Inhibition of Calcium Carbonate Scale in the Presence of EOR Chemicals

Abstract A field trial has been planned for a chemically enhanced oil recovery (EOR) project in Saudi Arabia. The injection chemicals will be a combination of surfactants and polymers. There is a concern that the breakthrough of these chemicals in produced water could affect scale formation process and interfere with the scale treatment program. The objective of this study is to investigate the potential impacts of the injected EOR chemicals on calcium carbonate (CaCO3) scale inhibitor performance. Laboratory tests were carried out using static bottle and dynamic tube blocking methods. CaCO3 scale inhibition was studied in the absence and presence of the EOR chemicals at the estimated peak breakthrough concentrations, i.e., 200 mg/L polymers and 150 mg/L surfactants. Three different types of inhibitors were evaluated: tri-phosphonate, penta-phosphonate, and polyacrylate. Inhibition (%) from the bottle test and minimum effective dose (MED) based on the tube blocking method were determined for each inhibitor at 160 °F. Scale precipitates from the bottle tests were also characterized for morphology and polymorphs using environmental scanning electron and X-ray diffraction (XRD) techniques. Obtained results showed significant reductions in scale inhibitor performance by the EOR chemicals. In dynamic tube blocking tests, the MED vaules of inhibitors were increased roughly 10 times with the EOR chemicals. The static bottle tests showed considerable changes under the test conditions. For example, the inhibition (%) of the penta-phosphonate based inhibitor at 20 mg/L was diminished from 100% to 20%; and the inhibition (%) of the tri-phosphonate inhibitor was decreased from 100% to below 50% and 70%, respectively, at 10 mg/L and 20 mg/L. The polymeric inhibitor completely lost its inhibition efficiency over the tested concentration range of 2 mg/L to 20 mg/L. The impact of EOR chemicals were also demonstrated by the remarkable ranges of crystal morphologies, changing from simple aragonite columns to nanorod, distorted spheroid, and flower-like superstructure in the presence of EOR chemicals and inhibitors. This paper presents the first reported comprehensive study on the impacts of the EOR chemicals on CaCO3 scale formation and prevention. Results suggest that the performance of scale inhibitors could be substantially affected by the EOR chemicals. Such potential impact should be determined and a new scale treatment program should be developed for the success of EOR projects.