Rock-physics templates establish a link between seismic properties (e.g., velocity, density, impedance, and attenuation) and reservoir properties such as porosity, fluid saturation, permeab...

Estimation of porosity and fluid saturation in carbonates from rock-physics templates based on seismic Q

The presence of bedding-parallel fractures at any scale in a rock will considerably add to its compliance and elastic anisotropy. Those properties will be more significantly affected when there is a relatively high degree of connectivity between the fractures and the corresponding interconnected pores. This contribution uses linear poroelasticity to reveal the characteristics of the full frequency-dependent compliance of an infinitely extended fracture model assuming the periodicity of the fractured structures. The fracture compliance tensor is complex-valued due to the wave-induced fluid flow between fractures and pores. The interaction between the adjacent fractures is considered under fluid mass conservation throughout the whole pore space. The quantitative effects of fracture (volume) density (the ratio between fracture thickness and spacing) and host rock porosity are analyzed by the diffusion equation for a relatively low-frequency band. The model in this paper is equivalent to the classical dry linear slip model when the bulk modulus of fluid in the fractures tends to zero. For the liquid-filled case, the model becomes the anisotropic Gassmann’s model and sealed saturated linear slip model at the low-frequency and high-frequency limits, respectively. Using the dynamic compliance definition, we can effectively distinguish the saturating fluids in the fractures with the same order magnitude of bulk modulus (e.g., water and oil) using the compliance ratio method. Additionally, the modified dynamic model can be simplified as acceptable empirical formulas if the strain on the fractures induced by the incoming waves is small enough.

Analysis of Dynamic Fracture Compliance Based on Poroelastic Theory. Part I: Model Formulation and Analytical Expressions

Effect of flow-independent viscosity on the propagation behavior of Rayleigh wave in partially saturated soil based on the fractional standard linear solid model

In Part I, a dynamic fracture compliance model (DFCM) was
 derived based on the poroelastic theory. The normal compliance of fractures is frequency-dependent and closely associated with the connectivity of porous media. In this paper, we first compare the DFCM with previous fractured media theories in the literature in a full frequency range. Furthermore, experimental tests are performed on synthetic rock specimens, and the DFCM is compared with the experimental data in the ultrasonic frequency band. Synthetic rock specimens saturated with water have more realistic mineral compositions and pore structures relative to previous works in comparison with natural reservoir rocks. The fracture/pore geometrical and physical parameters can be controlled to replicate approximately those of natural rocks. P- and S-wave anisotropy characteristics with different fracture and pore properties are calculated and numerical results are compared with experimental data. Although the measurement frequency is relatively high, the results of DFCM are appropriate for explaining the experimental data. The characteristic frequency of fluid pressure equilibration calculated based on the specimen parameters is not substantially less than the measurement frequency. In the dynamic fracture model, the wave-induced fluid flow behavior is an important factor for the fracture–wave interaction process, which differs from the models at the high-frequency limits, for instance, Hudson’s un-relaxed model.

Analysis of Dynamic Fracture Compliance Based on Poroelastic Theory. Part II: Results of Numerical and Experimental Tests

Based on the framework of elastic theory for unsaturated porous medium and considering the effects of non-isothermal conditions, this paper studies the influences of thermophysical properties on the attenuation characteristics of thermoelastic body waves in unsaturated soil. Firstly, the present work introduces the dispersion equations of thermoelastic body waves for three-phases unsaturated porous media. Secondly, the dispersion equations of thermoelastic body waves are theoretically solved by using a commercial math software. Finally, the evolutions of the attenuation coefficients of various thermoelastic body waves are analyzed by means of some numerical examples. The results demonstrate that the thermal expansion coefficient presents a great influence upon the attenuation coefficients for P1 and thermal waves; the thermal conductivity just results in a significant change in the attenuation coefficient of thermal wave, while the attenuation coefficients of all thermoelastic body waves except for P2 wave are very sensitive to the change of medium temperature.

Ding Wang

Papers

The effects of fracture permeability on acoustic wave propagation in the porous media: A microscopic perspective.