Sour Environments: ProtectingProduction and Equipment

摘要

Acid stimulation of sour wells, including gas, oil andwater injection, presents special challenges. Add hightemperatures and specialty equipment and sometimespermanent production damage can result. Avoidance ofdamaging precipitates from unwanted reactions, whichcan permanently plug a producing interval whileproviding protection of all production equipment, issometimes a tenuous balance of design.Precipitation of elemental sulfur, reaction productsfrom incompatible additives used in an acid stimulationfluid and re-precipitation of iron sulfide scale dissolvedduring the pumping of acid through corroded tubularsare the sources of potential permeability restrictions.Corrosion protection to the proper level of weight loss (<0.02 to 0.05 lb/ft2) and localized surface defects (pittingand stress cracking) both in live and spent acid solutions are essential to protecting the production equipment andtreating tubulars.This paper reviews those practices, which reduce therisks associated with coiled tubing failure and acidstimulation success of H2S producing wells. Discussionsof the methods of avoiding unwanted damagemechanisms, which could result from acid, H2S and/oracid additives interactions are presented. A case historyfrom Saudi Arabia is presented that discusses damage tothe outside surface of a coiled tubing string due to acidand H2S corrosion. A Canadian case history describing amechanical failure of coiled tubing as the result ofhydrogen embrittlement is presented. Guidelines areoffered for coiled tubing usage to obtain successfulstimulation while controlling risks of tubing failures.