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

Abstract

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 138 Ba/ 134 Ba) measured to date (δ 138 Ba = +0.36‰ to +1.49‰ ± 0.06‰) and are distinct from overlying Upper Devonian/Lower Mississippian reservoirs (δ 138 Ba = −0.83‰ to −0.52‰). Marcellus Shale produced water values do not overlap with drilling mud barite (δ 138 Ba ≈ 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.

A single column separation method for barium isotope analysis of geologic and hydrologic materials with complex matrices

“…The double spike was made using 135 Ba- and 137 Ba-enriched carbonate salts from the National Isotope Development Center at Oak Ridge National Laboratory and calibrated by running mixtures of double spike and NIST 3104a. Further details of spike calibration can be found in the Supporting Information of Tieman et al [ 20 ].…”

“…Mass fractionation of the sample was corrected for by iterative normalization to the 137 Ba/ 135 Ba of the double spike using an exponential law [ 45 ]. The detector configuration and additional details of the mass spectrometric methods can be found in Supporting Information in Tieman et al [ 20 ].…”

“…Barium (Ba) is a critical element of interest in studies of oceanic biogeochemical cycling and the diagenetic alteration of sediments (e.g., [ 1 – 5 ]), and the isotopic composition of Ba has been used to understand element cycling in marine, riverine, lacustrine and pedogenic environments [ 6 – 16 ]. More recently, Ba concentrations [ 17 – 19 ] and its isotope signatures [ 20 ] have been studied as indicators of Ba sources and mobility related to subsurface water–rock interactions and the fate and transport of contaminants in drilling mud, solid waste and produced waters related to hydraulic fracturing of oil and gas wells.…”

“…While Xe is only introduced during MC-ICPMS measurement from the atmosphere and Ar gas source, all other interferents (matrix major elements, La, and Ce) must be removed via chemical processing prior to analysis by TIMS or MC-ICPMS. For samples with high ratios of Ba to matrix and/or isobaric interferents (e.g., high-Ba formation waters or samples of barite, BaSO 4 ), the chemical separation of Ba is relatively straightforward [ 6 , 14 , 20 , 24 , 28 , 29 ]. However, silicate rock samples can have high rare earth element (REE) to Ba ratios, necessitating robust procedures for removing La and Ce prior to analysis.…”

Water–rock interaction and the concentrations of major, trace, and rare earth elements in hydrocarbon-associated produced waters of the United States

“…59 Barium isotopes have helped conrm that dissolution from drilling mud is not a substantial source of Ba to produced waters from the Marcellus shale, but values in produced waters are also not entirely explained by exchangeable or carbonate sources in the shale. 72,73 All of these isotopic studies point toward contributions of Li, Sr, and Ba from sources and processes related to diagenesis rather than water-rock interactions on shorter time scales.…”