Patent GB-1301531-A (GB)
IPC: G01V1/36
Filed: 1970-02-27
Abstract: 1301531 Seismic signal processing TEXAS INSTRUMENTS Inc 27 Feb 1970 [3 March 1969] 9656/70 Heading H4D Static corrections, for a set of seismic traces characterized by spatial redundancy, are obtained by (a) cross-correlating each trace with a respective reference signal synthesized by averaging the remaining traces of the set, (b) determining the correlation time lags of selected peaks in the correlation results, (c) averaging those time lags which are related to a common shot point, (d) averaging those time lags which are related to a common receiver location, and (e) generating correction signals in accordance with the averaged time lags. In the illustrated application to, e.g. common depth point (CDP) traces obtained by a rollalong field technique, approximate static and normal moveout corrections may be applied to the traces before the processing shown. The (corrected) traces provide an input at 100 (Fig. 5). Selected time-gates of the traces are subjected to conventional (e.g. frequency) filtering at 104 and predetermined residual moveout corrections at 106. At 108, each of the N gated and corrected traces in a CDP set is cross-correlated with the CDP stack of the remaining N-1 traces of the set, according to the Fig. 6 flow diagram. At 122, 124, iterative corrections for any residual normal moveout error are made according to the Fig. 7 flow diagram as follows: correlation functions associated with common shot-receiver spacings are averaged at 130, whereby static and random errors tend to average to zero leaving only those correlation peaks whose correlation lag represents residual moveout errors; the main peaks of the averaged correlation functions are picked out at 131 (according to the flow diagram of Fig. 9, not shown) on the basis that they are the peaks with the minimum correlation time lag, unless peaks of amplitude 10db above others are present in which case these higher amplitude peaks are picked; the correlation lags of the picked peaks are fitted at 132 to a hyperbolic curve; residual moveout corrections defined by the curve are then used to correct the trace gates prior to stacking and correlation at 108. The correlation lags of the picked peaks are multiplied at 170 (Fig. 5) by an empirical factor (N-I)/N to remove a bias error inherent in the correlation procedure. Those corrected lags associated with common shot positions are then averaged at 174 to provide values representing the shot static corrections, while the corrected lags associated with common receiver positions are averaged at 176 to provide values representing the receiver static corrections. The shot and receiver statics, are combined at 178 to give total static corrections. Very large static corrections are assumed to be spurious and are rejected by an iterative loop 182, 184, 188. The remaining static corrections are applied to the trace gates by iterative loop 192, 108 and the resulting new static corrections are applied at 196 to the complete traces. To monitor the processing, mean values of the correlation time lags for the set of CDP traces are computed at 194 and should be small if the processing is satisfactory. The processing may be done by analogue or digital methods.