Some Practical Aspects of Interference Attenuation in Routine Seismic Exploration
- H. Evans (Hudson's Bay Oil & Gas Ltd.)
- Document ID
- Petroleum Society of Canada
- Journal of Canadian Petroleum Technology
- Publication Date
- December 1962
- Document Type
- Journal Paper
- 162 - 166
- 1962. Petroleum Society of Canada
- 5.1.7 Seismic Processing and Interpretation
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- 117 since 2007
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An economic and a rather simplified scientific approach to the solution ofmore proper spacing of pattern holes and geophone arrays in the field isdiscussed. A method of recording and calculating the surface or apparent wavelength of interference waves is outlined. Several examples of actual fieldseismograms are included to illustrate the degree of interference attenuationthat can be obtained with a minimum amount of recording experimentation.
This paper is designed primarily to point out an economic and rathersimplified scientific approach to the solution of more proper spacing ofpattern holes and multiple geophone arrays in the field. The proceduresoutlined are not proposed as a "cure-all," but merely are intended to depict alogical sequence of steps which, in many instances, will yield at least apartial solution to the enhancement of the quality of seismic reflectionsignals.
Initially a few of the fundamental concepts of wave propagation should bereviewed. The word interference is defined as any unwanted signal generated atthe shot hole whereas noise is defined as any unwanted signal generated by someextraneous source such as wind, power lines, well pump, etc.
There are numerous types of interference such as Rayleigh waves, Love waves,ground roll, reflected refractions. Both the primary and the harmonic form ofthese various waves are frequently detected on or are suspected to be on thefield seismogram. This paper is primarily concerned with the attenuation of thetype of interference wave that travels from the shot through the weathered andsub-weathered near surface materials at velocities of 1000 to 8000/second andpossesses frequencies from 10 cps to 40 cps. The primary or fundamental lowfrequency wave can usually be cancelled by electrical filtering or, as in thecase of a strong low velocity surface wave, the employment of an in-line offsetspread removed sufficiently in distance to allow all reflection data to berecorded before the interference wave is recorded. However, in areas where thenear surface material possesses exceptional acoustic transmission properties(i.e. the ability to readily transmit most types of sound waves), the first,and even second harmonics of the low frequency interference waves aretransmitted through the near surface and are sufficiently strong in amplitudeto mask, or at least in part distort, the desired reflection signals.
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