Seismic Amplitude Variations and Detection of Sand Bodies: ABSTRACT

Abstract

An area offshore Louisiana with an abundance of well control and seismic data provides an opportunity to verify the presence of interpreted sand bodies. In gross aspect the seismic sections show two major zones: one with highly discontinuous reflections of modest amplitude and a deeper zone with continuous parallel reflectors of low amplitude. The latter is due to an overpressured shale section interrupted by poorly developed sands and hard streaks, while the former is dominated by laterally discontinuous blocky sands which can be readily mapped from seismic events. Looking at the sands in more detail, the reflectors are actually continuous, following time-lines, but the amplitudes diminish where the sands terminate. Thus, reflector amplitudes can be used to determine the distribution of sand bodies of the order of 70 to 100 ft thick. In one area a sand body can be mapped across a structural nose, delineating a structural/stratigraphic trap, and elsewhere the presence of gas is distinguishable from lithologic changes by the intensity and character of the associated seismic signature. One-dimensional modeling indicates that seismic response to the sand depends principally on density contrast with the shales. Two-dimensional modeling based on well log parameters and seismically derived geometries suggests that the sand bodies may be due to localized deposition and have been enhanced by differential compaction. End_of_Article - Last_Page 980------------