ABSTRACT
Precipitation of minerals such as barium sulfate in the production equipment and within reservoirs in petroleum and other hydrothermal producing (e.g. geothermal) systems is a major operational problem. Barium sulfate deposition can cause different problems such as loss in production, formation damage, and premature equipment failure. Mineral deposition is usually caused by changes in the producing fluid temperature or composition and chemistry. In these systems, aqueous systems thermodynamic modeling plays a central role in predicting the favorability of barite precipitation and dissolution. Predominance diagrams and speciation models demonstrate how solution properties such as pH and electrolyte composition impact the solubility limit of barite. Temperature and pressure have a strong influence on barite solubility. The solubility limit of barite varies from 5 to 25 μmol kg-1 depending on the temperature. Commercial software such as OLI Studio that relies on the Helgeson–Kirkham–Flowers (HKF) equation of state model (EOS) present disclaimers that the model does not work at high temperatures and low pressures above 300°C [1]. Here, we present a model that is able to predict the behavior of barite-containing species at high temperatures and pressures. This was accomplished using a molecular statistical thermodynamic-based model capable of predicting the solubility of barite beyond the critical point of water. The resulting predictions accurately captured increases in solubility from 0°C to 100°C, decreases in solubility from 100°C to 300°C, and then a steady increase to 400°C which covers the range of temperatures currently being explored by hydrothermal and petroleum systems.
