Page 105 - Fundamentals of Gas Shale Reservoirs

APPLICATIONS 85
vertical stratigraphy common and interpretable, but over overlain by an upper HST interval which exhibits a lower
long distances sequences and parasequences can be expected gamma ray response. In terms of geomechanical properties,
to downlap and terminate onto an organic‐rich condensed Slatt and Abousleiman (2011) refer to these as “Brittle–
section (Figs. 4.5 and 4.11 are examples). Ductile couplets.”
Another important application is the ability to relate Although it may seem that drilling into a CS/mfs
stratigraphic features to geomechanical, geochemical, and (ductile strata) might provide the opportunity to release
other features of shale strata, and through sequence strati­ more hydrocarbons than in more Brittle HST strata, these
graphic correlations, to be able to map those properties. An intervals tend to not fracture as well, and drilling can be
example is shown in Figure 4.17 where P‐wave impedance, more hazardous in the organic‐rich zones (Figs. 4.18 and
TOC, fracture gradient, and isopach thickness of two 4.19). By contrast, drilling into the Brittle zone of a Brittle–
Woodford Shale intervals (labeled GRP‐4 and GRP‐5) were Ductile couplet has the opportunity to produce longer vertical
mapped on the basis of logs from several wells (Amorocho‐ fractures that will release more hydrocarbons (sweet spot).
Sanchez, 2012). Taken together, these two intervals com­ In addition, proppant will tend to keep fractures open in
prise a high‐frequency sequence consisting of a lower, the Brittle zone, but not as readily in the ductile zone
organic rich, high gamma ray CS/mfs interval (GRP‐4) (Terracina et al., 2010).

Fracture Fracture
GR RT90 PE TOC Impedance RHOB Porosity gradient toughness
Bad_hole RT90 (derived)1 PE TOC P_Impedance PHOB Porosity FG Kic
0.00 10.00 2.0 ohm.m 200.0 2.00 4.00 0.00 20.00 xxxxxx 1.95 g/cm3 2.95 0.00 ft3/f13 0.60 0.40 psi/ft 0.90 0.00 MPa 1.80
GR Color ll Color ll Color ll Color ll Color ll Color ll Color ll Rock
0 gAPI 800
Color ll type
20 ft

GRP-10
Upper woodford
GRP-9

GRP-8

GRP-7
GRP-6

GRP-5

GRP-4 Middle woodford

GRP-3

GRP-2
Lower woodford
GRP-1

Rock type I Rock type II Rock type III
FIGurE 4.18 Properties of a Brittle–Ductile couplet, potential drilling target, Woodford Shale. After Amorocho‐Sanchez (2012).