Field Application of a New Method for Bicarbonate Alkalinity Measurement

Abstract

Accurate bicarbonate measurement is crucial in carbonate scales prediction. A common method for bicarbonate determination is through subtracting total alkalinity with carboxylates, but the measurement of carboxylates is time consuming and not applicable in the field. Since bicarbonate is hard to preserve in field brines, a field applicable method for bicarbonate detection was developed in a previous study. It was named the "head space method". The method is based on the head space pressure change due to carbon dioxide (CO2) releasing from test brine by adding strong acid to convert bicarbonate to CO2. This study is to further validate the method with synthetic and field brines and to investigate potential limitations. Based on the the tests of this study, the head space method can measure bicarbonate accurately without interference by the presence of carboxylates. In both synthetic and field brine analysis, the bicarbonates measured by head space method generally matched with the calculated bicarbonates through total alkalinity and total carboxylates. A case study further validated the accuracy of the head space method on bicarbonate determination. Moreover, this method is fast with low costs. Each sample analysis takes about 5 minutes. The capital cost of head space method equipment is less than 1,000 dollars. A limitation of the head space method identified that it is not applicable for high sulfide brines or brines with < 100 mg/L bicarbonate. Desipite the limitation, this low-cost bicarbonate detection method is fast, accurate, and applicable in the field, and able to provide instant bicarbonate monitoring in produced water in many cases.