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| | Abstract | | Seismic exploration results suggest evidence of free gas beneath bottom simulating reflector because of abrupt changes in seismic velocities. Although it is possible to prospect existence of free gas by using P-wave slowness - Vp/Vs crossplot, an abnormal tendency of Vp and Vp/Vs relationship is also recognized in the free gas zone beneath BSR. In order to explain the cause of this abnormal trend, and to discuss the existence of free gas in the formations, we propose a model in which free gas bubble could increase the sonic velocity. According to our model, velocity increase caused by free gas bubble is affected by bubble size and void ratio. We think that it is possible to derive amount of free gas from this velocity increase caused by free gas bubble. |
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