Fluid Identification and Estimation of Fracture Connectivity in Fluid Saturated Media



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This dissertation focuses on the effects of the fluid property, the fracture geometry, and fracture connectivity on the wave propagation in fluid-saturated media with fractures. We examined the anisotropy of the P-wave velocities and reflection coefficients in media with planar fractures, under conditions of saturation by various fluids and fracture apertures. We used numerical models to examine the behavior of P-wave dispersion in the normal direction to layering, in an impermeable or porous matrix with embedded planar fractures. The results showed that the concavity indicator of dispersion for gas saturation was higher than liquid saturation. Anisotropy was more sensitive to bulk modulus difference than to density difference between solids and fluids. The velocity difference between fast and slow waves was more sensitive to the difference in density than in bulk modulus. We then investigated the seismic attenuation and reflection coefficient concerning different fracture connectivity using the finite-element method. In the presence of connected fractures, fracture-fluid flow (a fluid flow inside or between fractures) dominated the attenuation of the S-wave and P-wave propagation parallel to fractures. Conversely, for unconnected fractures, the attenuation of the S-wave and P-wave propagating at all directions were dominated by the leak-off flow (a fluid flow from the fractures to the porous matrix). The fracture-fluid flow corresponds to a higher characteristic frequency than a leak-off flow. When the connectivity increases, the smallest angle of phase reversal becomes smaller for the case of PP reflection and larger for the cases of PS and SS reflection.



Fracture behavior, Anisotropy, S-wave, P-wave