An Advanced Clarification Process for Treating Produced Waters

Abstract

Summary An advanced clarification process that was based on enhanced floc removal with magnetite and magnetic ballast [M2 Water Treatment's Magnetic Ballast Clarification (MBC) system] was evaluated in a field study at a hydraulic-fracture wastewater disposal site in southwest Texas. In this process, suspended solids are chemically flocculated in the presence of magnetite, rendering dense floc particles that are also magnetic. Flocculated solids with high settling rates are removed by gravity separation. The settled solids are then removed by use of drum-styled magnetics. Magnetite is recovered and reused. Although technically called clarification, the MBC process is governed by magnetic flux as opposed to gravity forces, allowing for a much smaller unit footprint, a unit that is portable for mobile use, and more dynamic control compared with conventional clarification. Produced water from a total of nine wells was processed during a period of several weeks in July and August 2015 in a 5-gal/min (171-B/D) pilot unit. Most tests were operated at approximately 3.1 gal/min (106 B/D) for consistency with the highly variable wastes encountered. Treated water sufficiently met criteria for reuse on the basis of oil and grease (O&G), total suspended solids, and turbidity removal. The cost included two hypothetical treatment-plant sizes: a local processing unit plant (2,380 B/D or 100,000 gal/D) and a larger regional treatment system (11,900 B/D or 500,000 gal/D). Costs ranged from USD 0.79/bbl for the smaller treatment option to USD 0.22/bbl for the larger option, which included chemical costs and amortized (10 years) capital costs, installation, and labor. Estimates were based on assumptions for water requirements and treatment needs in the Barnett, Marcellus, and Eagle Ford shale plays, and included assumptions on freshwater availability, trucking costs, and treatment costs.