Frequency-Dependent Seismic Stratigraphy for High-Resolution Interpretation of Depositional Sequences

Zeng, Hongliu ^1
1 BEG, University of Texas at Austin, Austin, TX.

Seismic interpretation of stratigraphy and sedimentology is frequency or scale dependent. Classic seismic stratigraphy utilizes reflection patterns to identify depositional sequences and stratigraphic relationships. Further analysis of seismic facies (shape, configuration, amplitude, and continuity) leads to interpretation of lithology, facies, and depositional history of sequences. For study of large-scale sequences (hundreds of meters) where details are not crucial, this approach is highly effective. For high-resolution interpretation of depositional sequences (meters to tens of meters), however, details are key, and seismic-interpretation strategy should be changed accordingly.

Seismic events are a function of wavelet (frequency and phase) and acoustic impedance (AI) profile. Seismic interferences, or amplitude and frequency tuning effects, determine occurrence of seismic events and relationships among these events or seismic facies. By adjusting seismic frequency and phase, one can intentionally modify seismic facies to a certain degree. For high-resolution study, this adjustment may help optimize interpretation by reconditioning seismic events such that they selectively show thickness and AI distribution, stratigraphy, or depositional facies, depending on one’s purpose.

Tests on model and field data clearly reveal the value of frequency-dependent seismic stratigraphy in reservoir-level interpretation of sequences. For example, an erosional surface (e.g., an incised valley) or a lithofacies of certain thickness may occur on a section only in a selected frequency band but “disappear” in other bands. A thin, lowstand deltaic system may be observed as high-amplitude/high-continuity facies in low-frequency bands but as low-amplitude/low-continuity facies in high-frequency bands. Broad-banded seismic traces tend to correlate better with wireline lithology/porosity logs in wells, especially when thickness and AI have significant lateral changes, whereas narrow-banded traces seem more closely to follow stratal surfaces. As a result, use of the multiple-band display would reduce ambiguity of geologic interpretation and risk in drilling.

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