US 4,794,573 AGranted

Process for separating upgoing and downgoing events on vertical seismic profiles

AssigneeConoco Inc.

InventorsDavid W. Bell, Vernon D. Cox

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Abstract

A process for separating upgoing and downgoing seismic wave events in a vertical seismic profile, and particularly for vertical seismic profiles wherein the seismic energy source is offset from the borehole in which seismic detectors are located in vertical spaced array. The process operates on two detector signals at a time (as S.sub.1 and S.sub.2) and is based on the concept that waves traveling in opposite directions have spatial derivatives of opposite sign. The derivative is approximated by the difference of the two signals which is time integrated to recover the phase. The resulting integrated difference signal I is then amplitude scale corrected and combined by addition or substraction with a signal S.sub.0 representing the sum of the two detector signals to form a succession of filtered signals which, when recorded in alignment in order of detector depths to form a vertical seismic profile preserves either the upgoing or the downgoing seismic events.

Claims10

Dependent claims

A method of seismic geophysical surveying wherein a seismic energy source positioned at or near the earth surface is adapted to generate seismic wave energy which is detectable by seismic detectors in vertical spaced array in a borehole and the electrical signals generated by the seismic detectors in response thereto are processed for discriminating the seismic events which are upward traveling as they arrive at the detectors from those which are downward traveling as they arrive at the detectors, said method comprising the steps of:

(a) generating seismic waves in the earth at a given location,
(b) detecting the resultant seismic waves at a plurality of vertically spaced levels in a borehole penetrating earth formations below the energy source and generating representative electrical signals in response thereto by means of detector transducers positioned in the borehole at each said level,
(c) combining a pair of detector signals from a pair of detectors at adjacent levels in the borehole to form a sum signal,
(d) subtracting the signal from the lower detector of the pair from the signal of the other detector of the pair to form a difference signal,
(e) integrating the difference signal to form an integral signal,
(f) applying an estimated amplitude scale correction to the integral signal to form a resulting signal which is an approximate representation of a detector signal from a detector located midway between said pair of detectors, and
(g) subtracting the amplitude corrected signal from said sum signal to form a modified filtered signal wherein the amplitudes of the seismic wave events which are upwardly traveling as they arrive at the detectors are increased and the seismic wave events which are downwardly traveling as they arrive at the detectors are attenuated.

4 more elements

(a) generating seismic waves in the earth at a given location,
(b) detecting the resultant seismic waves at a plurality of vertically spaced levels in a borehole penetrating earth formations below the energy source and generating representative electrical signals in response thereto by means of detector transducers positioned in the borehole at each said level,
(c) combining a pair of detector signals from a pair of detectors at adjacent levels in the borehole to form a sum signal,
(d) subtracting the signal from the lower detector of the pair from the signal of the other detector of the pair to form a difference signal,
(e) integrating the difference signal to form an integral signal,
(f) applying an estimated amplitude scale correction to the integral signal to form a resulting signal which is an approximate representation of a detector signal from a detector located midway between said pair of detectors, and
(g) adding the amplitude corrected signal to said sum signal to form a filtered signal wherein the seismic wave events which are downwardly traveling as they arrive at the detectors are preserved.

4 more elements

Dependencies are inferred from the claim text.