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

Abstract

The solubilities of pure silica, iron-silicate and aluminum-silicate scales were measured in water from 25–250°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°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.