Theory of reflectivity blurring in seismic depth imaging

In Part I of this paper, we defined a focusing wave field as the time reversal of an observed point‐source response. We showed that emitting a time‐reversed field from a closed boundary yields a focal spot that acts as an isotropic virtual source. However, when emitting the field from an open boundary, the virtual source is highly directional and significant artefacts occur related to multiple scattering. The aim of this paper is to discuss a focusing wave field, which, when emitted into the medium from an open boundary, yields an isotropic virtual source and does not give rise to artefacts. We start the discussion from a horizontally layered medium and introduce the single‐sided focusing wave field in an intuitive way as an inverse filter. Next, we discuss single‐sided focusing in two‐dimensional and three‐dimensional inhomogeneous media and support the discussion with mathematical derivations. The focusing functions needed for single‐sided focusing can be retrieved from the single‐sided reflection response and an estimate of the direct arrivals between the focal point and the accessible boundary. The focal spot, obtained with this single‐sided data‐driven focusing method, acts as an isotropic virtual source, similar to that obtained by emitting a time‐reversed point‐source response from a closed boundary.

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“…Figure (c) shows that the focal spot is a band‐limited version of a delta function at

{boldx}_{normalH} = {boldx}_{H, A}

and

t = 0

. The band limitation is due to the band‐limited wavelet

s (t)

and the negligence of evanescent waves (Berkhout and van Wulfften Palthe ; Thomson, Kitchenside and Fletcher ). Finally, Fig.…”

Section: Single‐sided Focusing In Two‐ and Three‐dimensional Mediamentioning

confidence: 99%

Review paper: Virtual sources and their responses, Part II: data‐driven single‐sided focusing

Wapenaar

Thorbecke

Neut

et al. 2017

Geophysical Prospecting

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“…A conventional image can be computed by evaluating the extended image at zero time and zero subsurface offset. This methodology can be applied for various purposes, including structural reflection imaging (Claerbout, 1971;Berkhout, 1980), migration velocity analysis Mildner et al, 2017), and more quantitative subsurface characterization (de Bruin et al, 1990;Ordoñez et al, 2016;Thomson et al, 2016).…”

Section: Motivationmentioning

confidence: 99%

Target-enclosed seismic imaging

et al. 2017

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Seismic reflection data can be redatumed to a specified boundary in the subsurface by solving an inverse (or multidimensional deconvolution) problem. The redatumed data can be interpreted as an extended image of the subsurface at the redatuming boundary, depending on the subsurface offset and time. We retrieve target-enclosed extended images by using two redatuming boundaries, which are selected above and below a specified target volume. As input, we require the upgoing and downgoing wavefields at both redatuming boundaries due to impulsive sources at the earth’s surface. These wavefields can be obtained from actual measurements in the subsurface, they can be numerically modeled, or they can be retrieved by solving a multidimensional Marchenko equation. As output, we retrieved virtual reflection and transmission responses as if sources and receivers were located at the two target-enclosing boundaries. These data contain all orders of reflections inside the target volume but exclude all interactions with the part of the medium outside this volume. The retrieved reflection responses can be used to image the target volume from above or from below. We found that the images from above and below are similar (given that the Marchenko equation is used for wavefield retrieval). If a model with sharp boundaries in the target volume is available, the redatumed data can also be used for two-sided imaging, where the retrieved reflection and transmission responses are exploited. Because multiple reflections are used by this strategy, seismic resolution can be improved significantly. Because target-enclosed extended images are independent on the part of the medium outside the target volume, our methodology is also beneficial to reduce the computational burden of localized inversion, which can now be applied inside the target volume only, without suffering from interactions with other parts of the medium.

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“…Retrieved from surface seismic data, extended images (EIs) can be thought of as local reflectivity responses of the subsurface, for pseudo-sources and receivers placed inside of the medium (Vasconcelos et al, 2010;Thomson et al, 2016). Here, we further extend this concept by defining the block system , (1) where the quantities involved are (Figure 1) , (2) (3) and (4).…”

Section: Target-enclosing Extended Images (Teeis) and Marchenko-redatmentioning

confidence: 99%

“…A key enabler for our objective is the novel approach of Marchenko redatuming (Wapenaar et al, 2014; van der Neut et al, 2015;Ravasi et al, 2016): it allows us to obtain, from surface reflection data, subsurface redatumed waves that correctly handle internal multiples, while using conventional migration models. Combining this with the concepts of target-enclosing interferometry (van der Neut et al, 2013) and Reflectivity-based extended images (Vasconcelos et al, 2010;Thomson et al, 2016) we propose the new Target-Enclosing Extended Images. Here, we present this new concept, discuss how to estimate the associated fields, and support our claims with a field data example.…”

mentioning

confidence: 99%

Retrieving Reservoir-only Reflection and Transmission Responses from Target-enclosing Extended Images

Vasconcelos¹,

Ravasi²,

Neut³

et al. 2017

Proceedings

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Vasconcelos, I.; Ravasi, M.; van der Neut, Joost; Kritski, A.; Cui, T. Important noteTo cite this publication, please use the final published version (if applicable). Please check the document version above. CopyrightOther than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons. Takedown policyPlease contact us and provide details if you believe this document breaches copyrights. We will remove access to the work immediately and investigate your claim. This work is downloaded from Delft University of Technology. For technical reasons the number of authors shown on this cover page is limited to a maximum of 10. Retrieving reservoir-only reflection and transmission responses from target-enclosing extended images SummaryThe Marchenko redatuming approach reconstructs wavefields at depth that contain not only primary reflections, but also multiply-scattered waves. While such fields in principle contain additional subsurface information, conventional imaging approaches cannot tap into the information encoded in internal multiples in a trivial manner. We discuss a new approach that uses the full information contained in Marchenko-redatumed fields, whose output are local reflection and transmission responses that fully enclose a target volume at depth, without contributions from over-or underburden structures. To obtain the Target-Enclosing Extended Images (TEEIs) we solve a multidimensional deconvolution (MDD) problem that can be severely ill-posed, so we offer stable estimates to the MDD problem that rely on the physics of the Marchenko scheme. We validate our method on ocean-bottom field data from the North Sea. In our field data example, we show that the TEEIs can be used for reservoir-targeted imaging using reflection and, for the first time, local transmission responses, shown to be internal multiples retrieved by the redatuming scheme. Finally, we present local, TEEI-derived reflection and transmission images of the target volume at depth that are structurally consistent with a benchmark image from conventional migration of surface data. 2214-4609.201701222 Introduction With the goal of achieving increased imaging resolution of reservoirs at depth and better quantitative reservoir characterisation, here we aim at retrieving the local reflection and transmission responses of a target volume at depth from surface seismic data, with no influence of over-or underburden geology. More importantly, we would like to achieve this using subsurface models that are no more complex than those used in conventional migration. A key enabler for our objective is the novel approach of Marchenko redatuming (Wapenaar et al., 2014; van der Neut et al., 2015;Ravasi et al., 2016): it allows us to obtain, from surface reflection data, subsurface redatumed waves that correctly handle internal multiples, while using conventional migration mode...

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Theory of reflectivity blurring in seismic depth imaging

Cited by 12 publications

References 37 publications

Review paper: Virtual sources and their responses, Part II: data‐driven single‐sided focusing

Review paper: Virtual sources and their responses, Part II: data‐driven single‐sided focusing

Target-enclosed seismic imaging

Retrieving Reservoir-only Reflection and Transmission Responses from Target-enclosing Extended Images

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