Ever since formate brines were introduced in the oilfield in the 90's, test laboratories have struggled to determine their True Crystallization Temperature (TCT). The standard API procedure for measuring TCT in oilfield brines simply does not work in formate brines, and it is quite common to see TCT values reported as “too low to measure” even in cases where reference to other studies suggests that the TCT should be well within the measureable limit of the equipment. Factors that complicate the TCT measurements in formate brines are: a) the TCT values can be very low, and may be lower than the cooling capabilities of the measuring equipment, b) an enormous amount of supercooling, and c) the existence of metastable potassium formate crystals that form in formate brines that are rich in potassium formate.

A long-term research program has been aimed at understanding the unusual TCT behavior of potassium formate brine and developing a method to measure the TCT of all formate brines. This research program has delivered an accurate TCT determination procedure for formate brines that is simple, efficient, and involves no specialized equipment. The researchers found that special crystal seeding procedures were needed to get accurate TCT measurements in formate brines. Intelligent crystal seeding eliminates the TCT measurement problems caused by the formation of metastable phase crystals and supercooling.

In addition to full description of an accurate TCT measurement method for formate brines, this paper presents a complete set of TCT values for sodium, potassium, and cesium formate single salt brines and some cesium/potassium formate blends.

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