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

Waters coproduced with hydrocarbons from unconventional oil and gas reservoirs such as the hydraulically fractured Middle Devonian 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 disso...

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Bibliographic Details
Published in:Environmental science & technology 2020-04, Vol.54 (7), p.4275-4285
Main Authors: Tieman, Zachary G, Stewart, Brian W, Capo, Rosemary C, Phan, Thai T, Lopano, Christina L, Hakala, J. Alexandra
Format: Article
Language:English
Subjects:
Barite
Barium
Barium isotopes
Brines
Devonian
Dissolved solids
Drilling
Drilling muds
Fractures
Isotopes
Oil reservoirs
Reservoirs
Shale
Shale gas
Shales
Total dissolved solids
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Summary:Waters coproduced with hydrocarbons from unconventional oil and gas reservoirs such as the hydraulically fractured Middle Devonian 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 Marcellus Shale produced waters contain some of the heaviest Ba (high 138Ba/134Ba) measured to date (δ138Ba = +0.36‰ to +1.49‰ ± 0.06‰) and are distinct from overlying Upper Devonian/Lower Mississippian reservoirs (δ138Ba = −0.83‰ to −0.52‰). Marcellus Shale produced water values do not overlap with drilling mud barite (δ138Ba ≈ 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.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.0c00102