Page 104 - Fundamentals of Gas Shale Reservoirs

84 SEQUENCE STRATIGRAPHY OF UNCONVENTIONAL RESOURCE SHALES

To date, a final sequence stratigraphic framework has not the Brown Shale (Brito, 2014). Comparison of typical strati­
been fully developed for this shale, but it does have similar graphic sequences and gamma ray logs from these shales
gamma‐log stratigraphy at least at two scales. If the Brown reveals a similarity in their characteristics—most notably
Shale is entirely lacustrine in origin, it suggests that the a combined basal unconformity atop underlying strata
effects of sea‐level cyclicity can extend well into the paleo­ (sequence boundary‐SB) and a transgressive surface of
landward direction either through connections to the ocean erosion (TSE)—which are overlain by a fining‐upward
or by the lowering of fluvial base level. shaley interval capped by an organic‐rich, high gamma ray
shale, which in turn is overlain by an upward‐decreasing API
gamma ray pattern. This similarity among different‐aged/
4.9 CONCLuSIONS environment shales suggests a generally similar mode of
formation even though specific mineralogic and lithologic
In this chapter, we have compared stratigraphy from well compositions may differ. The formative processes adhere to
logs and from outcrop/core of a variety of shales of differing a general sequence stratigraphic model (Fig. 4.1) that can be
age. Traditional and conventional sequence stratigraphic applied at multiple scales within a shale sequence.
principles and analysis have been applied to the Barnett
Shale (Abouelresh and Slatt, 2012a, b; Loucks and Ruppel,
2007; Singh, 2008; Slatt et al., 2012); the Woodford Shale 4.10 aPPLICaTIONS
(Molinares‐Blanco, 2013; Serna‐Bernal, 2013); New Albany
Shale (Bohacs and Lazar, 2010), Marcellus Shale (Lash and The most important application of sequence stratigraphy to
Engelder, 2011), Haynesville Shale (Goldhammer, 1998; shales is the ability to correlate strata over long distances
Hammes et al., 2011), Eagle Ford Shale (Donovan and with some degree of confidence, even when chronostrati­
Staerker, 2010); LaLuna Shale (Torres‐Parada, 2013), and graphic information is not available. Not only is a predictable

Average P- Average P-
impedance map Average TOC map. impedance map Average TOC map.
GR
Bad_hole (a) P-impedance (b) (a) P-impedance (b)
0.00 10.00 Ft.g/s.cc TOC (wr%) Ft.g/s.cc W-4 TOC (wr%)
14.00
GR W-4 27000 W-4 14.00 W-4 27000
26000
12.00
0 gAPI 800 26000 10.00 25000 12.00
25000
24000
10.00
24000
Color ll W-19 23000 W-19 8.00 W-19 23000 W-19
22000
20 ft 22000 6.00 21000 8.00
21000
20000
W-6 W-16 19000 W-6 W-16 W-6 W-16 20000 W-6 W-16 6.00
19000
18000
18000
W-3 W-17 W-3 W-17 W-3 W-17 W-3 W-17
W-15
W-15
W-15
W-15
W-1 W-5 W-14 W-1 W-5 W-14 W-1 W-5 W-14 W-1 W-5 W-14
GRP-10 W-12 W-12 W-12 W-12
GRP-9 W-10 W-2 W-11 W-7 W-10 W-2 W-11 W-7 W-10 W-2 W-11 W-7 W-10 W-2 W-11 W-7
W-21 W-18 W-21 W-21 W-18 W-21
W-18 W-20 W-18 W-20 W-20
W-20
W-8 W-8
W-8 W-13 W-8 W-13
W-13 W-13
W-9 W-9 W-9 W-9
0 5000 10000ftUS 0 5000 10000ftUS 0 5000 10000ftUS 0 5000 10000ftUS
GRP-8
(c) FG (psi/ft) (d) Thickness(ft) (c) FG (psi/ft) (d) Thickness(ft)
19.60
10.00
W-4
0.75 W-4 9.60 W-4 0.75 W-4 19.20
0.70 9.20 0.70 18.80
8.80
18.40
0.65 8.40 0.65 18.00
W-19 W-19 8.00 W-19 W-19 17.60
GRP-7 0.60 7.60 0.60 17.20
0.55 7.20 0.55 16.80
W-6 W-16 0.50 W-6 W-16 6.80 W-6 W-16 0.50 W-6 W-16 16.40
GRP-6 W-3 W-17 W-3 W-17 W-3 W-17 W-3 W-17
W-15
W-15
W-15
W-15
W-1 W-5 W-14 W-1 W-5 W-14 W-1 W-5 W-14 W-1 W-5 W-14
W-12 W-12 W-12 W-12
GRP-5
W-10 W-2 W-7 W-10 W-2 W-7 W-10 W-2 W-7 W-10 W-2 W-7
W-11 W-11 W-11 W-11
W-21 W-21 W-21 W-21
W-18 W-18 W-18 W-18
GRP-4 W-20 W-20 W-20 W-20
W-8 W-8 W-8 W-8
W-13 W-13 W-13 W-13
W-9 W-9 W-9 W-9
GRP-3 0 5000 10000ftUS 0 5000 10000ftUS 0 5000 10000ftUS 0 5000 10000ftUS
Isopach map Average fracture Isopach map
Average fracture gradient map
GRP-2 gradient map
GRP 4 GRP 5
GRP-1
Ra Ductile–Brittle couplet
FIGurE 4.17 Woodford gamma ray log showing subdivision of high‐frequency sequences and systems tracts. GRP‐4 and GRP‐5 comprise
a TST–HST (Brittle–Ductile) couplet. Properties of average P‐wave acoustic impedance, average % TOC, average fracture gradient, and
isopach maps show lateral variations in these properties across the study area. Such maps can lead to improved drilling decisions and
locations. After Amorocho‐Sanchez (2012) who provided permission to publish this figure.