Challenges
for global gas shale production include infrastructural and geological with the
Marcellus providing an analogue for both.
(Infrastructural) The
production from the Marcellus gas shale presents unique challenges that include
issues associated with leasing, geology, landowners, virtually no deep disposal
wells, state governments without a severance tax, several river basin commissions,
an infrastructure designed for shallow gas production, an emotional group of
environmentalists, and one state that has yet to permit horizontal well
stimulation. This combination of
challenges makes for a very interesting set of lessons that operators will face
elsewhere in the world when attempting to play gas shales.
Challenges for global gas shale production
include infrastructural and geological with the Marcellus providing an analogue
for both.
Infrastructural
The production from the Marcellus gas shale
presents unique challenges that include issues associated with leasing,
geology, landowners, virtually no deep disposal wells, state governments
without a severance tax, several river basin commissions, an infrastructure
designed for shallow gas production, an emotional group of environmentalists,
and one state that has yet to permit horizontal well stimulation. This combination of challenges makes for a
very interesting set of lessons that operators will face elsewhere in the world
when attempting to play gas shales.
Geological
The Appalachian Basin is characterized by 2nd order depositional
sequences (approximately 10’s of million years duration) that make up thousands
of feet of strata in this basin, 3rd order sequences (1-10 million
years) with up to several hundred feet of strata, and parasequences, that comprise
tens of feet of strata. Middle Devonian Marcellus Formation
encompasses two third order transgressive-regressive (T-R) sequences, MSS1 and
MSS2, in ascending order.
Compositional elements of the Marcellus Formation
crucial to the successful development of this emerging shale gas play,
including quartz, clay, carbonate, pyrite, and organic carbon, vary predictably
within the proposed sequence stratigraphic framework. Tops of the parasequences commonly
contain a calcareous interval, commonly containing shell debris, overlain by a
sharp transition into the high TOC mudrocks of the next overlying
parasequence. Thickness trends of Marcellus T-R sequences and
lithostratigraphic units reflect the interplay of Acadian thrust-load-induced
subsidence, short-term base-level fluctuations, and recurrent basement
structures. Rapid thickening of both T-R
sequences, especially MSS2, toward the northeastern region of the basin
preserves a record of greater accommodation space and proximity to clastic
sources early in the Acadian orogeny. However, local variations in T-R sequence
thickness in the western, more distal, area of the basin may reflect the
reactivation of inherited Eocambrian basement structures to form a carbonate
bank.