A fibre-optical method for monitoring barite precipitation at high pressure/high temperature conditions

Abstract

Monitoring and controlling of mineral precipitation is a major challenge in several industry segments such as oil and gas or geothermal energy. Especially at elevated pressures, temperatures, and salinities, these reactions are poorly understood and difficult to predict. Real-time monitoring under such conditions, however, is crucial for reduction or prevention of scaling as well as for process modelling. In this study, a novel fibre-optical method for monitoring the barite precipitation process at high pressures and high temperatures was developed and tested. The applicability of a fibre-optical sensor was demonstrated and kinetic data derived from experiments using synthetic fluids that were oversaturated with barite. The ionic strength was varied between 0 and 5 mol/l NaCl to simulate geothermal brines typically found in deep sedimentary reservoirs. Experiments were performed at 25 and 150 °C. For the studied variations it was found that the ionic strength had a strong impact on the barite precipitation rate whereas temperature had only a minor influence. The kinetic rate constants were decreasing with increasing salinity ranging from 9 to 0.4 l‧mol−1‧s−1 at 25 °C and from 8.6 to 0.66 l‧mol−1‧s−1 at 150 °C.