--> --> Abstract: How to Distinguish Water- and Gas-Saturated Cracks? by Dileep K. Tiwary, Irina Bayuk, Mike Ammerman, and Evgeni M. Chesnokov; #90067 (2007)

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How to Distinguish Water- and Gas-Saturated Cracks?

 

Dileep K. Tiwary1, Irina Bayuk2, Mike Ammerman,3 and Evgeni M. Chesnokov1.  (1) Institute for Theoretical Geophysics, University of Oklahoma, Norman, USA, (2) Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia, (3) Devon Energy Inc., Oklahoma City, USA  [email protected]

 

Theoretical modeling results show that, in transversely isotropic media with vertical axis of symmetry (VTI), a relationship exists between Poisson's ratio and the different causes of anisotropy, such as alignment of mineral grains or cracks. At the same time, Poisson's ratio can be used to distinguish whether the cracks are filled with water or gas. Models in which the cracks and clay particles are aligned or chaotically distributed show differences in Young's moduli and Thomsen's parameters, when rocks are either saturated with water or gas. Generalized singular approximation (GSA) method has been used to calculate the effective elastic properties for models that are either dry or water-saturated, and clay/crack alignment is the source for the anisotropy. The components of Poisson's ratio (υ11υ13 and υ31) and Young's moduli (E11 and E33), as well as Thomsen's parameters (ε, γ and δ), have been calculated from the effective elastic constants. The relationship between anisotropic components of Poisson's ratio and the porosity shows a nonlinear increasing trend when the clay minerals are aligned and the cracks, with aspect ratio 0.03 and water-saturated, are randomly oriented. The opposite trend exists when the cracks are gas-saturated. Moreover, a gas-saturated medium shows higher value of Thomsen's parameters than the water-saturated medium. The different behavior of Young's moduli in clay-aligned and crack-aligned cases gives us a handy tool to discriminate among these various possible models that occur in nature.

 

AAPG Search and Discover Article #90067©2007 AAPG Mid-Continent Section Meeting, Wichita, Kansas