The use of VSP techniques for fault zone characterization: An example from the San Andreas Fault

Chavarria, J. Andres; Goertz, A.; Karrenbach, Martin; Paulsson, Björn; Milligan, Paul A.; Soutyrine, Vlad; A, Hardin; Dushman, David; LaFlame, Lisa

doi:10.1190/1.2748495

Cited by 10 publications

(6 citation statements)

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“…It has been proven that for some imaging applications, with IM or other similar methods that use crosscorrelated seismic data, part or all of the overburden effects can be avoided. These applications include migration of free-surface multiples in surface seismic data ͑Sheng, 2001; Shan and Guitton, 2004;Berkhout and Verschuur, 2006͒, migration of free-surface multiples in 2D ͑Yu and 3D ͑He et al, 2007͒ vertical seismic profile ͑VSP͒ data, and VSP near-wellbore imaging of vertical structures ͑He, 2006; Willis et al, 2006;Chavarria et al, 2007;Hornby and Yu, 2007͒. More interestingly, Xiao et al ͑2006͒ introduce a PP-PS IM method to image a lower horizontal salt boundary above a VSP array with a local velocity model.…”

Section: Introductionmentioning

confidence: 98%

Near-wellbore VSP imaging without overburden

Karrenbach

Paulsson

et al. 2009

GEOPHYSICS

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In seismic exploration a complex overburden can cause defocused and distorted seismic images of deeper target areas. While in surface seismic imaging it is difficult to overcome this problem, vertical seismic profile ͑VSP͒ borehole seismic imaging with its well-oriented recording geometry has proven able to circumvent the overburden's detrimental impact. Recently, VSP near-wellbore salt flank imaging without knowledge of the overburden has shown encouraging results. In this paper, we introduce another method for a more common imaging purpose: imaging near-wellbore horizons without knowledge of the overburden. A key component of our method is a reverse ray-tracing technique that uses actual VSP direct-wave traveltime picks and extrapolates through a local velocity model to obtain the direct-wave traveltimes in the vicinity of the well. The extrapolated traveltimes then serve as references for migration of the VSP reflected data from near-wellbore horizons. The merits of this method are that all source-side effects such as shot position and triggering time statics are avoided, and it can efficiently and robustly image the near-wellbore horizons because it does not need an estimated overburden velocity model prone to errors. However, the image is limited to a diamond-shaped area around the well whose size is proportional to the VSP array. A synthetic VSP experiment on the SEG/EAGE 2D overthrust model shows that this method, with a local ͑even an estimated 1D͒ velocity model, effectively images structural features, such as dip direction and discontinuities of the near-wellbore horizons.

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Section: Introductionmentioning

confidence: 98%

Near-wellbore VSP imaging without overburden

Karrenbach

Paulsson

et al. 2009

GEOPHYSICS

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“…In addition, an eighty-level, 240-component seismic array was made available by Paulsson Geophysical Services, Inc. (PGSI) and recorded by Geometrics at no cost to the project. This array was deployed in the borehole for a period of five weeks in order to test its suitability for recording microearthquakes and to record additional shots for structural imaging (Chavarria and Goerrtz, 2007). In addition to recording microearthquakes and shots during this period, a tectonic (i.e., non-volcanic) tremor was recorded on this array.…”

Section: Safod Main Boreholementioning

confidence: 99%

Scientific Drilling Into the San Andreas Fault ZoneAn Overview of SAFODs First Five Years

Zoback

Hickman

Ellsworth

2011

Scientific Drilling

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The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving due to a combination of repeating microearthquakes and fault creep. Geophysical logs define the San Andreas Fault Zone to be relatively broad (~200 m), containing several discrete zones only 2-3 m wide that exhibit very low P-and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented casing at measured depths of 3192 m and 3302 m. Cores from both deforming zones contain a pervasively sheared, cohesionless, foliated fault gouge that coincides with casing deformation and explains the observed extremely low seismic velocities and resistivity. These cores are being now extensively tested in laboratories around the world, and their composition, deformation mechanisms, physical properties, and rheological behavior are studied. Downhole measurements show that within 200 m (maximum) of the active fault trace, the direction of maximum horizontal stress remains at a high angle to the San Andreas Fault, consistent with other measurements. The results from the SAFOD Main Hole, together with the stress state determined in the Pilot Hole, are consistent with a strong crust/weak fault model of the San Andreas. Seismic instrumentation has been deployed to study physics of faulting-earthquake nucleation, propagation, and arrest-in order to test how laboratory-derived concepts scale up to earthquakes occurring in nature.

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“…Others imaged steep dikes (Brand, Hurich and Deemer ) or faults (Chavarria et al . ) with virtual sources from vertical boreholes. If receivers

x_{A}

and

x_{B}

are located in different boreholes, interferometric redatuming results in so‐called virtual crosswell data, which can be interpreted as the response to a virtual source in one borehole, observed by a receiver in the other borehole (Mehta et al .…”

Section: Interferometric Redatuming By Cross‐correlationmentioning

confidence: 99%

Point‐spread functions for interferometric imaging

Neut

Wapenaar

2015

Geophysical Prospecting

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A B S T R A C TInterferometric redatuming is a data-driven method to transform seismic responses with sources at one level and receivers at a deeper level into virtual reflection data with both sources and receivers at the deeper level. Although this method has traditionally been applied by cross-correlation, accurate redatuming through a heterogeneous overburden requires solving a multidimensional deconvolution problem. Input data can be obtained either by direct observation (for instance in a horizontal borehole), by modelling or by a novel iterative scheme that is currently being developed. The output of interferometric redatuming can be used for imaging below the redatuming level, resulting in a so-called interferometric image. Internal multiples from above the redatuming level are eliminated during this process. In the past, we introduced point-spread functions for interferometric redatuming by cross-correlation. These point-spread functions quantify distortions in the redatumed data, caused by internal multiple reflections in the overburden. In this paper, we define point-spread functions for interferometric imaging to quantify these distortions in the image domain. These point-spread functions are similar to conventional resolution functions for seismic migration but they contain additional information on the internal multiples in the overburden and they are partly data-driven. We show how these point-spread functions can be visualized to diagnose image defocusing and artefacts. Finally, we illustrate how point-spread functions can also be defined for interferometric imaging with passive noise sources in the subsurface or with simultaneous-source acquisition at the surface.

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The use of VSP techniques for fault zone characterization: An example from the San Andreas Fault

Cited by 10 publications

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Near-wellbore VSP imaging without overburden

Near-wellbore VSP imaging without overburden

Scientific Drilling Into the San Andreas Fault ZoneAn Overview of SAFODs First Five Years

Point‐spread functions for interferometric imaging

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The use of VSP techniques for fault zone characterization: An example from the San Andreas Fault

Cited by 10 publications

References 0 publications

Near-wellbore VSP imaging without overburden

Near-wellbore VSP imaging without overburden

Scientific Drilling Into the San Andreas Fault ZoneAn Overview of SAFODs First Five Years

Point‐spread functions for interferometric imaging

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Scientific Drilling Into the San Andreas Fault ZoneAn Overview of SAFODs First Five Years