Iron sulfide deposition in sour gas wells has caused severe flow assurance issues. It affects well deliverability, interferes with well surveillance and restricts well intervention. The mitigation of iron sulfide deposition is notoriously difficult. In order to make suitable strategies to manage iron sulfide, it is essential to understand the source of iron and mechanisms of iron sulfide deposition.
Combined with scale modelling and laboratorial tests, the source of iron and mechanisms of iron sulfide deposition during acidizing treatment have been studied. Results show high concentration of iron can be released from the tubular due to severe corrosion during acid injection. Iron sulfide will not deposit at the initial stage of acid injection due to low pH environment. However, iron sulfide can precipitate when spent acid with pH ~3.8 mixes with formation water saturated with sour gases. Large amount of iron sulfide could deposit in the near wellbore region or tubing, which potentially causes severe flow assurance issues.
This paper presents a fundamental study to understand the mechanisms of iron sulfide deposition during acid stimulation. It will benefit defining proper strategy to control iron sulfide deposition in downhole tubing and near wellbore matrix in carbonate reservoirs.
Key words: Iron sulfide, acid stimulation, mechanism