(75j) Evaluation of Pyrite Scale Reaction Kinetics in a Rotating Disk Apparatus Using Chelating Agents and a Converter

Pyrite is one of the hardest iron sulfide scales which causes major problems in oil and gas production by damaging production equipment. The use of inorganic acid in iron sulfide scale removal particularly pyrite is ineffective and produces toxic gases such as hydrogen sulfide. In this work, H₂-S free formulation composed of Diethylene Triamine Pentaacetic acid (DTPA) combined with potassium or cesium carbonate as converters are used. The reaction kinetics of pyrite dissolution using a specially designed rotating disk apparatus (RDA) is investigated. Different characterization techniques such as SEM-EDX, XRD and XPS were used for the characterization of pyrite surface before and after chemical treatment. The effects of temperature, rotational disk speed, and converter type on the kinetics are studied. At 130 °C and 150 °C, the reaction increased linearly with the disk rotational speed representing mass transfer limited reaction and the activation energy was obtained as 9.94 kJ/mol. The DTPA diffusion coefficients for the new formulation at 130°C and 150°C are evaluated as 1.023 x10^-9cm².s^-1and 1.177x10^-9cm².s^-1_, respectively. The replacement of potassium carbonate by cesium carbonate did not produce significant effect on the reaction kinetics. Coreflooding tests were carried out on the new formulation of DTPA with K₂CO₃ to simulate the real dissolution of the scale in pipes and a solubility of 140 ppm/hr has been achieved. The estimation of pyrite dissolution rate by DTPA is expected to support engineering design in iron sulfides removal from oil and gas wells.