Previous Talks

Wednesday, May 14th, 2008

The Effects of Reservoir Stress Paths on Acoustical Rock Properties and its Importance in 4D Seismic Imaging

Thurman E. (Gene) Scott, Jr. - Rock Dynamics, Houston, Texas

Abstract

Timeshifts on 4-D seismic images result from two basic causes: (1) acoustic velocity shifts due to changes in fluid properties or fluid composition; and (2) acoustic velocity shifts created by evolving reservoir stresses during depletion.  This seminar will concentrate on this latter process and will show experimental data derived from core samples to demonstrate the effect of stress on rock acoustic velocity.  The seminar will be divided into three parts.  The first will show the effects of triaxial, uniaxial strain, and hydrostatic deformational stress pathways on core samples conducted with simultaneous measurements of compressional and shear wave velocities along axial, lateral, and 45 degree directions.  The experiments indicate very dramatic changes along some stress pathways, such as triaxial deformation, which have large velocity shifts and show evidence of an increasing stress-induced anisotropy as deformation proceeds.  Other stress paths, such as uniaxial strain, show little or no change in either acoustic velocities or in anisotropy during deformation.  The second part of the seminar will present both the elastic and poroelastic velocity tensor components for ‘inherent’ anisotropy versus ‘stress induced’ anisotropy in rocks.  The results indicate that the ‘stress induced’ elastic anisotropy created in core samples can be just as large as the well documented ‘inherent’ acoustic anisotropy resulting from natural features such as bedding, layers, etc.   The final part of the seminar will illustrate how these experimental results would impact 4-D seismic images. 

Speaker Biography

Dr. Thurman E. (Gene) Scott, Jr. is currently president of Rock Dynamics.  He received a B.S. in Geology from the University of North Carolina in 1977, and a M.S. (1981) and Ph.D. (1989) from UT-Dallas.  He worked as a geologist with Enserch Exploration from 1981 to 1984 and was involved in exploration projects in the onshore and offshore U.S. Gulf Coast region.  Gene was employed as a research professor in the Rock Mechanics Institute (later PoroMechanics Institute) at the University of Oklahoma from 1991-2005.  There he concentrated on rock mechanics/rock physics research and conducted numerous laboratory experimental studies.  These included acoustic velocity tomographic imaging of rock damage, 3-D acoustic emission imaging of hydraulic fracturing, and measurement of anisotropic elastic and poroelastic rock mechanical properties under complex stress regimes.  At present his company (Rock Dynamics) specializes in making advanced acoustic anisotropy measurements on petroleum core samples.