Reducing sulfide in production fluids during oil recovery

Abstract

Methods are provided for treating production fluid in a production well in an oil reservoir to reduce the amount of sulfide in the production fluid. The production fluid is treated with nitrate and/or nitrite ions or inorganic oxidizing agent in an aqueous solution that is added to the well casing.

What is claimed is: 
     
         1 . A method for treating production fluid in an oil production well comprising:
 a) providing an oil production well in an oil reservoir having a well casing and a production pipe;   b) adding an aqueous solution comprising at least one inorganic oxidizing agent to the well casing wherein said solution flows down the well casing and contacts production fluid in the well bore below the production pipe; and   c) producing the production fluid through the production pipe;   wherein the sulfide concentration in the production fluid is reduced as compared to the sulfide concentration in production fluid obtained with omission of step (b).   
     
     
         2 . The method of  claim 1  wherein the inorganic oxidizing agent has a reaction standard half-cell potential that is greater than −0.478 volts. 
     
     
         3 . The method of  claim 2  wherein the inorganic oxidizing agent is selected from the group consisting of permanganates, persulfates, inorganic peracids, chromates, bromates, iodates, chlorates, perchlorates, chlorites, hypochlorites, inorganic peroxides, and oxides 
     
     
         4 . The method of  claim 3  wherein the inorganic oxidizing agent is selected from the group consisting of chlorine dioxide, hypochlorite, persulfate, and hydrogen peroxide. 
     
     
         5 . The method of  claim 1  wherein the inorganic oxidizing agent comprises nitrate ions, nitrite ions, or a mixture of nitrate and nitrite ions. 
     
     
         6 . The method of  claim 5  wherein the total molar concentration of nitrate ions, nitrite ions, or the mixture of nitrate and nitrite ions is at least about five-fold higher than the molar concentration of sulfide in production fluid of the production well measured prior to addition of the aqueous solution of (b). 
     
     
         7 . The method of  claim 5  wherein at least a portion of nitrate ions are reduced to nitrite ions in the production fluid mixture by nitrate reducing bacteria. 
     
     
         8 . The method of  claim 1  wherein the oil production well of (a) is a single well oil recovery system or in a multiple well oil recovery system. 
     
     
         9 . The method of  claim 1  wherein prior to step (b) the oil reservoir is injected with a nutrient solution and optionally with at least one microorganism. 
     
     
         10 . The method of  claim 1  wherein the aqueous solution of (b) is combined with power water added to the well casing. 
     
     
         11 . The method of  claim 1  wherein adding the aqueous solution to the well casing in (b) is intermittent or continuous, starting prior to producing from the well. 
     
     
         12 . The method of  claim 1  wherein the oil production well has a delivery tubing in side the well casing and outside of the production pipe, and the aqueous solution of (b) is added to the delivery tubing. 
     
     
         13 . The method of  claim 5  wherein the aqueous solution comprises nitrite ions. 
     
     
         14 . The method of  claim 13  wherein the aqueous solution comprises nitrite ions and omits nitrate ions. 
     
     
         15 . The method of  claim 2  wherein the total molar concentration of the inorganic oxidizing agent is at least about 1.5-fold higher than the molar concentration of sulfide in production fluid of the production well measured prior to addition of the aqueous solution of (b).