Prediction of Shallow Gas from Seismic Data

Abstract

Since prediction of shallow gas is essentially a prediction of pore fill, we have chosed to focus on seismic parameters which are significantly affected by a change in pore fill. These parameters are: Seismic velocity, attenuation, amplitude versus offset and seismic response. To study these parameters, different techniques are required, and in this paper we apply the techniques on real data for shallow gas prediction. If all the techniques described could be applied at the same site, the result should be a reliable prediction.

The attenuation of seismic energy is a promising parameter, but it requires that refracted waves are recorded.

The amplitude versus offset is expected to be a powerful prediction technique in the future, but at the present time more development is needed. This technique also has the potential of estimating the saturation under favourable conditions.

Single trace inversion is also a promising technique, and with further development and linked to velocity modelling it will become a powerful tool in shallow gas prediction.

Direct use of seismic velocities in shallow gas prediction requires refracted arrivals. These data are of special importance where no borehole data are available.

All techniques will benefit from borehole data, and they are absolutely necessary for a quantitative estimation of relevant parameters.