Evaluation of Produced Water Quality from Onshore Oil Fields in Edo State

Produced water co-extracted with crude oil from onshore fields in Edo State, South South Nigeria, constitutes the largest volume waste stream in oil production operations, yet its management and disposal practices in this sub-region lack systematic scientific evaluation relative to regulatory requirements. This study evaluates the geochemical quality of produced water from five onshore producing fields in Edo State, characterising its physicochemical composition and assessing the environmental risk of surface discharge and reinjection disposal options. Produced water samples were collected from wellhead separators at each field during both wet and dry season campaigns. Analyses included basic physicochemical parameters, chloride, total dissolved solids, dissolved organic carbon, benzene-toluene-ethylbenzene-xylene compounds, polycyclic aromatic hydrocarbons, naturally occurring radioactive materials, and a full suite of trace metals. Results are evaluated against the Department of Petroleum Resources Guidelines for the Prohibition of Gas Flaring and Produced Water Discharge. A hydrogeochemical classification scheme is applied to characterise the water type and formation water origin. The study evaluates the technical feasibility of beneficial reuse options including treated irrigation water and dust suppression, comparing volume-weighted treatment costs. Findings inform the environmental management plans of the operating companies and contribute to Department of Petroleum Resources regulatory enforcement capacity. Keywords: produced water, geochemistry, onshore fields, Edo State, disposal management.