The Marcellus waters of Pennsylvania and West Virginia commonly contain elevated levels of calcium, barium, and iron. Theoretical analyses of these waters indicate a propensity toward the formation of calcium carbonate, barium sulfate, strontium sulfate, and iron-related scales. The high level of dissolved iron commonly present in the water adversely affects the ability of the scale inhibitor to inhibit calcium carbonate scale. In this study, the inhibition performance of two new chemicals and some commercial products was evaluated under static and dynamic test conditions using synthetic Marcellus waters at varying iron concentrations. It was shown that both new chemicals were able to control calcium carbonate scale effectively in the presence of dissolved iron up to 200 ppm, whereas the performance of polycarboxylic acid, amino tri(methylene phosphonic) acid, and carboxymethyl inulin dropped sharply even in the presence of small amounts of Fe2+ (5 ppm). The inclusion of iron-sequestering agents with these chemicals and the effect of iron upon calcium sulfate inhibition are also discussed in this paper.
Mineral-scale formation is a problems for oil and gas operations that can result in the deterioration of assets, increased lifting costs, and lot production. Common mineral scales such as calcium carbonate, calcium sulfate, or barium sulfate can precipitate from produced water and create blockages in perforations, production tubulars, and equipment. The most common method of scale control is the use of low concentrations of specialty chemicals (inhibitors) that catalytically prevent the precipitation of solids. These chemical inhibitors are referred to as “threshold” inhibitors because they prevent scale formation at concentrations that are typically required with acid or chelate addition.