Because of the gas shortage in the United States, it is necessary to increase the nation's gas reserves. It is possible to utilize a very highly refined seismic technique for the direct detection of gaseous hydrocarbons in aquifers. This refinement is based on the increase in reflection coefficient caused by the addition or the replacement of the liquid in the pore space of an aquifer by the gas and an accompanying decrease in both the velocity and density of the aquifer. Refined data-acquisition techniques, including binary-gain amplifiers, accurately record the size of the reflections. Improved data-processing techniques with floating point processing, which preserves the amplitude of the reflections, make it possible to display a seismic section that the interpreter ca use to find subsurface locations where the reflection coefficient is increased in amplitude ("hot spots"). Because this technique depends on the uniformity of source and surface conditions, it is particularly suitable for offshore areas and should come into extensive use in future offshore-gas exploration in the United States. This technique probably was responsible in part for the very high prices paid for some of the blocks in the recent offshore Louisiana sale.

Like almost all seismic techniques, it is not unambiguous and there are phenomena which can be confused with the increase in amplitude due to the presence of gas. This increase in amplitude can be caused by focusing, lithologic changes, phases of reflections caused by multiples, and nonuniformity of source and surface. It is important that the acquisition and processing be done carefully so that the interpreter is presented with a high-quality section for interpretation. This interpretation requires a more careful treatment than in the past.

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