Research and Application of Prolonged-Effect Acidizing Technology for Water Injection Wells in the Bohai Oilfield

In response to the deteriorating reacidizing of water injection wells in the Bohai Oilfield, a study on the prolonged-effect acidizing technology for water injection wells was carried out. The prolonged-effect acid was prepared by adding an anti-swelling agent and surfactant to three kinds of deep retarded acid in low concentrations that enhanced the reservoir protection capability of acid. At 60 ℃, the as-prepared acid was tested with respect to its dissolution on field scale samples, calcium montmorillonite, and silica, its scaling inhibition of injected water, oil-washing performance, retardation, total dissolution performance, and prolonged effect with dynamic displacement. The results showed that the dissolution rate of the prolonged-effect acid on the calcium montmorillonite and scale samples could reach 45.23% and 86.08% respectively, while that on silica was only 0.22%. The acid had strong inhibition of scaling and a surface tension of 12.77 mN/m. Its dissolution rate on rock powder could reach 9.39%, 13.64%, and 24.54% after 2, 4, and 6 h, respectively. And after dynamic displacement, the increase in the permeability after the injection of water 20 times the pore volume remained at 1.8–1.9 times. The proposed technology was applied to 14 wells in the Bohai Oilfield, achieving good results. The results showed that the prolonged-effect acid, with a high total dissolution rate, performed well in unblocking the water injection wells, protecting the framework, retarding the reaction of acid and rock and prolonging effect, which makes it worthy of wide application.