Water recycling has become a strategic imperative in the oil and gas sector, driven by increasing water scarcity, stringent environmental regulations, and the high operational costs associated with freshwater use and wastewater disposal. Oilfield operations generate diverse and complex wastewater streams, including produced water, drilling fluids, flowback water, and cooling effluents, each containing a challenging mix of hydrocarbons, dissolved salts, heavy metals, and treatment-resistant chemicals. These contaminants require multi-stage treatment systems that incorporate physical, chemical, biological, and membrane-based processes for effective removal and reuse. This chapter presents a comprehensive review of both conventional and advanced technologies for water recycling in oilfield industry plants. It outlines the operational principles, advantages, and constraints of primary, secondary, and tertiary treatment methods, with emphasis on gravity separation, flotation, coagulation, biological treatment, membrane filtration, and desalination. The integration of emerging technologies, such as forward osmosis (FO), capacitive deionization (CDI), electrocoagulation (EC), and solar-powered desalination, is critically examined for their potential to enhance treatment efficiency and sustainability, particularly in remote or resource-constrained settings. Practical field-scale applications and hybrid treatment configurations are also discussed, providing a holistic perspective on the design and optimization of resilient water recycling systems. By combining technical, economic, and environmental considerations, this chapter offers valuable insights to researchers, engineers, and decision-makers seeking to implement sustainable water reuse strategies in upstream and midstream oilfield operations.
