120 Seismic Imaging 4.5 Conclusion Seismic reflection technology has been developed for the oil industry. The 3D seismic spread designs require the use of telemetric recording systems. Processing sequences enable high-resolution 3D seismic blocks to be obtained, due to sophisticated algorithms (3D prestack depth migration, full waveform inversion…) that are implemented on high performance computers. In this chapter we have shown that it is possible to obtain very high-resolution 3D blocks for near surface applications with very basic seismic spreads (48 channels recorders, a single geophone per trace, light seismic source). Near surface studies require specific test phases to define the optimum acquisition parameters (minimum offset, geophone interval). The processing sequence must be carefully adjusted to the field data, especially for the wave separation. In the near-surface karstic reservoir imaging example (Hydrogeological Experimental Site of Poitiers), we have shown that the velocity distribution obtained by refraction tomography in the first 30m can be merged with the velocities extracted from the amplitude of the reflected events, to obtain a continuous velocity model from the surface up to a depth of 120 m. The spread, designed for near-surface reflection surveying, can be used for refraction surveying and surface wave analysis. The results obtained using the different methods can be productively combined, which is explored further in the “Hybrid seismic methods” chapter. References Anstey N., 1986, Part 1: Whatever happened to ground roll? The Leading Edge, 5, 40-45, DOI:10.1190/1.1439239. Archie G.E., 1942, The electrical resistivity log as an aid in determining some reservoir characteristics, Petroleum Technology, 146, 54-62. Chaouch A., Mari J.L., 2006, 3D land seismic surveys: Definition of Geophysical parameters, Oil & Gas Science and Technology, Rev. IFP., 61 (5), 611-630, DOI: 10.2516/ogst:2006002. Cordsen A., Galbraith M., Peirce J., 2000, Planning land 3D seismic surveys – SEG Series No. 9, Bob A. Hardage Ed. Faust, L.Y., 1953, A velocity function including lithologic variation, Geophysics, 18, 271-288. Galbraith M., 2000, 3D seismic survey design: a solution, First break, 18 (5), 171176. Lansley M., 2000, 3D seismic survey design: a solution, First break, 18 (5), 162-166.
RkJQdWJsaXNoZXIy NjA3NzQ=