Ferrous Sulfide Solid Formation and Inhibition at Oxidation-Reduction Potentials and Scaling Indices Like Those That Occur in the Oil Field

Abstract

Ferrous sulfide deposition is a significant oilfield problem that has not been studied extensively, partly because of the difficulty in studying it under the reducing conditions found in the oilfield, partly because of a perception that its formation can not be controlled using current technology, and partly because of a perception that it is easy to remove when it does form. The difficulties in studying it may be overcome with careful work, and the perceptions are not entirely accurate. Ferrous sulfide is not a single entity; it exists in numerous solid forms. One of the determinants of the form taken by the solid is the oxidation-reduction potential of the system. This paper discusses precautions that need to be taken when conducting studies under reducing conditions. The paper presents laboratory data obtained at defined oxidation-reduction potential and pH. It shows how the deposition of ferrous sulfides may be reduced significantly using chemicals at mg/L levels. Introduction Iron sulfide is nearly as ubiquitous in the oilfield as calcium carbonate, yet it has received very little attention in the literature on scaling. There are several reasons for this.In small quantities iron sulfide can form a protective film by itself or with corrosion inhibiting compounds1,2,3. Thus, it may not always be seen as a problem.Iron sulfide often forms a softer scale than calcium carbonate. This scale may not always block tubing to the same degree that other mineral scales do. Thus, it may be seen as less of a problem than other mineral scales.Iron sulfide sometimes may be removed with dissolvers. Thus, remediation rather than control may be perceived as a more practical course of action.Inhibitors are commonly believed to be ineffective in controlling the formation of iron sulfide. Thus attempting to control it with inhibitors may be seen as futile.Iron sulfide is much more difficult to study in the laboratory than other common mineral scales. In addition to the variables of temperature, ionic strength and scaling ion concentrations that must be controlled for all mineral scales, and in addition to the pH, which must be controlled for calcium carbonate, the oxidation potential must be controlled on the strongly reducing side. This reducing environment is impossible to maintain in contact with breathable air. This difficulty in studying it may deter researchers from conducting those studies. Adherent Iron Sulfide Iron sulfide often is a problem. When too much iron sulfide is formed it no longer provides protection from corrosion. It may crack and portions of it may flake off. The remaining deposits may provide an ideal environment for under-deposit corrosion4. Adherent deposits may interfere with the operation of pumps, valves and other equipment. They may decrease the efficiency of heat exchangers and, in extreme cases, inhibit the flow of fluids through lines. In gas systems, over extended periods of time, enough pyrophoric iron sulfide may form to pose a safety hazard when the material is exposed to oxygen. Free Floating Iron Sulfide Free-floating precipitates of iron sulfide create additional problems.The solids content of water meant for re-injection may be increased.Iron sulfide may form sludges of such volume that they significantly decrease the volume of holding tanks and separators.Iron sulfide particles may acceleration corrosion5.Oil-wet iron sulfide particles at the oil-water interface often stabilize emulsions and interfere with the separation process.

Mechanisms of Environmentally Acceptable Inhibitors for Zinc Sulphide Inhibition

“…16,20 Two blank tests were conducted, and the turbidity of each examined over two hours. The results are summarised in Table 3 and illustrated in Figure 1, indicating reasonable reproducibility using the brine shown in Table 1.…”

Badania kompatybilności wód złożowych z utworów cechsztynu i czerwonego spągowca w aspekcie zatłaczania do warstw chłonnych

“…Wśród nich bardzo istotnym, przyczyniającym się do kolmatacji strefy przyodwiertowej, a co za tym idzie -do skrócenia czasu pracy i obniżenia ilości płynów możliwych do zatłoczenia danym odwiertem są osady. Składają się one zarówno z materiału skalnego (iły, drobiny skalne, piasek, pyły, koloidalna krzemionka i inne zanieczyszczenia mechaniczne), jak i z tlenków, wodorotlenków i siarczków metali (zwłaszcza żelaza i manganu) powstających i wytrącających się z roztworu pod wpływem zmian chemicznych i fizycznych, jakie zachodzą w trakcie eksploatacji złoża i magazynowania wód złożowych (Przybylinsky, 2003).…”

Mechanisms, New Test Methodology and Environmentally Acceptable Inhibitors for Co-deposition of Zinc Sulfide and Calcium Carbonate Scales for High Temperature Application

“…Zinc sulfide crystals often form a softer scale than conventional oilfield scales, which are difficult to adhere on the surface of a test coil in the traditional dynamic tubing blockage facilities (Przybylinski, 2003). Along with tiny amount of zinc sulfide mass deposition with field produced water chemistries, zinc sulfide scale may not block tubing to the same degree as other mineral scales.…”