Concentration of calcium
versus the concentration of sulfate in 1000 produced water records from the
Madison Group in the Williston basin within eastern Montana. The content
of calcium ranges from < 1 to 50 g/L. The content of sulfate ranges from
<1 to 14 g/L. The points plot such that records with high contents of sulfate
have low contents of calcium and visa versa. The array of points define a
curved (hyperbolic) upper limit between 0 and 8 g/L sulfate and 0 and 20 g/L
sulfate. The curved upper limit coincides approximately with the solubility
limit for gypsum known to occur within parts of the Madison Group.
