Experimental determination of barite dissolution and precipitation rates as a function of temperature and aqueous fluid composition

Abstract

Barite dissolution and precipitation rates were investigated in closed system reactors, in which total aqueous NaCl concentrations ranged from 0 to 1.5molal, pH from 2 to 9, and temperature from 25 to 90°C. Measured barite dissolution and precipitation rates exhibited a reaction order of 0.2 and 1, respectively, with respect to the barite saturation state. Although these different reaction orders suggest distinctly different mechanisms for dissolution and precipitation, the rates for both processes approach equilibrium with a similar slope on a rate versus saturation state plot, consistent with the concept of micro-reversibility. Barite dissolution rate constants increase as a linear function of the square root of ionic strength but vary only slightly with pH. The dissolution rate dependence on temperature is consistent with an activation energy of 25± 2kJmol−1. Barite dissolution and precipitation rates are not significantly affected by the presence of aqueous calcium, magnesium or strontium. The rates measured in the study were generated in fluids similar to those found in sedimentary basins, ocean floor sediments and oil field reservoirs so the data may provide close estimates for the reactivity of barite during a variety of natural and industrial processes.