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VOLUME XX, ISSUE 2 June 2006 'ATER RESOURCES DE*RTMENT OF NATURAL Dick Wolfe, P.E., Assistant State Engineer The material in this article is based on the study report prepared by S.S. Papadopulos and Associates, Inc. (SSPA), 2006, entitled " Coalbed Methane Stream Depletion Assess- ment Study — Northern San Juan Basin, Colorado'. A copy of the study is available for viewing at the Division of Water Resources website at: www.water.state.co.us. This study was a joint effort by the Colorado Oil and Gas Conservation Commission ( COGCC), the Colo- rado Geological Survey (CGS), the Colorado Division of Water Re- sources (DWR) and SSPA. The purpose of this study was to develop a quantitative assessment of the levels of stream depletion or reduction in formation outflows (spring flows or flowing stream systems gaining from contact with formations) that may be occurring as a result of the removal of water by coalbed methane (CBM) wells. This water historically has been disposed by one or more methods, including re- injection into deep formations, discharge to the surface stream system, and ponding /evaporation. The concern has been raised that the removal of ground water from aquifers that may be tributary to the surface stream system could be resulting in stream depletions or a reduction in spring flows and /or formation outflows (accretions) that are of a magnitude sufficient to cause injury to senior water rights holders on over - appropriated stream systems. This study sought to develop a reliable assessment as to the levels of depletion, definition of the areas where CBM is ongoing that might be classified as non - tributary, definition of any potential corre- lations of water quality, geology, aquifer geometry, or formation/ well depth that could lead to general guidelines about the potential for stream depletion that would be useful in either prompt- ing or avoiding more detailed studies, and development of recommendations for further data collection or investigations. The San Juan Basin is a produc- 9 5 tive source of CBM. In conjunc- tion with the production of CBM, is the production of water. A COGCC database of monthly CBM gas and water production for all wells in the basin from 1985 indicates that, through July 2005, more than 4.2 trillion cubic feet of gas and 400 million barrels (52,000 acre -feet) of water have been produced from CBM wells in the San Juan Basin in Colorado. The annual rate of gas production is continuing to rise and is projected to be above 450 billion cubic feet in 2005. Annual water production peaked in 1993 at nearly 34 million barrels (4,300 acre -feet) and has been relatively steady at close to 23 million barrels (3,000 acre - feet) since. CBM in the San Juan Basin is produced primarily from the coals in the late Cretaceous Fruitland Formation. The Fruit- land Formation and the adjacent Pictured Cliffs Sandstone, infor- mally referred to as the Fruitland - Pictured Cliffs aquifer, are the source of the CBM produced water. The Fruitland- Pictured Cliffs aquifer is bounded to the north by a well - delineated out- crop of its component formations. (Continued on page 2)