Location

Brunswick, ME

Start Date

1-1-1997 12:00 AM

Description

On a mesoscale the pore structure in natural rocks is strongly inhomogeneous. With an increase of the scale size one may find that the pore structure has preferred orientation (texture) which leads to anisotropy of permeability and tortuosity. In this paper the Biot theory was applied to an orthotropic fluid saturated porous medium. Such a medium supports four different wave types: fast quasilongitudinal, two quasishear and slow quasilongitudinal waves. The properties of the orthotropic frame are described by the nine independent elastic constants of the dry frame. Pore structure characteristics such as tortuosity, permeability and shape factor become direction-dependent and in the coordinate system collinear with the acoustical axes each of these parameters is represented by a second-rank tensor with the only non-zero elements on the diagonal. Our results show that the velocities of quasilongitudinal and two quasishear waves depend mostly on the properties of the frame and are not sensitive to the permeability and tortuosity directly (the frame stiffnesses, permeability and tortuosity are indirectly related due to dependence on pore structure; however they can formally be considered as independent parameters). Thus by measuring these velocities one can determine the frame elastic constants. The slow wave velocity, on the contrary, depends mostly on the pore geometry. Its angular dependence in a water- or air-saturated solid allows us to recover the components of the permeability and tortuosity tensors. This approach opens new possibilities for determination of such characteristics of porous materials as preferred pore orientation and tortuosity which have been previously inaccessible experimentally and thus to retrieve information about the pore structure.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

16A

Chapter

Chapter 1: Standard Techniques

Section

Elastic Waves

Pages

83-90

DOI

10.1007/978-1-4615-5947-4_11

Language

en

File Format

application/pdf

Share

COinS
 
Jan 1st, 12:00 AM

Ultrasonic Wave Propagation in Anisotropic Fluid-Saturated Porous Media

Brunswick, ME

On a mesoscale the pore structure in natural rocks is strongly inhomogeneous. With an increase of the scale size one may find that the pore structure has preferred orientation (texture) which leads to anisotropy of permeability and tortuosity. In this paper the Biot theory was applied to an orthotropic fluid saturated porous medium. Such a medium supports four different wave types: fast quasilongitudinal, two quasishear and slow quasilongitudinal waves. The properties of the orthotropic frame are described by the nine independent elastic constants of the dry frame. Pore structure characteristics such as tortuosity, permeability and shape factor become direction-dependent and in the coordinate system collinear with the acoustical axes each of these parameters is represented by a second-rank tensor with the only non-zero elements on the diagonal. Our results show that the velocities of quasilongitudinal and two quasishear waves depend mostly on the properties of the frame and are not sensitive to the permeability and tortuosity directly (the frame stiffnesses, permeability and tortuosity are indirectly related due to dependence on pore structure; however they can formally be considered as independent parameters). Thus by measuring these velocities one can determine the frame elastic constants. The slow wave velocity, on the contrary, depends mostly on the pore geometry. Its angular dependence in a water- or air-saturated solid allows us to recover the components of the permeability and tortuosity tensors. This approach opens new possibilities for determination of such characteristics of porous materials as preferred pore orientation and tortuosity which have been previously inaccessible experimentally and thus to retrieve information about the pore structure.