Analysis and filtering of near-surface effects in land multicomponent seismic data

Saul Ernesto Guevara

ABSTRACT

Multicomponent seismic data recorded on the earth's surface provide geologic information useful for natural resource exploration. However, this information is usually altered by propagation through the near-surface layers. In this thesis, effects of the nearsurface layer in multicomponent data are investigated and methods to overcome them are studied. The main effects studied are the free-surface effect, mode-leakage, ray bending, polarization change and statics.

Ray tracing and finite-difference modeling were conducted on basic geologic models and polarization analysis is applied to the results. From this analysis, the free-surface effect appears to have a larger effect at longer offsets, high dips and very high near-surface VP/VS values. Polarization analysis is also carried out on real data obtained from the Blackfoot oil field, Alberta. Horizontally polarized events generated in the near-surface layer are identified. Their polarization direction corresponds well to the actual shotreceiver geometry and, hence, can be used to improve geophone orientation. A method to separate P-P and P-S wave modes taking into account P- and S- wave statics is tested, resulting in improved seismic sections from the Blackfoot survey.

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