use of the surface active properties of such compounds in these types of liquids.

The invention comprises an aqueous composition, a method of reducing the surface tension of aqueous liquids and a method for treating subterranean formations to stimulate the flow of fluids therethrough.

The composition comprises an aqueous liquid containing an effective amount of a compound of the formula ##STR2## wherein A.sup.- is a halide and also another surfactant comprising an adduct of trimethyl-1-heptanol plus seven moles of ethylene oxide.

The other surfactant and the perfluorinated compound are combined in a weight ratio (other surfactant: perfluorinated compound) ranging from about 1:1 to about 40:1.

The aqueous liquids comprise acidic, neutral and alkaline solutions and can be gelled, contain noninterfering functional additives such as, corrosion inhibitors freeze point depressants, weighing agents, proppants, alcohols, and the like.

The combination of the perfluorinated compound and the other surfactant are employed in a combined amount ranging from about 0.005 to about 0.1 percent by weight of an aqueous liquid. The exact amount will depend on the particular aqueous liquid they are dispersed in. For example, in concentrated acid solutions, e.g., HCl, HF and the like, the combination of materials are employed in an amount ranging from about 0.05 to about 0.1 percent by weight of the aqueous acid solution. In brines, the combination of compounds is employed in an amount ranging from about 0.005 to about 0.05 percent by weight of the brine.

The aqueous liquids containing the combination of surfactants can be employed in many uses wherein low surface tension properties are desired, e.g., matrix acidizing, water-base fracturing, fracture-acidizing and emulsified acids employed in acidizing fracturing techniques. Such liquids are particularly useful for treating subterranean formations to perfect or make more efficient the recovery of fluids, e.g., petroleum fluids (oil and gas), water, other gases etc., therefrom.

In one particular utility, the efficiency of an acidizing solution is greatly increased by incorporating therein the mixture of the perfluorinated compound and the second surfactant. For example, in acidizing with HCl solutions, the surface tension of the resulting solution can be drastically reduced by employing therein from about 0.05 to about 0.1 percent by weight of the combination of surfactants previously identified. The acidizing solution is then used in standard acidizing procedures, i.e., it can be used in standard matrix acidizing process, in acidizing-fracturing processes, and the like. It has been found that such acidizing solutions penetrate the formation more easily, thereby effecting a greater stimulation of the production of fluids. Also, such solutions are more easily removed from the formation following the acidizing treatment. Moreover, the particular adduct employed herein does not significantly detrimentally affect the initial surface tension reducing properties of the perfluorinated compound, as do many other surfactants when employed in combination with the perfluorinated compounds.

It has been also discovered that the aqueous solution is quite effective for acidizing gas producing formations. The use of aqueous liquids to treat gas producing formations has produced particular difficulties because aqueous liquids tend to block the intricacies of the formation to the flow of gases. Thus, in many instances, such solutions have hindered instead of stimulated the flow of gas from the formation. When fracturing a gas producing formation, it has been the practice to employ nonaqueous fracturing fluids such as oils, CO.sub.2 -methanol mixtures and the like. However, because aqueous liquids can be considerably less expensive and also are generally more available than other such fluids, it is desired to use aqueous liquids if possible. The present discovery now permits such use.

The individual surfactants can be blended directly into an aqueous treatment liquid or they can be premixed and easily blended into a treatment liquid employing standard equipment employed in fracturing and acidizing treatments. The premix may also contain water, mono and/or polyhydric alcohols, and other functional additives.

One such preblend comprises a blend containing as parts by weight, 2916 parts H.sub.2 O; 3185 parts isopropyl alcohol; 1535 parts of a 60 percent by weight aqueous solution of an adduct of trimethyl-1-heptanol plus seven moles of ethylene oxide and 134 parts of the above identified perfluorinated compound wherein A.sup.- is iodide.

The above defined blend is employed in an amount ranging from about 2 to about 4 gallons per 1000 gallons of an acid, e.g. hydrochloric acid (3 to 28 percent strength), hydrochloric-hydrofluoric acid mixtures, aqueous fracturing fluids and other aqueous fluids to lower the surface tension thereof. Higher concentrations are recommended for matrix acidizing treatments while lower concentrations can be employed in fracturing treatments.

As indicated the aqueous liquids in which the combination of surfactants can be successfully employed can contain other functional additives such as thickening and gelling agents, weighing agents, corrosion inhibitors and the like. The compatibility of the combination of surfactants with other functional additives should be ascertained prior to preparing large quantities of such aqueous liquids.

A preblend was prepared containing as parts by weight: 2916 parts H.sub.2 O; 3185 parts isopropyl alcohol; 1535 parts of an adduct of tri-methyl-1-heptanol plus seven moles of ethylene oxide; and 40 parts of the iodide salt of the previously defined perfluorinated compound. Aqueous mixtures were prepared containing 2 gallons of the preblend with 1000 gallons of various liquids. The surface tension of the mixtures was determined employing a Dunouy Tensiometer. The liquids employed, their original surface tensions and the resulting surface tension are set forth in the following Table.