Research and Application of Buffered Direct Discharge Acid System in Oil Wells of Bohai Oilfield

In the Bohai Oilfield, production capacity decline is often caused by scaling during production. Conventional acidizing for plugging removal faces issues such as the need for neutralization of residual acid flowback, susceptibility to crude oil emulsification, equipment corrosion, and production process interruption, etc. Meanwhile, existing chelating neutral plugging removal agents generally suffer from insufficient dissolution capacity and susceptibility to secondary precipitation. To address these challenges, a buffered direct discharge acid plugging removal system was developed. This system used low-molecular-weight carboxylic acids and their ammonium salts as the main agents, supplemented with a small amount of hydrochloric acid, ammonium bifluoride, hydrofluoric acid, and a composite iron stabilizer consisting of HEDP and citric acid. Through a two-stage pH regulation mechanism, the pH of the residual acid was stabilized between 5 and 7, enabling direct discharge. Performance evaluation shows that the pad fluid of the buffered direct discharge acid plugging removal system achieves a calcium carbonate dissolution rate of 75.25%, while the treatment fluid exhibits dissolution rates of 34.70% for bentonite and 15.73%–20.91% for field cuttings, with an iron stabilization capacity of 175 mg/L. Its comprehensive performance is comparable to or better than that of conventional acid fluids. Following field application in multiple wells in the Bohai Oilfield, the system has achieved oil production increase ranging from 38% to 118 %. The flowback fluid can be directly routed into the production process without neutralization, demonstrating good plugging removal effectiveness and process compatibility. This technology provides a new solution for efficient and safe acidizing and plugging removal in offshore oilfields.