Use of Mineral Oils to Reduce Fluid Loss for Viscoelastic Surfactant Gelled Fluids

Abstract

Fluids viscosified with viscoelastic surfactants (VESS) may have their fluid loss properties improved with at least one mineral oil which has a viscosity greater than 20 cps at ambient temperature. The mineral oil may initially be dispersed oil droplets in an internal, discontinuous phase of the fluid. In one non-limiting embodiment, the mineral oil is added to the fluid after it has been substantially gelled in an amount between about 0.2 to about 10% by volume.

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   from about 0.2 to about 10% by volume (by) based on the total fluid of at least one mineral oil fluid loss control agent in an amount effective to reduce the fluid loss in a subterranean reservoir of the gelled aqueous fluid, where the mineral oil fluid loss control agent is added to the fluid before, during or after the VES, and where the mineral oil fluid loss control agent has a viscosity greater than 20 cps at ambient temperature, and where the viscosity is not reduced in less than one-half hour.   
   
   
       2 . The aqueous fluid of  claim 1  where the mineral oil fluid loss control agent is at least about 99 wt % paraffin. 
   
   
       3 . The aqueous fluid of  claim 1  where the mineral oil fluid loss control agent has a distillation temperature above about 300° C. 
   
   
       4 . 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 0.2 to about 10% by based on the total fluid of at least one mineral oil fluid loss control agent in an amount effective to reduce the fluid loss in a subterranean reservoir of the gelled aqueous fluid, where the mineral oil fluid loss control agent is added to the fluid before, during or after the VES, and where the mineral oil fluid loss control agent is at least about 99 wt % paraffin, has a distillation temperature above about 300° C. and has a viscosity greater than 20 cps at ambient temperature, and where the viscosity is not reduced in less than one-half hour.