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[PDF] Making the Transition from Discrete Shot Records to Continuous Wavefields – Real Data Application
Author: Tilman Klüver, Stian Hegna, Jostein Lima
EAGE - 4 June 2018
In this paper, we present real data applications of the acquisition and processing method outlined in the companion paper (Hegna, S., Klüver, T., and Lima J., 2018, Making the transition from discrete shot records to continuous
wavefields – Methodology: Expanded abstract submitted to the EAGE annual meeting). We discuss the design of sources that emit continuous wavefields approaching the properties of white noise using air-guns. The design
minimizes correlation between sources and allows a six-source configuration with a vessel towing six strings of airguns, thereby increasing efficiency or cross-line sampling. The environmental benefit of spreading source energy in time will be demonstrated. We illustrate the processing method based on continuous source and receiver wavefields on seismic data acquired on top of data acquired previously based on discrete shot records. Both data sets will be compared at image level.
[PDF] Intra-Chalk Porosity Variations in Norway-Danish Central Graben: Integrated Mapping Using Broadband Elastic Attributes
Author: Noémie Pernin, Tim Bird, Cyrille Reiser
EAGE - 4 June 2018
Understanding the influence of porosity on elastic properties through rock physics analysis is essential in seismic reservoir characterisation and key in the context of the chalk play. It is known that acoustic impedance is strongly correlated with porosity in carbonates but also that the chalk properties can vary widely creating intra-chalk layers of varying reservoir quality. This integrated study shows how reliable broadband relative elastic attributes tie at the wells and are able to map lateral and vertical changes of porosity within the Chalk interval in the Norwegian and Danish North Sea Central Graben.
Author: Jyoti Kumar, Marcus Bell, Mamdouh Salem, Tony Martin, Stuart Fairhead
First Break - 3 December 2018
The authors propose a method to attenuate converted mode energy to improve the imaging for prospective sub-salt targets.
Author: Nizar Chemingui, Alejandro Valenciano, Tony Martin
EAGE/PESGB Workshop on Velocities - 4 April 2019
Conventional velocity model building (VMB) in complex regimes, such as intra and subsalt data, requires time consuming manual intervention. It is a process that can produce unreliable models, leading to an increase in uncertainty for subsalt lead evaluation. We demonstrate an application of Full Waveform Inversion (FWI) to refine legacy velocity models generated by conventional VMB. We present our solution on a simultaneous long offsets (SLO) dataset from the Gulf of Mexico, acquired with dual-sensor streamers, which provided low frequency rich data. The SLO configuration recorded data with 16 km of offset, enabling both refractions and reflections to update the deeper parts of the velocity model. We employ an FWI velocity gradient that eliminates the migration isochrones. This provides support for the intra and subsalt model updates by removing the reflectivity imprint from the updated models. The FWI application successfully refined the geometry of the salt bodies including the base salt and the intrasalt enclosures. RTM images show a marked uplift, particularly for both the salt flanks and subsalt reflectors.
[PDF] Integrating FWI Models and Broadband Data for Elastic Property Generation, What is Appropriate?
Author: Tony Martin, Cyrille Reiser
EAGE/PESGB Workshop on Velocities - 4 April 2019
Full waveform inversion (FWI) produces high-resolution earth models, the use of which can improve seismic imaging. FWI can also help create absolute inversion products, by filling the low frequency spectral gap in the integration with amplitude seismic data. However, what frequency should be used for FWI to cost-effectively estimate absolute elastic properties remains an open question. We present analysis from a case study in the Norwegian Sea. Initially we demonstrate how imaging challenges have been overcome by the use of FWI and high-end imaging. Following this, we reveal there is a cost-benefit sweet-spot for the low frequency models from FWI and broadband seismic amplitude data in the generation of absolute seismic inversion products.
[PDF] From Feasibility to Reservoir Characterization: A fully integrated 4D seismic approach for reservoir management. A case study in the Western African offshore
Author: Cyrille Reiser, Didier Lecerf
SEG - 1 January 0001
The development and management of deep-water fields requires material investments and must be supported by the best technology solutions and tools. In this paper, we highlight how the seismic data was used to support the reservoir monitoring of a producing field in the West Africa Offshore. We also discuss how a dedicated 4D seismic project helped in the understanding of fluid movements and fault behaviors in the field in the aim of
identifying business opportunities and driving decision making over our Area of Interest.
[PDF] Application of Full Waveform Inversion to resolve an eroded shallow carbonate platform, North Madura, East Java, Indonesia
Author: David Cavalin, Nurrul Ismail, Tom Paten, Kola Agbebi, Dave Lim
IPA - 2 September 2019
Proven plays in North Madura have been identified in the Miocene carbonate and syn-rift Eocene clastic systems. 3D broadband seismic data was acquired in order to obtain higher resolution and deeper imaging of potential prospects and leads within these systems.
Besides improving resolution, penetration, imaging and seismic attributes, broadband data has another major advantage; it allows the low frequencies of the recorded data to drive a more complex velocity model update technique: Full Waveform Inversion (FWI).
Standard traveltime reflection tomography techniques provide long to mid wavelength velocity updates but generally fail in updating shallow water environments while giving limited resolution in the rest of the velocity model. However, a more accurate velocity model is needed to correct rapid vertical and lateral velocity heterogeneities. Small-scale velocity anomalies in this survey include gas bearing river channels, whereas eroded shallow carbonate platforms present additional challenges related to structural distortions observed on the time domain outputs. Such velocity anomalies must be resolved prior to imaging the deeper section.
FWI operates by minimizing residuals calculated between recorded shot records and modeled shots, within a certain frequency band. An iterative approach was used to update the velocity model starting with low frequencies available from the broadband seismic data. Using the lowest possible frequency data, containing coherent signal, minimizes the risk of cycle skipping thus allowing the FWI update to start from a benign velocity model. The successive passes of FWI introduced details into the velocity model conforming to the geological challenges identified at the beginning of the project.
Combining both broadband data and FWI velocity model building (VMB) is key in correcting for structural distortion and amplitude dimming particularly associated with shallow velocity anomalies. This methodology allowed us to confidently position in depth the potential plays and leads affected by velocity anomalies in the shallower section.
[PDF] Improved HSEQ and survey efficiency demonstrated with a new remotely operated streamer cleaning tool
Author: Andrew Long, Rune Tønnessen, Trygve Skadberg, James Wright
AEGC - 2 September 2019
Barnacle growth on seismic streamers creates noise on the recorded signals. Keeping a low noise level in barnacle areas is challenging to seismic crews: Frequent workboat trips are required for streamer cleaning, and workboat operations are weather-dependent and considered undesirable from an HSE perspective. In 2007 a purely mechanical and autonomous streamer cleaning unit (SCU) was introduced that is launched and recovered from the workboat. In 2016 we subsequently developed a
remotely operated streamer tool (ROST) that is capable of launching and recovering SCUs to/from the streamer without the use of a workboat, and which is therefore less
affected by weather. The ROST is operated from a support vessel that is independent of the seismic vessel. We present experiences from four surveys that were
subject to different operating conditions. Operation in high sea states is demonstrated on a survey offshore Namibia, and operation in extreme currents is demonstrated on another survey east of South Africa. A noise removal method is also presented that allows operation of the ROST while online during seismic recording. The method was first applied on the offshore South African survey, and later on two surveys in offshore Angola. It is demonstrated that work boat exposure hours can be reduced by 70-80%, and a 14 streamer spread can be cleaned twice a week while acquiring seismic in all types of operating conditions.
[PDF] North Sea case study: Heavy oil reservoir characterization from integrated analysis of Towed Streamer EM and dual-sensor seismic data
Author: Zhijun Du, Kerry Key
ASEG - 15 February 2015
Integrated analysis of geophysical data can provide valuable information on reservoir properties, on the basis of which exploration, appraisal, and development decisions can be made. Hence, we have introduced a quantitative interpretation workflow that integrates dual-sensor seismic and Towed Streamer controlled-source electromagnetic (CSEM) data. The workflow was designed to facilitate a reliable extraction of the complementary information from the two datasets. The seismic contribution starts with a depth-converted sparse horizon model to initialize the EM inversion, but it is not placed rigidly. This makes good sense when taking into account the uncertainties in seismic data, in the time to depth conversion, and more importantly, the fact that a reservoir can be hydrocarbon-charged to an unknown degree corresponding to the spill-point or less. We show how this approach enables a robust and reliable workflow for integrating EM and 3D seismic data with data examples acquired in an area with the complex geology of the Bressay, Bentley and Kraken (BBK) fields in the North Sea. The three heavy oil reservoirs are injectites, located in close proximity to other high resistivity settings, such as the shallow gas in the overburden, regional Balder Tuff and granite intrusions, resulting in challenging imaging issues.
Author: Shaoping Lu, Xiang Li, Alejandro Valenciano, Nizar Chemingui, Cheng Cheng
E&P Daily News - 14 June 2017
A new methodology for LS-WEM is much less compute-intense.