Direct Visualisation of Seismic Facies Boundaries and DHI Detection of Anomalous Gas

Complex seismic trace attribute analysis separates the amplitude and the phase information contained in the data and produces two basic attributes known as the instantaneous amplitude and instantaneous phase. Using these, two new attributes are being introduced, namely, the facies attribute called NRG derived as an extension of the instantaneous amplitude, and the second one based on instantaneous phase attribute is used to compute the reflector overlay times plotted on the display.

The NRG attribute is intended as a first step in the seismic interpretation process because it delineates subsurface boundaries both laterally and vertically. It also detects DHI effects for bright spot and non-bright or dim spot anomalies as well as indications of gas/oil migration through the subsurface. In one of the real data applications the bright spot colour display is calibrated to agree with the producible gas. Besides, there are attribute signatures for both oil and gas when the geology does not support bright spots. The application of the second attribute on real seismic data demonstrates how flat spots and faults are immediately recognisable. The unambiguous determination of geologically meaningful lateral as well as vertical boundaries cannot be overstated for direct facies analysis to be useful.