Reaction of Chelating Agents and Catalyst with Sandstone Minerals During Matrix Acid Treatment

Chelating agents were used recently to stimulate sandstone formations in oil and gas reservoirs. Chelating agents replaced the old sandstone acidizing fluids such as mud acid (HF + HCl). Mud acid has several problems such as high corrosion rate, reservoir unconsolidation problems, and incompatibility with the reservoir rocks. The objective of this study is to introduce different chelating agents diluted in deionized water and seawater combined with potassium carbonate as a catalyst and clay stabilizer to stimulate sandstones reservoirs. In this paper, solubility experiments were performed for Bandera and Berea sandstone rocks in high pH DTPA, ethylenediaminetetraacetic acid (EDTA), and hydroxyethylenediaminetriacetic acid (HEDTA) solutions. The optimum concentrations of both chelating agent and potassium carbonate were determined through the solubility experiments. Chelating agents were diluted using seawater and deionized water from an initial concentration of 40 wt%. Coreflooding experiments were performed on Berea and Bandera sandstone cores to assess the performance of the new formulation. Corrosion tests were conducted on actual tubing coupons made of L-80 alloy to check the corrosion rate of the new formulations. The enhancement in the core permeability was recorded after using the chelating agent and the catalyst to investigate the effectiveness of the formulation in sandstone acidizing. The solubility results showed Berea and Bandera sandstone have good solubility in HEDTA, EDTA, and DTPA chelating agents. EDTA chelating agent combined with potassium carbonate enhanced the permeability of both sandstone cores. EDTA chelating agent combined with catalyst has a corrosion rate of 0.01lbm/ft2 at 350∘C compared to 0.65lbm/ft2 for the mud acid plus 3 vol% corrosion inhibitor at the same temperature. The corrosion inhibitor additives will be eliminated in the new formulation which will reduce the cost of the stimulation fluid.