Geochemistry, origin and potential of valuable elements in oilfield brines, Dezful Embayment, Southern Iran

Produced water generated during hydrocarbon production is one of the largest industrial waste streams and represents a potential secondary resource for critical and industrial elements. This study investigates the hydrogeochemistry, origin, and resource recovery potential of formation brines from the Dezful Embayment, one of the principal petroleum provinces of southwestern Iran. Ten produced-water samples were collected from the Ahvaz, Marun, Aghajari, Masjed Soleyman, Lali, and Zilaie oilfields and analyzed for major, minor, and trace elements together with stable oxygen and hydrogen isotopes ( δ ¹⁸O and δ ²H). Electrical conductivity (EC) ranged from 9,785 to 324,554 μ S/cm, whereas total dissolved solids (TDS) varied between 6,360 and 210,960 mg/L, with mean values of 201,621 μ S/cm and 131,054 mg/L, respectively, confirming the highly saline nature of these formation waters. The brines are dominated by Cl–Na and Cl–Na–Ca hydrochemical facies. Major-ion relationships and stable isotope signatures indicate that the fluids were derived predominantly from evaporated palaeoseawater deposited in restricted lagoonal settings and subsequently modified through evaporation, halite dissolution, and long-term water–rock interaction during reservoir evolution. Variations in elemental concentrations among the investigated oilfields reflect differences in fluid evolution and geochemical exchange processes. Although Li and I concentrations are lower than those reported from commercially exploited oilfield brines elsewhere, Br (mean 360 mg/L), Sr (mean 254 mg/L), Mg (mean 690 mg/L), Na (mean 24,637 mg/L), and Cl (mean 87,919 mg/L) occur at comparatively elevated concentrations, highlighting their potential for future resource recovery following detailed techno-economic evaluation. From an environmental perspective, treatment and beneficial utilization of produced water could reduce disposal-related impacts while creating opportunities for the recovery of valuable dissolved constituents and the reuse of treated water for industrial applications in southern Iran.