Image-ray concept as the key to 20 years of success of time-to-depth conversion in Petrobras

Filpo, Eduardo; Portugal, Rodrigo de Souza; Zago, Neiva; Cunha, Paulo M.; Vicentini, Armando; Carbonesi, José L.

doi:10.1190/tle35040323.1

Cited by 4 publications

(2 citation statements)

References 5 publications

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“…The conversion of seismic sections from time to depth domains has been possible after the introduction of the concept of image ray (Hubral, 1977), which validity is subject to the same conditions of validity of time migration methods. Subsequently, the use of image rays was extended to the conversion of seismic images (Silva et al 2009, Filpo et al 2016 and time migration velocity models (Silva et al, 2009;Cameron et al 2007 andIversen et al 2008). In general, time-to-depth conversion algorithms based on image ray tracing or, equivalently, based on image wavefront construction, involve mapping of values distributed along a regular grid in the time domain into another regular grid in the depth domain.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 1: Velocity model in depth superimposed by a set of image rays and its corresponding wavefronts. Filpo et al (2016) presented a solution to the problem of spreading properties in the time-depth conversion with image rays that is the use of the Taylor series. Such strategy became feasible from the formulation of time-todepth conversion as a change of coordinates problem, where vertical lines in the time domain are mapped to image rays at depth, and the horizontal lines on originally flat wave that emerge from the datum.…”

Section: Introductionmentioning

confidence: 99%

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The concept of model rays in domain conversion

Filpo¹,

Portugal²

2019

Proceedings of the 16th International Congress of the Brazilian Geophysical Society&Expogef

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The concept of model rays in domain conversion

Filpo¹,

Portugal²

2019

Proceedings of the 16th International Congress of the Brazilian Geophysical Society&Expogef

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Velocity inversion by global optimization using finite-offset common-reflection-surface stacking applied to synthetic and Tacutu Basin seismic data

2019

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Estimation of an accurate velocity macromodel is an important step in seismic imaging. We have developed an approach based on coherence measurements and finite-offset (FO) beam stacking. The algorithm is an FO common-reflection-surface tomography, which aims to determine the best layered depth-velocity model by finding the model that maximizes a semblance objective function calculated from the amplitudes in common-midpoint (CMP) gathers stacked over a predetermined aperture. We develop the subsurface velocity model with a stack of layers separated by smooth interfaces. The algorithm is applied layer by layer from the top downward in four steps per layer. First, by automatic or manual picking, we estimate the reflection times of events that describe the interfaces in a time-migrated section. Second, we convert these times to depth using the velocity model via application of Dix’s formula and the image rays to the events. Third, by using ray tracing, we calculate kinematic parameters along the central ray and build a paraxial FO traveltime approximation for the FO common-reflection-surface method. Finally, starting from CMP gathers, we calculate the semblance of the selected events using this paraxial traveltime approximation. After repeating this algorithm for all selected CMP gathers, we use the mean semblance values as an objective function for the target layer. When this coherence measure is maximized, the model is accepted and the process is completed. Otherwise, the process restarts from step two with the updated velocity model. Because the inverse problem we are solving is nonlinear, we use very fast simulated annealing to search the velocity parameters in the target layers. We test the method on synthetic and real data sets to study its use and advantages.

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Depth-conversion techniques and challenges in complex sub-Andean provinces

Velásquez

Alfonso

2018

Interpretation

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The reliability of depth conversion in complex land areas is particularly challenging. Accuracy and precision are usually difficult to achieve simultaneously because of the limited amount and quality of seismic data and sparse control from well data. Ideally, depth-migration methods would be the right tools to produce such data for interpreters. However, despite recent significant breakthroughs in seismic imaging, the ability to provide precise depths is not always achievable with depth-imaging techniques. Therefore, depth conversion remains a crucial tool for converting a seismic image and its interpretation to geologic depth. We have developed an overview of the techniques used for depth conversion through a carefully selected set of geologically diverse field examples. We determine the challenges faced while applying each methodology and, more importantly, share our own experiences and pitfalls. We also evaluate the steps taken to overcome these limitations. All these studies highlight the pragmatic application of techniques and their common pitfalls to improve the workflows that can be implemented to solve other depth-conversion problems. Depth-conversion techniques can be classified depending on the approach used for velocity model building (VMB) (i.e., time-depth and instantaneous velocity functions, layer-cake models, or geostatistical velocity interpolations) and also depending on the ray-tracing procedure (i.e., vertical stretching or image ray). To verify the reliability of the VMB, we establish the following criteria for an acceptable velocity model: (1) honors hard data, (2) integrates all the available sources of velocity information, and (3) makes geologic sense. We reinforce the latter in complex areas where geologic control drives the chosen approach. For instance, in cases with strong velocity gradients (e.g., basement-involved structures), vertical depth conversion may not be able to solve all possible scenarios, resulting in an incomplete assessment of the structural uncertainty. To model such situations, we use a time-to-depth conversion based on the image-ray concept.

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Image-ray concept as the key to 20 years of success of time-to-depth conversion in Petrobras

Cited by 4 publications

References 5 publications

The concept of model rays in domain conversion

The concept of model rays in domain conversion

Velocity inversion by global optimization using finite-offset common-reflection-surface stacking applied to synthetic and Tacutu Basin seismic data

Depth-conversion techniques and challenges in complex sub-Andean provinces

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