Abstract

In the Rocky Mountain region of the United States, high-salinity brines (total dissolved solids > 250, 000 mg/L) present during oil and gas production cause severe scale problems in the Williston Basin. The scales include not only calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, but also sodium chloride (halite). This paper presents the development of test methods and their corresponding testing results for scale inhibitor evaluations in the laboratory and their applications in the field for high-salinity brines.

It is well known that there is no effective test method for halite scale inhibitor laboratory testing due to the difficulty of controlling the amount of halite precipitation and reproducibility in the test. The evaluation of scale inhibitor performance was conducted by using a tube-blocking test and a static bottle test with synthetic high-salinity brines from the Williston Basin. Two sets of brines were designed, based on the field brine, and were tested with two methods. One set of brine was for halite scale inhibitor evaluation by mixing near-saturated NaCl synthetic brine with a highly concentrated brine of CaCl2·2H2O + NaCl. The second set of brine was designed to evaluate scale inhibitor performance on calcium carbonate, calcium sulfate, barium sulfate, and strontium sulfate by modified brines. Three types of scale inhibitors were used for the performance evaluations, including halite scale inhibitors, general scale inhibitors, and a multifunctional scale inhibitor. The lab test results showed the multifuntinal scale inhibitor exhibited good scale inhibition performance for both sets of scale testing. Successful scale inhibitor implementations in the field applications and case history are also presented in this paper.

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