Precipitation of insoluble reaction products during the acid treatment of producing and injection wells is a problem which has long been recognized. These precipitates are capable of reducing the effectiveness of treatments or, in some cases, causing complete plugging of the formation. Among the precipitates which can form are iron compounds, such as ferric hydroxide and ferrous sulfide. When hydrofluoric acid is used, calcium fluoride, hydrated silica and various hexafluosilicates can precipitate. Acids also react with some crude oils to precipitate asphaltic sludges. An understanding of potential precipitates, conditions under which they form and methods of preventing or minimizing the problem is necessary to obtain optimum treatment results.

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