Abstract
To investigate the distribution and velocity attributes of gas hydrates in the northern continental slope of South China Sea, Guangzhou Marine Geological Survey conducted four-component (4C) ocean-bottom seismometer (OBS) surveys. A case study is presented to show the results of acquiring and processing OBS data for detecting gas hydrates. Key processing steps such as repositioning, reorientation, PZ summation, and mirror imaging are discussed. Repositioning and reorientation find the correct location and direction of nodes. PZ summation matches P- and Z-components and sums them to separate upgoing and downgoing waves. Upgoing waves are used in conventional imaging, whereas downgoing waves are used in mirror imaging. Mirror imaging uses the energy of the receiver ghost reflection to improve the illumination of shallow structures, where gas hydrates and the associated bottom-simulating reflections (BSRs) are located. We developed a new method of velocity analysis using mirror imaging. The proposed method is based on velocity scanning and iterative prestack time migration. The final imaging results are promising. When combined with the derived velocity field, we can characterize the BSR and shallow structures; hence, we conclude that using 4C OBS can reveal the distribution and velocity attributes of gas hydrates.
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This research is supported by the National Hi-tech Research and Development Program of China (863 Program) (Grant No. 2013AA092501) and the China Geological Survey Projects (Grant Nos. GZH201100303 and GZH201100305).
Sha Zhi-Bin graduated from China University of Geosciences (Wuhan) in June 1994. He is a presently a PHD. student in the Department of Marine Geology, Faculty of Resources, China University of Geosciences (Wuhan). His research interests are seismic surveying of gas hydrates.
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Sha, ZB., Zhang, M., Zhang, GX. et al. Using 4C OBS to reveal the distribution and velocity attributes of gas hydrates at the northern continental slope of South China Sea. Appl. Geophys. 12, 555–563 (2015). https://doi.org/10.1007/s11770-015-0515-z
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DOI: https://doi.org/10.1007/s11770-015-0515-z