Evaluation of the compatibility between scale inhibitor and matrices with different calcium concentrations based on experimental design

The oil production scenario in the pre-salt fields poses challenges for the oil industry. The chemical composition of the water associated to the produced oil differs from the traditional fields, and may represent a restriction to the application of some scale inhibitors (SI). In this way, the evaluation of the compatibility between SI and the matrix in which it will be used is very important for guaranteeing the flow of oil1. The combination of two or more factors may result in behavioral diagrams of the SI, identifying compatibility/incompatibility bands with the medium2. In this context, this work aims to verify the compatibility of SI (II52) using Doehlert design, for three variables: II52, Ca2+ and NaCl concentrations. The response was given in terms of the turbidity of the solutions, and the measurements performed on a HACH model 2100AN turbidimeter. The Pareto Diagram (Figure 1) shows that the concentrations of calcium and sodium chloride, as well as the interaction between these factors, are the most significant effects on the response variable (turbidity). The estimated coefficients show a tendency of turbidity increase directly proportional to the factors. The desirability function of the STATISTICA software allowed to obtain the optimum values of the investigated parameters (Table 1). These values indicate the highest compatibility condition checked. It is concluded that the application of the Doehlert design was efficient in identifying the factors that influence the response, besides allowing to identify an optimal condition of compatibility.