Research on the Ion-Extraction Demulsification Mechanism and Fiber-Particle-Induced Coalescence for Deep Oil Removal from High-Salinity Gas-Field Produced Water

Produced water from gas fields, under conditions of high emulsification, elevated salinity, and the coexistence of various interfacial active components, exhibits pronounced stability and poses significant challenges for treatment. Conventional physical separation techniques often fail to achieve effective demulsification and deep oil removal. Addressing this engineering bottleneck, the present study focuses on produced water from the western Sichuan gas field, conducting a systematic investigation into demulsification regulation, interfacial destabilization mechanisms, and the validation of particle coalescence-based oil removal processes.Initially, by examining the dynamic evolution of zeta potential, turbidity, interfacial tension, droplet size, and ion concentration during the alkaline conditioning of produced water, the study employs DLVO theory to quantitatively analyze the interaction potential between oil droplets and applies Gibbs adsorption theory to characterize interfacial film rigidity. The findings confirm that the rapid destabilization process is triggered by the precipitation and extraction of divalent ions, revealing a key mechanism whereby Ca²⁺ and Mg²⁺ enhance interfacial film rigidity through cross-linking with surfactants, thereby significantly reinforcing emulsion stability.Building on these insights, a synergistic purification strategy—“alkaline precipitation-induced destabilization coupled with randomly packed particle coalescence”—is proposed. Subsequent coalescence experiments demonstrate that an appropriately structured fiber bed can markedly reduce petroleum pollutant concentrations in the destabilized produced water. Pilot-scale validation shows that, with a bed thickness of 120 cm, pH maintained between 10.4 and 11, and a treatment capacity of 2–5 m³/h, the effluent oil content can be reduced to below 1 mg/L. The proposed integrated process offers notable advantages in reducing chemical dependency and enhancing system compactness, providing a scalable engineering solution for the efficient purification of highly emulsified gas field produced water.