Summary

Seismic facies within a constant time interval parallel to a horizon can be analyzed and defined into several classes of similar trace shapes using a neural network classification process. The resulting map which is similar to a classic seismic facies map shows patterns of trace shape variation which can be interpreted in geological terms. The process is fast and the ability to create numerous facies maps quickly and repetitively in the beginning of an exploration phase enables the interpreter to effectively scan through the data and to concentrate in areas of interest.

Generation and interpretation of a seismic facies map of Sligo limestone in a 3D vibroseis survey in central Lavaca county in South Texas is presented here as an example. The outer edge of lower Cretaceous carbonate platform in the northern and western Gulf of Mexico shows development of a reef trend which has been variously named as Stuart City, Glen Rose, Edwards, Sligo reef trend depending upon the location. Hydrocarbon production has been documented in this reef trend in Louisiana and East Texas. However, in central Lavaca county very few wells have penetrated the Sligo limestone.

Our interpretation of a seismic facies map of a 90 ms interval consisting of Pearsall shale and upper Sligo limestone shows a linear NE-SW trending reef at the shelf edge for the entire 14 km length of the survey. West of this fringing reef, there are parallel interior reefs, back reef sediment filled basins, patchy reefs and tidal flats. The facies map was created in the beginning of interpretation in a short time and has helped us to outline the various geologic provinces of an exploration play. The facies map is shown in black and white here but normally it is displayed in color and is easy to interpret. Additional amplitude maps indicate possible porosity development in the reef.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah