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Using Water Layer Normal Modes to Detect Shallow Gas and CO2 Leakage
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, EAGE Workshop on Permanent Reservoir Monitoring (PRM) - Using Seismic Data 2011, Feb 2011, cp-220-00019
- ISBN: 978-94-6282-063-0
Abstract
It is proposed to use the refracted wave associated with the guided waves propagating in the water layer to detect shallow gas or CO2 close to the seabed. At long distances from the source, the refracted wave train in the water layer is clearly observed on field data, and by measuring changes in amplitude and traveltime for this wave, we think this can offer a nice alternative to more conventional methods. Simple formulas for amplitude and traveltime changes based on ray theroy is presented. The optimal configuration is for a situation where the leakage is midway between source and receiver. Major limitations are coupled to the size of the anomaly (a lateral extension of 100 m is probably needed) and the water depth. Deep waters are more challenging for this method. Further investigations related to seismic modeling and eventually a field test is necessary to clearify the practical use of the method.