Internal breakers for viscoelastic surfactant fluids
Internal breakers are given that break fluids viscosified with non-polymeric viscosifiers such as viscoelastic surfactants, inside formation pores. The breakers are polyols, for example natural and synthetic sugars, monoalcohols, and mixtures of the two. The sugars may be ketones and aldehydes. The sugars are also breaker aides for oxidizing agents used as breakers. Methods of using the breakers and breaker aides in oilfield treatment fluids are given.
1. A composition comprising an aqueous fluid, a betaine surfactant as a viscosifier, and an internal breaker consisting of a polyol and an oxidizing agent soluble in the fluid, wherein the polyol is 1, 3 propanediol, a sugar alcohol or sugar ketone, wherein the oxidizing agent comprises a bromate, iodate or persulfate.
2. The composition of claim 1 wherein the surfactant comprises oleylamidopropyl betaine or erucylamidopropyl betaine.
3. The composition of claim 1 wherein the polyol is selected from sorbitol, fructose, sucrose, lactose, dextrose, maltodextrin, sucralose, and mixtures thereof.
4. The composition of claim 1 wherein the fluid comprises a heavy brine.
5. The composition of claim 1 further comprising a monoalcohol.
6. The composition of claim 5 wherein the monoalcohol comprises from 1 to 24 carbon atoms, may be linear, branched, or cyclic, and may be saturated or unsaturated, and may be a mixture of such monoalcohols.
7. A method of treating a subterranean formation penetrated by a wellbore comprising a) injecting into the pores of the formation an aqueous fluid comprising a betaine surfactant as viscosifier and an internal breaker consisting of a polyol and an oxidizing agent soluble in the fluid, wherein the polyol is 1, 3 propanediol, a sugar alcohol or sugar ketone, wherein the oxidizing agent comprises a bromate, iodate or persulfate, and b) allowing said fluid to lose viscosity in the pores after the injection.
8. The method of claim 7 wherein the surfactant comprises oleylamidopropyl betaine or erucylamidopropyl betaine.
9. The method of claim 7 wherein the polyol is selected from sorbitol, fructose, sucrose, lactose, dextrose, maltodextrin, sucralose, and mixtures thereof.
10. The method of claim 7 wherein the fluid comprises a heavy brine.
11. The method of claim 7 wherein the fluid further comprises a monoalcohol.
12. The method of claim 11 wherein the monoalcohol comprises from 1 to 24 carbon atoms, may be linear, branched, or cyclic, and may be saturated or unsaturated, and may be a mixture of such monoalcohols.
13. The method of claim 12 wherein the monoalcohol comprises isopropanol.