Communications – electrical: acoustic wave systems and devices – Seismic prospecting – Offshore prospecting
Reexamination Certificate
1998-09-28
2001-06-12
Williams, Hezron (Department: 2862)
Communications, electrical: acoustic wave systems and devices
Seismic prospecting
Offshore prospecting
C367S022000, C367S020000, C367S046000, C181S110000
Reexamination Certificate
active
06246637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to seismic exploration and, more particularly to a system for separating compression waves from shear waves and up-going from down-going waves.
2. Description of the Related Art
A problem encountered in marine seismic surveying, as well as vertical seismic profiling, is that of water column reverberation, or multiple reverberation. Reverberations arise as a result of the inherent reflectivity of boundaries such as the water surface and bottom. A seismic wave generated in, or reflected off of, the earth's strata passes into the water in a generally up-going direction. This reflected wave of interest travels through the water and past the seismic detector or receiver, which records the wave. The wavefield continues upward to the water's surface where it is reflected back in a down-going direction. This reflected, or ghost, wavefield also travels through the water and past the receiver where it is again recorded. This reverberation of the seismic wavefield in the water obscures seismic data, amplifying certain frequencies and attenuating others, thereby making it difficult to analyze the underlying earth formations.
Ruehle, U.S. Pat. No. 4,486,865, incorporated herein by reference, discloses a seismic multiple suppression method employing inverse filters designed from the differing response characteristics of co-located hydrophones and geophones to primary and multiple seismic reflections. Loewenthal et al., U.S. Pat. No. 4,752,916, incorporated herein by reference, proposed the use of co-located hydrophones and geophones to estimate the source wavelet and then to use a deconvolution based on this wavelet to deghost the observed seismic data. Barr, U.S. Pat. No. 4,979,150, incorporated herein by reference, and Barr et al., U.S. Pat. No. 5,163,028, also incorporated herein by reference, disclose methods for reducing multiple reverberations in marine seismic reflection data by calibrating, scaling and summing together co-located hydrophone and geophone seismic data. Dragoset, U.S. Pat. No. 5,365,492, incorporated herein by reference, teaches an improved method of scaling the geophones to the hydrophones based on application of adaptive noise reduction techniques. Moldoveanu, U.S. Pat. No. 5,621,700, incorporated herein by reference, teaches an improved method of attenuation of reverberations by combining reverberation signals having identical amplitudes but opposite polarities wherein the reverberations are cancelled and only primary waves of interest remain.
These methods do not allow for multiple-free, single-component-type (e.g. hydrophone or geophone) data. Thus, there is a need for a process that will allow for a simple production of single-component-type sections.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a method for processing seismic signals, is provided, the method comprising:
reading seismic data received at a multi-component receiver;
generating a mask trace as a function of the seismic data; and
identifying a single type of seismic signals from the seismic data utilizing the mask trace. In one embodiment, the seismic data received at a multi-component receiver includes pressure data received at a pressure sensor and velocity data received at a vertical component velocity detector.
In a more specific embodiment, the seismic data received at a multi-component receiver includes velocity data received at a horizontal component velocity detector.
In still another embodiment, the generating the mask trace further comprises: multiplying the seismic data received at the pressure sensor with the seismic data received at the vertical component velocity detector to produce a first result; identifying a positive
egative sign of the first result to produce a first binary result; and dividing the first binary result by a scaling factor to produce the mask trace. In one example embodiment, the identifying the single type of seismic signals further comprises: multiplying the pressure data received at the pressure sensor with the mask trace wherein the method for processing extracts the single type of seismic signals representing seismic waves received at the pressure sensor. In another example embodiment, the identifying the single type of seismic signals further comprises: multiplying the velocity data received at the vertical component velocity detector with the mask trace wherein the method for processing extracts the single type of seismic signals representing seismic waves received at the vertical component velocity detector.
In either such example embodiment, an additional option comprises displaying the single type of seismic signals remaining after the seismic waves are extracted.
In another more specific embodiment of the present aspect, the generating the mask trace further comprises: multiplying the seismic data received at the pressure sensor with the seismic data received at the vertical component velocity detector to produce a first result; identifying a positive
egative sign of the first result to produce a first binary result; multiplying the seismic data received at the vertical component velocity detector with the seismic data received at the horizontal component velocity detector to produce a second result; identifying a positive
egative sign of the second result to produce a second binary result; multiplying the first binary result with the a second binary result to produce a third result; and dividing the third result by a scaling factor to produce the mask trace.
Similar to an earlier described embodiment, in an additional option, the identifying the single type of seismic signals further comprises: multiplying the horizontal component velocity data received at the horizontal component velocity detector with the mask trace wherein the method for processing extracts the single type of seismic signals representing seismic waves received at the horizontal component velocity detector. In an alternative embodiment, the identifying the single type of seismic signals further comprises multiplying the pressure data received at the pressure sensor with the mask trace wherein the method for processing extracts the single type of seismic signals representing seismic waves received at the pressure sensor. In still a further alternative, the identifying the single type of seismic signals further comprises: multiplying the velocity data received at the vertical component velocity detector with the mask trace wherein the method for processing extracts the single type of seismic signals representing seismic waves received at the vertical component velocity detector. In any such alternatives, a further option is provided comprising displaying the single type of seismic signals remaining after the seismic waves received are extracted.
In still a further example of the present aspect of the invention, a further step is provided, comprising generating seismic waves in a water environment for reflection from earth strata wherein the seismic data results from the seismic waves. In an even further example, reading the seismic data further comprises: receiving the seismic data from the multi-component receiver; and recording the seismic data by a multi-channel seismic recording system. In any such example embodiments, example pressure sensors comprise hydrophones and example velocity detectors comprise geophones. Further, such examples operate in methods in which the seismic data represents compressional seismic waves, shear waves, and/or compressional to shear mode converted seismic waves.
In another aspect of the invention, a method for extraction of down-going seismic waves is provided, the method comprising:
reading seismic data received at a multi-component receiver including pressure data received at a pressure sensor and velocity data received at a vertical component velocity detector;
multiplying the pressure data and the velocity data to produce a first result;
identifying a positive
egative sign of the first result to produce a binary result &agr;;
Arnold & Associates
Jolly Anthony
PGS Tensor Inc.
Williams Hezron
LandOfFree
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