Lateral Resolution In Seismic Reflection-A Physical Model Study

Abstract

SUMMARY Physical seismic model experiments have been undertaken to study the detectability and lateral resolution of buried linear reflecting targets (slits in an aluminium plate) which might simulate a range of interesting geological structures, e.g. fracture zones, fault blocks, reefs, facies changes, cavities. The reflector length was varied from one-thirtieth to over 20 wavelengths. The depth of burial was 17 wavelengths. Even the smallest target yielded discernible diffractions on receivers located in the shadow zone of the reflector. The lateral extent of the reflector can be accurately determined in the subwavelength range by utilizing together the amplitude, frequency, moveout and polarity information contained in the composite diffractionlreflection signals. As the reflector length increases, the amplitude and travel time increase, but the predominant frequency decreases. The dominant polarity of the interference waveform changes as the reflector length exceeds one wavelength. For targets extended horizontally more than one wavelength, the time difference between the two edge-diffracted waves is a good measure of reflector extent. In the case of an inclined reflector, the moveout pattern of the two diffractions was asymmetrical, forming a convergence zone (and higher amplitude) on the downdip side of the shotpoint. The offset at which the diffraction wavelets merge serves to define the reflector dip. The reflector length can be estimated from the time separation between the two weaker diffractions observed on receivers located updip of the shot, after appropriate correction for target inclination.