Method of removing dissolved iron in aqueous systems

Abstract

Oilfield completion, drilling and workover fluids containing iron are treated to remove the iron by passing them through a cavitation device together with an oxidizing agent. The cavitation device intimately mixes the oxidizing agent with the fluid while increasing the temperature of the fluid, thus promoting the oxidation reaction. Ferric hydrate and other solids or colloidal iron are removed in a filter capable of removing particles as small as 0.5 micron. The system may be enhanced by the addition of a bed of activated carbon capable of catalyzing the oxidation reaction.

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.