3-D Seismic Experimentation and Advanced Processing/Inversion Development for investigations of the Shallow Subsurface
We are proposing to continue work on advanced seismic image formation for the shallow subsurface. This proposal specifically has a multi-tiered approach that emphasizes data acquisition, conventional processing, and advanced processing, including:
- New seismic imaging/inversion technology development,
- New seismic experimentation in the form of a shear wave (3-component) seismic survey at Hill Air Force Base, Ogden, Utah (HAFB), and
- A 3-D survey at an as-yet-unspecified DOE site.
Under our previous DOE contact (DOE - ) we acquired a 2-D seismic dataset in 1998, a 3D reflection, 3D tomography and 2-D vertical seismic profile/surface datasets in 2000 at HAFB.
We have completed processing the 2D datasets with conventional and advanced techniques and have published results from this survey. To date we have we have completed the 2-D processing of the 1998 data producing 2-D tomography, post- and pre-stack depth migrated images using conventional reflection processing methods, pre-stack depth migrated images using advanced image focusing techniques, and Kirchhoff inversions.
The 3D datasets are now in the final stages of processing with conventional and advanced techniques. The 3-D tomography data are now completely processed and interpreted. The 3-D reflection data are currently being processed using traditional reflection processing techniques and 3D post-stack depth migration.
This proposal reviews results from the HAFB data, algorithm development, outlines additional work to be done with this data, proposes two new surveys, and elaborates on additional seismic processing technologies we propose to develop specifically for shallow investigations including elastic inversion using waveform tomography and the generalized Radon transform.
The HAFB 2-D and 3-D images clearly delineate the bopunds of a buried paleochannel in which DNAPLs have settled, ponding at the lowest points of the channel, atop a clay aquiclude.
The 3-D reflection and tomography datasets clearly image the channel in 3-D, and show the highly variable nature of the channel structure. The 3-D tomography experiment shows that compressional velocities increase by a factor of ~7.5-10 from the surface to the top of the aquiclude at 4-14m depth. The VSP/Surface seismic experiment waveform tomography images underscore the rapid vertical and lateral seismic velocity heterogeneity of the test site. The VSP-surface seismic waveform inversion shows that velocities change laterally by a factor of about 2-4 on a scale of 2-3m at any given depth.
We are proposing to acquire 2-D S wave data at HAFB and another 3-D reflection/tomography dataset with limited S-wave data at another location. We are proposing to extend the waveform tomography methods to the elastic case, to more completely characterize the mechanical properties of the subsurface, extend the wide-angel migration techniques to 3-D for application to the 3-D reflection datasets, and to develop and apply 3-D acoustic and elastic Generalized Radon Transform methods for 3-D reflection data inversion.