Inhibition of Antimony Sulphide Scale by Chemical Additives: Laboratory and Field Test Results

Abstract

The PC-26 well, the first exploratory deep well in the Piancastagnaio field (Mt. Amiata area), was at the end of the 1970s. It started production in 1980. Heavy scaling problems were soon experienced; these started a few meters downhole in the production casing, and occurred mainly inside the pressure separator. This scale consisted mainly of antimony sulphide and amorphous silica, with the latter prevailing in the low-temperature part of the separating equipment. The aim of the first laboratory tests was to screen possible chemical additives capable of inhibiting the sulphide scaling and to develop effective concentrations of the most promising products. In subsequent field tests two selected inhibitors were both effective in preventing antimony sulphide scaling, although with different side effects on silica precipitation. Since these positive field test results, an inhibitor addition has been used in the PC-26 well, and it is no longer subject to any appreciable operating problem deriving from scale build-up in the surface plant.