Coupling Well Log Data with Chemical Thermodynamic Modeling for Predicting Mineral Precipitation Along the Wellbore Depth Profile

Abstract Inorganic scale formation is a significant challenge to flow assurance and well productivity, which can result from incompatible brine mixing or shifts in temperature and pressure. This study aims to accurately model scaling due to injection and formation fluid interactions and to integrate temperature and pressure logs to predict mineral saturation along the wellbore depth profile. Thermodynamic modeling employed Pitzer’s equations to account for deviations from ideality in electrolyte solutions, with excess Gibbs free energy describing interactions among cations, anions, and neutral species. This enabled accurate calculations of activity coefficients, osmotic pressures, and other solution thermodynamics properties. The Peng-Robinson equation of state modeled the single-component gas phase fugacity. Five brines, representing different injection and formation fluid mixing scenarios, were analyzed and used. Depth-dependent pressure and temperature profiles were incorporated to assess mineral saturation. Experimental validation was done using ion chromatography and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) to measure the ionic composition of brines after reaching equilibrium. Modeling results closely matched experimental data, confirming the accuracy of ionic composition predictions at equilibrium. Mixing seawater, rich in sulfate, with barium, strontium, and calcium-containing brines demonstrated that barium sulfate is the most thermodynamically stable scale, followed by strontium and calcium sulfate, consistent with hard-soft acid-base (HSAB) theory where more electronically rich inorganic cations tend to bind more with soft anions that have a diffuse electronic structure like sulfate. Along the wellbore depth profile, calcite saturation showed significant variation; supersaturation occurred at shallow depths due to rising pH and carbonate ion activity, promoting precipitation. In contrast, minerals like halite, celestite, and barite exhibited fluctuating behavior, influenced more by temperature and pressure than pH. Gypsum and anhydrite saturation indices crossed due to opposing temperature stability trends, gypsum being stable at lower temperatures and anhydrite at higher. This study shows the promise of integrating thermodynamic models with pressure and temperature log data to make informed decisions for mitigating inorganic scale depositions. This work presents a novel approach that integrates thermodynamic models with pressure and temperature well log data for the accurate prediction of mineral saturation along the wellbore depth profile. This approach offers petroleum engineers a valuable tool to predict precipitation depths and design mitigation strategies, enhancing well integrity and reducing scale-related risks.