Abstract: Through, the observation of the acid sludges formation in qualitative tests and the inves-tigation of the effect of acid concentration and iron(Ⅲ )content on sludge一forming as well as that of the prevention-of sludge一forming with mutual solvents in quantitative tests，the au-thors in this paper find that the quantity of sludges formed will increase together with acid
concentration and the spent acid will produce a relatively smaller amount of acid sludges than initial acid. They also find the presense of iron(Ⅲ )will reinforce the sludge一forming ten-dencies，but a certain amount of mutual sol_vents(ethyleneglycol dibutylether) in acid will be effective in decreasing the quantity of acid aludges. Accordingly, some approaches have beem
put forward to prevent the formation of acid sludges.

Key words: Acid sludges, Asphaltene, Mutual solvents, Acid