scope:

The test methods described in this standard are static laboratory screening tests designed to measure the ability of chemicals to remove gypsum scale deposits. There are two types of scale-removal chemicals: dissolvers and converters. Scale dissolvers, generally chelating or sequestering agents, can effect the dissolution and removal of gypsum scale in one step. Converters, such as those formulations based on sodium (or potassium) glycolate and sodium (or ammonium) carbonate (or bicarbonate), are used to alter or convert the calcium sulfate to another compound which is then removed by dissolution with a dilute mineral acid (typically hydrochloric acid). Test methods for screening both gypsum scale dissolvers and converters are described.

These test methods are recommended only for ranking the performance of different scale-removal chemicals under the laboratory conditions set by these test methods.

Many factors such as reaction kinetics, fluid velocity, variable temperatures and pressures, scale surface area, and scale composition can significantly affect scale removal under field conditions. Detailed consideration of these parameters is outside the scope of this standard. However, field conditions, field brine composition, and other variables noted above should be considered at some point in the evaluation prior to final selection of a scale remover for field use.

Tests can be conducted using varying amounts of gypsum to obtain a better comparison of scale removers under the laboratory conditions set by these test methods. The actual ratio of scale remover to gypsum required for a field application may be different from that established by these test methods.

This standard lists the necessary apparatus, reagents, and procedures for conducting screening tests of both gypsum dissolvers and converters.

A reference scale dissolver, tetrasodium ethylenediaminetetraacetate (Na4EDTA), or a reference scale converter, potassium glycolate (the potassium salt of hydroxyacetic acid, HOCH2 COOK), is run along with the scale removers being screened. The test results obtained using a reference chemical of known scale-removal capacity provide a benchmark to use in verifying that the screening test procedures were properly conducted.