Development of an electrocoagulation based treatment train for produced water with high concentrations of organic matter

Abstract

Well stimulation in the form of hydraulic fracturing has made unconventional oil and gas extraction economically feasible, significantly increasing the number of producing oil and gas wells in the United States in the last several decades. Both the hydraulic fracturing process and shale play development has created a large amount of oil and gas associated wastewater. Deep well injection or disposal wells are the preferred and most widely used method for managing produced water. This industry standard both eliminates valuable water resources from the hydrologic cycle and can be linked to the increasing frequency of seismic events in parts of the United States. This paper investigates water treatment processes in the context of beneficial reuse towards irrigation. Treating produced water on well pad locations followed by agricultural use within close proximity minimizes trucking costs and environmental impacts as well as recycles industrial wastewater back into the hydrologic cycle. High concentrations of salts and organic matter must be removed in addition to other contaminants (Benzene, Boron, Calcium, and Magnesium) from produced water collected from Noble Energy's Wells Ranch Central Processing Facility (CPF) before being applied towards a secondary use. Electrocoagulation coupled with a strong oxidant creates a more effective coagulation process prior to ultrafiltration, granular activated carbon and reverse osmosis processes. Organic matter removal and its potential for significant fouling of reverse osmosis membranes remains a major challenge as concentrations of total organic carbon in Noble Energy CPF produced water are typically around 1,500 mg/L after ultrafiltration. Four treated produced water effluent qualities generated in the CSU Environmental Engineering lab, in addition to freshwater were used to irrigate two non-food crops. Switchgrass and canola were arranged at the CSU greenhouse and watered using a drip irrigation system. The fate of regulated volatile organics and impact of salt accumulation are the primary parameters of interest for impaired water usage. This study is constructed to provide a baseline for the development of a larger scale pilot designed to treat produced water from an operator's storage tanks and used to irrigate nearby agricultural land. The concentration of dissolved organic carbon can be linked directly to the economic feasibility and operational challenges of treatment, both in the context of pretreatment and required maintenance for reverse osmosis. Although produced water from gel-based hydraulic fracturing in the Denver-Juleseburg can be very difficult to treat, beneficial reuse should be an important consideration for future shale play development in Colorado and other parts of the United States.