Effect of Treatment Conditions on Matrix Stimulation of Carbonate Rocks with Chelating Agents

Abstract

This study aimed to optimize the acidizing efficiency during stimulation treatments with chelating agents. The performance of hydroxylethylethylenediaminetriacetic acid (HEDTA), diethylenetriaminepentaacetic acid (DTPA), and ethylenediaminetetraacetic acid (EDTA) in stimulating carbonate rocks were investigated. In this paper, the effect of injection rate, chemical type, pH, and concentration on the stimulation performance was studied. Also, the optimum treatment conditions were identified utilizing the acid volume and treatment time. Different measurements were carried out, including solubility tests, coreflooding experiments, and CT scan analysis. Solubility tests were performed to study the impact of solution concentration and pH on the performance of the chelating agent. Coreflooding experiments were carried out at high-pressure, high-temperature conditions to assess the performance of chelating agents in different treatment situations. In addition, CT scan analysis was carried out before and after the acid injections to capture the changes induced in the carbonate matrix due to the stimulation treatment. The success of acidizing treatment was identified by the creation of the dominant wormholes. The pressure-drop profiles and the CT scan analysis were used to confirm the generation of wormholes. Finally, the normalized volume and time to breakthrough were utilized to identify the optimum treatment conditions. In this work, chelating agents successfully created dominant wormholes (WHs) in carbonate rocks at different injection rates and treatment conditions. However, applying an injection rate between 0.7 and 1 cm3/min significantly improved the acidizing performance and reduced the acid volume that was required to create wormholes. EDTA and HEDTA chelating agents showed better performance at low pH. Using a solution pH of 4.5 resulted in reducing the acid volume by 30% compared to using a solution pH of 10 at the same conditions. However, DTPA chelating agent showed better performance at high pH, and dominant WHs were created at a pH of 12 using less acid volume. Finally, the optimum acidizing treatment can be achieved by using EDTA chelating agent with a concentration of 9.25 wt.% and pH of 4.5. Applying the optimum treatment parameters can reduce the acid volume by 40% and the chemical cost by a factor of 6, on average. Overall, this study indicates that chelating agents’ solution can be injected at optimum conditions in terms of chemical concentration, pH, and injection rate, to maximize the treatment efficiency and reduce the cost.