Method for treating production water from a method for enhanced oil and/or gas recovery

Abstract

The present invention concerns a method for treating the production water originating from enhanced hydrocarbon recovery, and containing one or more water-soluble polymers and Fe.sup.2+ ions, consisting of at least partially oxidizing the Fe.sup.2+ ions by introducing at least one reaction activator and oxygen into said production water, the molar ratio of introduced oxygen to Fe.sup.2+ ions being less than or equal to 0.25.

Claims

1. A method for treating production water originating from enhanced hydrocarbon recovery, and containing one or more water-soluble polymers and Fe.sup.2+ ions, the method comprising at least partially oxidizing the Fe.sup.2+ ions by introducing at least one reaction activator and oxygen into said production water, the molar ratio of introduced oxygen to Fe.sup.2+ ions being less than or equal to 0.25.

2. The method according to claim 1, wherein the activator is introduced into the production water according to one of the following introduction modes: before the introduction of the oxygen; during the introduction of the oxygen; after the introduction of the oxygen; before and during the introduction of the oxygen; before and after the introduction of the oxygen; during and after the introduction of the oxygen; before, during and after the introduction of the oxygen.

3. The method according to claim 2, wherein the activator is chosen from the group consisting of: stearyl citrate, monoammonium citrate, calcium citrate, calcium disodium ethylenediaminetetraacetate, monocalcium phosphate, tricalcium phosphate, calcium phytate, citric acid, disodium ethylenediaminetetraacetate, glycine, sodium tripolyphosphate, phosphoric acid, monopotassium phosphate, tetrapotassium pyrophosphate, dipotassium phosphate, sodium acid pyrophosphate, sodium citrate, tetrasodium pyrophosphate, monosodium phosphate, disodium phosphate, sodium hexametaphosphate, N,N′-bis(2-hydroxybenzyl)-ethylenediamine-N,N′-diacetic acid, N-(1,2-dicarboxyethyl)-D,L aspartic acid, diethylene triamine pentacetic acid, humic acid, fulvic acid, polyacrylate, polyitaconate, polymaleate, and polyaspartate.

4. The method according to claim 2, wherein between 1 and 30 ppm of activator is introduced into the production water, relative to the weight of the production water.

5. The method according to claim 2, wherein between 0.25 and 7 ppm of oxygen is introduced into the production water, relative to the weight of the production water.

6. The method according to claim 1, wherein the activator is chosen from the group consisting of: stearyl citrate, monoammonium citrate, calcium citrate, calcium disodium ethylenediaminetetraacetate, monocalcium phosphate, tricalcium phosphate, calcium phytate, citric acid, disodium ethylenediaminetetraacetate, glycine, sodium tripolyphosphate, phosphoric acid, monopotassium phosphate, tetrapotassium pyrophosphate, dipotassium phosphate, sodium acid pyrophosphate, sodium citrate, tetrasodium pyrophosphate, monosodium phosphate, disodium phosphate, sodium hexametaphosphate, N,N′-bis(2-hydroxybenzyl)-ethylenediamine-N,N′-diacetic acid, N-(1,2-dicarboxyethyl)-D,L aspartic acid, diethylene triamine pentacetic acid, humic acid, fulvic acid, polyacrylate, polyitaconate, polymaleate, and polyaspartate.

7. The method according to claim 6, wherein between 1 and 30 ppm of activator is introduced into the production water, relative to the weight of the production water.

8. The method according to claim 6, wherein between 0.25 and 7 ppm of oxygen is introduced into the production water, relative to the weight of the production water.

9. The method according to claim 1, wherein between 1 and 30 ppm of activator is introduced into the production water, relative to the weight of the production water.

10. The method according to claim 9, wherein between 0.25 and 7 ppm of oxygen is introduced into the production water, relative to the weight of the production water.

11. The method according to claim 10, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced during the separation step.

12. The method according to claim 10, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced between the separation and the flotation and/or decanting and/or coalescence and/or centrifugation steps.

13. The method according to claim 10, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced during the flotation and/or decanting and/or coalescence and/or centrifugation step.

14. The method according to claim 10, wherein the concentration in Fe.sup.2+ ions initially present in the production water is at least 1 ppm relative to the weight of the production water; or if prior to the introduction of the oxygen, the quantity of Fe.sup.2+ ions is less than 1 ppm, then Fe.sup.2+ ions are introduced before the introduction of the oxygen.

15. The method according to claim 1, wherein between 0.25 and 7 ppm of oxygen is introduced into the production water, relative to the weight of the production water.

16. The method according to claim 1, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced during the separation step.

17. The method according to claim 1, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced between the separation and flotation and/or decanting and/or coalescence and/or centrifugation steps.

18. The method according to claim 1, wherein the production water is successively treated by: separation of the production water and residual hydrocarbons; flotation of the production water and/or decanting of the production water and/or coalescence of the production water and/or centrifugation of the production water; filtration of the production water; and wherein the oxygen is introduced during the flotation and/or decanting and/or coalescence and/or centrifugation step.

19. The method according to claim 1, wherein the concentration in Fe′ ions initially present in the production water is at least 1 ppm relative to the weight of the production water; or if prior to the introduction of the oxygen, the quantity of Fe.sup.2+ ions is less than 1 ppm, then Fe.sup.2+ ions are introduced before the introduction of the oxygen.

20. An enhanced hydrocarbon recovery method comprising injecting a polymer solution into an underground formation and recovering the hydrocarbons, wherein the polymer solution contains treated production water containing one or more water-soluble polymers and Fe.sup.2+ ions, wherein the treated production water is obtained by a method for treating production water originating from enhanced hydrocarbon recovery, and containing one or more water-soluble polymers and Fe.sup.2+ ions, the treating method comprising at least partially oxidizing the Fe.sup.2+ ions by introducing at least one reaction activator and oxygen into said production water, the molar ratio of introduced oxygen to Fe.sup.2+ ions being less than or equal to 0.25.

Description

FIGURES

(1) FIG. 1 shows a specific embodiment of the invention implementing a compressor to introduce the oxygen into a deviated fraction of the production water.

EXAMPLE EMBODIMENTS OF THE INVENTION

(2) The decrease in the viscosity of a polymeric aqueous solution was studied over time.

(3) Protocol

(4) A synthetic brine is prepared containing deionized water and the following salts: NaCl: 3.3 g/L CaCl.sub.2, 2 H.sub.2O: 0.1 g/L MgCl.sub.2, 6 H.sub.2O: 0.1 g/L NaHCO.sub.3: 1.5 g/L Na.sub.2SO.sub.4: 0.2 g/L

(5) Part of the brine is next degassed by bubbling with nitrogen under anoxic atmosphere (less than 50 ppb of oxygen) for one hour.

(6) A polymer solution is prepared in the degassed brine under anoxic atmosphere. The polymer used is an acrylamide/acrylic acid copolymer (70/30 by weight), having a molecular weight of 7 Million g/mol.

(7) During different tests, ferrous chloride, an activator (EDTA—ethylenediaminetetraacetic) and non-degassed brine (oxygen content=7 ppm) are sequentially added to the polymer solution so as to obtain a polymer concentration of 600 ppm.

(8) The solution is kept under agitation and the residual viscosity is measured at 5 minutes and at 30 minutes (Brookfield viscosimeter, UL spindle at 6 rpm at 25° C.; rpm=revolutions per minute). At 30 minutes, the residual oxygen level is measured.

(9) All of the tests are done under anoxic atmosphere (less than 50 ppb of oxygen).

(10) TABLE-US-00001 TABLE 1 Quantities of oxygen, Fe.sup.2+ ions and activator implemented in the counterexamples (CE) and examples according to the invention (INV). CE-1 CE-2 CE-3 CE-4 CE-5 CE-6 INV-1 INV-2 Oxygen 0 7 1 7 7 7 1 1 (ppm) Iron II 0 10 10 0 0 10 10 10 (ppm) Activator 0 0 0 0 20 15 20 5 (ppm)

(11) TABLE-US-00002 TABLE 2 Decrease in viscosity (cps) as a function of time for a solution according to counterexamples CE-1 to CE-6. CE-1 CE-2 CE-3 CE-4 CE-5 CE-6 Initial 10 10 10 10 10 10 viscosity Viscosity at 10 7.5 10 10 9.5 6 5 minutes Viscosity at 10 5.5 8.5 10 9.5 6 30 minutes Residual 0 6 0.8 7 7 6 oxygen at 30 minutes (ppm)

(12) TABLE-US-00003 TABLE 3 Decrease in viscosity (cps) as a function of time for a solution according to the examples according to the invention INV-1 to INV-2. INV-1 INV-2 Initial viscosity 10 10 Viscosity at 5 minutes 6 7 Viscosity at 30 minutes 5 5.5 Residual oxygen at 30 minutes (ppm) 0.1 0.3

(13) An acceptable degradation of the viscosity is obtained at a high oxygen and iron concentration (CE-2 and CE-6) as well as at a high oxygen, iron and activator concentration. In these two cases, the residual oxygen content remains high, which is a drawback in the method used due to the corrosion caused. One major advance is the use of an activator that, combined with iron and a lower oxygen concentration (INV-1 and INV-2), will lead to a decrease in viscosity and a residual oxygen concentration between 100 and 500 ppb. This low oxygen concentration may be reduced by a post-addition of a reducing agent to maintain low oxygen levels.

(14) In the following 3 counterexamples (CE-7 to CE-9), the oxygen is replaced by another oxidizing agent, sodium hypochlorite, as in document EP 2 450 314.

(15) TABLE-US-00004 TABLE 4 Quantities (by weight) of sodium hypochlorite, Fe.sup.2+ ions and activator implemented in counterexamples CE-7 to CE-9. CE-7 CE-8 CE-9 Sodium hypochlorite (ppm) 1 1 1 Iron II (ppm) 0 10 10 Activator (ppm) 0 0 5

(16) TABLE-US-00005 TABLE 5 Decrease in viscosity (cps) as a function of time for a solution according to counterexamples CE-7 to CE-9. CE-7 CE-8 CE-9 Initial viscosity 10 10 10 Viscosity at 5 minutes 10 8 8.5 Viscosity at 30 minutes 9.5 7.5 8.5

(17) Although using an oxidizing agent described in the prior art, the decrease in viscosity is not sufficient at this level.

(18) In the following 3 counterexamples (CE-10 to CE-12), the oxygen is replaced by another oxidizing agent, hydrogen peroxide.

(19) TABLE-US-00006 TABLE 6 Quantities (by weight) of hydrogen peroxide, Fe.sup.2+ ions and activator implemented in counterexamples CE-10 to CE-12. CE-10 CE-11 CE-12 Hydrogen peroxide (ppm) 1 1 1 Iron II (ppm) 0 10 10 Activator (ppm) 0 0 5

(20) TABLE-US-00007 TABLE 7 Decrease in viscosity (cps) as a function of time for a solution according to counterexamples CE-10 to CE-12. CE-10 CE-11 CE-12 Initial viscosity 10 10 10 Viscosity at 5 minutes 10 8.5 9 Viscosity at 30 minutes 9 8 8.5

(21) Although using an oxidizing agent, the decrease in viscosity is not sufficient at this level.

(22) In the following 3 counterexamples (CE-13 to CE-15), the oxygen is replaced by another oxidizing agent, potassium permanganate.

(23) TABLE-US-00008 TABLE 8 Quantities (by weight) of potassium permanganate, Fe.sup.2+ ions and activator implemented in counterexamples CE-13 to CE-15. CE-13 CE-14 CE-15 Potassium 1 1 1 permanganate (ppm) Iron II (ppm) 0 10 10 Activator (ppm) 0 0 5

(24) TABLE-US-00009 TABLE 9 Decrease in viscosity (cps) as a function of time for a solution according to counterexamples CE-13 to CE-15. CE-13 CE-14 CE-15 Initial viscosity 10 10 10 Viscosity at 5 minutes 10 9 9.5 Viscosity at 30 minutes 9.5 8 8.5

(25) Although using an oxidizing agent, the decrease in viscosity is not sufficient at this level.

(26) Reusing the treated water to dissolve a “new” polymer was studied.

(27) Two solutions containing 1000 ppm of an acrylamide/acrylic acid copolymer (70/30 by weight), having a molecular weight of 18 Million g/mol, are prepared. Each solution is respectively prepared with the treated water of counterexample CE-3 and example INV-1 according to the invention.

(28) The viscosity of the solutions is measured at 20° C. after 3 days of incubation at 55° C.

(29) The viscosity of the solution prepared with the treated water of counterexample CE-3 is 16.5 cps.

(30) The viscosity of the solution prepared with the treated water of example INV-1 according to the invention is 26.5 cps.

(31) The results indeed demonstrate that the method according to the invention makes it possible to obtain a water suitable for polymer dissolution.