Application of DFT in iron sulfide scale removal from oil and gas wells

Abstract

Scale formation including those formed by iron sulfides have been a major hassle in the upstream sector of the oil and gas industry for many decades. Iron Sulfide scales including pyrite (FeS2) and troilite (FeS) often form a precipitate in the matrix formation, tubulars and other downhole equipment in the wells resulting in plant shutdown. Herein, a molecular modelling tool known as Density Functional Theory (DFT) is used to study the binding affinity of chelating agents to ferrous ion, which is the state of iron in pyrite scale. The calculated binding affinity of the chelating agents to Fe2+ increased in the order; GLDA < HEDTA < EDTA < DTPA which correlated with what has been reported experimentally. The number of nitrogen atoms in a chelating agent plays a predominant role in its binding ability. This could give insights on how novel chemicals could be designed which would be more effective and environmentally friendly in iron sulfide scale removal.