Extension of the grain-shearing theory of wave propagation in marine sediments to include pore-fluid viscosity

Velocity dispersion is a common phenomenon for fluid-charged porous rocks and carries important information on the pore structure and fluid in reservoir rocks. Previous ultrasonic experiments had measured more significant non-Biot velocity dispersion on saturated reservoir sandstones with increasing pore-fluid viscosity. Although wave-induced local squirt-flow effect could in theory cause most of the non-Biot velocity dispersion, its quantitative prediction remains a challenge. Several popular models were tested to predict the measured velocities under undrained conditions, but they either underestimated the squirt-flow effect or failed to simultaneously satisfy P- and S-wave velocity dispersions (especially for higher viscosity fluids). Based on the classic double-porosity theory that pore space is comprised of mainly stiff/Biot’s porosity and minor compliant porosity, an effective “wet frame” was hypothesized to account for the squirt-flow effect, whose compliant pores are filled with a hypothesized fluid with dynamic modulus. A new dynamic elastic model was then introduced by extending Biot theory to include the squirt-flow effect, after replacing the dry-frame bulk/shear moduli with their wet-frame counterparts. In addition to yielding better velocity predictions for P- and S-wave measurements of different fluid viscosities, the new model is also more applicable because its two key tuning parameters (i.e., the effective aspect ratio and porosity of compliant pores) at in situ reservoir pressure could be constrained with laboratory velocity measurements associated with pore-fluid viscosities.

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In situ measurements of compressional and shear wave propagation in marine sediments and comparison to geoacoustic models

The Journal of the Acoustical Society of America ◽

10.1121/1.5068565 ◽

2018 ◽

Vol 144 (3) ◽

pp. 1960-1960

Author(s):

Kevin M. Lee ◽

Megan S. Ballard ◽

Andrew R. McNeese ◽

Gabriel R. Venegas ◽

Preston S. Wilson

Keyword(s):

Wave Propagation ◽

Shear Wave ◽

Marine Sediments ◽

In Situ Measurements

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Tortuosity and the Averaging of Microvelocity Fields in Poroelasticity

Journal of Applied Mechanics ◽

10.1115/1.4007923 ◽

2013 ◽

Vol 80 (2) ◽

Cited By ~ 5

Author(s):

M. F. Souzanchi ◽

L. Cardoso ◽

S. C. Cowin

Keyword(s):

Porous Media ◽

Kinetic Energy ◽

Energy Loss ◽

Cancellous Bone ◽

Quantitative Measure ◽

Pore Fluid ◽

Fluid Viscosity ◽

Anisotropic Porous Media ◽

Pore Architecture ◽

Kinetic Energy Loss

The relationship between the macro- and microvelocity fields in a poroelastic representative volume element (RVE) has not being fully investigated. This relationship is considered to be a function of the tortuosity: a quantitative measure of the effect of the deviation of the pore fluid streamlines from straight (not tortuous) paths in fluid-saturated porous media. There are different expressions for tortuosity based on the deviation from straight pores, harmonic wave excitation, or from a kinetic energy loss analysis. The objective of the work presented is to determine the best expression for tortuosity of a multiply interconnected open pore architecture in an anisotropic porous media. The procedures for averaging the pore microvelocity over the RVE of poroelastic media by Coussy and by Biot were reviewed as part of this study, and the significant connection between these two procedures was established. Success was achieved in identifying the Coussy kinetic energy loss in the pore fluid approach as the most attractive expression for the tortuosity of porous media based on pore fluid viscosity, porosity, and the pore architecture. The fabric tensor, a 3D measure of the architecture of pore structure, was introduced in the expression of the tortuosity tensor for anisotropic porous media. Practical considerations for the measurement of the key parameters in the models of Coussy and Biot are discussed. In this study, we used cancellous bone as an example of interconnected pores and as a motivator for this study, but the results achieved are much more general and have a far broader application than just to cancellous bone.

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Acoustic modeling in fluid‐saturated porous media

Geophysics ◽

10.1190/1.1443060 ◽

1991 ◽

Vol 56 (4) ◽

pp. 424-435 ◽

Cited By ~ 33

Author(s):

Siamak Hassanzadeh

Keyword(s):

Porous Media ◽

Wave Propagation ◽

Acoustic Wave ◽

Seismic Waves ◽

Single Phase ◽

Reservoir Characterization ◽

Acoustic Modeling ◽

Fluid Viscosity ◽

Acoustic Wave Propagation ◽

Hydrocarbon Reservoir

An acoustic modeling method with possible application to enhanced hydrocarbon reservoir characterization is presented. The method involves numerical simulation of two‐dimensional (2‐D), low‐frequency transient acoustic‐wave propagation in porous media and is based on the explicit finite‐difference formulation of Biot’s system of equations in a fluid‐saturated poroacoustic medium. The scheme is second‐order accurate in space and time. Synthetic seismograms computed using this approach indicate that transient acoustic‐wave propagation in unbounded fluid‐filled porous media and in the presence of fluid viscosity closely mimics that in an equivalent nonporous (single‐phase) solid. However, in the presence of heterogeneities, such as layering, inclusions, and discontinuities, the results show that acoustic‐wave characteristics are affected by spatial variations in reservoir parameters such as porosity, permeability, and fluid content as well as the fluid‐solid interaction. The effects of permeability and fluid viscosity are discernible in dispersion and dissipation of the compressional wave, whereas porosity affects the compressional velocity as well. The results of this study suggest that no equivalent single‐phase model can adequately describe the effects of permeability and porosity on seismic waves propagating through heterogeneous fluid‐filled porous media.

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