David C. Henley

Gabor deconvolution: Estimating reflectivity by nonstationary deconvolution of seismic data

We have extended the method of stationary spiking deconvolution of seismic data to the context of nonstationary signals in which the nonstationarity is due to attenuation processes. As in the stationary case, we have assumed a statistically white reflectivity and a minimum-phase source and attenuation process. This extension is based on a nonstationary convolutional model, which we have developed and related to the stationary convolutional model. To facilitate our method, we have devised a simple numerical approach to calculate the discrete Gabor transform, or complex-valued time-frequency decomposition, of any signal. Although the Fourier transform renders stationary convolution into exact, multiplicative factors, the Gabor transform, or windowed Fourier transform, induces only an approximate factorization of the nonstationary convolutional model. This factorization serves as a guide to develop a smoothing process that, when applied to the Gabor transform of the nonstationary seismic trace, estimates the magnitude of the time-frequency attenuation function and the source wavelet. By assuming that both are minimum-phase processes, their phases can be determined. Gabor deconvolution is accomplished by spectral division in the time-frequency domain. The complex-valued Gabor transform of the seismic trace is divided by the complex-valued estimates of attenuation and source wavelet to estimate the Gabor transform of the reflectivity. An inverse Gabor transform recovers the time-domain reflectivity. The technique has applications to synthetic data and real data.

Coherent noise attenuation in the radial trace domain

Coherent noise is a persistent problem in seismic imaging, and a number of techniques have been developed to attenuate it. The radial trace (RT) transform, a simple seismic data mapping algorithm, can be used as the basis for a particularly flexible and effective method for attenuating coherent noise on both prestack and poststack seismic data. Described here are the principles and some practical application details for attenuating coherent noise in the RT domain. A comparison between frequency–wavenumber (f–k) and RT domain filtering on a synthetic model is presented, and some of the differences and advantages of RT methods are identified. Next, RT coherent noise attenuation is demonstrated using a set of good‐quality field data; it is then applied to a very noisy data set. The results obtained with this last set prove to be as good as, or better than, those produced using f–k filtering.

Gabor deconvolution revisited

Gabor deconvolution has been updated and experience has been obtained on real data. The updates are (1) a new method of spectral smoothing called hyperbolic smoothing, (2) a Gabor transform using compactly supported windows that improves run times by one to two orders of magnitude (3) a post-deconvolution time-variant bandpass filter whose maximum frequency tracks along a hyperbola in the timefrequency plane. We discuss the technical details of these improvements and present a data example.

Full-waveform processing and interpretation of kilohertz cross-well seismic data

High‐frequency, cross‐well seismic data, from the Midale oil field of southeastern Saskatchewan, are analyzed for direct and reflected energy. The goal of the analysis is to produce interpretable sections to assist in enhanced oil recovery activities (CO2 injection) in this field. Direct arrivals are used for velocity information while reflected arrivals are processed into a reflection image. Raw field data show a complex assortment of wave types that includes direct compressional and shear waves and reflected shear waves. A traveltime inversion technique (layer stripping via ray tracing) is used to obtain P‐ and S‐wave interval velocities from the respective direct arrivals. The velocities from the cross‐well inversion and the sonic log are in reasonable agreement. The subsurface coverage of the cross‐well geometry is investigated; it covers zones extending from the source well to the receiver well and includes regions above and below the source/receiver depths. Upgoing and downgoing primary reflections ...

Raypath interferometry : Statics in difficult places

Methods for correcting reflections for near-surface effects are among the earliest techniques developed for seismic processing. Most fall into the category of statics correction techniques, which attempt to remove near-surface effects by applying a simple time shift (or “static”) to each seismic trace to align corresponding events before stacking. The time shift applied to each trace has contributions associated with the surface locations of both source and geophone, and sometimes a contribution from residual moveout, an error attributable to slightly incorrect moveout velocity.

Single-well imaging using the full waveform of an acoustic sonic

Summary This work evaluates single-well imaging using the full waveform acquired by an acoustic well-logging tool. It begins by reviewing wave propagation in a fluid-filled borehole. Next we introduce a waveform processing flow using known seismic processing methods and apply it to a real field data set. The ultimate goal of this work is to image scattered energy beyond the borehole wall and thus gain a better picture of the reservoir characteristics around the borehole.

Attenuating the Ice Flexural Wave On Arctic Seismic Data

Satisfactorily attenuating source-generated coherent noise on seismic data can be a challenging exercise for the processor, especially when the noise is as strong as the notorious ice flexural wave often observed in the arctic. One of the strongest known coherent noises, the flexural wave originates in uniform plates of ice floating on liquid water, commonly associated with both river channels and offshore sea ice. The flexural wave is distinguished not only by its strength, but by the large dispersion often observed. High frequencies often travel at speeds approaching that of the compressional wave in ice, while low frequencies are sometimes slower than the air wave. These properties make the ice flexural wave difficult to attenuate with most conventional coherent noise techniques. We demonstrate here that the Fourier-transformed radial trace (R-T) domain provides a natural framework for the separation of highly dispersed source-generated source noise from reflections. Using a set of experimental multi-component seismic data from Hansen Harbour in the MacKenzie Delta, we demonstrate significant attenuation of the ice flexural wave in spite of the substantial spatial aliasing of the noise.

Raypath interferometry: Statics in difficult places

Successful seismic imaging relies not only on adequate sampling of the seismic reflection wavefield during data acquisition, but on the use of appropriate processing techniques to compensate the data for various effects introduced by the particular environment in which they were collected. We demonstrate here a technique designed to remove some of the distorting effects of the near-surface layer of the earth on the reflection wavefield. It differs from previous methods in that it does not assume surfaceconsistency or stationarity, as do most ‘statics correction’ methods, and it uses interferometric principles to apply corrections along raypath directions, rather than vertically.

Hybrid Raypath Interferometry: Correcting Converted Wave Receiver Statics

In the most general sense, seismic interferometry includes acquisition and processing techniques which use crosscorrelations of raw traces to help image the data, or to remove various effects from the traces before imaging. A surge of interest in this broad field has led to a number of new techniques for passive seismic imaging (Draganov et al., 2009), migration (Zhou et al., 2006), and removal of near-surface effects, including statics (Bakulin and Calvert, 2006), (Henley, 2008), for example.

Single-well seismic imaging using full waveform sonic data: An update

Summary The sonic waveform processing and imaging flow presented in this paper uses full-waveform data recorded with conventional well-logging tools, then adapts known surface seismic processing steps and optimizes them for the borehole environment. This paper presents improvements brought to the original sonic-waveform processing and imaging flow introduced by Chabot et al. (2001). Those improvements are better geometry assignment, the application of refraction statics, better noise attenuation, better data enhancement, and the application of prestack time migration with improved parameters. The new flow is tested on a portion of a full-waveform sonic data set, recorded over a section of the 8-8-23-23W4 well, Blackfoot field, Alberta, intersecting three coal seams at an angle. The composite sonic image obtained shows promising indications of the three coal seams. The sonic image is next compared with a coinciding surface seismic section to validate the observed dip and to explore the impact of single-well imaging on the resolution gap. More work is planned to improve on the demonstrated processing flow.