Channel Tracing25 05

Channel tracing using seismic attribute data

By Schlumberger DCS Moscow team: Mikhail Gostev, Mikhail Kourenko, Veronica Grabskaya

Starting point… The initial data was structure map (based on seismic interpretation) and log response curves, clearly identifying channel section. The thickness of body (22 m) and depth (2450 m) suggest, that object fits within lower margin vertical seismic resolution.

Starting point… Seismic amplitude section provided clear signal (blue phase) in the interval of interest.

Starting point… But it didn’t give much hints on the spatial distribution of the body.

Workflow Series of seimic maps between surfaces confining the interval of interest were built then (a primitive Petrel workflow was used to generate a pack of maps of the same interval, but different summing formula to asses the differences in summing method & then choose the most representative one) Still no major insights. So we started looking for attribute to visualize the dimensions and location of channel body.

Seismic map: interval average amplitude (minimum)

Attribute analysis Envelope Some signal in the interval of interest (though too wide).

Attribute analysis Envelope Interval average attribute maps: it can be seen here, that best signal comes from zones of structrural high, which is not appropriate position for the channel*. *In the platform environment like the one we have, there is no evidences, that structrural style was inverted so much that it cannot serve as qualitative representation of paleotopography

Seismic map: interval average “envelope” (arithmetic)

Attribute analysis - Variance – didn’t give any signal in interval of  interest at all.

Relative Acoustic Impedance Gave clear signal in the vicinity of well tops, so we shifted to attribute maps

Attribute analysis - Relative Acoustic Impedance The geometric summing gave first clues (see zone with zero-signal)

Attribute analysis - Relative Acoustic Impedance Mininum summing (remember, that on section, the bottom of the channel was marked with negative blue phase) gave us picture that we assumed satisfactory and shifted to modeling.

Modeling The latter workflow was ordinary – we’d built polygons marking the channel belt margin and presumable axis.

Modeling Then, used “Channels” option “Artificial  Algorithms” in Make/Edit Surface process to draw an artificial gross thickness map of channel body. The requested input parameters like width and thickness of channel were decided from regional geologic data and then adjusted to fit in observed data.

The resulting artificial isohore map was then used in Make Zones process* *the goal of the modeling was to get a zone with separate layering scheme in already built model with non-alterable number of horizons, so we didn’t try to m odel it as horizon, though realizing that modeling channel based on

Notes • Spectral decomposition (isofrequency analysis) didn’t give much result (at least in GG’s hands…), although we’d extracted a wavelet around the object interval & scanned the effective frequency interval with 3 hz increment. • Unfortunately, there will be no chance to validate the model in the near future, for no drilling is planned in the area now. • The overall workflow starting with log data and horizon interpretation and finishing with complete structural model, took ~1 week.

Thanks • We’d like to thank everyone who gave feedback on PetrelBB inquiry: Sergei Filin, Alexis Carrillat, Andy MacGregor, Jayanta Ray, Mohamed Sobhy and Dr. Lothar Schulte. • Special thanks to Gaston Bejarano for pointing out Rel. Ac. Impedance attribute and “express seismic processing & handling workshop” he conducted with us exactly at the right moment.