AREAL SEISMIC METHODS FOR DETERMINING THE EXTENT OF ACOUSTIC DISCONTINUITIES

It is shown how areal seismic techniques can provide an added dimension in determining the extent of acoustic discontinuities in areas where the strata are generally flat. Seismic reflection data were collected in a water tank over a flat plate containing an acoustic discontinuity of irregular shape and small size. The data were migrated to create seismic sections through the discontinuity, and sufficient sections were produced to define the areal extent of the anomaly. The resolution on the seismic sections at the change in acoustic properties was improved by increasing the migration aperture. Similar experiments were carried out in the field in an area over essentially flat lying layers and a pinnacle reef. A common-depth-point (CDP) stacked section had shown that the seismic expression of the reef was the classical degradation of the reflection from the depth of the reef in the seismic section. The diagnostic loss of reflectivity was also seen on the sections, constructed from the areal data that intersected the anomaly. A composite interpretation based on the migrated areal data allowed the areal extent of the reef to be determined. When two known producing wells were located on the map, they were found to lie within the discontinuity in reflectivity. In addition, an interpretation based on a CDP section from a line crossing the anomaly showed that the anomaly in the vertical plane of the line coincided with the interpretation based on areal data.