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AAPG Bulletin

Abstract

AAPG Bulletin, V. 93, No. 11 (November 2009), P. 15351549.

Copyright copy2009. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/08110909100

Natural Previous HitfractureNext Hit 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; [email protected]
2Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78713-8924; [email protected]
3Geocosm LLC, 3311 San Mateo Drive, Austin, Texas 78738; [email protected]

ABSTRACT

Accurate predictions of natural Previous HitfractureNext Hit flow attributes in sandstones require an understanding of the underlying mechanisms responsible for Previous HitfractureNext Hit growth and aperture preservation. Poroelastic stress calculations combined with Previous HitfractureNext Hit mechanics criteria show that it is possible to sustain opening-mode Previous HitfractureNext Hit growth with sublithostatic pore pressure without associated or preemptive shear failure. Crack-seal textures and Previous HitfractureNext Hit aperture to length ratios suggest that preserved Previous HitfractureNext Hit 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 Previous HitfractureNext Hit apertures open and reduces the possibility of aperture loss on unloading and relaxation. Previous HitFractureNext Hit pattern development caused by subcritical Previous HitfractureNext Hit growth for a limited range of strain histories is demonstrated to result in widely disparate Previous HitfractureNext Hit pattern geometries. Substantial opening-mode growth can be generated by very small extensional strains (on the order of 10minus4); consequently, Previous HitfractureNext Hit arrays are likely to form in the absence of larger scale structures. The effective permeabilities calculated for these low-strain Previous HitfractureNext Hit patterns are considerable. To replicate the lower permeabilities that typify tight gas sandstones requires the superimposition of systematic cement filling that preferentially plugs Previous HitfractureNext Hit tips and other narrower parts of the Previous HitfractureTop pattern.

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