Spatial distribution and temporal variation of methane, ethane and propane background levels in shallow aquifers – A case study from Lower Saxony (Germany)

Schloemer, Stefan; Oest, J.; Illing, Christian J.; Elbracht, Jörg; Blumenberg, Martin

doi:10.1016/j.ejrh.2018.07.002

Cited by 10 publications

(11 citation statements)

References 91 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At 25°C, the free-water diffusion coefficient, D 0 , for C 1 , 1.88 × 10 −9 m 2 /s, is greater than those of C 2 and C 3 , 1.52 × 10 −9 m 2 /s and 1.21 × 10 −9 m 2 /s, respectively (Witherspoon & Saraf, 1965) and differences of similar magnitudes have been observed for diffusion coefficients estimated from experiments with a variety of natural rock samples at varying temperatures and pressures (Krooss & Leythaeuser, 1988). Experimental studies measuring isotopic fractionation as a result of diffusive transport in natural rock samples have reported fractionation factors (α 13C1/12C1 ) ranging between 0.9891 (Pernaton et al, 1996) and 0.9986 (Schloemer & Krooss, 2004;Zhang & Krooss, 2001). These values suggest that diffusion may produce fractionation comparable in magnitude to that from microbial oxidation.…”

supporting

confidence: 62%

“…Although it is recognized that identification of the source for hydrocarbon gas can be complicated by microbially‐mediated molecular and isotopic fractionations (Humez, Mayer, Nightingale, et al., 2016; Loomer et al., 2020; McMahon et al., 2017; Sherwood et al., 2016), mixing between sources (Moritz et al., 2015; Sherwood et al., 2016) and, less frequently, fractionations due to variable gas solubility (Eymold et al., 2018), possible fractionations resulting from diffusive transport are commonly neglected (Alperin et al., 1988; Darrah et al., 2015; Humez et al., 2019; Schloemer et al., 2018; Schoell, 1984; Whiticar, 1999). Recently however, Wanner and Hunkeler (2018) noted the importance of diffusive isotopic fractionation for a wide range of chemical species.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Reactive Transport Modeling of Natural Gas Molecular and Isotopic Evolution During Diffusive Transport in the Subsurface

Loomer

MacQuarrie

2021

Water Resources Research

View full text Add to dashboard Cite

Reactive transport modeling was employed to investigate the relative importance of fractionations associated with gas solubility, sorption and diffusive transport on dissolved methane, ethane and propane concentrations and the isotopic composition of carbon in methane (δ13C1) in groundwater. Temperature, pressure and salinity dependencies for the hydrocarbon gases were incorporated. Gas molecular ratios, C1/(C2 + C3), increased with diffusive transport, transitioning from thermogenic values to values typically indicative of biogenic gas sources, >1,000, at the leading edge of the diffusive front. Diffusive isotopic fractionation had a large effect on δ13C1 values, with fractionations ranging from −36‰ to −107‰, the difference being a function of the diffusive fractionation factor (αD0). Larger fractionations resulted from αD0 determined at relatively low pressures, 5–50 atm, and temperatures, 20°C–25°C. Less fractionation occurred with αD0 measured at higher pressures and temperature, 30–89 atm and 90°C. The extremely depleted δ13C1 values indicated from the modeling, less than −110‰, have not been observed in shallow groundwater, suggesting that diffusive fractionation of δ13C1 is offset by other processes such as microbial oxidation. 2k factorial analysis was used to assess the model sensitivity to specific parameters: estimations of hydrocarbon travel distance are most sensitive to porosity and tortuosity, while the molecular ratio was most sensitive to the free‐water diffusion coefficient, and the isotopic fractionation was most sensitive to αD0. The magnitude of diffusive fractionation on the molecular and isotopic composition of transported hydrocarbon gas may be similar to fractionations from microbial oxidation and mixing between different sources.

show abstract

supporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Reactive Transport Modeling of Natural Gas Molecular and Isotopic Evolution During Diffusive Transport in the Subsurface

Loomer

MacQuarrie

2021

Water Resources Research

View full text Add to dashboard Cite

show abstract

“…The bottles were sealed with a Teflon coated butyl rubber seal and were closed with aluminum crimp caps. Dissolved gas concentrations were determined applying a headspace equilibration technique described in detail by Schloemer et al (2018). 25 ml of the water samples were replaced by laboratory grade Helium (5.9) and the samples equilibrated to ambient temperature varying from 23 • to 28 • C (since the laboratory was not air-conditioned) for at least 2 h on a laboratory shaker.…”

Section: Water Samplingmentioning

confidence: 99%

“…We assume that the low observed methane/ethane ratios found in the depressions at Britta (∼40) are the result of the preferential oxidation of methane compared to ethane occurring during a slow diffusive ascend of the fluid. Equally low methane/ethane ratios were assigned to partly oxidized biogenic gases in ground waters based on enrichments in 13 C isotopes of methane (Schloemer et al, 2018). Propane, which would be an indicator for a migrated deeper sourced thermal (natural) gas, was not found, neither in the samples from the depressions in the Britta area nor in bottom waters at the Dogger Bank seep site.…”

Section: Dissolved Methane In the Water Column And Bottom Watersmentioning

confidence: 99%

Seafloor Methane Seepage Related to Salt Diapirism in the Northwestern Part of the German North Sea

et al. 2021

View full text Add to dashboard Cite

This study focuses on seafloor methane seep sites and their distribution in the northwestern part of the German North Sea. Methane seepage is a common phenomenon along marine shelves and known to occur in the North Sea, but proof of their existence was lacking in the study area. Using a ship-based multibeam echosounder we detected a minimum of 166 flares that are indicative for free gas releases from the seafloor in the German “Entenschnabel” area, which are not related to morphologic expressions at the seafloor. However, a group of small depressions was detected lacking water column anomalies but with indications of dissolved fluid release. Spatial analysis revealed that flares were not randomly distributed but show a relation to locations of subsurface salt diapirs. More than 60% of all flares were found in the vicinity of the salt diapir “Berta”. Dissolved methane concentrations of ∼100 nM in bottom waters were ten times the background value in the “Entenschnabel” area (CH4 < 10 nM), supporting the finding of enhanced seepage activity in this part of our study area. Furthermore, locations of flares were often related to acoustic blanking and high amplitude reflections in sediment profiler echograms, most prominently observed at location Berta. These hydroacoustic signatures are interpreted to result from increased free gas concentrations in the sediments. Electromagnetic seabed mapping depicts local sediment conductivity anomalies below a flare cluster at Berta, which can be explained by small amounts of free gas in the sediment. In our area of interest, ten abandoned well sites were included in our mapping campaign, but flare observations were spatially not related to these wells. Naturally seeping methane is presumably transported to the seafloor along sub-vertical faults, which have formed concurrently to the updoming salt. Due to the shallow water depths of 30 to 50 m in the study area, flares were observed to reach close to the sea surface and a slight oversaturation of surface waters with methane in the flare-rich northeastern part of the working area indicates that part of the released methane through seepage may contribute to the atmospheric inventory.

show abstract

“…It is important to monitor background levels in surface water in regions with frac activities. Therefore, a comprehensive survey has been performed in Lower Saxony (Germany), where the occurrence of methane, ethane and propane in near-surface groundwater of ~ 1000 groundwater wells was analyzed (Schloemer et al 2018). Lower Saxony is the largest hydrocarbon province in Germany, where 327 hydraulic stimulations in 148 production wells at depths of > 3000 m have been performed since 1961 (BGR 2016).…”

Section: Methane Baseline Monitoring In Lower Saxony Germanymentioning

confidence: 99%

Critical evaluation of human health risks due to hydraulic fracturing in natural gas and petroleum production

Wollin¹,

Damm

Foth³

et al. 2020

Arch Toxicol

View full text Add to dashboard Cite

The use of hydraulic fracturing (HF) to extract oil and natural gas has increased, along with intensive discussions on the associated risks to human health. Three technical processes should be differentiated when evaluating human health risks, namely (1) drilling of the borehole, (2) hydraulic stimulation, and (3) gas or oil production. During the drilling phase, emissions such as NO x , NMVOCs (non-methane volatile organic compounds) as precursors for tropospheric ozone formation, and SO x have been shown to be higher compared to the subsequent phases. In relation to hydraulic stimulation, the toxicity of frac fluids is of relevance. More than 1100 compounds have been identified as components. A trend is to use fewer, less hazardous and more biodegradable substances; however, the use of hydrocarbons, such as kerosene and diesel, is still allowed in the USA. Methane in drinking water is of low toxicological relevance but may indicate inadequate integrity of the gas well. There is a great concern regarding the contamination of ground-and surface water during the production phase. Water that flows to the surface from oil and gas wells, so-called 'produced water', represents a mixture of flow-back, the injected frac fluid returning to the surface, and the reservoir water present in natural oil and gas deposits. Among numerous hazardous compounds, produced water may contain bromide, arsenic, strontium, mercury, barium, radioactive isotopes and organic compounds, particularly benzene, toluene, ethylbenzene and xylenes (BTEX). The sewage outflow, even from specialized treatment plants, may still contain critical concentrations of barium, strontium and arsenic. Evidence suggests that the quality of groundwater and surface water may be compromised by disposal of produced water. Particularly critical is the use of produced water for watering of agricultural areas, where persistent compounds may accumulate. Air contamination can occur as a result of several HF-associated activities. In addition to BTEX, 20 HF-associated air contaminants are group 1A or 1B carcinogens according to the IARC. In the U.S., oil and gas production (including conventional production) represents the second largest source of anthropogenic methane emissions. High-quality epidemiological studies are required, especially in light of recent observations of an association between childhood leukemia and multiple myeloma in the neighborhood of oil and gas production sites. In conclusion, (1) strong evidence supports the conclusion that frac fluids can lead to local environmental contamination; (2) while changes in the chemical composition of soil, water and air are likely to occur, the increased levels are still often below threshold values for safety; (3) point source pollution due to poor maintenance of wells and pipelines can be monitored and remedied; (4) risk assessment should be based on both hazard and exposure evaluation; (5) while the concentrations of frac fluid chemicals are low, some are known carcinogens; therefore, thorough, well-designed st...

show abstract

Spatial distribution and temporal variation of methane, ethane and propane background levels in shallow aquifers – A case study from Lower Saxony (Germany)

Cited by 10 publications

References 91 publications

Reactive Transport Modeling of Natural Gas Molecular and Isotopic Evolution During Diffusive Transport in the Subsurface

Reactive Transport Modeling of Natural Gas Molecular and Isotopic Evolution During Diffusive Transport in the Subsurface

Seafloor Methane Seepage Related to Salt Diapirism in the Northwestern Part of the German North Sea

Critical evaluation of human health risks due to hydraulic fracturing in natural gas and petroleum production

Contact Info

Product

Resources

About