Hydrocarbon production is often accompanied by the production of a brine. Minerals may precipitate from a brine and deposit within the production system. The scale deposits can be located both downhole and in surface equipment. Often the deposit has an adverse effect on production and must be removed.

Producers and service companies devote considerable effort to developing and marketing effective treating chemicals because of the serious impact that gypsum (CaS04 • 2H20) scale formation can have on hydrocarbon production. The performance of these treating chemicals used for scale removal can be verified most effectively after an actual field trial. However, field testing can be very difficult and time-consuming, especially when many chemicals are being evaluated. Although most laboratory tests cannot exactly duplicate field conditions, the advantage of such tests is to provide the user with a comparison of the performance of one scale remover against that of another under standard laboratory conditions. The industry has not established a standard test method by which to evaluate gypsum scale removers. Consequently, performance tests on a scale remover or collection of scale removers yield widely differing absolute and relative results depending on the test procedure used.

Responding to an expressed need for a standard test method for the evaluation of chemical-based gypsum scale removers, NACE Unit Committee T-1 D formed Task Group T-1 D-32 in 1987. The initial task group assignment was to compose and publish a technical committee report. That report was issued in 1991 (NACE Publication 1 D191. The subsequent assignment was to develop standard test methods for screening gypsum scale remover chemicals, which are addressed in this standard.

This standard presents test methods for screening the effectiveness of two types of gypsum scale removers, one for scale dissolvers, and another for scale converters. These are primarily intended for use by those in the petroleum industry who need to use treating chemicals to remove gypsum scale deposits.

This NACE standard was prepared by Task Group T-1D-32, a component of Unit Committee T-1 D on Corrosion Monitoring and Control of Corrosion Environments in Petroleum Production Operations, and is issued by NACE under the auspices of Group Committee T-1 on Corrosion Control in Petroleum Production.

 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. Historical Document 1997