Aluminum silicate scale formation and inhibition (2): Scale solubilities and laboratory and field inhibition tests

The solubilities of pure silica, iron-silicate and aluminum-silicate scales were measured in water from 25-250 degrees C in a laboratory pressure reactor. Iron- and aluminum-silicate scales are significantly less soluble than pure amorphous silica. Aluminum- and iron-rich silica scales at equilibrium conditions are predicted to deposit from near-neutral, low salinity brines at temperatures that are 25 and 75 degrees C above the saturation point for pure amorphous silica, respectively. This laboratory study demonstrates that higher brine injection temperatures are required to mitigate aluminum- and iron-rich silica scaling compared with pure amorphous silica. In a laboratory scale test, pure amorphous silica and aluminum-rich silica deposition rates have been measured at high degrees of supersaturation in the presence of potential inhibitors. Scale deposition was best inhibited by brine pH modification techniques. A commercially available dispersant successfully inhibited amorphous silica scaling, but exacerbated aluminum silicate scaling. Scale inhibition was also achieved in the presence of aluminum complexing/sequestering agents in a patent-pending process. Screening of these potential silica- and aluminum-silicate scale inhibitors in the laboratory will focus the efforts of ongoing field pilot scale testing. The effect of complexing/sequestering agents on scale inhibition was monitored in preliminary field pilot tests. These complexing agents achieved 25% to 80% aluminum silicate scale inhibition. (C) 1998 CNR. Published by Elsevier Science Ltd. All rights reserved.