It has been known since the 1930's that concentrated brines release barium into solution from barite. The amount of barium released into solution is a function of the molar salt concentration, brine type, temperature, and pressure. Brines containing very high molar concentrations of solute are the most effective at solubilizing barite in well operations. Given the HSE hazard posed by fluids containing soluble barium it is important to know exactly what levels of this heavy metal may be present in high molarity oilfield brine systems that have been contaminated with barite.
An extensive test program has now been conducted to provide new and reliable information on the soluble barium content of potassium- and cesium formate brines that have been exposed to analytical grade barium sulfate at elevated temperatures and then cooled. The effects of formate concentration and the ratio of cesium to potassium in the formate brines were investigated. The brines were tested with and without the addition of carbonate/bicarbonate pH buffer, as a function of exposure temperature and exposure time.
The results of this research confirm results of previous research reported by Shell, indicating that up to 3,500 mg/L of barium can be released from barium sulfate at 100°C (212°F) in the most concentrated potassium formate brines. However, the good news is that soluble barium levels are low in all formate brines that contain carbonate/bicarbonate pH buffer. This is because any dissolved barium will precipitate out as barium carbonate, which is barely soluble in concentrated formate brines.
This new insight into the mechanisms of barite dissolution in buffered and unbuffered formate brines could open the door for the formulation of more advanced fluids for filter cake removal and scale dissolution applications.