An Effective Optimization Method of One-Step Sandstone Acid Systems at Formation Conditions

The one-step acid systems, mainly based on the chelating agents, can greatly simplify process of sandstone acidizing operation, and have a great application prospect. But for now, there are still no standard one-step acids optimization methods. Existing studies mostly conduct at room temperature conditions, and cannot reflect the field situation under the reservoir conditions. So current optimized acids still produce secondary precipitation and difficultly apply in sandstone acidizing. Herein, based on the complexometric titration, an effective optimization method of one-step sandstone acid systems at formation conditions is proposed. The method can quantitatively measure the chelating ability of chelating agents with respect to each type of metal ions under different formation conditions, especially temperature. According to this method, five chelating acids for four metal ions are tested. The results show chelating acid 4# can better chelate the four metal ions under different temperature. The core permeability after treatment of the preferred chelating acid 4# is increased by 1.68 times, 3.14 times, and 9.21 times at 25 C°, 60 C°, and 90 C°. In addition, mineral composition tests indicate the core after the treatment with chelating acid 4# has no secondary precipitation.