The correlation distance of incoherent seismic noise in geophone arrays

The behavior of incoherent seismic noise in geophone arrays was investigated as a function of geophone spacings by recording several noise strips during variable production conditions. A dense geophone patch with dimensions of 26.67x26.67 m of single geophones was deployed using an additional receiver line on a conventional 3D survey. The patch had 17X17 single geophones with inter-geophone spacing of 1.67 m in the inline and cross-line directions. Geophone arrays with various geophone spacings were subsequently formed from the original geophone patch. The incoherent noise was evaluated by comparing the RMS signal amplitude of the simulated geophone arrays to the RMS amplitude predicted by the square-root law. The square-root law states that summing N traces enhances the signal-to-noise (S/N) ratio by the N. In addition, cross-correlations at zero-time lag for all possible geophone spacings of the geophone patch were computed. Results confirmed the existence of seismic-noise-correlation-distances below which the simulated-geophone-array-trace curve raises 3 db above the square-root-law value. The seismic-noise-correlation distance is frequency dependent, increasing with decreasing frequency of the incoherent noise. Therefore, larger geophone spacing is required to attenuate low-frequency incoherent noise. The results of this study can be used to determine the optimum geophone spacing required for enhancing the S/N ratio in a specific frequency band.