Heterogeneity of Shape and Microscale Spatial Distribution in Organic-Matter-Hosted Pores of Gas Shales
Pores that formed in the organic matter of mudrocks are thought to play an important role in gas storage and flow. Samples have been examined from a number of units, including Barnett Shale, Woodford Shale, Haynesville Shale, Bossier Shale, and Eagle Ford Shale. Pore morphology and development are complex, and many questions remain about their evolution in gas shales. Data suggest that pore development is driven primarily by the thermal maturation of organic matter, with pores beginning to form around VRo = 0.8%.
Differences have been noted in both shape and distribution of pores within organic matter—spheroidal to elliptical shapes are developed in some organic grains. Other grains show larger, more complex shapes that are perhaps the result of merging of simpler forms during pore enlargement. Pores with complex shapes appear to be more interconnected than those with simpler shapes. Pore diameter varies from nanometers to hundreds of nanometers, with the more complexly shaped pores generally being larger. Some grains show linear arrangements of pores that appear to be related to either underlying structure of the organic matter or phyllosilicate inclusions in the organic matter. Most samples have at least some organic matter that does not develop pores.
Pore distribution and morphology in organic matter
are more homogeneous in samples with dispersed webs of organic matter. In
samples with more isolated grains of organic matter, pore development is
typically heterogeneous, with differences in morphology and distribution
occurring even between adjacent grains.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California