Distribution and origin of dissolved methane, ethane and propane in shallow groundwater of Lower Saxony, Germany

摘要: Abstract More than 90% of Germany's domestic natural gas production and reserves are located in Lower Saxony, North Germany. Recently, research has been intensified with respect to unconventional shale gas, revealing a large additional resource potential northern However, many concerns arise within the general public government/political institutions over groundwater contamination from wells through hydraulic fracturing operations. In order determine naturally occurring background methane concentrations, ∼1000 wells, covering ∼48 000 km 2 , have sampled subsequently analyzed for dissolved methane, ethane propane isotopic composition (δ 13 C). Dissolved concentrations cover range ∼7 orders magnitude between limit quantification at ∼20 nl/l 60 ml/l. The majority exhibit low ( 10 ml/l. 27% all samples 8% was detected. median concentration both components is generally very (ethane 50 nl/l, 23 nl/l). Concentrations reveal bimodal distribution which might mirror regional trend due different hydrogeological settings. normally distributed (mean ∼ −70‰ vs PDB), but shows variation between −110‰ and +20‰. Samples δ C values lower than −55‰ PDB (66%) indicative methanogenic biogenic processes. 5% unusually enriched (≥25‰ PDB) can best be explained by microbial oxidation. According standard diagnostic diagram based on ratio sum plus (“Bernard”-diagram) less 4% plot into field typical thermogenic gases. most cases only detected remaining 15 demonstrate an uncommon compared hydrocarbons. These data do not suggest migration deeper sourced gases, source cannot excluded entirely some samples. also generated processes therefore represent ubiquitous abundances these Nevertheless, our that exceedingly propane, respective changes prove more sensitive parameter detect possible (thermally generated) hydrocarbons aquifer.