An analysis of horizontal microcracking during catagenesis

Example from the Catskill delta complex

Gary G. Lash, James Terry Engelder

Research output: Contribution to journalArticle

91 Citations (Scopus)

Abstract

Horizontal bitumen-filled microcracks are common within clay laminae of the finely laminated organic carbon-rich shale in the lower half of the heavily jointed Upper Devonian Dunkirk Shale, western New York state. Such cracks are not found higher in the Dunkirk Shale, where moderate bioturbation resulted in a relatively porous and permeable microfabric. Horizontal microcracks in a hydrocarbon source rock that carries regional vertical joints indicating a horizontal least principal stress owe their presence to material properties of the fractured shale and the magnitude and orientation of the crack-driving stress during kerogen maturation. Three material properties favored the horizontal initiation of microcracks in the Dunkirk Shale: (1) the abundance of flat kerogen grains oriented parallel to layering; (2) a marked strength anisotropy in large part caused by the laminated nature of the rock; and (3) the tight, strongly oriented planar clay-grain fabric produced by gravitational compaction of flocculated clay at shallow-burial depth. The latter was especially important to sustaining elevated pore pressure, the crack-driving stress, which was generated by the conversion of kerogen to bitumen. Poroelastic deformation of the low-permeability laminated shale pressurized by catagenesis, perhaps enhanced by compaction disequilibrium prior to kerogen conversion, elevated the in-situ horizontal stress in excess of the vertical stress, which remained constant during pore-pressure buildup, thereby favoring the propagation of microcracks in the horizontal plane.

Original languageEnglish (US)
Pages (from-to)1433-1449
Number of pages17
JournalAAPG Bulletin
Volume89
Issue number11
DOIs
StatePublished - Nov 1 2005

Fingerprint

catagenesis
Microcracking
Shale
Kerogen
shale
asphalt
microcrack
Microcracks
kerogen
Clay
crack
Pore pressure
bitumen
Cracks
clay
pore pressure
compaction
Materials properties
Compaction
Rocks

All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Energy Engineering and Power Technology
  • Geology
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)

Cite this

Lash, Gary G. ; Engelder, James Terry. / An analysis of horizontal microcracking during catagenesis : Example from the Catskill delta complex. In: AAPG Bulletin. 2005 ; Vol. 89, No. 11. pp. 1433-1449.
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An analysis of horizontal microcracking during catagenesis : Example from the Catskill delta complex. / Lash, Gary G.; Engelder, James Terry.

In: AAPG Bulletin, Vol. 89, No. 11, 01.11.2005, p. 1433-1449.

Research output: Contribution to journalArticle

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