Abstract: Conventional mud acid acidification generally causes problems such as excessive reaction speed, short operating distance, serious secondary and triple damage, excessive erosion, and serious corrosion. Aiming at the above problems, the technicians developed a new acid solution containing hydrochloric acid, hydrofluoric acid, organic acid, fluoroboric acid, and a variety of additives with low corrosion, low damage, low reaction speed, and good compatibility. The performance of the new acid solution was evaluated and the results showed that compared with conventional mud acid, the acid rock reaction speed of the new acid solution is slower; the reaction time is longer; there was no obvious sediment in the reaction product; and the damage to the formation is small. The acidity change of the new acid solution is relatively moderate; the acid duration is long and it has buffer property. It is a kind of acid solution with low acidity and low reaction speed which is suitable for deep acidification. The new acid solution has strong inhibition of carbonate and silicate precipitation capacity, but with the increase of concentration, the capacity of the new acid solution to inhibit carbonate and silicate precipitation decreases.

Key words: pressure reduction and injection enhancement, deep acidification, organic acid, fluoboric acid, conventional mud acid