Iron sulfide removal in oilfield applications
Dissolving iron sulfide on the carbon steel tubing to yield chelated iron is achieved by treating the carbon steel tubing with a composition including an iron chelant and an additive. The additive includes at least one of an oxidizing agent and a base. A weight ratio of the iron chelant to the additive is in a weight range of 50:1 to 5:1.
1. A method of treating carbon steel tubing in a subterranean formation, the method comprising:
providing a composition comprising an iron chelant, a base, and an oxidizing agent, wherein the oxidizing agent comprises 3 to 15 wt % of sodium nitrite;
contacting the carbon steel tubing with the composition for a length of time; and dissolving iron sulfide on the carbon steel tubing with the composition to yield chelated iron.
2. The method of claim 1 , wherein dissolving the iron sulfide does not result in formation of hydrogen sulfide.
3. The method of claim 1 , wherein dissolving the iron sulfide comprises dissolving 5 wt % to 100 wt % percent of the iron sulfide.
4. The method of claim 1 , wherein the length of time is in a range of 4 hours to 72 hours.
5. The method of claim 1 , wherein, after the length of time, corrosion of the carbon steel tubing is less than 0.05 lb/ft 2 .
6. The method of claim 1 , comprising, after the length of time, removing the composition from the subterranean formation.
7. The method of claim 1 , wherein the concentration of the iron chelant in the composition as provided is in a range of 10 wt % to 80 wt %.
8. The method of claim 1 , wherein the composition is free of hydrochloric acid.
9. The method of claim 1 , wherein the pH of the composition as provided is in a range of 3 to 14.