科研之友
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摘要
In recent years, a number of methane-venting mud volcanoes have been found in the southwest area of the Dongsha waters from multi-channel seismic, sub-bottom profiling and dredging survey. Studying mud volcanoes has great significance for oil and gas reserves. In this paper, a buried anticline was found near a mud volcano, MV3, with reversed polarity on a multi-channel seismic profile, where the absolute amplitude increases with offset. To detect whether it contains natural gas, velocity analysis, AVO inversion and frequency absorption attenuation analysis were carried out. There is a low P-wave velocity layer under the reflector of reversed polarity. AVO inversion shows that the polarity reversal zone features negative values in intercept and gradient sections, and falls in the third quadrant in P and G cross-plot. The polarity reversal zone features positive in S-wave reflectivity section, and is highly negative in Poisson ratio change rate section. Frequency absorption and attenuation analysis shows rapid energy loss of high frequency and relative increase of low frequency. Multiple attributes point to gas accumulation there, likely associated with the methane seepage from deep.
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