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[PDF] No-compromise marine seismic: A full-azimuth survey design for total-wavefield velocity model building and imaging in the deep-water Gulf of Mexico
Author: Andrew Long, Steve Campbell, Steven Fishburn, Sverre Brandsberg-Dahl, Nizar Chemingui, Volker Dirks
SEG - 26 October 2014A first-ever five-vessel towed streamer configuration with all vessels participating in a simultaneous shooting scheme is presented that delivers uniformly-sampled offset-azimuth bin populations. With a maximum offset of 16 km, the survey has been designed to illuminate all potential targets below extensive and rugose salt cover in the Garden Banks and Keathley Canyon areas of the Gulf of Mexico, including ultra-deep sub-salt plays such as the BP Tiber discovery. TTI RTM anisotropic pre-stack depth imaging of both primary and surface multiple seismic events is facilitated by true wavefield separation of dual-sensor streamer data. The latter imaging pursuit, separated wavefield imaging (SWIM) exploits subsurface sampling (illumination) substantially more dense and spatially-extensive than traditional primaries-only imaging as each of the 13,000 receivers associated with each shot become secondary sources. 18 second continuous recording will ensure several orders of multiples are recorded from all target depths. Ghost-free acquisition will also improve deep sub-salt signal penetration, whilst simultaneously providing the broadest bandwidth data required for shallow geohazard imaging.
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[PDF] Recovering the Reflectivity Matrix and Angle-dependent Plane-wave Reflection Coefficients from Imaging of Multiples
Author: Alba Ordoñez, Walter Söllner, Tilman Klüver, Leiv Gelius
SEG - 26 October 2014A joint migration approach employing the complete wavefield (containing primary and multiple reflections) requires properly imaged multiples of all orders. By solving a Fredholm integral equation of the first kind, we compute the reflected impulse response (i.e., reflectivity) matrix at every image level and extract the angledependent plane wave reflection coefficients. We tested this imaging technique employing a simple 1D layered model with multiple reflections included. We obtained the correct Amplitude Versus Angle (AVA) response of the estimated plane wave reflection coefficient. By simultaneously imaging primaries and multiples, we also achieved an overall better image.
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[PDF] Dynamic angle and azimuth decomposition of RTM images
Author: Dan Whitmore, Sean Crawley, Chaoguang Zhou, Armando Sosa
SEG - 26 October 2014In the application of reverse time migration (RTM) to wide and full azimuth data, it important not only to produce a final RTM image, but also to decompose the data into prestack gathers that can be used both for processing and tomography. We discuss here a method where the RTM image can be mapped into angle-azimuth gathers by direct binning at each time step, where the RTM backscattered noise is minimized during the propagation process by the application of an inverse scattering imaging condition. We demonstrate the angle-azimuth decomposition to the application of RTM imaging and 3D angle tomographic model building in wide azimuth data from the Gulf of Mexico. Also, in preparation for the processing of a full azimuth survey in the Gulf of Mexico, we also examine the angle-azimuth decomposition for 3D RTM imaging using a full azimuth 3D synthetic based on the SEG SEAM model.
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[PDF] Anisotropic model building with well control
Author: Chaoguang Zhou, Zijian Liu, Dan Whitmore, Samuel Brown
SEG - 26 October 2014Anisotropic depth model building using surface seismic data alone is non-unique and one of the major reasons is that there is ambiguity among the anisotropy parameters.Additional well data can help reduce such ambiguity and thus yield a more accurate anisotropic model for depth imaging. In this paper, we present a tomographic model building approach that uses well data together with surface seismic data. It consists of four major steps: preparing data, estimating the local anisotropic parameters at the well locations, extrapolating the local parameters to generate a volumetric anisotropic model for further tomographic update, and finally tomographic updating with well control.
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[PDF] Towed Streamer EM – reliable recovery of sub-surface resistivity
Author: Allan McKay, Johan Mattsson, Zhijun Du
First Break - 1 April 2015The authors present a seismically guided inversion and illustrate the workflow of the data integration, which remains driven purely by the seismic and EM data.
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[PDF] A Robust FWI Method for Model Updating in High Contrast Bodies
12 June 2017
We present a robust method for Full Waveform Inversion (FWI), enabling the recovery of long-wavelength features of a velocity model. By using both transmitted and reflected waves the dynamically weighted FWI gradient enables high-resolution model building deeper than those achieved by diving waves alone. This reduces the dependency on long offset data acquisition.
The FWI approach uses a sophisticated regularization scheme to stabilize the inversion space. This methodology, which forms an extra constraint on the objective function, overcomes some of the limitations of the inversion in the presence of high contrast bodies. The implementation uses the split Bregman method, making it efficient and accurate.
We demonstrate the benefits of using the new gradient and regularization scheme by presenting the results on an intra-volcanic reservoir velocity model build from the Faroes-Shetland Basin. -
[PDF] A New Look at the Geology and Prospectivity of a North Sea Frontier Area with Modern Seismic - The East Shetland Platform
12 June 2017
The greater East Shetland Platform (ESP) area is characterized by numerous proven Devonian-Eocene fields, but is still one of the few remaining underexplored regions of the UK Continental Shelf. In particular, Permo-Carboniferous carbonates and sandstones, Devonian sandstones and fractured basement in prominent structural traps have been successful, proving these units to be viable reservoirs. Some of these are large producing fields in nearby areas (e.g., Buchan, Clair, Auk, with >100 MMboe).
The improved imaging of the 3D broadband dual-sensor towed streamer data has allowed the interpretation of the Paleozoic horizons over the entire outer ESP region (17,500 km2), enabling interpreters to spread new light on its evolution.
Possible Paleozoic structural traps are often sealed by the overlying Cretaceous strata. Source rocks could be provided by the ‘classical’ upper Jurassic Kimmeridge Clay (lateral migration from the basin depocenters lying further east). Potential additional oil-prone sources may be provided by middle Devonian shales (c.f., Beatrice Field).
Burial history modelling indicates that the best case scenario (late generation) did occur over parts of the study area. This supports previous geochemical analyses in analogue areas, which suggested a contribution from the Devonian source for the oils of large fields (e.g., Claymore and Clair fields). -
[PDF] Intelligent Adaptive Subtraction for Multiple Attenuation
12 June 2017
A lot of improvements have been seen in the last decade in 3D multiple modelling techniques, such as 3D Surface Related Multiple Elimination (SRME) and 3D wavefield modelling. These processes create accurate multiple models in terms of kinematics and amplitude. The main challenge now is to improve the subtraction of multiples, with a reduction in both residual multiple and primary leakage. This paper describes a new approach for multiple adaptive subtraction, which combines different techniques (least squares filtering in the time-space domain and
curvelet-based subtraction) and improves primary preservation by using true multiple adaptive subtraction. The ultimate aim is to automatically get the best subtraction according to the complexity of the geology with minimum testing for the geophysicist. -
[PDF] Enhanced Angular Illumination from Separated Wavefield Imaging (SWIM)
1 June 2014
In exploration geophysics, both primaries and multiples can be used for depth imaging. This is feasible after applying wavefield separation to generate up-going and down-going wavefields. The separated wavefields can be used as boundary data for migration using sea surface related multiples – Separated Wavefield Imaging (SWIM). The areal source (recorded down-going wavefield) in SWIM covers larger surface spread than the point source in primaries imaging. Therefore, SWIM can enhance the areal illumination of subsurface and angular illumination of a point in the subsurface, especially when shots sampling is coarser. Angle gathers are generated from imaging of primaries and SWIM. As expected, the SWIM angle gathers prove to be denser, and less affected by coarse source sampling than the primaries angle gathers. The concept is illustrated by using a wide azimuth (WAZ) field data example.
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[PDF] 3D Anisotropic Inversion of Towed Streamer EM Data over the Mariner Field in the North Sea
1 June 2014
Towed streamer electromagnetic (EM) data over the Mariner oilfield in the UK sector of the North has been inverted using a fast and efficient 3D anisotropic inversion code. The electric field data were acquired with a single vessel using a horizontal bipole source and sensors housed in a towed streamer in a densely sampled grid over the subsurface volume of interest. The inversion algorithm is based on the 3D contraction integral equation method and utilizing a re-weighted regularized conjugate gradient technique to minimize an objective functional.
This inversion method is proven to be fast and efficient for large data sets and is here shown to be suitable for towed streamer EM data from complex geological environments such as the Mariner area. In this case, the final 3D resistivity cube after inversion and with a corresponding misfit of 6.4 %, agrees well with the expected structure from seismic data and well logs. In particular, the 3D cube contains a resistive anomaly of 8-10 Ωm corresponding to the Maureen and Heimdal reservoirs on top of the resistive chalk and basement.