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Fluid Production from Tight-Gas Systems, Greater Green River and Wind River Basins, Wyoming

Nelson, Philip H.1
1 U.S. Geological Survey, Denver, CO.

Gas and water production records provide a basis for examining the differences among tight gas reservoirs. For this purpose, wells with production records spanning at least seven years are selected for each formation in a field. To reduce well interference effects, wells with the earliest production from a field are preferred. Instead of using decline curve analysis, average daily rates of fluid production are computed twice, once after two years of initial production and again five years later; the two averages are then plotted on log-log plots of water vs. gas. The two production points form a vector that shows whether production is increasing or decreasing with time and whether the change in water production is tracking the change in gas production. Also, the water-gas ratio is apparent and can be compared with the expected amount of water condensed from gas for that reservoir. Thus, for all available wells in each field, the plots show production rate magnitudes, water-gas ratios, and production trends over a five-year time span.

Examples from the Greater Green River and Wind River basins in Wyoming illustrate the variability in gas and water production rates from different geological settings. Of all reservoirs studied, Jonah field shows the least well-to-well variation in water and gas production rates. The Pinedale field displays the most uniform declines in water and gas production rates. Production from the upper part of the Almond Formation shows the slowest decline rates. Production within fields in the Wind River basin is more variable than from the Greater Green River basin; for example, water production rates and water-gas ratios vary by a factor of ten or more among wells in the Madden field. Geological factors such as depositional setting and degree of fracturing appear to be responsible for the variation among fields.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009