Channel waves in cross‐borehole data

Lines, Larry; Kelly, Kenneth R.; Queen, John

doi:10.1190/1.1443247

Cited by 17 publications

(8 citation statements)

References 8 publications

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“…The regional dip of the formations is less than 1"WSW. As noted in Queen & Rizer (1990), two orthogonal sets of vertical fractures have been mapped: a systematic set striking N70"E and a non-systematic set at N25"W. The velocity variations in the section are sizable: contrasts of 2 to 1 exist (Lines, Kelly & Queen 1992;Harlan 1990). Such large variations in seismic velocity give rise to strong refractions and channel waves {Lines et al 1992).…”

Section: Seismic Traveltime Tomography At the Conoco Borehole Test Famentioning

confidence: 98%

Singularity and Branching: A Path-Following Formalism For Geophysical Inverse Problems

Vasco

1994

Geophysical Journal International

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S U M M A R YA path-following technique is presented as an alternative to the direct minimization of a misfit functional. The algorithm is based upon the iterative adjustment of an Earth model to fit a set of generated 'data'. These values vary from a purely artificial set, produced from some prior model, to the observed data. The changes in the model that are required to satisfy the conditions for minimum misfit are calculated at each iteration. Multiple solutions appear when the path-following equations become singular and linear approximations fail. Using techniques from singularity theory in Hilbert space, the number, type and stability of solutions appearing at a singular point can be calculated. It is possible to project beyond a singular point and follow the additional solutions that emerge. Thus the algorithm allows one to track multiple solutions to a given inverse problem. The technique is used to infer velocity variations between two boreholes at the Conoco Borehole Test Facility. From a set of 471 arrival times, three velocity models are deduced. All of the models satisfy the conditions for minimum misfit. One model is very similar to the solution produced by a conjugate gradient algorithm. The three models all contain high velocities overlying low velocities. The path-following algorithm is also applied to a set of airborne gravity gradiometry data gathered in SW Oklahoma. An upthrown block of high-density basement material is found to coincide with a positive vertical gravity gradient anomaly. This conclusion agrees with the depths to basement observed in numerous oil wells in the region.

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Section: Seismic Traveltime Tomography At the Conoco Borehole Test Famentioning

confidence: 98%

Singularity and Branching: A Path-Following Formalism For Geophysical Inverse Problems

Vasco

1994

Geophysical Journal International

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“…Due to the different acquisition setup, the dispersion analysis cannot be applied. Such deeper waveguides between boreholes have been investigated for seismic data (e.g., Lines et al, 1992;Greenhalgh et al, 2007) and for crosswell radar data (Ellefsen, 1999), but have not been reliably inverted due to the resolution limit of conventional ray-based techniques. To reliably image deeper waveguides, a new high-resolution technique is necessary that is able to include complicated wavefield modeling in the inversion.…”

Section: Introductionmentioning

confidence: 99%

Crosshole GPR full-waveform inversion of waveguides acting as preferential flow paths within aquifer systems

et al. 2012

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High-contrast layers caused by porosity or clay content changes can have a dominant effect on hydraulic processes within an aquifer. These layers can act as low-velocity waveguides for GPR waves. We used a field example from a hydrological test site in Switzerland to show that fullwaveform inversion of crosshole GPR signals could image a subwavelength thickness low-velocity waveguiding layer. We exploited the full information content of the data, whereas ray-based inversion techniques are not able to image such thin waveguide layers because they only exploit the first-arrival times and first-cycle amplitudes. This lowvelocity waveguide layer is caused by an increase in porosity and indicates a preferential flow path within the aquifer. The waveguide trapping causes anomalously high amplitudes and elongated wavetrains to be observed for a transmitter within the waveguide and receivers straddling the waveguide depth range. The excellent fit of amplitudes and phase between the measured and modeled data confirms its presence. This new method enables detailed aquifer characterization to accurately predict transport and flow and can be applied to a wide range of geologic, hydrological, and engineering investigations.

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“…There is a slight regional dip to the formation, about 1 degree to the westsouthwest. Of the numerous vertical fractures mapped in the area, two dominant sets emerge: a systematic set striking N70"E and a non-systematic set at N25"W. The velocity variations at the Concoco borehole test facility are quite significant, with channel waves and head waves observed during cross-well seismic experiments (Lines, Kelly & Queen 1992). Thus, a simple linearization may not be valid in the interpretation of cross-well traveltimes.…”

Section: Conoco Cross-well Experimentsmentioning

confidence: 97%

A transformational approach to geophysical inverse problems

Vasco

1995

Geophysical Journal International

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S U M M A R YA set of coordinate transformations is used to linearize a general geophysical inverse problem. Statistical and analytic techniques are employed to estimate the parameters of such linearization transformations. In the transformed space, techniques from linear inverse theory may be utilized. Consequently, important concepts, such as model parameter covariance, model parameter resolution and averaging kernels, may be carried over to non-linear inverse problems. I apply the approach to a set of seismic cross-borehole traveltimes gathered at the Conoco Borehole Test Facility. The seismic survey was conducted within the Fort Riley formation, a limestone with thin interbedded shales. Between the boreholes, the velocity structure of the Fort Riley formation consists of a high-velocity region overlying a section of lower velocity. It is found that model parameter resolution is poorest and spatial averaging lengths are greatest in the underlying low-velocity region.

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Channel waves in cross‐borehole data

Cited by 17 publications

References 8 publications

Singularity and Branching: A Path-Following Formalism For Geophysical Inverse Problems

Singularity and Branching: A Path-Following Formalism For Geophysical Inverse Problems

Crosshole GPR full-waveform inversion of waveguides acting as preferential flow paths within aquifer systems

A transformational approach to geophysical inverse problems

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