Investigation of Sulfide Scavengers in Well Acidizing Fluids
- H.A. Nasr-El-Din (Saudi Aramco) | A.Y. Al-Humaidan (Saudi Aramco) | B.A. Fadhel (Saudi Aramco) | W.W. Frenier (Schlumberger) | D. Hill (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE International Symposium on Formation Damage Control, 23-24 February, Lafayette, Louisiana
- Publication Date
- Document Type
- Conference Paper
- 2000. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 4.1.5 Processing Equipment, 4.2.3 Materials and Corrosion, 2.5.2 Fracturing Materials (Fluids, Proppant), 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene, 1.8 Formation Damage, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.3.4 Scale, 4.2 Pipelines, Flowlines and Risers, 4.1.2 Separation and Treating, 3 Production and Well Operations, 3.2.4 Acidising
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This paper describes the development of acidizing systems that use several different aldehyde-based sulfide suppression chemicals in conjunction with new acid corrosion inhibitors. Specific combinations of these chemicals have allowed the acid to dissolve FeS, suppress H2S and still enable the acid to be inhibited to industry corrosion standards. Laboratory tests include dissolution of FeS, measurement of H 2S evolved, measurement of acid concentration and chloride ion concentrations. We also determined the effect of FeS and H2S on the corrosion of oilfield steels with these additives. Laboratory measurements covered the temperature range from 75 to 275°F (reservoir temperature).
Experimental results were compared with that previously published data.1 The new system enabled the acid to dissolve more FeS than fluids containing previously tested suppressors, while controlling H2S evolution and corrosion.
During field testing, samples of the spent acid were captured and were analyzed for [Fe], [S2-] and [HCl]. The data will contribute to an understanding of the corrosion processes and sulfide control during acid treatments. The field acid treatments were accomplished successfully without significant changes in procedures and resulted in large increase in gas production. This system is designed primarily for "tube cleaning" operations prior to acid stimulation (matrix and fracture acidizing), but the control chemicals have also been tested for use in the actual stimulation fluid stages.
The new chemicals and procedures will allow the operators to safely remove large amounts of fouling deposits, while controlling the toxic and corrosive effects of H2S much more effectively than previously used products.
In many wells, pipelines, or in the hydrocarbon processing units of refineries, iron-based surfaces may come into contact with sulfur-containing fluids. At the temperatures present in the various sections or reactors, and during long periods of contact, iron sulfide deposits (generally FeS, but sometimes, FeS2) will form. The reduced sulfur minerals with approximately 1:1 Fe/S mol ratios (makinawite, troilite, pyrrhotite) can be dissolved using mineral acids, while pyrite and marcasite (FeS2) have low acid solubility.
While scale removal using mineral acids is a very effective procedure, it produces large amounts of hydrogen sulfide.
FeS + 2H+ = Fe2+ + H2S (1).
Hydrogen sulfide causes severe safety and operational problems once the acid leaves the system being treated, and H2S stimulates corrosion of the base metal. For pipelines or in refinery operations, surface cleaning is the major goal of the operation. Lawson et al.3 reviewed the major procedures for safely removing iron sulfide deposits: 1) mineral acids with an acid-gas scrubber; 2) mineral acids with hydrogen sulfide suppression chemicals; 3) multiple stages of oxidizing agents with acids; and 4) alkaline cleaners.
Several different suppression technologies have been developed for surface cleaning operations. Frenier and co-workers4-6 and Buske7 developed suppression chemicals that contain aldehydes. The most efficient agent is formaldehyde, which reacts stoichiometrically with hydrogen sulfide to produce trithiane, a very insoluble material.8
In treating sour oil and gas wells, as compared with treating surface equipment, corrosion suppression (not elimination of sulfide gas) and dissolution of FeS are of major concern. The inhibitor package must protect several types of steel at high temperatures in the presence of concentrated acid containing numerous additives. The various additives are required since the purpose of the treatment may include removal of inorganic and organic damage from producing formations (matrix treatments).
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