Dual retarded acid system for well stimulation
A composition in the form of an emulsion having: (i) a continuous oil phase comprising: (a) an oil; (b) an emulsifier; and (ii) an internal aqueous phase comprising: (a) water; (b) acid such that the aqueous phase has an initial pH of less than about 2; (c) a viscosity-increasing agent; and (d) a crosslinker, wherein the crosslinker is selected or controlled to crosslink the viscosity-increasing agent at a pH range somewhere in a range of about 1.5 to about 6.5 and that is at least higher than the initial pH of the aqueous phase. A method of acidizing a treatment zone of a subterranean formation in a well includes the steps of: (A) forming a treatment fluid comprising such a composition; and (B) introducing the treatment fluid into a well.
1. A method of acidizing a treatment zone of a subterranean formation in a well, the method comprising the steps of:
(A) forming a treatment fluid in the form of an emulsion, the treatment fluid comprising:
(i) a continuous oil phase comprising:
(a) an oil; and
(b) an emulsifier; and
(ii) an internal aqueous phase comprising:
(a) water;
(b) acid such that the aqueous phase has an initial pH of less than about 2;
(c) a viscosity-increasing agent; and
(d) a crosslinker, wherein the crosslinker is selected or controlled to crosslink the viscosity-increasing agent at a pH range somewhere in a range of about 1.5 to about 6.5 and that is at least higher than the initial pH of the aqueous phase; and
(B) introducing the treatment fluid into a well, wherein a design temperature in the subterranean formation is at least about 121° C. (about 250° F.).
2. The method according to claim 1 , wherein the oil of the external oil phase comprises an oil selected from the group consisting of petroleum, diesel, kerosene, or synthetic oil.
3. The method according to claim 1 , wherein the emulsifier is a cationic amine.
4. The method according to claim 1 , wherein the acid comprises a strong acid.
5. The method according to claim 4 , wherein the strong acid comprises hydrochloric acid in a concentration of at least 5% by weight of water of the internal aqueous phase.
6. The method according to claim 4 , wherein the strong acid comprises hydrochloric acid in a concentration in the range of about 24% to about 28% by weight of water of the internal aqueous phase.
7. The method according to claim 1 , wherein the viscosity-increasing agent comprises a polyacrylamide based-polymer.
8. The method according to claim 1 , wherein the crosslinker comprises ferric chloride.
9. The method according to claim 1 , additionally comprising a corrosion inhibitor.
10. The method according to claim 9 , additionally comprising a corrosion inhibitor intensifier.
11. The method according to claim 1 , wherein the subterranean formation is a carbonate formation.