Produced water accounts for greater than 80 percent by volume of the residual material generated in the natural gas industry. Cost-effective and environmentally acceptable disposal of these waters is critical to the continued economic production of natural gas. The Gas Research Institute (GRI) has recently completed a comprehensive assessment of the demographics of produced water characterized according to volumes and geographic location of the gas producing geologic provinces of the United States. This information in association with both the federal and state environmental regulations has been used to identify potential cost-effective produced water treatment research opportunities which are described in this paper.

The study involved the use of a computer-based engineering-economic model, Produced Water Management Options Model (PWMOM), which combines engineering process models with a cost performance data base to predict the economics of a spectrum of unit water treatment processes and treatment trains. Various produced water scenarios, i.e., volumes, qualities and regulatory requirements, were evaluated and categorized to focus on the natural gas producing regions of the U.S. where produced waters could be surface discharged under the National Pollutant Discharge Elimination System (NPDES). Residual brines from produced water treatment would continue to be injected. Unit process technologies evaluated include deoiling (removal of free oil & grease), iron removal, dissolved organic removal (soluble organic treatment) and partial demineralization. Federal and state regulations were reviewed to identify where surface discharge could be or has been practiced to determine where cost-effective treatment could increase the opportunity for non-injection disposal alternatives.

To complete this analysis, surface treatment costs were generated with PWMOM and compared to deep well injection costs. Costs for deep well injection were generated using Salt Water Injection Model (SWIM), a model developed by GRI earlier in this research project. Promising technologies that have been identified include aerobic biological oxidation using fluidized beds, partial demineralization using electrodialysis and reverse osmosis, and a natural freeze-thaw evaporation process for cold climates. Laboratory and pilot studies that have been initiated to evaluate these processes are described here. Additional surface water discharge opportunities may exist where beneficial use such as irrigation or watering livestock is possible and where treatment will ensure that the release to surface waters will not violate water quality standards.

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