Physicochemical Pathways Governing Sludge Formation in Tank Farm Storage: Comparative Analysis of Crude, Brine, and Sludge.

Petroleum sludge accumulation in crude oil storage terminals leads to significant operational inefficiencies impacting tank capacities and unplanned maintenance shutdowns. To understand the mechanistic origin of sludge formation, we performed an integrated physicochemical characterization of the source crude, tank farm crude, associated brine, and tank bottom sludge. The source and tank farm crude oils have measurable differences in their properties such as density, viscosity, SARA fractions, and metal content, which indicates compositional evolution during midstream transport. The sludge sample contains ∼30 wt % inorganic solids, comprising sand, corrosion products, and carbonate scale; ∼53.5 wt % hydrocarbons; ∼47 wt % asphaltenes; and ∼16.5 wt % associated water. Rheological measurements show pronounced non-Newtonian behavior, with a yield stress of ∼102 Pa at 25 °C, which decreases by more than half above 45 °C, consistent with a densely percolated particulate-asphaltene network. SEM imaging reveals irregular inorganic particles with crystalline phases such as FeCO3, CaCO3, and silica-based minerals as confirmed by XRD. The associated brine contains ∼9 g/L dissolved salts, elevated bicarbonate, and a basic pH, conditions that favor carbonate scaling, which promotes incorporation of inorganic phases into the sludge. Overall, the results demonstrate that the sludge accumulation process is heavily governed by asphaltene aggregation as well as midstream-derived inorganic particulates and entrained water, resulting in a rigid composite structure. This comprehensive analysis provides a mechanistic basis for sludge mitigation strategies focused on corrosion control, solids management, and brine chemistry conditioning.