Fluid inclusion stratigraphy (FIS) uses gas analyses of fluid inclusions to determine fluid types in geothermal systems. Peaks in FIS data are assumed to be related to location of fractures. The working hypothesis is that open fracture systems can be identified by their FIS chemical signature; that there are differences based on the mineral assemblages and geology of the system; and that there are chemical precursors in the wall rock above open, large fractures. Correlating fracture locations in cores to peaks in the FIS data indicate that select chemical species are useful in distinguishing large fracture zones from small fractures. FIS data for Steamboat Springs, Karaha, and Glass Mountain wells supports our hypothesis that the fluid inclusion gas concentration of select species such as CO2, H2S, and select organic species are useful in locating fractures. High concentrations in fluid inclusions of CO2 and H2S occur 100 percent and 75 percent of the time within 10 feet of large fractures but only 18 and 13 percent of time in areas without fractures for Steamboat Springs Well 87-29. Identifying dense fracture areas as well as large open fractures from small fracture systems would assist in fracture stimulation selection for enhanced geothermal systems.

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