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Seismic reservoir characterization of a U.S. Midcontinent fluvial system using rock physics, poststack seismic attributes, and neural networks

Rock Solid Images, Houston, Texas, U.S.

Jock Drummond, Donn McGuire, Stan Morris, John Bregar and James Lakings

Anadarko Petroleum Corporation, Houston, Texas, U.S.

Corresponding author: j.walls@rocksolidimages.com

The first 20% of the full text of this article appears below.

In a U.S. Midcontinent gas field, a channel feature contained shale and reservoir sands ranging in porosity from 6% to 20%. Well logs, core data, and 3D seismic data were combined in a reservoir characterization study to map the lithology and variability of porosity within the target sand. The project was conducted in two phases—a qualitative, uncalibrated seismic attribute study and a detailed well-log-calibrated reservoir characterization.

In the first phase, multiple seismic attributes were computed and a statistical tool was used to combine them to illuminate variations in lithology and porosity. These rapidly computed "hybrid" attributes can reveal important structural and stratigraphic features.

In the second phase, well log and core data were used to calibrate the velocity-porosity relationship. This model was subsequently used to perturb the porosity of the reservoir sands using representative wells. The resulting "pseudo wells" were used as input into a 1D ray-tracing synthetic seismic program. Prestack and poststack seismic attributes were computed. The well logs were used to classify the geologic column into carbonate, shale, and four different sand porosity classes. A neural network was then trained to relate these classes to the modeled seismic attributes. Once trained, this neural network was used to classify the entire 3D seismic volume. This classification provided a more reliable indication of higher quality reservoir zones than available from the uncalibrated seismic attributes.

The geologic setting of the study area includes Mississippian St. Louis and St. Genevieve carbonates and overlying Mississippian Chester clastics deposited in a broad, flat shelf environment north of the deep Anadarko Basin. The Chester sands targeted by this study were deposited in a narrow channel cut through the St. Genevieve carbonates and into the underlying St. Louis limestone. At the end of Meramacian deposition (St. Genevieve), sea level dropped, exposing the broad carbonate platform. A . . . [Full Text of this Article]