GB1065980A - Seismic exploration - Google Patents

Abstract

1,065,980. Geophysical prospecting. JERSEY PRODUCTION RESEARCH CO. Dec. 7, 1964, No. 49738/64. Heading H4D. In a seismic signal processing system the average amplitude in a portion of a seismic signal is determined and only indications representative of those parts of the signal portion which exceed the average amplitude are displayed. In the embodiment of Fig. 4 (not shown), the number of significant events, C, in the signal portion is determined by integrating the output pulses of a zero-crossing picker (68), and the cumulative amplitude, B, of the signal portion is determined by integrating the signal portion after rectification. The quotient B/C, i.e. the average amplitude, is obtained from a divider (76), is held, and is subsequently subtracted from the rectified signal portion, D, to give a " residual amplitude " signal F which may be recorded as a black.and-white or coloured trace of the combined variable-area-variable-density type on a photographic medium by means of a recorder similar to that disclosed in Specification 967,481. The mean energy, as represented by the area under the " residual amplitude " curve F, in a selected part of the signal portion may be determined by a further integration step (integration of curve F) and plotted on a map as a function of the seismic location (Fig. 8, not shown). For preparing a seismic section in which a plurality of traces are displayed side by side, the total energy in each seismic signal to be displayed is determined by rectifying and integrating each signal, and the gain of an amplifier (97) (Fig. 3) through which the signals are fed to the recorder is so adjusted that the mean amplitude in each amplified signal is the same. Alternatively, mechanical adjustments to the recorder may be made to accommodate the dynamic range of the several traces. In the embodiment of Fig. 10 (not shown), the average amplitude of a seismic signal portion is determined with respect to time rather than with respect to the number of significant events in the signal portion. In a modification, the signal processing is carried out by digital computer. Use of the invention enables disturbing effects due to variations in shot hole conditions or geophone coupling to be substantially eliminated from the seismic section. A recording of " residual cycle breadth," i.e. of those portions of a seismic signal in which the oscillatory period exceeds the mean period, may also be made.