The Middle Devonian Marcellus Black Shale Play as an Infrastructural and Geological analogue for the World's Gas Shale Plays
Pennsylvania State University, University Park, PA
Challenges for global gas shale production include infrastructural and geological with the Marcellus providing an analogue for both.
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.
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.
AAPG Search and Discovery Article #90198 © 2014 AAPG Foundation Distinguished Lecture Series 2013-2014