Potential environmental impacts of natural gas production have become the focus of increased regulatory activity in recent years. Because produced water accounts for greater than 80 percent by volume of the residual materials generated in the production of natural gas, cost-effective and environmentally acceptable disposal of these waters is critical to the continued economic production of natural gas. This Gas Research Institute (GRI) sponsored study is evaluating the technical and economic feasibility of a spectrum of produced water treatment and disposal options using an engineering economic management model developed by the study team.

This paper describes the model which was developed in a PC-based, linked spreadsheet format to allow the user to interactively evaluate alternative scenarios for treatment and disposal of a specific produced water with a stated volumetric production rate and water quality. The model contains twelve treatment process modules ranging from gravity settling to thermo-mechanical evaporation. Final disposal modules include: surface discharge; reinjection via Class II Injection Well; evaporation; and reuse. Modules for water transportation from well head to treatment site are included. Each process module contains a performance-cost relationship to facilitate computation of capital and operating cost for a given produced water management scenario.

The model is used to compute unit costs for produced water treatment and disposal according to a number of possible management scenarios ranging from discharge to surface waters to reinjection via Class II Injection Well. These computed costs are then compared to published costs for several existing produced water disposal operations. Modifications of the model to specifically address the management of produced water from offshore gas production activities are described.

The model developed in this study may be useful to natural gas producers both as an initial screening tool for evaluating produced water management options in the development of a new gas field and also in the consideration of the economically feasible responses to increased regulatory requirements. In addition, the model is being used by GRI to assist in delineating productive areas for research on produced water treatment which have the potential for reducing the future cost of disposal.

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