Abstract This paper examines the discrepancy between good field results with Ironite Sponge in alkaline drilling muds, and the low rates of reaction between Ironite Sponge and H S predicted by a previously published rate law for the reaction. Two explanations are proposed, based on further laboratory studies at high pH:An intrusion-reaction effect, where the pH is significantly lowered during intrusion of H S, allowing the reaction to proceed rapidly before the pH again rises due to consumption of H S. This effect can result in removal of 40 percent or more of initial sulfides even for highly buffered alkaline muds.
Ironite Sponger) catalyzes the reaction between dissolved oxygen and H S at high pH. In the mud pits at a drilling site this effect can account for rapid removal of residual sulfides in circulated drilling fluids. Both effects, together with the instantaneous rate law, can account for low sulfide levels and absence of drill pipe failures reported by other authors for alkaline Ironite Sponge slurries used with sour gas systems.
Introduction Several years ago a laboratory study of kinetics for the Ironite Sponge -H S reaction was presented. Data obtained over e pH range 7.5 - 9.8 implied a strongly decreasing rate of reaction with increasing pH. The derived rate law is given by
(1)
where S = total dissolved sulfides in filtrate, ppm; t = time, minutes; (H+) = hydrogen ion concentration, moles/liter; and (I) = Ironite Sponge concentration, pounds per barrel (lbs/bbl).
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