Application of Albert W. Musgrave

431 F.2d 882, 57 C.C.P.A. 1352
CourtCourt of Customs and Patent Appeals
DecidedOctober 8, 1970
DocketPatent Appeal 8292
StatusPublished
Cited by29 cases

This text of 431 F.2d 882 (Application of Albert W. Musgrave) is published on Counsel Stack Legal Research, covering Court of Customs and Patent Appeals primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Application of Albert W. Musgrave, 431 F.2d 882, 57 C.C.P.A. 1352 (ccpa 1970).

Opinions

RICH, Judge.

This appeal is from the decision of the Patent Office Board of Appeals1 affirming the rejection of claims 1-14, 17-39, 47-58 and 60 of application serial No. 496,735, filed September 30, 1965, and entitled “Corrections for Seismic Data Obtained from Expanding-Spread.” Six apparatus claims have been allowed. We reverse.

THE INVENTION

The principal object of appellant’s invention is to obtain seismograms which delineate with a high degree of precision the nature of the subsurface formations in the earth’s crust.

Background

Appellant’s brief states:

A seismogram is a record of earth vibrations. In a reflection seismic survey, dynamite is detonated at a shotpoint, as in a shallow borehole, for the generation of seismic energy. A part of the downwardly traveling energy is reflected upwardly at each subsurface interface. A reflecting interface is a region where there is a change in the velocity [of the seismic energy] as between adjoining layers of the earth, such as a layer of rock (high velocity) and a layer of sand (low velocity). In addition to change in velocity of the seismic energy in the earth due to the velocity charaeteris-[883]*883tics of layers, the velocity through the earth increases with depth.
At the earth’s surface, the upwardly reflected energy is detected by a plurality of seismic detectors of geo-phones. These extend linearly along a line of exploration. After each explosion of dynamite [along the line of exploration], each detector ever a period of several seconds generates a plurality of electrical signa’s representative, inter alia, of reflected energy, multiples, and noise due to random earth movements unrelated to the effect of the reflected seismic energy.

[Bracketed insertions ours.]

A seismogram is produced by recording, on a magnetic tape for example, the electrical signals generated by each detector. Ordinarily, a “family” of seismograms is produced for each dynamite blast-— there being one seismogram for each detector. A plurality of dynamite blasts along a line of exploration will therefore yield a plurality of families of seis-mograms.

Appellant refers to two ways in which the detectors may be arranged with respect to the shotpoints along the line of exploration, one being referred to as a “split-spread” and the other as an “expanded-spread.” In a split-spread, the shotpoint is located in the center of a spread of detectors. In an expanded-spread the shotpoint is located on the line of exploration but at some distance from the spread of detectors. It is unnecessary for an understanding of this opinion to be aware of further details cf these arrangements. It will suffice to note that appellant uses both arrangements simultaneously to produce two families of seismograms for each dynamite blast.

To render meaningful the seismogram produced as described above, it is necessary to apply to it a so-called “weathered-layer correction” and a so-called “normal move-out correction.” With respect to the former, appellant explains that at the earth’s surface there is an unconsolidated, weathered layer (commonly called “soil”) of variable depth and inclination. The velocity of seismic energy passing through this layer is much lower than in the consolidated layer just beneath it. Since the weathered layer is of variable thickness and of low velocity, it is necessary to subtract the travel time of the seismic energy in the weathered layer from the tc-tal travel time.

Because of the high velocity contrast which exists between the base of the weathered layer and the adjoining consolidated layer, some of the seismic energy produced at the shotpoint will travel downward to the interface of the weathered and consolidated layers and be reflected upward to the detectors. The time-occurrence of the first reflection on the seismogram (time-zero being the instant the dynamite is detonated) provides the time-correction needed to eliminate the effect of the weathered layer on the time or depth measurements of interest.

A normal move-out correction is necessary to compensate for the geometrical spreading of the detectors. Since the measurements of interest are depths below the earth’s surface, the identification of reflections in terms of vertical travel time is desired. Obviously, the travel path, and therefore travel time, from a shotpoint to a given reflecting interface or “horizon” and then to a given detector is greater for a detector located some distance from the shotpoint than for a detector directly adjacent the shot-point. In correcting a family of seismo-grams for normal move-out, however, it must also be taken into account that the effect of geometrical spreading of the detectors decreases with increases in the depth from which a given seismic wave is reflected. Therefore, normal move-out corrections must be “dynamic”; that is, the magnitude of each correction for each detector must be varied inversely with the depth from which a wave is reflected — the greater the depth the less the correction. Stated differently, the longer the time-occurrence of a given wave is from time-zero [884]*884on a seismogram, the less it is corrected for normal move-out.

Correction of a family of seismograms for the weathered-layer and normal move-out yields, in effect, a new family of seismograms on which the positions of the representations of seismic waves relative to one another more nearly correspond to the relative depths of the horizons from which those waves were reflected. Perfect corrections would cause all the reflection signals corresponding to a given horizon to be lined up across the set of seismograms. However, since the corrections are ordinarily somewhat imperfect, further adjustments are made by reproducing the seis-mograms as traces on an oscilloscope and manipulating knobs on the oscilloscope to bring the reflections into horizontal alignment.

Refinement of this “new” seismogram is accomplished by identification and elimination of “multiples.” Multiples represent unwanted signals which must be eliminated to avoid errors in measurements of the time-occurrence of reflections. These unwanted signals occur by reason of multiple reflection of seismic waves, for example, as shown in Fig. 5A:

Reflections Ri, R2, and R3 arise because of seismic waves reflected to the earth’s surface from horizons RHi, RH2, and RH3, respectively. Multiple Mi arises because a wave is reflected from the earth’s surface to horizon RHi and thence again to the surface. Its travel time is twice that for reflection Rx. Mu and Mi2 illustrate other types of multiple reflections. There are still others which may obscure the time-appearance of the reflections which are the features of principal interest.

Appellant describes still other techniques used to refine seismograms, such as removal of noise signals due to random earth movements, but these are not critical to appellant’s invention.

Appellant’s Discovery

Appellant has discovered that a family of seismograms obtained by using an expanded-spread of detectors can be most precisely corrected for the effect of the weathered layer by deriving the necessary time-correction from the time-occurrence of the first reflection on a corresponding family of seismograms obtained using a spirt-spread of detectors.

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Bluebook (online)
431 F.2d 882, 57 C.C.P.A. 1352, Counsel Stack Legal Research, https://law.counselstack.com/opinion/application-of-albert-w-musgrave-ccpa-1970.