Iron Sulfide Deposition in Sour Gas Wells: A Root Cause Analysis

摘要

Iron sulfide is one of the exotic scales formed in oil and gas fields,particularly for those deep sour gas wells producing from high-pressure,high temperature(HPHT)reservoirs.Compared to the conventional carbonate and sulfate scale,the mitigation of iron sulfide deposition is notoriously difficult.To develop a suitable mitigation strategy,it is essential to understand the formation mechanisms of iron sulfide in the given production system.In this work,we combined laboratory tests,thermodynamic modeling,and field monitoring to understand the source of iron,and the mechanisms of iron sulfide deposition in sour gas wells during acidizing treatment and the production stage.The study results indicate that iron sulfide deposition in sour gas wells is a corrosion-induced scaling problem.During acidizing treatment,a high concentration of iron is released from the tubular due to acid attack,despite a corrosion inhibitor being used in the stimulation fluid package.Large amounts of iron sulfide can precipitate when spent acid mixes and reacts with hydrogen sulfide(H2S)in the reservoir,and potentially causes severe formation damage.During the production stage,the iron released from the tubular due to corrosion in the produced water under HPHT,is the major contribution of iron sulfide deposited at the surface of the tubing.These iron sulfide deposits,although appearing as a porous layer,can protect the downhole completion from the highly corrosive fluids,which leads to the unexpected long service lives of the mild carbon steel tubulars in many wells.Accelerated corrosion can occur when the protective iron sulfide film or deposit is disturbed,or if there is only a partial coverage.This article presents a fundamental study to understand the root cause of iron sulfide deposition in sour gas wells.The study results demonstrate that effective corrosion inhibition is key to mitigate the iron sulfide deposition problem in the sour gas wells.