Abstract

In previous unpublished work, we found that anomalous values of instantaneous frequency (that is, frequency values that are negative or that have positive magnitudes greater than the Nyquist limit) are valuable indicators of alterations in reflection waveshape that occur commonly at stratigraphic terminations. Inspection of 3-D seismic data across Nash Draw Field on the northwest slope of the Delaware Basin showed that appreciable wavelet alterations occurred at the boundaries of distinct seismic facies within the targeted Brushy Canyon reservoirs that are being produced in this field. Based on this observation, we used instantaneous frequency as the fundamental database to define the edge positions and areal shapes of individual reservoir facies within this complex, slope-basin distribution of siltstones and sand-stones, commonly thought to be a succession of turbidite depositions. We compared the compartmentalization detail derived from this frequency-based approach with compartmentalization models provided by an amplitude-based interpretation and by coherency/continuity cube technology. These comparisons led us to conclude that a properly executed 3-D interpretation of instantaneous frequency behavior can provide a good first guess of the internal compartmented structure of many reservoirs. We offer our work here for peer evaluation by people who support reservoir characterization studies similar to what we describe. We have used instantaneous frequency behavior to successfully detect lateral disruptions in stratigraphic continuity for several years--long before the current concept of a coherency (or continuity) cube was publicized for this same purpose. This study shows that interpreters who do not have ready access to coherency-cube technology, but who do have Hilbert transform algorithms available to them, can create 3-D volumes of instantaneous frequency that provide valuable indications of reflection discontinuity, much in the same way that continuity/coherency cube technology does.

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