Publication Date:
2015-02-01
Description:
The number of Marcellus Shale gas wells drilled in the Appalachian Basin has increased rapidly over the past decade, leading to increased interest in the highly saline water produced with the natural gas which must be recycled, treated, or injected into deep disposal wells. New geochemical and isotopic analyses of produced water for 3 time-series and 13 grab samples from Marcellus Shale gas wells in southwest and north central PA are used to address the origin of the water and solutes produced over the long term (〉12 months). The question of whether the produced water originated within the Marcellus Shale, or whether it may have been drawn from adjacent reservoirs via fractures is addressed using measurements of 228Ra/226Ra and 226Ra activity. These parameters indicate that the water originated in the Marcellus Shale, and can be more broadly used to trace water of Marcellus Shale origin. Rapid increases in salinity and positive shifts in δ18O values in the first weeks of production were followed by more gradual changes until a plateau was reached within approximately one year. The δ18O values and relationships between Na, Cl, and Br, provide evidence that the water produced after compositional stabilization is natural formation water, whose salinity originated primarily from evaporatively concentrated paleoseawater. The rapid transition from the injected water to a chemically and isotopically distinct water while 〈50% of the injected water volume had been recovered, supports the hypothesis that significant volumes of injected water were removed from circulation by imbibition.
Print ISSN:
0149-1423
Electronic ISSN:
1943-2674
Topics:
Geosciences
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