Barium Isotopes Track the Source of Dissolved Solids in Produced Water from the Unconventional Marcellus Shale Gas Play.

Author(s) Tieman, Z.G.; Stewart, B.W.; Capo, R.C.; Phan, T.; Lopano, C.; Hakala, A.
Journal Environ Sci Technol
Date Published 2020 Mar 06

Waters co-produced with hydrocarbons from unconventional oil and gas reservoirs such as the hydraulically fractured Marcellus Shale in the Appalachian Basin, USA, contain high levels of total dissolved solids (TDS), including Ba, which has been variously ascribed to drilling mud dissolution, interaction with pore fluids or shale exchangeable sites, or fluid migration through fractures. Here we show that Middle Devonian Marcellus Shale produced waters contain some of the heaviest Ba (high Ba/Ba) measured to date (δBa = +0.4‰ to +1.5‰ ±0.06‰), and are distinct from overlying Upper Devonian/Lower Mississippian reservoirs (δBa = -0.8‰ to -0.5‰). Marcellus Shale produced water values do not overlap with drilling mud barite (δBa ≈ 0.0‰), and are significantly offset from Ba reservoirs within the producing portion of the Marcellus Shale, including exchangeable sites and carbonate cement. Precipitation, desorption and diffusion processes are insufficient or in the wrong direction to produce the observed enrichments in heavy Ba. We hypothesize that the produced water is derived primarily from brines adjacent to and most likely below the Marcellus Shale, although such deep brines have not yet been obtained for Ba isotope analysis. Barium isotopes show promise for tracking formation waters and for understanding water-rock interaction under downhole conditions.

DOI 10.1021/acs.est.0c00102
ISSN 1520-5851
Citation Environ Sci Technol. 2020.

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