Method of removing dissolved iron in aqueous systems

1 . Method of treating a used oilfield fluid containing iron to remove iron therefrom comprising (a) passing said used oilfield fluid through a cavitation device in the presence of added oxygen, thereby mixing said oxygen with said oilfield fluid, elevating the temperature of said oilfield fluid, and forming iron oxide solids therein, and (b) passing said used oilfield fluid through a filter capable of removing said iron oxide solids.

2 . Method of claim 1 including recycling at least a portion of said used oilfield fluid from the outlet of said cavitation device to the inlet thereof.

3 . Method of claim 1 including (c) passing at least a portion of said used oilfield fluid to a flash tank from said cavitation device, and (d) recycling at least a portion of said used oilfield fluid from said flash tank to said cavitation device, wherein oxygen is incorporated into said used oilfield fluid in said flash tank from the atmosphere therein

4 . Method of claim 1 wherein at least a portion of said oxygen is added in the form of air.

5 . Method of claim 1 wherein at least a portion of said oxygen is added in the form of hydrogen peroxide.

6 . Method of claim 1 wherein said filter is capable of removing particles as small as 0.5 micron.

7 . Method of claim 1 including maintaining temperatures of at least 60° C. within said cavitation device.

8 . Method of claim 1 including maintaining a pH of at least 2.5 within said cavitation device.

9 . Method of claim 4 wherein said air enters said fluid in a pump.

10 . Method of claim 1 wherein said filter is a crossflow filter.

11 . Method of claim 1 wherein said used oilfield fluid also contains a viscosity-enhancing polymer, and including impairing the viscosity-enhancing effect of said polymer in said cavitation device.

12 . Method of claim 2 wherein about 10% to about 90% of said fluid is substantially continuously recycled from the outlet of said cavitation device to its inlet.

13 . Method of claim 1 including passing said fluid from said cavitation device to a flash tank, evaporating at least some water from said fluid to achieve a fluid of less volume, and passing said fluid of less volume to a filter capable of removing particles as small as 1 micron.

14 . Method of claim 1 which is substantially continuous and wherein the concentration of oxygen in said fluid is maintained at 2 mg/L or greater.

15 . Method of treating an oilfield drilling, workover or completion fluid to remove iron therefrom comprising adding an oxidizing agent to said fluid and passing said fluid through a bed of activated carbon capable of enhancing the oxidation of ferrous iron.

16 . Method of removing iron from an oilfield drilling, completion or workover fluid containing iron comprising (1) passing said fluid through a cavitation device in the presence of an oxidizing agent (2) controlling the operation of said cavitation device to maintain it effective to (a) elevate the temperature, (b) dissolve and mix said oxygen with said fluid, and (c) achieve the reaction of said oxidizing agent and said iron to form insoluble iron oxide, and (3) separating said insoluble iron oxide from said fluid in a filter.

17 . Method of claim 16 wherein said filter is capable of removing particles of 0.5 micron.

18 . Method of claim 16 including passing said fluid containing iron and also containing said oxidizing agent through an activated carbon bed capable of enhancing the oxidation reaction between said oxidizing agent and said iron.

19 . Method of claim 16 including recycling at least a portion of said fluid through said cavitation device.

20 . Method of claim 16 wherein said temperature is elevated to at least 60° C.