Pyrite Scale Removal Using Green Formulations for Oil and Gas Applications: Reaction Kinetics

Abstract

Pyrite is one of the toughest iron sulfide scales to remove, 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 diethylenetriamine pentaacetic acid (DTPA) combined with potassium or cesium carbonate as the converter is used. The reaction kinetics of pyrite dissolution using a specially designed rotating disk apparatus is investigated. Different characterization techniques such as SEM–EDX, XRD, and XPS were used for the characterization of the pyrite surface before and after chemical treatment. The effects of temperature, rotational disk speed, and converter type on the kinetics are studied. At 130 and 150 °C, the reaction rate increased linearly with the disk rotational speed representing mass-transfer-limited reaction, and the activation energy was 9.94 kJ mol–1. The DTPA diffusion coefficients for the new formulation at 130 and 150 °C were 1.023 × 10–9 and 1.177 × 10–9 cm2 s–1, respectively. The replacement of potassium carbonate by cesium carbonate did not produce a significant effect on the reaction kinetics. Coreflooding tests were carried out using the new formulation of DTPA with K2CO3 to simulate the real dissolution of the scale in pipes, and a solubility of 140 ppm h–1 has been attained. The estimation of the pyrite dissolution rate by DTPA is expected to support engineering design in iron sulfide removal from oil and gas wells.