Patent EA-005102-B1 (EA)
Title: Method for treating a subterranean formation
Inventor: FRENIER WAYNE
IPC: C09K8/86
Filed: 2002-05-10
Abstract: 1. A method of treating a subterranean formation to increase permeability comprising injecting into the formation matrix an amount of an aqueous mixture, sufficient to increase the permeability of the formation, the aqueous mixture comprising an aqueous liquid comprises from about 5 to about 20 weight percent of the aminopolycarboxylic anionic species selected from EDTA anion, DTPA anion, and mixtures thereof, and cationic species selected from potassium ion, lithium ion, ammonium ion, and mixtures thereof, in a ratio of said cationic species to said aminopolycarboxylic anionic species of at least 1. 2. The method of claim 1 wherein the aqueous mixture is formed by blending an aqueous liquid and an ammonium, lithium, or potassium salt composition of an aminopolycarboxylic acid selected from ethylenediamine tetraacetic acid, diethylenetriaminepentaacetic acid, and mixtures thereof. 3. The method of claim 2 wherein at least a portion of the ammonium, lithium, or potassium salt composition is supplied as a hydrate or hydrates. 4. The method of claim 2 in which the ammonium or potassium salt composition is selected from dipotassium ethylenediaminetetraacetate or diammonium ethylenediaminetetraacetate, hydrates thereof, and mixtures thereof. 5. The method of claim 2 in which the ammonium or potassium salt composition of an aminopolycarboxylic acid selected from potassium ethylenediaminetetraacetate, ammonium ethylenediamine tetraacetate, dipotassium ethylenediaminetetraacetate or diammonium ethylenediaminetetraacetate, hydrates thereof, and mixtures thereof. 6. The method of any claims 1-5 in which the pH of the aqueous mixture is from about 4 to about 6. 7. The method of any claims 1-6 in which the pH of the aqueous mixture is from about 4 to about 12. 8. The method of any claims 1-7 wherein the aqueous mixture further comprises a non interfering component. 9. The method of claim 9 wherein the non-interfering component is a pH-adjuster. 10. The method of any claims 1-9 wherein the aqueous liquid is fresh water, brine or dilute acids. 11. The method of any claims 1-10 wherein the aqueous mixture comprises from about 5 to about 20 weight percent of the aminopolycarboxylic anionic species. 12. The method of any claims 1-11 wherein the formation temperature ranges from about 13 degree C to about 205 degree C. 13. The method of any claims 1-12 wherein a preflush fluid is injected prior to injection of the aqueous mixture. 14. The method of any claims 1-13 wherein a pumping rate and a pH of the aqueous mixture and a composition of the aqueous mixture are selected in combination based on the solubility of and reactivity of anaminopolycarboxylic anionic species, in the aqueous mixture, selected from EDTA anion, DTPA anion, and mixtures thereof, and a cationic species, in the aqueous mixture, selected from potassium ion, lithium ion, ammonium ion, and mixtures thereof, whereby the volume of the aqueous mixture required to create wormholes is minimized. 15. The method of any claims 1-14 wherein a pH of the aqueous mixture and an aminopolycarboxylic anionic species component, of the aqueous mixture, selected from EDTA anion, DTPA anion, and mixtures thereof, and a cationic species component, of the aqueous mixture, selected from potassium ion, lithium ion, ammonium ion, and mixtures thereof, are selected in combination, whereby the pumping rate of the aqueous mixture required to create wormholes is minimized.