Sep. 11, 2014  1  US 2014/0256604 Al  CATIONIC VISCOELASTIC SURFACTANT  WITH NON-CATIONIC CORROSION  INHIBITOR AND ORGANIC ANION FOR  ACIDIZING  TECHNICAL FIELD  BACKGROUND  Oil & Gas Wells  Well Servicing and Well Fluids  Acidizing  Acidizing Sandstone or Carbonate Formations  Hydraulic Fracturing  [0001]  The inventions are in the field of producing crude oil  or natural gas from subterranean formations. More specifi› cally, the inventions relate to increasing the viscosity of a well  fluid for acidizing a subterranean formation, for example,  matrix or fracture acidizing of carbonate formations, leak-off  control in acid fracturing, and diversion in matrix acidizing.  [0002]  To produce oil or gas from a reservoir, a well is  drilled into a subterranean formation, which may be the res› ervoir or adjacent to the reservoir. Typically, a well bore of a  well must be drilled hundreds or thousands of feet into the  earth to reach a hydrocarbon-bearing formation.  [0003]  It is desirable to extend the production of wells and  to avoid early abandonment when productivity decreases as a  result of low natural permeability or formation damage.  [0004]  Well services can include various types of treat› ments that are commonly performed in a wellbore or subter› ranean formation. For example, stimulation is a type of treat› ment performed to enhance or restore the productivity of oil  or gas from a well. Even small improvements in fluid flow can  yield dramatic production results.  [0005]  Stimulation treatments fall into two main groups:  hydraulic fracturing and matrix treatments. Fracturing treat› ments are performed above the fracture pressure of the sub› terranean formation to create or extend a highly permeable  flow path between the formation and the well bore. Fracturing  treatments are often applied in treatment zones having poor  natural permeability. Matrix treatments are performed below  the fracture pressure of the formation. Matrix treatments are  often applied in treatment zones having good natural perme› ability to counteract damage in the near-wellbore area.  [0006]  The purpose of a hydraulic fracturing treatment is to  provide an improved flow path for oil or gas to flow from the  hydrocarbon-bearing formation to the well bore. In addition, a  fracturing treatment can facilitate the flow of injected treat› ment fluids from the well into the formation. A treatment fluid  adapted for this purpose is sometimes referred to as a fractur› ing fluid. The fracturing fluid is pumped at a sufficiently high  flow rate and pressure into the wellbore and into the subter› ranean formation to create or enhance one or more fractures in  the subterranean formation. Creating a fracture means mak› ing a new fracture in the formation. Enhancing a fracture  means enlarging a pre-existing fracture in the formation.  [0007]  A newly-created or newly-extended fracture will  tend to close together after the pumping of the fracturing fluid  is stopped. To prevent the fracture from closing, a material is  usually placed in the fracture to keep the fracture propped  open and to provide higher fluid conductivity than the matrix  of the formation. A material used for this purpose is referred  to as a proppant.  [0008]  A proppant is in the form of a solid particulate,  which can be suspended in the fracturing fluid, carried down› hole, and deposited in the fracture to form a proppant pack.  The proppant pack props the fracture in an open condition  while allowing fluid flow through the permeability of the  pack. The proppant pack in the fracture provides a higher› permeability flow path for the oil or gas to reach the well bore  compared to the permeability of the matrix of the surrounding  subterranean formation. This higher-permeability flow path  increases oil and gas production from the subterranean for› mation.  [0009]  A particulate for use as a proppant is usually  selected based on the characteristics of size range, crush  strength, and solid stability in the types of fluids that are  encountered or used in wells. Usually, but not in all applica› tions, a proppant should not melt, dissolve, or otherwise  degrade from the solid state under the downhole conditions.  [001 OJ  The purpose of acidizing is to dissolve acid-soluble  materials. A treatment fluid including an aqueous acid solu› tion is introduced into a subterranean formation to dissolve  the acid-soluble materials. In this way, oil or gas can more  easily flow from the formation into the well. In addition, an  acid treatment can facilitate the flow of injected treatment  fluids from the well into the formation.  [0011]  Acidizing techniques can be carried out as acid frac› turing procedures or matrix acidizing procedures.  [0012]  In acid fracturing, an acidizing fluid is pumped into  a formation at a sufficient pressure to cause fracturing of the  formation and to create differential (non-uniform) etching  leading to higher fracture conductivity. Depending on the  formation mineralogy, the acidizing fluid can etch the frac› tures faces, whereby flow channels are formed when the  fractures close. The acidizing fluid can also enlarge the pore  spaces in the fracture faces and in the formation.  [0013]  In matrix acidizing, an acidizing fluid is injected  from the well into the formation at a rate and pressure below  the pressure sufficient to create a fracture in the formation.  [0014]  Acidizing is commonly performed in sandstone and  carbonate formations, however, the different types of forma› tions can require that the particular treatments fluids and  associated methods be quite different.  [0015]  For example, sandstone formations tend to be rela› tively uniform in composition and matrix permeability. In  sandstone, a range of stimulation techniques can be applied  with a high degree of confidence to create conductive flow  paths, primarily with hydraulic fracturing techniques, as  known in the field.  [0016]  In sandstone  formations,  acidizing  primarily  removes or dissolves acid soluble damage in the near-well› bore region. Thus, in sandstone formations acidizing is clas› sically considered a damage removal technique and not a  stimulation technique. An exception is with the use of spe› cialized hydrofluoric acid compositions, which can dissolve  the siliceous material of sandstone.  [0017]  Carbonate formations tend to have complex poros› ity and permeability variations with irregular fluid flow paths.  Although many of the treatment methods for sandstone for-