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| Titel |
Numerical assessment of potential impacts of hydraulically fractured Bowland Shale on overlying aquifers |
| VerfasserIn |
Zuansi Cai, Ulrich Ofterdinger |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086235
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| Publikation (Nr.) |
 EGU/EGU2014-62.pdf |
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| Zusammenfassung |
| The success of unconventional gas extracted from shale formations (shale gas) over the
last decade has changed the energy landscape in the United States. Shale gas rose
from 2% of US gas production in 2000 to 30% in 2011, and is projected to rise to
more than 50% by 2030. On the global scale, shale gas could increase total natural
gas resources by approximately 32%, with an estimate of the total 7,299 trillion
cubic feet (~200 trillion cubic meter) technically recoverable gas worldwide. In
the UK, onshore shale gas reserve potential was first estimated to be 150 billion
cubic meter by the British Geological Survey (BGS) in 2010. A recent study by
BGS revised the previous estimates, with best estimate (50% probability) of total
in-place gas resource of 37.6 trillion cubic meters in the Bowland Shale across
central Britain. However, there are concerns of potential environmental impacts of
hydraulic fracturing of the shale formations, particularly those related to water
quality, such as gas migration, contaminant transport through induced and natural
fractures.
To evaluate the potential impact of hydraulically fractured shale on overlying aquifers, we
conduct numerical modelling simulations to assess flow and solute transport from a
synthetic Bowland Shale over a period of 1000 years. The synthetic fractured shale was
represented by a three-dimensional discrete fracture model that was developed
by using the data from a Bowland Shale gas exploration in Lancashire, UK. The
assessment was carried out to investigate chloride mass fluxes from the fractured
Bowland Shale for a range of upward fracture height growths from 200 to 1850
meters, with three sets of hydraulic conductivities over three orders of magnitude for
a multi-layered geological system. Of eighteen scenario analyses, the maximum
upward mass flux towards the overlying Sherwood Sandstone aquifer is < 0.02 ton
Cl-/ yr when a constant chloride concentration of 100 g Cl-/L is applied for the
brine in the fractured shale. With this mass flux rate into the fracture area of ~0.75
km2, it is unlikely to create average chloride concentration over the UK maximum
concentration level of 188 mg Cl-/L in groundwater, although upward mass flux via
fractures could create pollution ’hot spot’ areas exceeding this concentration level. The
model study also reveals that the upward mass flux is significantly intercepted by the
horizontal mass flux within a high permeable layer between the Bowland Shale and its
overlying aquifers, preventing further upward flux towards the overlying aquifers. |
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