Use of Mineral Oils, Hydrogenated Polyalphaolefin Oils and Saturated Fatty Acids for Breaking VES-Gelled Fluids

Abstract

Fluids viscosified with viscoelastic surfactants (VESs) may have their viscosities reduced (gels broken) by the direct or indirect action of a breaker composition that contains at least one mineral oil, at least one polyalphaolefin oil, and/or at least one saturated fatty acid. The breaker may initially be dispersed oil droplets in an internal, discontinuous phase of the fluid. In one non-limiting embodiment, the breaker, e.g. mineral oil is added to the fluid after it has been substantially gelled. The breaking composition is believed to act possibly by rearranging, disaggregating or otherwise attacking the micellar structure of the VES-gelled fluid in a non-spontaneous, rate controlled manner at elevated fluid temperatures. In a specific, non-limiting instance, a brine fluid gelled with an amine oxide surfactant can have its viscosity broken with a light, low viscosity paraffinic mineral oil.

1 . An aqueous fluid comprising:
 water;   at least one viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the aqueous fluid; and   at least one breaker present in an oil-soluble internal phase of the aqueous fluid in an amount effective to reduce the viscosity of the gelled aqueous fluid at a time other than essentially instantaneously when the fluid is heated to an effective temperature, where the breaker is added to the fluid after the fluid is substantially gelled, and where the breaker is selected from the group consisting of mineral oils, hydrogenated polyalphaolefin oils, saturated fatty acids and combinations thereof.   
     
     
         2 . The aqueous fluid of  claim 1  where the breaker is a mineral oil and is at least about 99 wt % paraffin. 
     
     
         3 . The aqueous fluid of  claim 1  where the breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
         4 . The aqueous fluid of  claim 1  where the effective temperature ranges from about 70 to about 300° F. (about 21 to about 149° C.). 
     
     
         5 . The aqueous fluid of  claim 1  where the breaker is a mineral oil and effective amount of the mineral oil ranges from about 0.1 to about 15 gptg based on the total fluid. 
     
     
         6 . The aqueous fluid of  claim 1  where the only viscosity reducing agent is the breaker. 
     
     
         7 . An aqueous fluid comprising:
 water;   at least one viscoelastic surfactant (VES) in an amount effective to increase the viscosity of the aqueous fluid; and   from about 0.1 to about 15 gptg based on the total fluid of a mineral oil breaker present in an oil-soluble internal phase of the aqueous fluid effective to reduce the viscosity of the gelled aqueous fluid at a time other than essentially instantaneously when the fluid is heated to a temperature ranging from about 70 to about 300° F. (about 21 to about 149° C.), where the breaker is added to the fluid after the fluid is substantially gelled, where the mineral oil is at least about 99 wt % paraffin.   
     
     
         8 . The aqueous fluid of  claim 7  where the breaker is a mineral oil and has a distillation temperature in the range from about 160 to about 550° C., and a kinematic viscosity at 40° C. of from about 1 to about 250 cSt. 
     
     
         9 . The aqueous fluid of  claim 7  where the only viscosity reducing agent is the breaker.