Close full-size image and return to story.
Figure 2 – Use of P and S reflection data to distinguish gas sandstone reservoirs from lignite beds. Both gas-brine contact boundaries (a) and lignite-sand contact boundaries (b) generate strong P-wave reflections compared with P-wave reflection amplitudes at laterally equivalent brine-saturated sandstones. In contrast, S-wave reflections associated with gas-brine contacts (c) tend to be the same magnitude as those at laterally equivalent brine-saturated sandstones, but S-wave reflections associated with lignite-sand contacts (d) create a bright-spot reflection just as P-wave data do. Lignite can thus be distinguished from gas reservoirs if both P and S data are used in this comparative manner. Data examples taken from Ensley (1985).