Thursday, 10 December 2015

"Can Envelope help us understand the subsurface" GeoTeric response

Following the analysis and recommendations of our guest writer, David M Roberts, (see original blogpost here and David's reply here) further attempts have been made to investigate the dipping events in the 3D data set from offshore New Zealand (courtesy of New Zealand Petroleum & Minerals). 

First let’s have a larger scale view of them, and use XL 8654 and IL 4550 for illustration:  

The dipping events (high envelope values in red colour) of the crossline can also be identified along the inline, but their geometry is different.
David’s hypothesis was that the events had been caused by the steeply dipping faint noise observable in the data set. This coherent noise is less obvious along the inlines. While the sub-parallel, bright seismic reflections do not reveal significant changes in the studied interval (besides moderate, cyclic changes in reflection strength along the events), the Envelope shows significant variations in the geometry of the dipping features, which is especially obvious along the crosslines. Please note that the noise itself does not change dip along the crossline. To test the effect of the noise an extremely heavy noise cancellation was applied to the data set. Warning: this level of noise cancellation was not necessary at all; the resulting volume is heavily smoothed and lacks fine details.

Comparison of the original and the “noise cancelled” volume shows that the dipping events did not disappear with the removal of the faint, steeply dipping noise. After this analysis, we are fairly confident to say that the dipping events and the steep noise referred to by David are not related, although the jury is still out on their origin.

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