Seismology and Incerse Methods
Office: 105 Noble Research Center
1. Multi-scale P- and S- velocity model building though traveltime and waveform tomography.
Seismic frequencies resolve the subsurface at different length scales; lower frequencies can only resolve the bigger features of the subsurface. “Multi-scale” refers to a scheme wherein the resolution of a velocity model is stepwise improved by building upon simpler low-resolution models.
I usually do the multi-scale model building through inverse methods. Generally speaking, the process of going from seismic data to physical property model (velocity, density, attenuation) is termed as inversion. I invert both the “arrival time” and the “waveform” (frequency and phase) attributes of seismic data.
Traveltime inversion is an easy, intuitive, and wide-accepted method of constructing P-wave velocity models with the help of ray propagation. Models from traveltime inversion describe large-scale features of the subsurface. Waveform inversion is a step ahead. It constructs a velocity (and attenuation, density, etc.) model that can replicate the observed seismogram as a whole. A combination of traveltime and waveform inversion can yield accurate velocity models that are not only fit for pre-stack migration but also for direct interpretation of the geology.
2. Depth imaging
Depth imaging is the process of reconstructing reflectivity sections that are “accurate” representations of earth’s structure and stratigraphy. Depth imaging is usually a two-step process. First, a velocity model that describes characteristics of the subsurface at large-scale is constructed following which the seismic energy is migrated to estimate finer scale features using the velocity model in the first step. Due to a general lack of quantitative methods for judging the fidelity of the migration velocity model, conventional depth imaging has to heavily rely upon interpreter’s intuitiveness. Depth images, as a result, can sometimes be quite subjective.
If the ultimate aim of seismic processing is creating valid geological models, why not integrate “interpretation” in velocity model building itself? A new technology for seismic imaging, referred to as Unified Imaging (UI; US patent pending), overcomes several drawbacks of conventional velocity model building. The idea is simple – if tomography updated velocities and migration focuses reflection energy, why not combine these two to yield common structural solution of geology? The structural solution is suggested by the interpreter.
Linear poroelasticity includes coupling between deformation of a porous solid and diffusion of the mobile pore-fluid as a result of seismic wave propagation. Although this theory has been tested in hydro-geological conditions, modeling methods at multi-scale reservoir geometries are severely lacking. Our long term goal is to develop a generalized 3D anisotropic, visco-elastic finite-element based modeling code which can then be combined with any existing time-domain inversion methods.
4. Ground Roll Inversion
Inversion methods for surface-wave (Raleigh Waves) have been well established and developed. The poor constrains on the S-wave velocity model due to dispersive nature of ground roll has been a long standing problem. We are trying to develop practical ways of addressing these concerns in real data. We are also trying to develop models for inversion of Love waves.
5. “Unconventional” Seismic rock physics of
Seismic rock physics is an established field of research. Most of the model however have been tested for siliciclastic systems, which is exemplified by a clean sandstone. The constrains on porosity-moduli relation in low-permeability shales and carbonates have not been tested adequately. We are addressing the problem from both ends – by collecting fundamental stress data and developing models to incorporate idiosyncrasies of tight, unconventional rocks.
The novel aspect of UI is its ability to combine long-offset reflections and turning rays in tomography and quantitatively measure the accuracy of a migration velocity model. The scheme is a composite of refection-traveltime tomography and pre-stack depth migration.
Funded Projects (role as PI unless otherwise specified)
• A physical test model based on stress-shadowing to optimize drilling operations during fracking, Oklahoma Center for Advancement of Science and Technology (OCAST)
• Oklahoma State - Halliburton Geoscience Ambassador Program, Halliburton Inc.
• Comprehensive Study of the Stratigraphy, Sedimentology and Diagenesis of the Mississippian Carbonates of the Southern Mid-Continent, Industry Consortium
• Structural and stratigraphic controls on methane hydrate occurrence and distribution: Gulf of Mexico, Walker ridge 313 and green canyon 955. US Department of Energy
• Atlas of Shale Pits, 2012 – 2013. American Association of Petroleum Geologists,
• Converted-Wave Imaging, 2011 – 2012. Dawson Geophysical
• MRI: Acquisition of a High Performance Compute Cluster for Multidisciplinary Research, 2011. National Science Foundation (Senior Personnel)
• Velocity-Depth Modeling of Upper Assam Shelf, 2010 – 2011. Oil India Limited
• Detection and quantification of gas hydrate, 2009 – 2011. US Department of Energy (Co-PI)
Back to Faculty Home Page