The Middle Oligocene Frio sandstone reservoirs of the Texas Gulf Coast are dominated by amalgamated thin fluvial channel and crevasse-splay reservoirs as characterized by those found in Stratton Field, but analogous to reservoir sys-tems that are found throughout Southeast Asia. At Stratton, the field is draped over a broad dome shaped structure in the Vicksburg Flexure Trend above the Vicksburg fault system. The channel sands are 3 to 10 m thick and channel splay deposits are 1.5 to 7 m thick with porosities as high as 25 percent. Based on the log data the individual amalgamated channel fill deposits are up to 850 m wide. Production is challenging given fluvially dominated setting where thin hetero-geneous reservoirs cause significant compartmentalization and stranded reserves. Such reservoirs tend to have low ulti-mate recoveries.

These reservoirs have highly tuned seismic responses, for example, a 10 m thick reservoir at 3080 m/s is 6 ms thick and thus is still tuned at or below a dominant frequency of 83 Hz. The seismic data used in this study consists of a full stack dataset with an effective bandwidth of 10 – 60 Hz and a dominant frequency of 35 Hz which is well below the level need-ed to resolve individual channel systems through conventional interpretation methods.

To mitigate some of the resolution issues we apply advanced seismic analysis techniques consisting of post-stack seis-mic processing, attribute analysis and detailed interpretation. Post stack processing includes steps to reduce noise, broaden and balance spectra resulting in a 10 – 80 Hz bandwidth. Attribute analysis of the post-stack processed data in-cludes calculation of bandlimited instantaneous attributes from a high-fidelity spectral decomposition for both amplitude and phase, a unique tuned similarity, volumetric curvature and other attributes. The results are calibrated to well data us-ing rock physics relations to select key attributes for statistical analysis and time-varying waveform characterization. The results are interpreted in detail using stratal slices and well data for channel related stratigraphic features.

Results show decreased tuning thickness and enhancement of visible channel geometries compared to the original data.

Stratton Field

Fluvial systems in South-East Asia(marked with )

Upper Miocene

Blocked Well 9 Data

Coloured Inversion Allows:

1. Increased Bandwidth2. Geology-driven Spectral Balance3. Estimation of Relative Acoustic Impedance

3-D Seismic data covers an area of Stratton Field in Nueces County, Texas: 1.6 x 3.2 km

The seismic data consist of 20,000 seismic traces of 3 second record length with a 2ms sample rate, distributed over 100 Inlines by 200 Crosslines with a square 16.7 spacing.

Log Spectrum

Seismic Spectra

Bandlimited Instantaneous Frequency at 35 Hz, with highlights from Tuned Similarity 30-40 Hz (35 Hz CF)

Bandlimited Envelope at 35 Hz, with highlights from Tuned Similarity 30-40 Hz (35 Hz CF)

Observations:Interference between reflectors helps to produce low values of Tuned Similarity.

Amplitude notches are simultaneously observed in Spectral Envelope and as spikes in BandlimitedInstantaneous Frequency.

Data Acknowledgement:Levey, R.A., B.A. Hardage, R. Edson, and V. Pendle-ton, 1994. “3D Seismic and Well Log Data Set, Fluvial Systems - Stratton Field, South Texas”Texas Bureau of Economic Geology