Page 98 - Fundamentals of Gas Shale Reservoirs

78 SEQUENCE STRATIGRAPHY OF UNCONVENTIONAL RESOURCE SHALES

GR(API units)
0 250 500 750
Jonhson et al. (1985) Sycamore
Age T-R cycles 400 SB/TSE
Carb Missi Regression Transgression ASE 75D
(Ma) Limestone?
360 ASE 75C
Upper
350
Regre woodford HST?
?
365
ASE 61B
Famennian ? ASE 58B CS/mfs?
300
370 ASE 51D SB/TSE TST
Late devonian 250 ASE 50 ASE 49 CS/mfs
ASE 47D
375 UK C5

LK Transgressive Thickness (ft) 200 C2 C3 C4
Frasnian Regressive ASE 32 woodford
380 hemicycle C1 Middle TST
hemicycle 150 ASE 30
ASE 27
385 ASE 25
HST arrow vertical 100
length: Time span Area = mfs level ASE 18
during regression intensity + duration ASE 15 Lower
ASE 13 woodford
HST arrow horizontal length: 50
sea level fall intensity during the HST - parasequences
Hunton Lm ASE 7C
Frasnian regressions SB/TSE
Wyche farm quarry Hunton limestone
0
0 500 1000 1500 2000
McAlester cemetary quarry
FIGurE 4.9 McAlester Cemetary Quarry outcrop gamma ray log compared with a gamma ray log from the Wyche Farm Quarry well.
Both logs compare favorably with the Devonian relative sea‐level curve of Johnson et al. (1985), including not only the larger transgressions
(labeled UK and LK), but also smaller cycles. Modified from Serna‐Bernal (2013) who provided permission to publish this figure.

interval in both Woodford stratigraphic sections with alternating Deposition corresponds to a middle Eifelian rise in sea
high and low gamma ray responses. At depths of ASE47D and level (Lash and Engelder, 2011). The Oatka Creek member,
ASE50 in the McAlester Quarry section are two low gamma the product of a late Eifelian rise in sea level, comprises
ray peaks which correspond to very clean, porous radio­ another third‐order sequence consisting of a basal “regressive
larian‐rich beds, suggesting that these two strata might have surface of erosion,” a relatively thin TST and a thicker
been deposited from algal blooms. Such marker horizons are “regressive systems tract.” In some wells, high‐frequency,
excellent for long‐distance correlation of Woodford strata in high gamma ray API TSTs are more readily observable than
the tectonically complex terrain in which they reside. in other wells (Fig. 4.10); however, the gamma ray patterns
are similar to those described earlier for the other Paleozoic
shales. Small‐scale cleaning‐upward gamma ray intervals
4.6.3 marcellus Shale (Devonian)
within the Oatka Creek member may be fourth‐order para­
The Marcellus Shale is an emerging hydrocarbon producer in sequences, but verification is not possible without biostrati­
the northeastern United States. According to Lash and graphic resolution.
Engelder (2011) it was deposited as a second‐order sequence.
It is divided into a lower Union Springs member and an upper 4.6.4 New albany Shale (upper Devonian–Lower
Oatka Creek member (Fig. 4.10). The Union Springs member mississippian)
overlies an unconformity surface, interpreted as a SB/TSE
(Fig. 4.1) at the top of the Onondaga Limestone. Lash and The New Albany Shale, in the Illinois Basin of the United
Engelder (2011) interpret the Union Springs member as a States, is a longtime producer of natural gas. Bohacs and
third‐order depositional sequence which is composed of a Lazar (2010) have indicated that the New Albany Shale,
lower, upward‐increasing API gamma ray TST and an upper, which overlies the eroded top (SB/TSE) of the Mount Vernon
upward‐decreasing API gamma ray “regressive systems tract,” Limestone, is a second‐order depositional sequence deposited
with an mfs constituting the highest gamma ray shale. over a 20 Myr time interval (Fig. 4.11). They have subdivided