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Seismic Noise

Seismic Noise. Kandiah Balachandran Dallas Geophysical Society, October 20, 2011. The Main Points. Common receiver gathers are “always” more coherent than common shot gathers (field records) Cause: Scattering close to receivers is more important than those close to the source

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Seismic Noise

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  1. Seismic Noise Kandiah Balachandran Dallas Geophysical Society, October 20, 2011

  2. The Main Points • Common receiver gathers are “always” more coherent than common shot gathers (field records) • Cause: Scattering close to receivers is more important than those close to the source • Anomalous event on horizontal component seismograms suggests the possibility of direct detection

  3. Anomalous Event: P- to SV- wave Conversion at Near Normal Incidence May Be An Indicator Of Mobile Fluids • Fractures and heterogeneities may be associated with guided waves – the strength and persistence

  4. Typical good record • Refractions • Ground Roll • Reflections • Multiples • P-S converted reflections

  5. Typical NG Record • Refraction • ??? • Scattered noise • Elastic Scattering converts P-waves to S-waves partially

  6. Hammer Blow Experiment Powder River Basin X X … X O O O … O R1 … R24 S1 S2 S3 S8 R1 – R 24: 6 in. (15 cm) spacing S1 – S8: 12 ft (3.66 m) spacing S – R offset: 6 in. to 96 ft (29.3 m)

  7. HAMMER BLOW EXPERIMENTOn a clinker mesa Powder River Basin

  8. Common Receiver Gathers from Hammer Blow Experiment

  9. VSP – Eastern Saudi Arabia Elevation view Plan View Shots up the hole nearest four seismometers 590 ft to 10 ft at 10ft10 ft from hole

  10. Reversed VSPSignals recorded at one surface seismometer for shots at depths ranging from 590 feet to 10 feet at 10-foot intervals

  11. Another reversed VSP

  12. Comparison of signals from the deepest 4 shots at the four surfaceseismometerssurrounding the Borehole

  13. Field Layout – Sapulpa, OK

  14. Normal Wave Tests

  15. Transposed Wave TestEach panel is a collection of signals recorded at one particular receiver station from weight drops at the 2-ft spaced source locations

  16. CONCLUSIONS • P- to SV- wave Conversion at Near Normal Incidence may be an Indicator of MOBILE FLUIDS • FRACTURES and other inhomogeneities may be the cause of guided waves

  17. Selected References • Balachandran, K., Horizontal Component Seismograms: SPE preprint 7437, 1978 • Balachandran, K., Seismic problems in clinker areas, http://classes.kvcc.edu/kbalachandran/, 1972 • Balachandran, K., Noninterchangeability of sources and receivers, Geophysics, 39,73-80, 1974 • Frankel, A., and Clayton, R.W., 1986, Finite difference simulations of seismic scattering, JGR, 91, 6465 - 89 • Hudson,J.A., The Attenuation of surface waves by scattering: Proc. Camb. Phil. Soc., 67, 221-32,1970

  18. References (continued) • Levander, A.R. and Hill, N.R., 1985, P – SV resonances in irregular low-velocity surface layers, Bull. Seis. Soc. Am., 75, 847 – 64 Can we use dynamic elastic nonlinearity measurements of rocks to map reservoir properties? Tawassul Khan, Sofia McGuire, OGJ Sept.10, 2001 In situ seismic shockwaves, Sergei Kostrov, William Wooden, Peter Roberts: OGJ Sept.3, 2001

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