Oil Field Case Study: Eliminating Iron Sulfide in Oil Wells
The Issue: Iron Sulfide Plugging in Wellbore
The Solution: Treatment with Sabre's DiKlorSM service, using chlorine dioxide (ClO2) stimulation process
A Texas-based oil company operates a producing field in west Texas. With a history of iron sulfide related problems, one of their wells experienced excessive workover costs and downtime.
Chlorine Dioxide Application Considerations
It wasn’t unusual for the well’s electric submersible pump (ESP) to plug as many as four times in a two-week period. During each two-week period, two acid jobs were completed in an attempt to correct the problem. Both stimulations proved unsuccessful and the ESP had to be replaced, costing over $21,000 plus lost production revenue.
Samples were taken from the ESP, confirming that the plugging material consisted mainly of iron sulfide and calcium carbonate.
Chlorine Dioxide Treatment Approach
A complete study resulted in the recommended use of Sabre's DiKlorSM service, using chlorine dioxide stimulation process, to remove the iron sulfide by oxidation to a soluble form.
250 bbls of DiKlor® staged with an acid containing micellar solvent, corrosion inhibitor and iron chelant was pumped into the wellbore to remove the plugging material.
Conventional acid stimulation will solubilize carbonate and iron sulfide which remains in solution as long as the pH remains below 2. Once the acid is spent and the formation fluid pH rises above 2, the iron sulfide re-precipitates, plugging the pore spaces and the pump intake.
The DiKlorSM treatment enhances conventional acid stimulation by oxidizing the preferentially oil-wet hydrous ferric oxide, which is chelated, while the insoluble sulfide is oxidized to water-soluble sulfate.
Iron sulfide plugged within the ESP, which cost the operator as much as $38,000 every two weeks. As a result of using the DiKlorSM service, there were no iron sulfide related pump failures in over two years. Other costs associated with pulling, well cleanout, and the lost revenue created by downtime were also eliminated. As a result, the operator’s payout for the DiKlorSM service was less than 30 days. Other ESP problem wells were then treated with equal success.
The Science of Success
Unlike alternative technologies, chlorine dioxide is a true gas that is a relatively stable oxidant, reacting only with reduced compounds such as sulfides, phenols, and biomass. Additionally, chlorine dioxide kills both active and inactive bacteria, unlike conventional biocides. Chlorine dioxide has also been shown to kill bacterial spores with relatively low contact times, and bacteria cannot build resistance to chlorine dioxide. It is also a well-established EPA-registered biocide for use in the drinking water and food industries.
Sabre has over a decade of experience in the petroleum industry, with a perfect safety record to match. This is due to inherent functionality, where chemical precursors are vacuum fed to the point of reaction to form chlorine dioxide in the absence of dilution. This formation of chlorine dioxide independent of the water stream allows Sabre systems to operate with any fluid, including oil, water, emulsions, and slurries. This unique chlorine dioxide system has been patented by Sabre.
Chemical precursors on portable Sabre chlorine dioxide systems are separated by secondary steel containment to further protect from accidental mixing. Sabre has a unique understanding of the health and safety issues related to the use of chlorine dioxide due to its extensive experience with chlorine dioxide in both gas and solution phases.