STRESS AND FREQUENCY DEPENDENT PROPERTIES OF POROELASTIC ANISOTROPIC ROCK

The poroelastic response of fluid saturated porous rock due to stress variations is of interest in geophysics and geomechanics as it has practical applications in reservoir depletion, fluid injection, time-lapse monitoring, and carbon dioxide sequestration. The effective stress in a poroelastic medium relates to applied pressure and pore pressure, with the Biot parameter (α) as a scaling factor of the pore pressure. This work offers an independent derivation of the tensor characteristics of α through elastic moduli, a microscopic effective medium derivation, and frequency-dependent behavior of α for an anisotropic medium. We derived simplified equations for isotropic rock subjected to confining pressure and pore pressure, isotropic rock under uniaxial stress considering the nonlinear part of elastic constants, and an equation of α for the frequency-dependent case. In the effective medium derivation, we assumed that the rock contains both isolated pores and connected pores saturated with liquid. We use the GSA method to Barnett shale core samples to link ultrasonic velocities with mineral composition and porosity data. We also use the GSA method in subsequent chapters to estimate the effective properties of a rock. We corroborate our theoretical formulations by applying those equations to experimental data for different scenarios such as changes in confining pressure, pore pressure, and uniaxial stress. We calculated the Biot tensor for sandstone and shale. We found excellent agreement between theoretical prediction and experimental data. It is known that α varies significantly for changes in porosity and rock microstructure in isotropic rock. We also see as much as a 21% difference between horizontal and vertical components of α for transversely isotropic (TI) rock for changes in uniaxial stress. We then estimated the frequency-dependent Biot tensor for TI models using numerical calculations. We noticed significant differences between vertical (α33) and horizontal (α11) components of α, especially at the surface seismic frequency band. However, uniaxial stress and horizontally aligned microstructure influence the elastic moduli and Biot tensor contrarily. In general, anisotropy due to uniaxial stress shows lower α33 and higher α11. The anisotropy due to microstructure shows the opposite.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Geophysics

Grantor

University of Houston

Year dc:date.issued

2021

Author dc:creator

• Morshed, Sharif Munjur

Advisor dc:contributor.advisor

• Chesnokov, Evgeni M.

Committee members dc:contributor.committeemember

• Li, Aibing
• Colli, Lorenzo
• Metwally, Yasser M.

• Biot tensor
• stress
• anisotropy
• rock physics

Statement dc:rights

• The author of this work is the copyright owner. UH Libraries and the Texas Digital Library have their permission to store and provide access to this work. UH Libraries has secured permission to reproduce any and all previously published materials contained in the work. Further transmission, reproduction, or presentation of this work is prohibited except with permission of the author(s).

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/10657/10232

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/10232