Steve Kelly

A comparison of inversion results for two full-waveform methods that utilize the lowest frequencies in dual-sensor recordings

Summary In this abstract, we test the capability of full-waveform inversion to exploit the lowest frequencies available from dual-sensor, single-streamer recordings. Two different, time-domain methods are tested. The first method follows the “conventional” approach of iteratively updating interval velocity by using the gradient obtained from back-projected residuals between modelled and recorded data. The second method constructs perturbations in impedance from the gradient, which is then used to update the velocity. These methods are tested on 2-D and 3-D, synthetic data, using a wavelet with realistic bandwidth. They are also applied to field data for one cable from a dual-sensor field survey. Both this inversion and the synthetic inversion study indicate that features ~ 0.5 km can be accurately recovered at depths of a few kilometres using maximum offsets of only 8 km.

Full-waveform Inversion By Pseudo-analytic Extrapolation

In this abstract, we examine the benefits of performing full-waveform inversion with a pseudo-analytic extrapolator. We first demonstrate the high kinematic accuracy of this extrapolator for a medium with strong, vertical transverse isotropy. We then show that under isotropic assumptions, an inversion performed with a high-order, space-time extrapolator can be gridded to yield results comparable to those obtained using pseudo-analytic extrapolation, but at four times the cost. Extrapolation by the pseudoanalytic method is thus the most efficient method currently available for performing 3-D full-waveform inversion assuming an acoustic medium.

Methods for expediting the computation of angle gathers during shot record migration

This paper suggests three methods for expediting the formation of common image point gathers, during shot record migration, versus incidence angle at a reflector. All the methods require a preliminary, windowed Fourier transform of the downgoing and upgoing wavefields. Reflectivities are then formed and summed using these plane-wave components. In the general 3D case, and in the absence of any additional constraints, we show that reflectivities must be formed for all possible combinations of downgoing and upgoing wavetypes. The cost of forming angle gathers under these circumstances exceeds the cost of extrapolation by orders of magnitude.