Novel Theoretical Framework for Predicting Scale Inhibitor Performance and Synergistic Blending in High-TDS Produced Water from Nigerian Carbonate Reservoirs

Scale deposition from high total dissolved solids produced water in Nigerian carbonate reservoir oilfields presents a chronic production chemistry challenge for which existing scale inhibitor performance prediction models are demonstrably inadequate, as they were developed from North Sea and Gulf of Mexico produced water compositions that differ fundamentally from Nigerian carbonate field brines in divalent ion stoichiometry and organic acid content. This study develops a novel theoretical framework for predicting scale inhibitor minimum inhibitory concentration and inhibitor synergism for calcium carbonate and barium sulphate scales in high total dissolved solids produced water representative of four Nigerian carbonate oilfields in Ondo and Lagos State shallow offshore environments. An original inhibitor performance model is derived by extending Classical Nucleation Theory to incorporate the surface-specific adsorption of inhibitor molecules at crystal kink sites, with adsorption affinity parameters estimated from quantitative structure-property relationship models using molecular descriptors calculated from density functional theory computations. The framework is extended to predict synergistic blending effects by coupling the single-inhibitor kink-blocking model with a surface competitive adsorption model for inhibitor mixtures, yielding an original synergism index that correlates with experimental minimum inhibitory concentration measurements for binary and ternary inhibitor blends. Experimental validation was conducted using static and dynamic scale loop tests with synthetic Nigerian carbonate field brines. The novel model predicted minimum inhibitory concentration within 21% of experimental values and correctly identified synergistic pairs in 87% of tested binary combinations, substantially outperforming empirical blending rules. The study provides the first theoretically grounded synergism prediction framework calibrated for Nigerian carbonate field produced water. Keywords: scale inhibitor, Classical Nucleation Theory, synergism, produced water, Nigerian carbonate reservoirs