During the production of natural gas from Dutch Rotliegend and Kupferschiefer sediments, next to "conventional" carbonate and sulphate scales, sometimes also lead deposits are formed. These deposits, which vary in composition from galena (lead sulphide) to elemental - metallic - lead and complex lead(hydr)oxides, may form a serious thread to operations because of their tendency to cause the blocking of production equipment or (water) injection pumps and tubing. In some cases radioactive lead (lead-210; half life 22.3 years) is incorporated into these compounds at levels above regulatory concern, which necessitates additional safety measures during operations and maintenance.

In sour gas wells, the deposition of galena can be explained by local supersaturation (caused by a sudden temperature or pressure drop) where bisulphide anions react with lead cations in the produced water, in which concentrations of up to 150 mg lead per litre brine have been detected. In the absence of hydrogen sulphide and even in "dry" gas wells, the deposition of metallic lead has been observed locally at rates of 10 grams per day or more. An electrochemical mechanism is held responsible for lead deposition on carbon steel tubing: iron from the tube wall is oxidised by lead ions in solution, leading to corrosion of the wall and the deposition of lead scales with a thickness of 10 mm or more. Under unfavourable conditions or during maintenance operations, metallic lead is easily converted into secondary lead minerals.

Detailed knowledge on the (geological) origin, the transport pathways to surface facilities and the mechanisms of lead scale formation, might enable the future development of techniques by which lead deposition can be prevented.

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