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| Titel |
The Noble Gas Fingerprint in a UK Unconventional Gas Reservoir |
| VerfasserIn |
Rory McKavney, Stuart Gilfillan, Domokos Gyore, Fin Stuart |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135594
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| Publikation (Nr.) |
 EGU/EGU2016-16478.pdf |
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| Zusammenfassung |
| In the last decade, there has been an unprecedented expansion in the development of
unconventional hydrocarbon resources. Concerns have arisen about the effect of this new
industry on groundwater quality, particularly focussing on hydraulic fracturing, the technique
used to increase the permeability of the targeted tight shale formations. Methane
contamination of groundwater has been documented in areas of gas production1 but
conclusively linking this to fugitive emissions from unconventional hydrocarbon production
has been controversial2. A lack of baseline measurements taken before drilling, and the
equivocal interpretation of geochemical data hamper the determination of possible
contamination.
Common techniques for “fingerprinting” gas from discrete sources rely on gas
composition and isotopic ratios of elements within hydrocarbons (e.g. δ13CCH4), but the
original signatures can be masked by biological and gas transport processes. The noble gases
(He, Ne, Ar, Kr, Xe) are inert and controlled only by their physical properties. They exist in
trace quantities in natural gases and are sourced from 3 isotopically distinct environments
(atmosphere, crust and mantle)3. They are decoupled from the biosphere, and provide a
separate toolbox to investigate the numerous sources and migration pathways of
natural gases, and have found recent utility in the CCS4 and unconventional gas5
industries.
Here we present a brief overview of noble gas data obtained from a new coal bed methane
(CBM) field, Central Scotland. We show that the high concentration of helium is an ideal
fingerprint for tracing fugitive gas migration to a shallow groundwater. The wells show
variation in the noble gas signatures that can be attributed to differences in formation water
pumping from the coal seams as the field has been explored for future commercial
development. Dewatering the seams alters the gas/water ratio and the degree to which
noble gases degas from the formation water. Additionally the helium and neon
isotopic signatures exhibit a small but resolvable mantle input previously unseen
onshore in the United Kingdom. We will outline the potential sources of this mantle
input.
1. Osborn et al. (2011). Proc. Natl. Acad. Sci. U. S. A. 108, 10.1073/pnas.1100682108
2. Baldassare et al. (2014). Am. Assoc. Pet. Geol. Bull. 98, 10.1306/06111312178
3 .Ballentine et al. (2002). Rev. Min. Geochem. 47, 10.2138/rmg.2002.47.13
4. Gilfillan & Wilkinson (2011). Int. J. 5, 10.1016/j.ijggc.2011.08.008
5. Darrah et al. (2014). Proc. Natl. Acad. Sci. 111, 10.1073/pnas.1322107111 |
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