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Published: 2009

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Water associated with coalbed methane (CBM) production is a significant and costly process waste stream, and economic treatment and/or disposal of this water is often the key to successful and profitable CBM development. In the past decade, advances have been made in the treatment of CBM produced water. However, produced water generally must be transported in some fashion to a centralized treatment and/or disposal facility. The cost of transporting this water, whether through the development of a water distribution system or by truck, is often greater than the cost of treatment or disposal. To address this economic issue, BC Technologies (BCT), in collaboration with Oak Ridge National Laboratory (ORNL) and International Petroleum Environmental Consortium (IPEC), proposed developing a mechanical unit that could be used to treat CBM produced water by forming gas hydrates at the wellhead. This process involves creating a gas hydrate, washing it and then disassociating hydrate into water and gas molecules. The application of this technology results in three process streams: purified water, brine, and gas. The purified water can be discharged or reused for a variety of beneficial purposes and the smaller brine can be disposed of using conventional strategies. The overall objectives of this research are to develop a new treatment method for produced water where it could be purified directly at the wellhead, to determine the effectiveness of hydrate formation for the treatment of produced water with proof of concept laboratory experiments, to design a prototype-scale injector and test it in the laboratory under realistic wellhead conditions, and to demonstrate the technology under field conditions. By treating the water on-site, producers could substantially reduce their surface handling costs and economically remove impurities to a quality that would support beneficial use. Batch bench-scale experiments of the hydrate formation process and research conducted at ORNL confirmed the feasibility of the process. However, researchers at BCT were unable to develop equipment suitable for continuous operation and demonstration of the process in the field was not attempted. The significant achievements of the research area: Bench-scale batch results using carbon dioxide indicate>40% of the feed water to the hydrate formation reactor was converted to hydrate in a single pass; The batch results also indicate>23% of the feed water to the hydrate formation reactor (>50% of the hydrate formed) was converted to purified water of a quality suitable for discharge; Continuous discharge and collection of hydrates was achieved at atmospheric pressure. Continuous hydrate formation and collection at atmospheric conditions was the most significant achievement and preliminary economics indicate that if the unit could be made operable, it is potentially economic. However, the inability to continuously separate the hydrate melt fraction left the concept not ready for field demonstration and the project was terminated after Phase Two research.