SOUTHWEST RESEARCH INSTITUTE

As a nonprofit research facility, Southwest Research Institute (SwRI) continually reinvests in expanding the capabilities of the staff to offer services to industry and the public. One avenue for this is the Internal Research Program. Many internal research projects have focused on reservoir geophysics.

1. Analytical Study of Multi-pole Acoustic Logging
   An internal research project was completed pertaining to theoretical and numerical modeling studies for the design and interpretation of advanced-concept acoustic logging tools. In particular, a theoretical analysis of acoustic wave propagation using a multi-pole source in a borehole surrounded by a transversely isotropic elastic formation was performed and numerically modeled. This project was completed in July 1989.

    

2. Analysis of Interwell Seismic Logging for Reservoir Characterization
   The objective of this IR project was to investigate advanced theoretical and numerical models to evaluate interwell seismic logging measurements to improve detectability, spatial resolution, and distribution of rock physical properties between well in heterogeneous hydrocarbon reservoirs. This project was completed December 1991.
    

3. Analysis of Seismic Wave Propagation through Fracture Rock
   The objective of this IR project was to investigate advanced theoretical and numerical models of subsurface seismic wave measurements to improve the detectability resolution, and characterization of fractured rock that is encountered in many underground rock formations including that at the Yucca Mountain site. This project was completed in October 1991.
    

4. Heterogeneous, Fluid-Filled Geologic Media
   The main objective of this research project was to investigate and analyze the response of pore pressures within a geologic medium to mechanical disturbances including natural earthquakes and other dynamic events. These phenomena are of concern in the case of a geologic high-level nuclear waste repository such as the proposed Yucca Mountain site. The goal was to determine the sensitivity of fluid pressure response to hydraulic and mechanical rock properties under realistic conditions of rock heterogeneity and anisotropy, which may be caused by fracturing and faulting. This project was completed in December 1994.
    

5. Coupled Hydro-Mechanical Response due to Seismic Wave Propagation in Heterogeneous Poroelastic Geologic Media
   This IR project developed the complete solution of the dynamic response of poroelastic media to a dislocation source. In addition, software was developed to calculate pressure-transient responses and the displacement of the fluid relative to solid associated with a dislocation and a force. Furthermore, we have developed computer-modeling techniques to solve reservoir site characterization problems for the oil and gas industry, as well as to address environmental and geotechnical issues. As a consequence, we have tested and applied the hydrologic coupling concept (between the elastic formation and the fluid flow) using the solution of the poroelastic wave equation when the Biot and the squirt flow mechanisms are included. We have used crosswell seismic data recorded between two wells located in the Fluvial Gypsy sandstone reservoir in Oklahoma. We have demonstrated that our present solution can be useful to solve practical problems by predicting the average of the intrinsic material properties of the formation. The real example showed that the present solution can be considered as a first-order approximation to evaluate observed phase velocity distributions. To explain, the variability of the phase velocity distribution associated with the Gypsy sandstone will require modeling intrinsic and scattering effects together. Such a modeling approach corresponds to the stochastic methodology, which is he second part of our current internal research project. This project was completed in June 1996.

Papers:

• Parra, J.O., and B.J. Zook, 2001, "Stochastic Wave Field Solution of the 2D Elastic Wave Equation Based on the Random Fourier-Stieltjes Increments," accepted for publication in the Journal of Applied Geophysics. [PDF]

6. Dispersive Boundary Conditions for FDTD Electromagnetic Modeling
   The purpose of this IR project was to develop dispersive absorbing boundary conditions (ABC) for finite-difference time-domain modeling of electromagnetic waves. The main motivation was to be able to model ground penetrating radar (GPR). ABCs in electromagnetics at that time would not work for the earth, which is lossy and dispersive (frequency-dependent). We successfully developed a dispersive ABC, subsequently using it in a project for GRI.  The project was completed in July 1994.
    

   Acoustic Logging in Formations with Layers and Fluid-Filled Fractures
   In this IR project we developed a new modeling approach to simulate full waveform multi-pole (i.e., monopoles and dipoles) acoustic measurements in a fluid-filled borehole, surrounded by a system of fractures oriented parallel of the axis of the borehole. To include the fluid borehole and fracture geometries, we have implemented the Boundary Integral Equation Method (BIEM). this approach allows us to simulate the fractured apertures, the number of fractures, the fracture spacing, the fluid-filled borehole effect as well as the fluid properties and the material properties of the medium. The solution predicts acoustic waves that are not presently detected by the current logging instruments. We demonstrated this modeling approach by conduction a parametric study to examine the effects of an open, vertical and fluid-filled fracture on full waveform dipole sonic logs. This project was completed in March 1998.
    

   Dynamic Response of a Fractured Tunnel to Seismic Waves
   This research project is aimed at developing a novel version of the boundary integral equation method (BIEM) to simulate the dynamic response of fractured tunnels to seismic waves. The fracture will be modeled using a slip boundary condition, which has been extensively analyzed and verified by experiment in the literature. Displacement and stresses along the fracture and tunnel wall were related to the material properties of the rock, the fracture stiffness, the tunnel shape and fracture orientation, and the frequency and incident angle of the seismic wave. Cases of no fracture, one fracture, and two parallel fractures were examined. Result of the modeling is being validated by comparison with experimental data. For the case of two fractures in particular, simultaneous slippage on both fracture faces could lead to rock fall. This project was completed in December 2000.

    

   Papers and Presentations:

   • Xu, P.-C., J.O. Parra, and C.L. Hackert. 2001, "Dynamic Response of a Fractured Excavation to Blast and Seismic Waves," Proceedings, 38th U.S. Rock Mechanics Symposium, the American Rock Mechanics Association, Washington, D.C.[PDF]

   • A Study of the Dynamic Response of a Fractured Tunnel to Plane Waves (September 2000). [Downloadable viewer if you do not have PowerPoint® installed on your machine.][PPT]

   • Results of Numeric Tests and Preliminary Parametric Study (September 2000). [Downloadable viewer if you do not have PowerPoint® installed on your machine.][PPT]

For more information about our reservoir geophysics internal research projects, or how you can contract with SwRI, please contact Jorge O. Parra, Ph.D., at jparra@swri.org or (210) 522-3284.

reservoirgeophysics.swri.org

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012