Environmental Engineering Reference
In-Depth Information
Methane Isotherm Results
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Adsorbed gas controlled by:
• pressure / depth (saturation)
temperature
TOC
OM type
maturity
60
50
High TOC
40
30
20
Moderate TOC
10
0
0
500
1,000
1,500
2,000
2,500
3,000
Equiv. depth - hydrostatic (m):
700
1400
2100
Pressure, psia
Figure 11 Methane adsorption relationship with organic matter content.
(Modified from Core Laboratories).
Figure 12 Variable relationship between methane adsorption and organic matter
content for two gas shales.
(Modified from Core Laboratories).
of porosity and gas in the organic matter and the brittle nature of the matrix
are critical factors. This is reflected in the ability to hydraulically fracture a
shale (''frac'ability'') which is related to the fracture strength of the shale and
the ability to initiate fractures (high Young's Modulus and low Poisson's
Ratio). This is dependent both on the shale matrix composition and the
indigenous tectonic stress regime. Brittleness is cited as the key mineral-
ogical parameter in determining the creation of an artificial fracture network
connecting the wellbore to the shale micro or nanoporosity,
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with optimum
values of 45% quartz and 27% clay for the Barnett Shale of the Fort Worth
