Polymer-Based Scale Inhibition and Desorption Behavior in Carbonate Reservoirs: Core Flooding Investigation and...

Scale deposition, particularly calcium sulfate, poses a major challenge in carbonate reservoirs, leading to permeability reduction and operational inefficiencies. In this study, the performance of a polymeric scale inhibitor, polyphosphinocarboxylic acid (PPCA), was systematically investigated through dynamic core flooding experiments combined with statistical modeling. To address scale inhibition performance and minimum inhibitor requirements, additional static jar tests and dynamic tube blocking experiments were conducted. The results confirmed a minimum inhibitory concentration (MIC) of 40 ppm PPCA, where inhibition efficiency exceeded 90% at elevated temperatures. Moreover, the desorption behavior of PPCA was evaluated under a wide range of operational conditions, including pore volume (0-40 PV), temperature (50-100 °C), injection rate (2-6 mL/min), and pH (6-8). Effluent concentrations were quantified using a spectrophotometric method and expressed as the C_f/C_i ratio (effluent concentration to injected concentration) to characterize inhibitor return behavior. A comprehensive dataset comprising 224 experimental runs was analyzed using Response Surface Methodology (RSM), leading to the development of two predictive models for low (0-10 PV) and high (10-40 PV) pore volume ranges. The models demonstrated excellent predictive capability, with R² values of 0.9934 and 0.9979, respectively. In addition, statistical analysis confirmed that pore volume and injection rate were the most influential parameters, while pH exhibited a comparatively minor effect. Results showed that increasing PV, temperature, injection rate, and pH led to a decrease in C_f/C_i, indicating enhanced desorption. For instance, C_f/C_i decreased from approximately 0.12 at 10 PV to 0.06 at 40 PV under reference conditions. Furthermore, optimization results revealed that maintaining an effective inhibitor concentration (C_f/C_i more than 0.05) is strongly dependent on operating conditions. At 60 °C, a wide operational window was observed, whereas at 100 °C, the effective region significantly narrowed due to accelerated desorption. Furthermore, permeability reduction analysis (K_d/K_i) demonstrated significant suppression of scale-induced formation damage in the presence of PPCA, while blank tests showed severe permeability decline. The integrated results validate the dual role of PPCA in both scale inhibition efficiency and formation protection under dynamic conditions. The novelty of this work lies in integrating polymer-specific behavior with dynamic core flooding and multivariable statistical modeling, providing a robust predictive framework for optimizing squeeze treatment design in carbonate reservoirs.