GB1208424A - Optimum seismic velocity filters - Google Patents

Abstract

1,208,424. Seismic prospecting. MOBIL OIL CORP. 20 Oct., 1967, No. 47885/67. Heading H4D. A method of filtering coherent noise from n seismic data traces derived from n spaced detectors in response to generation of a seismic disturbance comprises applying each of the traces to a different one of n filters each having an amplitude spectrum G j (#) given by the equation: where i is #-1, e is the base of Naperian logarithms, j represents successive integers between - n/2 and +n/2 (excluding zero), m represents successive integers betweenn/2 and +n/2 (excluding zero), # is the frequency of the seismic disturbance, T is the primary reflection moveout per trace, #T is the coherent noise moveout per trace, a j is a number equal to the distance from a reference point to the detector producing the jth trace divided by the spacing between successive detectors, am is a similar number for the mth trace, # mj is equal to 1 for m=j but is otherwise zero, R N (#) is the coherent noise-to-signal ratio, R U (#) is the random noise-to-signal ratio, p(#) is an assumed probability density function for primary reflection moveout, and #p(##) is an assumed probability density function for coherent noise moveout and summing the outputs of the filters to form a composite trace. Details are given of a FORTRAN programme for computing filter coefficients; the actual filtering may be done by digital computer or by analogue timedomain filters. The filtering separates primary and multiple reflections on the basis of their difference in apparent horizontal propagation velocities, permits upper and lower limits to be set on the velocities suppressed by the filtering, and permits account to be taken of the dependence of R N and R U on frequency for obtaining optimum suppression of multiple reflections.