Automating Shallow Seismic Imaging

Steeples, Don W.

University of Kansas. Center for Research.

关键词: Pumping;    02 Petroleum;    Reflection;    Monitoring;    Testing;   

DOI  :  10.2172/835007
RP-ID  :  DOE/ER/14826-F
RP-ID  :  FG07-97ER14826
RP-ID  :  835007

美国|英语

来源: UNT Digital Library

【 摘 要 】

This seven-year, shallow-seismic reflection research project had the aim of improving geophysical imaging of possible contaminant flow paths. Thousands of chemically contaminated sites exist in the United States, including at least 3,700 at Department of Energy (DOE) facilities. Imaging technologies such as shallow seismic reflection (SSR) and ground-penetrating radar (GPR) sometimes are capable of identifying geologic conditions that might indicate preferential contaminant-flow paths. Historically, SSR has been used very little at depths shallower than 30 m, and even more rarely at depths of 10 m or less. Conversely, GPR is rarely useful at depths greater than 10 m, especially in areas where clay or other electrically conductive materials are present near the surface. Efforts to image the cone of depression around a pumping well using seismic methods were only partially successful (for complete references of all research results, see the full Final Technical Report, DOE/ER/14826-F), but peripheral results included development of SSR methods for depths shallower than one meter, a depth range that had not been achieved before. Imaging at such shallow depths, however, requires geophone intervals of the order of 10 cm or less, which makes such surveys very expensive in terms of human time and effort. We also showed that SSR and GPR could be used in a complementary fashion to image the same volume of earth at very shallow depths. The primary research focus of the second three-year period of funding was to develop and demonstrate an automated method of conducting two-dimensional (2D) shallow-seismic surveys with the goal of saving time, effort, and money. Tests involving the second generation of the hydraulic geophone-planting device dubbed the ''Autojuggie'' showed that large numbers of geophones can be placed quickly and automatically and can acquire high-quality data, although not under rough topographic conditions. In some easy-access environments, this device could make SSR surveying considerably more efficient and less expensive, particularly when geophone intervals of 25 cm or less are required. The most recent research analyzed the difference in seismic response of the geophones with variable geophone spike length and geophones attached to various steel media. Experiments investigated the azimuthal dependence of the quality of data relative to the orientation of the rigidly attached geophones. Other experiments designed to test the hypothesis that the data are being amplified in much the same way that an organ pipe amplifies sound have so far proved inconclusive. Taken together, the positive results show that SSR imaging within a few meters of the earth's surface is possible if the geology is suitable, that SSR imaging can complement GPR imaging, and that SSR imaging could be made significantly more cost effective, at least in areas where the topography and the geology are favorable. Increased knowledge of the Earth's shallow subsurface through non-intrusive techniques is of potential benefit to management of DOE facilities. Among the most significant problems facing hydrologists today is the delineation of preferential permeability paths in sufficient detail to make a quantitative analysis possible. Aquifer systems dominated by fracture flow have a reputation of being particularly difficult to characterize and model. At chemically contaminated sites, including U.S. Department of Energy (DOE) facilities and others at Department of Defense (DOD) installations worldwide, establishing the spatial extent of the contamination, along with the fate of the contaminants and their transport-flow directions, is essential to the development of effective cleanup strategies. Detailed characterization of the shallow subsurface is important not only in environmental, groundwater, and geotechnical engineering applications, but also in neotectonics, mining geology, and the analysis of petroleum reservoir analogs. Near-surface seismology is in the vanguard of non-intrusive approaches to increase knowledge of the shallow subsurface; our work is a significant departure from conventional seismic-survey field procedures.