Sep. 11, 2014  10  US 2014/0256604 Al  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. 