Technical Evaluation of Produced Water Treatment Technologies at NAOC Operated Fields in Imo State, South East Nigeria

Produced water management is a significant operational and environmental challenge in Nigerian onshore fields, where increasing water cuts from maturing reservoirs demand effective treatment systems capable of meeting regulatory discharge standards. This study conducts a technical evaluation of produced water treatment technologies currently deployed at Nigerian Agip Oil Company operated fields in Imo State, South East Nigeria. The study reviews the design basis, operational performance, and environmental compliance history of three produced water treatment plants processing water from different reservoir intervals. Treatment train configurations including de-oiling hydrocyclones, gas flotation units, and polishing filters are evaluated against the DPR guidelines for produced water discharge, which specify maximum oil-in-water concentrations of 40 milligrams per litre for onshore discharges. Operational data covering 2019 to 2023 indicate that the hydrocyclone-based plants consistently achieve effluent oil-in-water concentrations between 25 and 35 milligrams per litre, marginal to compliance limits during peak production periods. The addition of chemical demulsifier to the upstream feed has been tested and found to reduce effluent oil-in-water by an additional 8 milligrams per litre on average. The study concludes with a technology upgrade roadmap recommending installation of induced gas flotation polishing stages to ensure consistent regulatory compliance as water production volumes increase over the next five years. Keywords: produced water treatment, NAOC, Imo State, oil-in-water, DPR regulations.