Spectral Inversion for Meaningful and Accurate Seismic Interpretation

Chopra, Satinder ¹; Marfurt, Kurt J.^2
1 Arcis Corporation, Calgary, AB, Canada.
² University of Oklahoma, Norman, OK.

Seismic sections are expected to bear a striking resemblance to geological cross-sections. When this happens, interpretation becomes straight-forward. If this does not happen, seismic interpreters resort to the art of geological interpretation of the seismic data based on their knowledge of the basic principles of geology and geophysics and their experience. In the practical scenario a certain amount of imagination is relied on when the bandwidth of the data is not supportive of the interpretation. Spectral reflectivity inversion helps the seismic interpreters by narrowing the gap between the two extremes mentioned above and produces sparse reflectivity estimates that resolve thin layers below the tuning thickness. The process differs from other inversions in that it is driven by geological rather than mathematical assumptions, and is based on aspects of the local frequency spectrum obtained using spectral decomposition of various types. The resolution of spectral inversion is far superior to the input data and so makes it very suitable for characterization of thin reservoirs. This aspect makes the method ideal for detailed delineation and characterization of thin reservoirs.

An interesting aspect about spectral inversion is about an important attribute of the reflection process that a seismic interpreter looks for (in addition to four other attributes, namely, reflection polarity, strength, continuity and relationship to other reflections). While thin-bed reflectivity serves to provide four of these characteristics clearly, the reflection character can be studied by convolving the reflectivity with a wavelet of a known frequency bandpass. Finally, relative acoustic impedance run on thin-bed reflectivity yields valuable information in terms of subsurface rock layers rather than interfaces. Examples will be shown to illustrate how spectral inversion can help the seismic interpreter carry out meaningful and accurate interpretation.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009