Viscoelastic compositions

Abstract

The present invention provides aqueous viscoelastic compositions comprising a cleavable surfactant and possibly also an electrolyte. The cleavable surfactants useful in the present invention comprise at least one weak chemical bond, which is capable of being broken under appropriate conditions, to produce oil soluble and water soluble products typically having no interfacial properties and surface activity compared with the original surfactant molecule. Further, the rheological properties of the aqueous viscoelastic composition are usually altered upon cleavage of the cleavable surfactant generally resulting in the elimination of the viscosifying, viscoelastic and surfactant properties of the composition. Aqueous viscoelastic compositions in accordance with the present invention are suitable for use in oil-field applications, particularly for hydraulic fracturing of subterranean formations. Thus, the present invention also relates to a wellbore service fluid and a method of fracturing a subterranean formation. The present invention also concerns novel cleavable surfactants.

What is claimed is: 
     
         1 . A wellbore service fluid, comprising:
 an aqueous viscoelastic composition that comprises a cleavable surfactant, the cleavable surfactant comprising an amide surfactant or an ester surfactant having the structure of formula 1, formula 2 or formula 3:
   R 1 —X—(CR 5 R 6 ) m —Y ⊕ Z ⊖   Formula 1
 
   or 
   R 1 —X—(CR 5 R 6 ) m -A ⊖ B ⊕   Formula 2
 
   or 
   R 1 —X—(CR 5 R 6 ) m —Y ⊕ -A ⊖   Formula 3
 
   where: (i) R 1  is a saturated or unsaturated, linear or branched aliphatic chain of at least 18 carbon atoms;   (ii) X is an O(CO), (CO)O, or (CO)NR 7  group;   (iii) m is at least one;   (iv) Y ⊕  is —NR 2 R 3 R 4 ;   (v) R 2 , R 3 , R 4 , R 5 , R 6  and R 7  are each independently hydrogen; a linear or branched, saturated aliphatic chain of at least 1 carbon atom; or a linear or branched, saturated aliphatic chain of at least 1 carbon atom with one or more of the hydrogen atoms replaced by a hydroxyl group, wherein for cleavable surfactants of formula 3, the R group linked to A ⊖  is not hydrogen;   (vi) A ⊖  is a sulfonate anionic group; and   (vii) Z ⊖  and B ⊕  are ionic counterions associated with a cleavable surfactant of formula 1 or formula 2, where Z ⊖  is a monovalent anion or divalent anion and B ⊕  is hydrogen or a monovalent cation,   excluding surfactants of formula 1 in which X is O(CO), R 5  and R 6  are each independently hydrogen, m is greater than or equal to 1 but less than 5 and Y ⊕  is —NR 2 R 3 R 4 .   
     
     
         2 . The wellbore service fluid of  claim 1 , wherein the cleavable surfactant has the structure of Formula 3 (R 1 —X—(CR 5 R 6 ) m — Y ⊕ -A ⊖ ). 
     
     
         3 . The wellbore service fluid of  claim 2 , wherein R 1  is a erucyl group. 
     
     
         4 . The wellbore service fluid of  claim 2 , wherein X is a (CO)NR 7  group, R7 being a hydrogen atom. 
     
     
         5 . The wellbore service fluid of  claim 2 , wherein Y ⊕  is —NR 2 R 3 R 4  and at least 1 of R 2 , R 3  and R 4  are —CH3. 
     
     
         6 . The wellbore service fluid of  claim 1 , further comprising an electrolyte. 
     
     
         7 . The wellbore service fluid of  claim 6 , wherein the electrolyte comprises at least one inorganic water soluble salt, organic water soluble salt, or mixtures thereof. 
     
     
         8 . The wellbore service fluid of  claim 1 , wherein the aqueous viscoelastic composition comprises an aqueous viscoelastic gel. 
     
     
         9 . A wellbore service fluid of  claim 1 , further comprising a rheology enhancer in a concentration sufficient to shorten the shear recovery time of said fluid, said rheology enhancer being a polymer comprising at least one portion selected from the group consisting of partially hydrolyzed polyvinyl esters, partially hydrolyzed polyacrylates, and sulfonate-containing polymers. 
     
     
         10 . A wellbore service fluid, comprising:
 an aqueous viscoelastic composition that comprises a cleavable surfactant amidopropyl hydroxypropylsultaine having the structure of:   
       
         
           
           
               
               
           
         
         wherein R 1  is a saturated or unsaturated, linear or branched aliphatic chain of at least 18 carbon atoms. 
       
     
     
         11 . A wellbore service fluid of  claim 10 , wherein R 1  is erucyl. 
     
     
         12 . A wellbore service fluid of  claim 10 , wherein R 1  is oleyl.