GAPPED DECONVOLUTION FILTERING FOR SUPPRESSING REVERBERATIONS IN ELECTRICAL SEISMIC TRACES

摘要

1,195,263. Seismic prospecting. TEXAS INSTRUMENTS Inc. 22 June, 1967 [23 June, 1966], No. 28808/67. Heading H4D. Reverberations in a seismic trace are suppressed by deriving the auto-correlation function X of a limited time-gate of the trace, deriving the cross-correlation function Z of the said time-gate with the same time-gate of the trace delayed by a time T substantially equal to the two-way travel time of seismic energy reflected from the subsurface horizon giving rise to the reverberations, time-domain filtering the trace with a filter function Y obtained from the matrix equation XY = Z, delaying the filtered trace by the time T and subtracting the delayed filtered trace from the original undelayed trace. In the Fig. 1 embodiment, analogue processing of the trace from geophone 11 of an array is considered; similar processing is applied to traces from the other geophones. The trace is recorded as traces 36, 36SP1/SP on magnetic drums 31 to 34, the traces 36SP1/SP being delayed by time T (the travel time in water layer 12) relative to trace 36, and the recorded traces are then reproduced repetitively while stepping devices 83, 84 apply incremental time-shifts T between the drums. The reproduced signals pass to multiplier-integrators 45, 48 which develop respectively the cross-correlation function Z and autocorrelation function X of a time gate of the signals. Programmed potentiometers 85-87 provide a smooth initiation and termination of the time gate. The correlation functions are stored on drum 47. The original trace from geophone 11 is filtered by a seven-point time-domain filter comprising drum 34, delay outputs 61- 67, weighting resistors (or variable-gain amplifiers) 68-74 and adder 75. Drum 34 provides a delay of T Πnr (n = - 3 to + 3) on outputs 61-67, and the sum of the delayed output signals is subtracted from the original (undelayed) trace in adder 75 to give a reverberation-free trace which is applied to storage unit 81 and recorder 82. Weighting factors for the filter are determined by computer 60 which derives the filter function Y by solving the matrix equation [Y] = [X]-SP1/SP[Z]. Spread corrections may be applied to the geophone traces before the above processing, and the processing may be done digitally instead of by the analogue, Fig. 1, system. Time-domain filters longer than seven points may be used.