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Updating salt model using FWI on WAZ data in the Perdido area: benefits and challenges

In this case study, we discuss the impact of using a not-so-appropriate Wide Azimuth Data (WAZ) data which lacks good usable low frequencies and long offset full azimuth coverage for FWI based model building. We use Time-Lag FWI (TLFWI) demonstrated to be an appropriate algorithm by Zhigang et al 2018. We observe significant uplift in the shallow velocity model and salt overhang definitions at most locations. In this abstract, we discuss the limitations of using WAZ data for FWI and the additional effort to obtain better starting models to overcome the lack of sufficient diving energy and lack of low-frequency signal (<3Hz). We also briefly discuss the uncertainties in the inverted models esp. beyond the penetration depth of transmission waves.

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Adaptive quadratic Wasserstein full-waveform inversion

we present a FWI scheme based on the quadratic Wasserstein metric, with adaptive normalization and integral wavefield. We show that this scheme has better convexity than traditional metrics, and therefore can mitigate cycle-skipping issues, while being insensitive to amplitude effects. We demonstrate the effectiveness of our approach with a streamer data set in an area of complex salt geometry. In addition, we show that this approach can work naturally on reflection data, without the extra procedure of scale separation by either decomposition or demigration. With these learnings, we believe that the fundamentals of FWI research are starting to converge.

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Gini 3D High Productivity Acquisition & Imaging – A case study from the Delaware Basin

The Gini 3D survey, acquired in the summer of 2018 in the Delaware Basin, provided a test area for which this type of design and acquisition could be tested and compared with traditional operations used onshore US. The test was planned to be operationally efficient & cost effective (in terms of equipment), with the aim of proving that blended acquisition can be as effective as traditional designs in terms of imaging. Operationally the test exceeded expectations and with processing still ongoing, initial results show that the two designs are comparable.

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Norway: New play models for Patch Bank Ridge, east of Utsira High

NVGS, a recently acquired southward extension of the NVG survey in the northern Norwegian North Sea, is a high-quality broadband seismic data set, which reveals detailed stratigraphy from the Permian Salt to the Quaternary section for stratigraphic and lithological interpretation. In the deeper parts, old basin configurations can be mapped. Including Caledonian fold and faults and Paleozoic basins. The regional scale of the data set makes it ideal for establishing a geological model for this region. Including prediction of potential source and reservoir rocks. Although the North Sea is a mature region, the Patch Bank Ridge area is under-explored.

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Determination of reservoir thickness and distribution using improved rescaled cokriging

The characteristics of lithologic reservoirs, such as complex channels with distinctly lateral variations and variable thickness, make such reservoir features difficult to identify when using conventional geostatistical methods or applying seismic attribute methods. To decrease the uncertainty and improve the lateral distribution of the predicted map over such features, we present an improved cokriging system which combines well logs and multiple attributes directly, instead of using a data fusion method. The improved technique was applied to predict a distribution and thickness map of a channel system. The results demonstrate that improved our cokriging system can enhance the lateral resolution of the channel and reduce the uncertainty of prediction due to the use of more seismic attributes than traditionally used.

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Wave height guided multi-shot receiver deghosting

Free-surface datum variations cause complications for hydrophone only receiver deghosting algorithms that assume a horizontal free-surface. We describe a multi-shot receiver deghosting approach that derives a tau-psht-prec model of ghost free data at mean free-surface datum. The model is derived so as to simultaneously satisfy the recorded primary and ghost wavefields in the presence of a non-horizontal free-surface at the source and receiver sides. The approach is shown to produce high resolution receiver deghosting results with improved spatial consistency on a broadband variable depth streamer dataset from the North Sea.

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Dynamic-warping full-waveform inversion to overcome cycle skipping

In this paper, we develop Dynamic-warping Full Waveform Inversion (D-FWI) to address cycle skipping problem which is a well-known challenging issue in conventional FWI. The dynamic warping technique is used to detect the travel time difference between the predicted and the observed wave fields. We make use of the time shift to partially warp the observed data and thus generate a series of wave fields that connect the predicted and the observed wave fields. We then use these modified observed wave fields in the framework of FWI and solve a sequence of conventional FWIs to avoid cycle skipping issue. The applications on synthetic and real data examples show that D-FWI can converge successfully by overcoming the cycle skipping problem while conventional FWI result in a spurious model. With this new approach, we can get reasonable velocity model even starting with a smooth model at higher frequency. It will greatly save the processing duration since velocity model building can be done at the same time of pre-processing such as denoise, demultiple and interpolation.

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Primary-preserving multiple attenuation for broadband data

Multiple attenuation is a key step of broadband marine processing which could be challenging for primary preservation, spatial continuities and low frequencies. Rather than a cascaded de-multiple sequence, which could lead to cumulate mistakes and uncertainties, with final results potentially questionable for further pre-stack inversion, we propose an optimized multiple attenuation methodology, as well as new Quality Control tools based on correlations and pseudo-Impedance.

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