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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2009. The American Association of Petroleum Geologists. All rights reserved.
DOI:10.1306/08110909100
Natural
fracture
characterization in tight gas sandstones: Integrating mechanics and diagenesis


Jon E. Olson2, Stephen E. Laubach3, Robert H. Lander1
1Petroleum and Geosystems Engineering, Cockrell School of Engineering, University of Texas at Austin, 1 University Station C0300, Austin, Texas 78712; jolson@mail.utexas.edu
2Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78713-8924; steve.laubach@beg.utexas.edu
3Geocosm LLC, 3311 San Mateo Drive, Austin, Texas 78738; roblander@geocosm.net
ABSTRACT
Accurate predictions of natural fracture
flow attributes in sandstones require an understanding of the underlying mechanisms responsible for
fracture
growth and aperture preservation. Poroelastic stress calculations combined with
fracture
mechanics criteria show that it is possible to sustain opening-mode
fracture
growth with sublithostatic pore pressure without associated or preemptive shear failure. Crack-seal textures and
fracture
aperture to length ratios suggest that preserved
fracture
apertures reflect the loading state that caused propagation. This implies that, for quartz-rich sandstones, the synkinematic cement in the fractures and in the rock mass props
fracture
apertures open and reduces the possibility of aperture loss on unloading and relaxation.
Fracture
pattern development caused by subcritical
fracture
growth for a limited range of strain histories is demonstrated to result in widely disparate
fracture
pattern geometries. Substantial opening-mode growth can be generated by very small extensional strains (on the order of 10
4); consequently,
fracture
arrays are likely to form in the absence of larger scale structures. The effective permeabilities calculated for these low-strain
fracture
patterns are considerable. To replicate the lower permeabilities that typify tight gas sandstones requires the superimposition of systematic cement filling that preferentially plugs
fracture
tips and other narrower parts of the
fracture
pattern.
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