Preferably, a concentration of an organic acid anions or any combination of organic acid ions is sufficiently low so as not to interfere with the YES building viscosity as the strong acid spends. Most preferably, the treatment fluid does not include weak organic acids. 

[0174] Preferably, the aluminum mono-carboxylates, alu› minum di-carboxylates, and aluminum tri-carboxylates of the weak carboxylic acid are water soluble at a pH in the range of 6-7. It is believed this will help protect against any aluminum precipitation. 

[ 017 5] It should be understood, however, that in an embodi› ment the treatment fluid need not and does not include hydrof› luoric acid, which is not normally required for acidizing of carbonate formations. Preferably, the treatment fluid contains less than 5% by weight HF. More preferably, it does not contain any HF. 

[0176] The weak acid as a pH-adjuster is preferably present in the treatment fluids suitable for use in the present invention in a concentration sufficient to help keep the pH of the fluid below 4. In some embodiments, the pH-adjuster may be present in a concentration sufficient to maintain or adjust the pH of the fluid below a pH in the range of from about 1 to about 4. In other embodiments, the pH-adjuster may be present in a concentration sufficient to help maintain or adjust the pH of the fluid to a pH in the range of from about 1 to about 4, and preferably in the range of from about 2 to about 3. Preferably, the weak acid has a pKa(l) sufficiently low and is in a sufficient concentration in the water such that the water would have a pH less than 3 without the presence of any strong acid. 

[0177] A pH-adjuster may be included in the treatment fluid for, among other things, adjust the pH of the treatment fluid to, or help maintain the pH of the treatment fluid near, a pH that balances the duration of certain properties of the treatment fluid ( e.g. the ability to suspend particulate) with the ability of the breaker to reduce the viscosity of the treat› ment fluid or a pH that will result in a decrease in the viscosity of the treatment fluid such that it does not hinder production of hydrocarbons from the formation. 

[0178] In certain embodiments, the pH-adjuster comprises a salt of an organic acid such as sodium or potassium formate, sodium or potassium acetate, sodium or potassium citrate, sodium or potassium glycolate, sodium or potassium maleate, sodium or potassium phosphate, potassium dihydrogen phos› phate, cesium formate, and any combinations thereof. In other embodiments, the pH-adjuster may be any other sub› stance known in the art capable of maintaining the pH of the breaker above or below a desired limited range. One of ordi› nary skill in the art, with the benefit of this disclosure, will recognize the appropriate pH-adjuster and concentration thereof to use for a chosen application. 

[0179] Viscosifying Surfactants (i.e. Viscoelastic Surfac› tants) 

[0180] It should be understood that merely increasing the viscosity of a fluid may only slow the settling or separation of distinct phases and does not necessarily stabilize the suspen› sion of any particles in the fluid. 

[0181] Certain viscosity-increasing agents also increase the elastic modulus of the fluid. The elastic modulus is the measure of a substance’s tendency to be deformed non-per› manently when a force is applied to it. The elastic modulus of a fluid, commonly referred to as G’, is a mathematical expres› sion and defined as the slope of a stress versus strain curve in the elastic deformation region. G’ is expressed in units of 

pressure, for example, Pa (Pascals) or dynes/cm 2 . As a point of reference, the elastic modulus of water is negligible and considered to be zero. 

[0182] An example of a viscosity-increasing agent that is also capable of increasing the suspending capacity of a fluid is to use a viscoelastic surfactant. As used herein, the term "viscoelastic surfactant" refers to a surfactant that imparts or is capable of imparting viscoelastic behavior to a fluid due, at least in part, to the three-dimensional association of surfac› tant molecules to form viscosifying micelles. When the con› centration of the viscoelastic surfactant in a viscoelastic fluid significantly exceeds a critical concentration, and in most cases in the presence of an electrolyte, surfactant molecules aggregate into species such as micelles, which can interact to form a network exhibiting elastic behavior. 

[0183] As used herein, the term "YES fluid" ( or "surfactant gel") refers to a fluid that exhibits or is capable of exhibiting viscoelastic behavior due, at least in part, to the association of a YES contained therein that forms viscosifying micelles, for example, under conditions of appropriate concentration of the YES and the salinity of the fluid. 

[0184] Viscoelastic surfactants may be characterized as cationic, anionic, or amphoteric in nature according to the charge on the polar head functional group. 

[0185] Cationic surfactants contain cationic functional groups at their head, such as the permanently charged quater› nary ammonium cation or pH-dependent primary, secondary, or tertiary amines. In general, primary amines become posi› tively charged at pH less than 10, secondary amines become charged at pH less than 4. 

[0186] Anionic surfactants contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates. 

[0187] Amphoteric (zwitterionic) surfactants have both cationic and anionic centers attached to the same molecule. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. The anionic part can be more variable and include sulfonates. 

[0188] The viscoelastic surfactants can include any number of different compounds, including ester sulfonates, hydro› lyzed keratin, sulfosuccinates, taurates, amine oxides, ethoxylated amides, alkoxylated fatty acids, alkoxylated alcohols (e.g., lauryl alcohol ethoxylate, ethoxylated nonyl phenol), ethoxylated fatty amines, ethoxylated alkyl amines ( e.g., cocoalkylamine ethoxylate ), betaines, modified betaines, alkylamidobetaines (e.g., cocoamidopropyl betaine ), quaternary ammonium compounds ( e.g., trimethyl› tallowammonium chloride, trimethylcocoammonium chlo› ride), derivatives thereof, and combinations thereof. 

[0189] Anionic Component 

[0190] The anionic component is believed to help the rheo› logical properties of the fluid for use in acidizing a zone of a well. The anionic component has at least 4 carbon atoms. Without necessarily being limited by any theory, it is believed that the anionic organic portion having at least 4 carbon atoms can interact with the cationic YES to improve the rheological properties of the treatment fluid in a way that organic mol› ecules with few carbons cannot. Preferably, the anionic com› ponent has between 4 and 20 carbon atoms. The anionic component is preferably alkyl. The anionic component can be straight chain or branched. The anionic component should be water soluble. 

[0191] Preferably, the anionic component in acid form has a pKa(l) less than about 6.5, and more preferably less than 6. 

