Temperature‐dependent Li isotope ratios in Appalachian Plateau and Gulf Coast Sedimentary Basin saline water

Abstract

Lithium (Li) concentrations of produced water from unconventional (horizontally drilled and hydraulically fractured shale) and conventional gas wells in Devonian reservoirs in the Appalachian Plateau region of western Pennsylvania range from 0.6 to 17 mmol kg À1 , and Li isotope ratios, expressed as in d 7 Li, range from +8.2 to +15&. Li concentrations are as high as 40 mmol kg À1 in produced waters from Plio-Pleistocene through Jurassicaged reservoirs in the Gulf Coast Sedimentary Basin analyzed for this study, and d 7 Li values range from about +4.2 to +16.6&. Because of charge-balance constraints and rock buffering, Li concentrations in saline waters from sedimentary basins throughout the world (including this study) are generally positively correlated with chloride (Cl), the dominant anion in these fluids. Li concentrations also vary with depth, although the extent of depth dependence differs among sedimentary basins. In general, Li concentrations are higher than expected from seawater or evaporation of seawater and therefore require water-mineral reactions that remove lithium from the minerals. Li isotope ratios in these produced waters vary inversely with temperature. However, calculations of temperature-dependent fractionation of d 7 Li between average shale d 7 Li (À0.7&) and water result in d 7 Li water that is more positive than that of most produced waters. This suggests that aqueous d 7 Li may reflect transport of water from depth and/or reaction with rocks having d 7 Li lighter than average shale.

New Tracers Identify Hydraulic Fracturing Fluids and Accidental Releases from Oil and Gas Operations

“…25 Note that the Appalachian Basin PW samples reported here, which contain the highest Li/Cl ratios with the lowest δ 7 Li (9−13‰) that overlap with the Marcellus HFFF range, were collected specifically from Lower Silurian formations that apparently experienced the greatest burial temperatures of any samples in this study. Consequently, the overlap of Li/Cl and δ 7 Li in PW from Lower Silurian conventional oil and gas wells and Marcellus HFFF is similar to that observed in other studies from the Appalachian Basin 25 and infers limitation of the use of Li as a tracer. Nonetheless, Upper Devonian PW has lower Li/Cl (2.5−6.8 × 10 −4 ) and higher δ 7 Li (17−20‰) that are distinctive from the HFFF composition.…”

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

“…In all samples, lithium was separated from the sample matrix prior to measuring isotopic ratios. The lithium separation procedure developed in this study was modified from Choi et al (2013) and previous studies (Tomascak et al, 1999;James and Palmer, 2000;Jeffcoate et al, 2004;Magna et al, 2004;Millot et al, 2004;Macpherson et al, 2014), in order to completely separate lithium from the matrix of limestone, shale, and saline water. Choi et al (2013) reported a simple method that effectively separated lithium isotopes in variety of geological samples by only one column separation.…”

“…Evaporation of sea water can explain the high TDS (Haluszczak et al, 2013;Rowan et al, 2015) but does not adequately explain the elevated Li concentrations in the Marcellus produced water (Macpherson et al, 2014). Diagenetic reactions with Li-bearing minerals in the shale could possibly account for anomalously high Li in Marcellus formation water (Macpherson et al, 2014). This study further investigates sources of Li by characterizing Li concentration and isotopic composition in both formation waters and rock samples of the Marcellus Shale.…”

“…Lithium (Li) isotopes have been widely used as a tracer for Earth surface processes, including origin and evolution of basinal brines (Bottomley et al, 1999;Macpherson et al, 2014) and weathering of silicate rocks (Millot et al, 2010b;Misra and Froelich, 2012;Pogge von Strandmann et al, 2013). Lithium is a fluid-mobile element whose concentration and isotopic composition vary widely among geologic materials.…”

Lithium in fluids from Paleozoic-aged reservoirs, Appalachian Plateau region, USA

“…Chemical analyses of saline water produced from oil and gas wells in the study area were compiled from the literature (Breen et al, 1985;Lowry et al, 1988;Dresel and Rose, 2010;Macpherson et al, 2014). Some data sets were incomplete.…”