Lunchbox Geophysics

Interference and the art of static correction: Raypath interferometry

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David C. Henley
CREWES

Wednesday, January 16th, 2013 – 11:00 AM
Aquitaine Auditorium, +15 level of 540 - 5 Avenue SW

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Abstract

Raypath interferometry was developed to apply near-surface corrections to reflection seismic data sets for which conventional statics corrections are unsatisfactory. Statics fail for some data because one or more basic assumptions behind statics corrections methods are violated by the particular near-surface conditions. We show how two of the assumptions can be generalized in order to accommodate these conditions. First, the surface-consistency constraint common to most conventional statics methods can be extended to the concept of 'raypath consistency'. Second, the assumption that a simple weathered layer causes only a pure time delay for a discrete reflection arrival can be replaced by a model in which a 'surface function', characterizing a more complex weathered layer, is convolved with a discrete reflection arrival to capture not only the time shift of a reflection event, but any multi-path and scattered arrivals associated with the surface location. Adoption of the surface function alters the near-surface correction procedure from time shifting to deconvolution, where the surface function for each source/receiver position is estimated and removed from a trace by inverse filtering. Raypath consistency is introduced by re-defining the surface function to include variation with the near-surface raypath angle. Use of the angle-dependent surface function requires that raw seismic data be mapped into a domain in which near-surface raypath angle is a coordinate. In the raypath interferometry procedure, the radial trace (RT) transform is used to map raw seismic data to an approximate raypath-angle domain, a simple interferometric method is used to deconvolve surface functions in this domain, and the corrected data are re-mapped to the original XT domain for CMP stack imaging.

We first demonstrate raypath interferometry on a data set from the MacKenzie Delta, where statics assumptions are seriously violated and conventional statics correction fails. We then apply raypath interferometry to a surface-consistent data set from Hussar, Alberta, where conventional statics are completely successful. Since surface consistency is just a special case of raypath consistency, raypath interferometry works well also, but the comparative results are interesting nevertheless.

Biography

David C. Henley received his BSc. in physics from Colorado State University in 1967 and his MSc. in physics from the University of Michigan in 1968. Joining Shell in 1969, Dave spent 29 years with Shell (interrupted by 2 years in the US Army), the last 20 years in Calgary. Since 1999, he has been a part-time researcher with CREWES. Dave's professional specialties include coherent noise attenuation, novel statics techniques, and high-resolution acquisition. Outside interests include hiking and scrambling, road cycling, woodcarving, and classical music.