Page 34 - Fundamentals of Gas Shale Reservoirs

14 GAS SHALE: GLOBAL SIGNIFICANCE, DISTRIBUTION, AND CHALLENGES

vertical distance above the gas shale. Thus literature recog­ • Management of air quality as a result of omissions
nizes the distinction between shale gas plays associated with associated with production infrastructure, plant, and
deep pay zones and shallow pay zones. For example, as noted equipment (US DOE, 2009).
by Fisher (2010), “even in areas with the largest measured • Carbon emissions management, in a carbon pricing
vertical fracture growth, such as the Marcellus, the tops of the economy, may have a significant impact from an envi­
hydraulic fractures are still thousands of feet below the deepest ronmental and commercial perspective (Staff, 2010).
aquifers suitable for drinking water.” However, there can be • Competing land use, since shale gas is an onshore
relatively close proximity between a gas pay zone and an activity, and can overlap with agricultural land (i.e.,
aquifer. As an example, in the United States, the Antrim and Australia), and even some towns and cities (e.g., Barnett
New Albany shale gas plays are quite shallow and hence closer Shale wells within Fort Worth, USA) (EIA, 2011a).
to groundwater aquifers than the likes of the Marcellus Shale
(US DOE, 2009).
1.7.1.5 Regulatory Framework The aforementioned
environmental risks and issues are generally addressed at a
1.7.1.2 Sustainable Use of Groundwater Resources
for Formation Fracturing Approximately three million regulatory level within the United States. However, litera­
gallons of freshwater is required on average for complete ture suggests that other countries mentioned within this lit­
treatment of a shale gas well, although this value varies con­ erature review do not yet have the regulatory framework
siderably. The water is also required over a relative short for ensuring adequate environmental controls are put in
period of time; hence, there is significant demand on surface place. As such, regulatory uncertainties are slowing down
water, groundwater, and municipal sources (US DOE, 2009). shale gas develop ment in many countries (World Energy
Water resource management is therefore very important, in Council, 2011).
particular, in more arid areas.
1.7.2 Commercial/Economic
1.7.1.3 Responsible Treatment and Disposal of Exploration
and Production-Related Water Wells produce fracture Shale gas is a relative young industry, especially outside the
treatment fluids mixed with formation fluid after pressure United States. There is therefore considerable uncertainty
associated with treatment has been relieved from the well. surrounding the commercial viability of shale gas in many
The quality of this fluid ranges from fresh to saline, and the regions. For example, although many shale gas develop­
volume may range from 30 to 70% of the original volume ments appear to be profitable within the United States, the
pumped into the formation (US DOE, 2009). Environmental economics are not necessarily comparable in other areas for
management of produced water is an important part of the the following reasons:
overall environmental management plan, and successful
management will directly influence the successful expansion 1. It has been suggested that it may cost as much as three
of shale gas production (US DOE, 2009). Some of the methods times to drill a shale gas well in Poland compared to
being adopted and considered for disposal of produced water the United States (Pfeifer, 2012). This reflects the
include the following: limited supply of rigs, with only 34 land rigs operating
in all of Western Europe in 2010 (Stevens, 2012).
• On‐site injection into deep permeable and porous 2. Commercial viability hinges on EUR/well, which is
formations, when available in the play notoriously difficult to predict.
• Transportation and disposal at remote injection sites
• On‐site treatment
• Reuse of fluid for treatment of other wells 1.8 DISCUSSION
• Supplying the water to other users who may benefit (e.g., The geology of shale gas has much in common with
nearby mines, Queensland, Australia) (Staff, 2010) source rock geology. However, geomechanical characteris­
tics play a key role in shale gas plays. Geomechanical prop­
1.7.1.4 Other Environmental Considerations Some erties are somewhat influenced by mineralogy/clay content,
other environmental considerations associated with shale and the tectonic stress history of the basin. As such, there
gas developments include the following: would seem to be potential for such properties to be assessed
during early exploration phase using basin history analysis,
• Management of naturally occurring radioactive mate­ sequence stratigraphy, and facies association.
rials produced from the ground, which can be within Although the geological characteristics presented for the
drill cuttings and dissolved within produced water, and various shale gas deposits are directly influencing the TRR
can precipitate out over time (US DOE, 2009). volume presented, it remains unclear what the real factors