Factors controlling Li concentration and isotopic composition in formation waters and host rocks of Marcellus Shale, Appalachian Basin

Abstract

In this study, water and whole rock samples from hydraulically fractured wells in the Marcellus Shale (Middle Devonian), and water from conventional wells producing from Upper Devonian sandstones were analyzed for lithium concentrations and isotope ratios ( 7 Li). The distribution of lithium concentrations in different mineral groups was determined using sequential extraction. Structurally bound Li, predominantly in clays, accounted for 75-91 wt. % of total Li, whereas exchangeable sites and carbonate cement contain negligible Li (< 3%). Up to 20% of the Li is present in the oxidizable fraction (organic matter and sulfides). The δ 7 Li values for whole rock shale in Greene Co., Pennsylvania, and Tioga Co., New York, ranged from-2.3 to +4.3‰, similar to values reported for other shales in the literature. The  7 Li values in shale rocks with stratigraphic depth record progressive weathering of the source region; the most weathered and clay-rich strata with isotopically light Li are found closest to the top of the stratigraphic section. Diagenetic illite-smectite transition could also have partially affected the bulk Li content and isotope ratios of the Marcellus Shale. In Greene Co., southwest Pennsylvania, the Upper Devonian sandstone formation waters have  7 Li values of +14.6 ± 1.2 (2SD, n = 25), and are distinct from Marcellus Shale formation waters which have  7 Li of +10.0 ± 0.8 (2SD, n = 12). These two formation waters also maintain distinctive 87 Sr/ 86 Sr ratios suggesting hydrologic separation between these units. Applying temperature-dependent illitilization model to Marcellus Shale, we found that Li concentration in clay minerals increased with Li concentration in pore fluid during diagenetic illite-smectite transition. Samples from north central PA show a much smaller range in both δ 7 Li and 87 Sr/ 86 Sr than in southwest Pennsylvania. Spatial variations in Li and δ 7 Li values show that Marcellus formation waters are not homogeneous across the Appalachian Basin. Marcellus formation waters in the northeastern Pennsylvania portion of the basin show a much smaller range in both δ 7 Li and 87 Sr/ 86 Sr, suggesting long term, cross-formational fluid migration in this region. Assessing the impact of potential mixing of fresh water with deep formation water requires establishment of a geochemical and isotopic baseline in the shallow, fresh water aquifers, and site specific characterization of formation water, followed by long-term monitoring, particularly in regions of future shale gas development.

Optimisation of Lithium Chromatography for Isotopic Analysis in Geological Reference Materials by MC‐ICP‐MS

“…() and Phan et al . (); see details in Table . Our in‐house designed dual‐column system was also evaluated.…”

“…, Phan et al . ) or without (Misra and Froelich , Gao and Casey , Van Hoecke et al . ) an organic solvent (i.e., methanol) are usually adopted as the eluent.…”

“…Refined single-and dual-column cation-exchange chromatography have been described in the literature (Tomascak et al 1999, Nishio and Nakai 2002, Jeffcoate et al 2004, Rosner et al 2007, Huang et al 2010, Gao and Casey 2012, Choi et al 2013, Van Hoecke et al 2015, Lin et al 2016. Inorganic acids with (Tomascak et al 1999, Nishio and Nakai 2002, Jeffcoate et al 2004, Rosner et al 2007, Huang et al 2010, Choi et al 2013, Lin et al 2016, Phan et al 2016 or without (Misra and Froelich 2009, Gao and Casey 2012, Van Hoecke et al 2015 an organic solvent (i.e., methanol) are usually adopted as the eluent.…”

“…To achieve satisfactory Li/matrix elements separation, relatively large resin loads, high aspect ratios and large eluent volumes are required. Therefore, the single-column system elution rates are significantly slowed, resulting in 7-10 h separation procedures (Tomascak et al 1999, Van Hoecke et al 2015, Lin et al 2016, Phan et al 2016. Thus, the efficiency of onecolumn systems must also be reconsidered.…”

Automated Analyte Separation by Ion Chromatography Using a Cobot Applied to Geological Reference Materials for Li Isotope Composition

“…In addition, organic matter can affect Li isotope ratio measurements, both by ‘cryptic’ matrix effects or directly through isobaric interferences [ 6 Li being interfered by doubly charged 12 C 2+ (Magna et al )]. To remediate these issues, various ion chromatography separation methods have been developed involving different steps of purification and varying targeted amounts of Li to be separated (You and Chan , Moriguti and Nakamura , Tomascak et al , James and Palmer , Magna et al , Misra and Froelich , Huang et al , Van Hoecke et al , Phan et al , Bohlin et al , Yoshimura et al , Li et al , Lin et al ).…”