Enhanced prestack depth imaging of wide-azimuth data from the Gulf of Mexico: A case history

We present a case study of enhanced imaging of wide-azimuth data from the Gulf of Mexico utilizing recent technologies; and we discuss the resulting improvements in image quality, especially in subsalt areas, relative to previous results. The input seismic data sets are taken from many large-scale wide-azimuth surveys and conventional narrow-azimuth surveys located in the Mississippi Canyon and Atwater Valley areas. In the course of developing the enhanced wide azimuth processing flow, the following three key steps are found to have the most impact on improving subsalt imaging: (1) 3D true azimuth surface-related multiple elimination (SRME) to remove multiple energy, in particular, complex multiples beneath salt; (2) reverse-time migration (RTM) based delayed imaging time (DIT) scans to update the complex subsalt velocity model; and (3) tilted transverse isotropic (TTI) RTM to improve image quality. Our research focuses on the depth imaging aspects of the project, with particular emphasis on the application of the DIT scanning technique. The DIT-scan technique further improves the accuracy of the subsalt velocity model after conventional ray-based subsalt tomography has been performed. We also demonstrate the uplift obtained by acquiring a wide-azimuth data set relative to a standard narrow-azimuth data set, and how orthogonal wide-azimuth is able to enhance the subsalt illumination.

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Application of RTM 3D angle gathers to wide-azimuth data subsalt imaging

Geophysics ◽

10.1190/geo2010-0396.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB175-WB182 ◽

Cited By ~ 9

Author(s):

Yan Huang ◽

Bing Bai ◽

Haiyong Quan ◽

Tony Huang ◽

Sheng Xu ◽

...

Keyword(s):

Model Updating ◽

Velocity Model ◽

Azimuth Angle ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Additional Information ◽

Time Migration ◽

Reflection Angle ◽

Subsalt Imaging

The availability of wide-azimuth data and the use of reverse time migration (RTM) have dramatically increased the capabilities of imaging complex subsalt geology. With these improvements, the current obstacle for creating accurate subsalt images now lies in the velocity model. One of the challenges is to generate common image gathers that take full advantage of the additional information provided by wide-azimuth data and the additional accuracy provided by RTM for velocity model updating. A solution is to generate 3D angle domain common image gathers from RTM, which are indexed by subsurface reflection angle and subsurface azimuth angle. We apply these 3D angle gathers to subsalt tomography with the result that there were improvements in velocity updating with a wide-azimuth data set in the Gulf of Mexico.

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Use of RTM full 3D subsurface angle gathers for subsalt velocity update and image optimization: Case study at Shenzi field

Geophysics ◽

10.1190/geo2011-0065.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB27-WB39 ◽

Cited By ~ 8

Author(s):

Zheng-Zheng Zhou ◽

Michael Howard ◽

Cheryl Mifflin

Keyword(s):

Model Building ◽

Transverse Isotropy ◽

Velocity Model ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Edge Diffraction ◽

Time Migration ◽

Image Optimization ◽

Free Generation

Various reverse time migration (RTM) angle gather generation techniques have been developed to address poor subsalt data quality and multiarrival induced problems in gathers from Kirchhoff migration. But these techniques introduce new problems, such as inaccuracies in 2D subsurface angle gathers and edge diffraction artifacts in 3D subsurface angle gathers. The unique rich-azimuth data set acquired over the Shenzi field in the Gulf of Mexico enabled the generally artifact-free generation of 3D subsurface angle gathers. Using this data set, we carried out suprasalt tomography and salt model building steps and then produced 3D angle gathers to update the subsalt velocity. We used tilted transverse isotropy RTM with extended image condition to generate full 3D subsurface offset domain common image gathers, which were subsequently converted to 3D angle gathers. The angle gathers were substacked along the subsurface azimuth axis into azimuth sectors. Residual moveout analysis was carried out, and ray-based tomography was used to update velocities. The updated velocity model resulted in improved imaging of the subsalt section. We also applied residual moveout and selective stacking to 3D angle gathers from the final migration to produce an optimized stack image.

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Reconstructing the primary reflections in seismic data by Marchenko redatuming and convolutional interferometry

Geophysics ◽

10.1190/geo2015-0377.1 ◽

2016 ◽

Vol 81 (2) ◽

pp. Q15-Q26 ◽

Cited By ~ 29

Author(s):

Giovanni Angelo Meles ◽

Kees Wapenaar ◽

Andrew Curtis

Keyword(s):

Velocity Model ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Seismic Reflection Data ◽

Surface Reflection ◽

Reflection Data ◽

Reference Velocity ◽

Time Migration ◽

Recorded Data

State-of-the-art methods to image the earth’s subsurface using active-source seismic reflection data involve reverse time migration. This and other standard seismic processing methods such as velocity analysis provide best results only when all waves in the data set are primaries (waves reflected only once). A variety of methods are therefore deployed as processing to predict and remove multiples (waves reflected several times); however, accurate removal of those predicted multiples from the recorded data using adaptive subtraction techniques proves challenging, even in cases in which they can be predicted with reasonable accuracy. We present a new, alternative strategy to construct a parallel data set consisting only of primaries, which is calculated directly from recorded data. This obviates the need for multiple prediction and removal methods. Primaries are constructed by using convolutional interferometry to combine the first-arriving events of upgoing and direct-wave downgoing Green’s functions to virtual receivers in the subsurface. The required upgoing wavefields to virtual receivers are constructed by Marchenko redatuming. Crucially, this is possible without detailed models of the earth’s subsurface reflectivity structure: Similar to the most migration techniques, the method only requires surface reflection data and estimates of direct (nonreflected) arrivals between the virtual subsurface sources and the acquisition surface. We evaluate the method on a stratified synclinal model. It is shown to be particularly robust against errors in the reference velocity model used and to improve the migrated images substantially.

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Reverse time migration of multiples: Reducing migration artifacts using the wavefield decomposition imaging condition

Geophysics ◽

10.1190/geo2016-0354.1 ◽

2017 ◽

Vol 82 (4) ◽

pp. S307-S314 ◽

Cited By ~ 15

Author(s):

Yibo Wang ◽

Yikang Zheng ◽

Qingfeng Xue ◽

Xu Chang ◽

Tong W. Fei ◽

...

Keyword(s):

Complex Function ◽

Synthetic Data ◽

Velocity Model ◽

High Amplitude ◽

Frequency Noise ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Time Migration ◽

Wavefield Decomposition

In the implementation of migration of multiples, reverse time migration (RTM) is superior to other migration algorithms because it can handle steeply dipping structures and offer high-resolution images of the complex subsurface. However, the RTM results using two-way wave equation contain high-amplitude, low-frequency noise and false images generated by improper wave paths in migration velocity model with sharp velocity interfaces or strong velocity gradients. To improve the imaging quality in RTM of multiples, we separate the upgoing and downgoing waves in the propagation of source and receiver wavefields. A complex function involved with the Hilbert transform is used in wavefield decomposition. Our approach is cost effective and avoids the large storage of wavefield snapshots required by the conventional wavefield separation technique. We applied migration of multiples with wavefield decomposition on a simple two-layer model and the Sigsbee 2B synthetic data set. Our results demonstrate that the proposed approach can improve the image generated by migration of multiples significantly.

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Reverse time migration of multiples: Eliminating migration artifacts in angle domain common image gathers

Geophysics ◽

10.1190/geo2013-0441.1 ◽

2014 ◽

Vol 79 (6) ◽

pp. S263-S270 ◽

Cited By ~ 17

Author(s):

Yibo Wang ◽

Yikang Zheng ◽

Lele Zhang ◽

Xu Chang ◽

Zhenxing Yao

Keyword(s):

Free Surface ◽

Radon Transform ◽

Synthetic Data ◽

Velocity Model ◽

Migration Velocity ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Time Migration ◽

Nonzero Curvature

Free-surface-related multiples are usually regarded as noise in conventional seismic processing. However, they can provide extra illumination of the subsurface and thus have been used in migration procedures, e.g., in one- and two-way wave-equation migrations. The disadvantage of the migration of multiples is the migration artifacts generated by the crosscorrelation of different seismic events, e.g., primaries and second-order free-surface-related multiples, so the effective elimination of migration artifacts is crucial for migration of multiples. The angle domain common image gather (ADCIG) is a suitable domain for testing the correctness of a migration velocity model. When the migration velocity model is correct, all the events in ADCIGs should be flat, and this provides a criterion for removing the migration artifacts. Our approach first obtains ADCIGs during reverse time migration and then applies a high-resolution parabolic Radon transform to all ADCIGs. By doing so, most migration artifacts will reside in the nonzero curvature regions in the Radon domain, and then a muting procedure can be implemented to remove the data components outside the vicinity of zero curvature. After the application of an adjoint Radon transform, the filtered ADCIGs are obtained and the final denoised migration result is generated by stacking all filtered ADCIGs. A three-flat-layer velocity model and the Marmousi synthetic data set are used for numerical experiments. The numerical results revealed that the proposed approach can eliminate most artifacts generated by migration of multiples when the migration velocity model is correct.

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Visibility analysis for optimal imaging of target areas and its application to a Gulf of Mexico deep-water data set

Geophysics ◽

10.1190/geo2010-0389.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB119-WB126 ◽

Cited By ~ 2

Author(s):

Elive Menyoli ◽

Shengwen Jin ◽

Shiyong Xu ◽

Stuart Graber

Keyword(s):

Gulf Of Mexico ◽

Synthetic Data ◽

Target Area ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Visibility Analysis ◽

Velocity Models ◽

Time Migration ◽

Subsalt Imaging

Marine wide-azimuth data in the Gulf of Mexico, reverse time migration (RTM) and anisotropic velocity models have led to significant improvement in subsalt imaging. However, imaging of some steeply dipping subsalt targets such as three-way closures against salt is still difficult. This can be attributed to poor illumination and noise contaminations from various shot records. We apply the visibility analysis method that quantitatively determines which shot records contribute most energy on a specific subsalt prospect area. As a result we selectively migrate only those shot records thereby reducing noise contamination from low energy contributing shot records, improving signal continuity and better trap definition in the target area. Like conventional illumination analysis, the computation takes into account the overburden velocity distribution, acquisition geometry, target reflectivity and dip angle. We used 2D and 3D synthetic data examples to test the concepts and applicability of the method. A Gulf of Mexico case study example using wide-azimuth data demonstrated its use in an industry scale project. It is shown that for the particular 60°–65° subsalt target of interest only 30% of the wide-azimuth shot records are sufficient for the imaging. By reducing noise, the image results show significant improvement in the subsalt area compared to the full shot record RTM volume.

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3D high-resolution seismic imaging of the iron-oxide deposits in Ludvika (Sweden) using full-waveform inversion and reverse-time migration

10.5194/se-2021-122 ◽

2021 ◽

Author(s):

Brij Singh ◽

Michał Malinowski ◽

Andrzej Górszczyk ◽

Alireza Malehmir ◽

Stefan Buske ◽

...

Keyword(s):

Waveform Inversion ◽

Velocity Model ◽

Mine Planning ◽

Full Waveform Inversion ◽

Reverse Time ◽

Reverse Time Migration ◽

Depth Imaging ◽

Velocity Models ◽

Full Waveform ◽

Time Migration

Abstract. A sparse 3D seismic survey was acquired over the Blötberget iron-oxide deposits of the Ludvika Mines in south-central Sweden. The main aim of the survey was to delineate the deeper extension of the mineralisation and to better understand its 3D nature and associated fault systems for mine planning purposes. To obtain a high-quality seismic image in depth, we applied time-domain 3D acoustic full-waveform inversion (FWI) to build a high-resolution P-wave velocity model. This model was subsequently used for pre-stack depth imaging with reverse time migration (RTM) to produce the complementary reflectivity section. We developed a data preprocessing workflow and inversion strategy for the successful implementation of FWI in the hardrock environment. We obtained a high-fidelity velocity model using FWI and assessed its robustness. We extensively tested and optimised the parameters associated with the RTM method for subsequent depth imaging using different velocity models: a constant velocity model, a model built using first-arrival traveltime tomography and a velocity model derived by FWI. We compare our RTM results with a priori data available in the area. We conclude that, from all tested velocity models, the FWI velocity model in combination with the subsequent RTM step, provided the most focussed image of the mineralisation and we successfully mapped its 3D geometrical nature. In particular, a major reflector interpreted as a cross-cutting fault, which is restricting the deeper extension of the mineralisation with depth, and several other fault structures which were earlier not imaged were also delineated. We believe that a thorough analysis of the depth images derived with the combined FWIRTM approach that we presented here can provide more details which will help with better estimation of areas with high mineralization, better mine planning and safety measures.

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Comparison of Kirchhoff and reverse‐time migration methods with applications to prestack depth imaging of complex structures

Geophysics ◽

10.1190/1.1444416 ◽

1998 ◽

Vol 63 (4) ◽

pp. 1166-1176 ◽

Cited By ~ 30

Author(s):

Jinming Zhu ◽

Larry R. Lines

Keyword(s):

Velocity Model ◽

Complex Structures ◽

Reverse Time ◽

Reverse Time Migration ◽

Depth Imaging ◽

Exact Answer ◽

Time Migration ◽

Exploration Seismology ◽

Improved Accuracy ◽

Kirchhoff Integral

The performance of two popular migration methods—the Kirchhoff integral and reverse‐time migrations—is evaluated through applications to imaging complex structures using prestack shot records. The migration results from the Marmousi model data demonstrate that reverse‐time migration is more accurate than Kirchhoff migration in imaging the steeply dipping faults. However, the improved accuracy of reverse‐time migration requires higher computational costs. In the application to the Alberta Foothills data where a good estimate of the velocity model is available, however, both the Kirchhoff and the reverse‐time migration methods produce almost identical results. This implies that in the real world of exploration seismology, it will be relatively difficult to identify which method performs better because we never know the exact answer of the subsurface.

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Dirty salt velocity inversion: The road to a clearer subsalt image

Geophysics ◽

10.1190/geo2010-0392.1 ◽

2011 ◽

Vol 76 (5) ◽

pp. WB169-WB174 ◽

Cited By ~ 15

Author(s):

Shuo Ji ◽

Tony Huang ◽

Kang Fu ◽

Zhengxue Li

Keyword(s):

Model Building ◽

Synthetic Data ◽

Velocity Model ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Velocity Inversion ◽

Time Migration ◽

And Migration ◽

Subsalt Imaging

For deep-water Gulf of Mexico, accurate salt geometry is critical to subsalt imaging. This requires the definition of both external and internal salt geometries. In recent years, external salt geometry (i.e., boundaries between allochthonous salt and background sediment) has improved a great deal due to advances in acquisition, velocity model building, and migration algorithms. But when it comes to defining internal salt geometry (i.e., intrasalt inclusions or dirty salt), no efficient method has yet been developed. In common industry practices, intrasalt inclusions (and thus their velocity anomalies) are generally ignored during the model building stages. However, as external salt geometries reach higher levels of accuracy, it becomes more important to consider the once-ignored effects of dirty salt. We have developed a reflectivity-based approach for dirty salt velocity inversion. This method takes true-amplitude reverse time migration stack volumes as input, then estimates the dirty salt velocity based on reflectivity under a 1D assumption. Results from a 2D synthetic data set and a real 3D Wide Azimuth data set demonstrated that the reflectivity inversion scheme significantly improves the subsalt image for certain areas. In general, we believe that this method produces a better salt model than the traditional clean salt velocity approach.

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Simultaneous reverse time migration of primaries and free-surface related multiples without multiple prediction

Geophysics ◽

10.1190/geo2012-0450.1 ◽

2014 ◽

Vol 79 (1) ◽

pp. S1-S9 ◽

Cited By ~ 23

Author(s):

Yibo Wang ◽

Xu Chang ◽

Hao Hu

Keyword(s):

Free Surface ◽

Field Data ◽

Synthetic Data ◽

Velocity Model ◽

Reverse Time ◽

Reverse Time Migration ◽

Data Set ◽

Imaging Condition ◽

Time Migration ◽

Multiple Prediction

Prestack reverse time migration (RTM) is usually regarded as an accurate imaging tool and has been widely used in exploration. Conventional RTM only uses primaries and treats free-surface related multiples as noise; however, free-surface related multiples can sometimes provide extra illumination of the subsurface, and this information could be used in migration procedures. There are many migration methods using free-surface related multiples, but most approaches need to predict multiples, which is time consuming and prone to error. We discovered a new RTM approach that uses the primaries and the free-surface related multiples simultaneously. Compared with migration methods that only use free-surface related multiples, the proposed approach can provide comparable migration results and does not need multiple predictions. In our approach, the source function in conventional RTM was replaced with recorded field data including primaries and free-surface related multiples, together with a synthetic wavelet; the back-propagated primaries in the conventional RTM were replaced with complete recorded field data. The imaging condition of the proposed approach was the same as the crosscorrelation imaging condition of conventional RTM. A three-layer velocity model with scatterers and the Sigsbee 2B synthetic data set were used for numerical experiments. The numerical results showed that the proposed approach can cover a wider range of the subsurface and provide better illumination compared with conventional RTM. The proposed approach was easy to implement and avoided tedious multiple prediction; it might be significant for general complex subsurface imaging.

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