TechLink
TechLink is a Technical e-newsletter written by the technology and R&D groups in PGS Geophysical. Each month TechLink will highlight key PGS technology developments and applications, covering our complete breadth of products and services.
Listed below are the recently published TechLinks. To sign-up to receive TechLink, click here.
An accurate velocity model is key to improved seismic imaging. In this Nile Delta case study, PGS demonstrates that multi-azimuth reflection tomographic inversion is able to resolve smaller scale velocity variations than narrow-azimuth inversion, and hence enables more accurate velocity model building in depth. Multi-azimuth inversion is capable of resolving these small scale velocity heterogeneities because of the azimuthal diversity. The gathers obtained from multi-azimuth inversion are flatter and the stack is improved compared to narrow-azimuth inversion. The resolved small scale velocity variations correlate very well with geology.
As we finalise this TechLink, PGS has been named as the recipient of the E&P Meritorious Award for Engineering Innovation in Exploration Technology for its development of PGS hyperBeam, a fully integrated real-time model building and depth imaging workflow environment.
Depth imaging workflows can take days to complete with time spent not only running the various applications, but also with data and system management. PGS hyperBeam allows for real-time analysis and interaction with velocity models and seismic depth images and gathers. It provides scenario testing and real-time data analysis of all steps in the depth imaging workflow. The seamless integration with 3D visualization makes the tool ideal for collaborative work on depth image projects for exploration and well planning. The impact of
model updates and changes can be analyzed realtime, in a setting that is familiar to such crossdisciplinary teams.
A towed EM system has been successfully tested over the shallow gas discovery Peon in the North Sea. One vessel was used for data acquisition to tow simultaneously both the electric dipole current source and the receivers in an EM streamer. The objective was to investigate the system performance with respect to detection and characterization of the known hydrocarbon target.
Full-waveform inversion (FWI) is an automated method for refining a velocity model by iteratively attempting to match modelled data with recorded data. Each iteration represents a linearization of the non-linear problem by the Born approximation (refer to Tarantola, 1984). Examples in the literature have shown that FWI is capable of providing a remarkable improvement in model resolution, particularly for small-scale features.
A full-scale time-lapse 3D (4D) test in the North Sea with a GeoStreamer® monitor survey over a conventional streamer baseline survey yielded excellent repeatability that is fully in line with industry requirements. The flexibility of the GeoStreamer platform was exploited to reconstruct the total pressure field at the acquisition depth of the baseline survey prior to 4D comparison. Thus, 3D GeoStreamer is fully backwards-compatible with conventional (hydrophone-only) streamer data for 4D differencing, and GeoStreamer unequivocally represents the premier towed streamer solution for all 2D, 3D and 4D applications.
Two PGS technology innovations are described that are helping to improve the quality and efficiency of PGS towed streamer operations. PGS has installed GPS receivers and acoustic ranging units on the paravanes of several Ramform vessels. The resultant benefit is improved streamer positioning accuracy. A solution to the associated power requirements has been the development of a unique generator technology that is mounted on each paravane.
True-azimuth 3-D surface-related multiple elimination (TA 3-D SRME) has rapidly become the preferred method in complex multiple removal due to its independence from any a priori information about the subsurface geology. Applications to Narrow-Azimuth Towed Streamer (NATS) and Wide-Azimuth Towed Streamer (WATS) datasets acquired over complex geology have led to significant improvements in multiple removal compared to any other method.
PGS now has fully 3D acquisition and processing solutions for the dual-sensor GeoStreamer® technology. Independent measurements of the total pressure and particle velocity wavefields with collocated sensors allow separation in processing of the data into up- and down-going components. Case examples demonstrate that the PGS frequency-wavenumber domain methods are both robust and accurate.
A progression in survey effort and investment is described that is intended to provide an overview of how the acquisition of larger azimuths throughout a marine 3D survey area will improve data quality under various scenarios. Based upon the convenience of established narrow-azimuth (NAZ) processing methodologies, the comparative benefits of multi-azimuth (MAZ) and wide-azimuth (WAZ) survey strategies can be contrasted in terms of benefits to target illumination or the attenuation of complex coherent noise.
We present results of a multi-transient electromagnetic repeatability experiment conducted over the North Sea Harding field in 2007 and 2008. The segment of the field under investigation had produced 3.9 MMbbls of oil during this time interval.
The Haltenbanken dual streamer data was acquired in 2007 on the mid-Norwegian continental shelf in the Norwegian Sea. The objectives are at various prospective target depths in a deep and relatively complex structural and stratigraphic geological setting.
Though there is a lot of historical data around, its condition, quality and availability varies. Exploration would be easier if it were generally more accessible and in a versatile format. The SAMDA is a digital, map-based library covering all of Australia's Southern Margin hydrocarbon provinces.
CUBE MANAGER is the principal seismic data processing system developed by PGS for efficiently processing the ever-increasing massive amounts of data acquired in 3-D and 4-D seismic surveys. Running on the latest Linux cluster technology, CUBE MANAGER uses advanced parallel processing techniques and over 300 geophysical applications to handle all seismic survey types – land and marine, 2-D, 3-D, and 4-D, streamer and oceanbottom cable, P-wave and S-wave.
A minimal impact philosophy with respect to both the natural and local community environments is helping PGS successfully undertake the first onshore seismic survey in the Kingdom of Cambodia. An accelerated weight drop system is helping the onshore crew move quickly and efficiently along established roads and tracks, through local communities and culturally sensitive areas, and across any rough terrain with reduced risk from UXO and no disturbance to existing infrastructure.
PGS provides several options for automated time velocity analysis. The interactive tool tVAT performs continuous velocity analysis and traditional auto-picking, while the optivel program provides a fast and automated batch approach. This combination of methods provides a range of flexible auto-picking solutions that can be applied singularly, or in combination, for efficient and accurate high density velocity analysis.
March 2009
This TechLink discusses a simultaneous source wide-azimuth towed streamer (WATS) acquisition experiment that was performed in the Gulf of Mexico. Four source arrays were deployed such that pairs of source arrays were fired simultaneously, with all firing times being randomized within a small window.
February 2009
Quantitative analysis of GeoStreamer® data acquired in a spatially-coincident manner with conventional streamer data demonstrate a four to five-fold boost in the low frequency signal content, about twice the high frequency signal content (before the application of any spectral enhancement processing), and a higher signal-to-noise content for all frequencies and for all depths.
January 2009
The evolution of towed seismic streamers is summarized, following the development from fluidfilled to solid-filled streamers, and the progression from sensors that only record the scalar pressure field to combined pressure and particle velocity sensors within the streamer.
December 2008
Multiple elimination remains one of the key challenges in seismic data processing. Particularly in complex 3-D geological areas, the success of multiple elimination approaches depends heavily upon their underlying assumptions and/or a priori information.
November 2008
This TechLink edition addresses some of the key technical aspects of one-way wavefield extrapolation migration, or WEM for short. Migration algorithms based on one-way wavefield extrapolation are rapidly becoming the norm for prestack depth imaging, and can be found in a variety of implementations, from the geophysically intuitive shot migration to phase-encoded schemes such as delay-line and plane-wave migration.
October 2008
PGS has extended the capabilities and scope of the Nucleus modeling package to a new platform known as Nucleus+. A project-based and project sharing capability is now offered, enabling greater flexibility and easier user access to libraries of results and files.
September 2008
In 1999 AGS (now part of PGS) started development of Beam Pre-Stack Depth Migration (BPSDM). The anticipated merits were simplicity, economy, flexibility and future development possibilities. The unknowns were the migration accuracy and quality.
August 2008
The sheer variety of multiple removal techniques is a testament to the importance and complexity of the demultiple problem in seismic processing. Perhaps the most widely used class of techniques over the past of couple of decades has been those based on the Radon transform.
July 2008
This study has used the laterally-extensive PGS CNS (Central North Sea) MegaSurvey 3D seismic volume and all relevant released exploration and appraisal wells (over 1,200 wells) to create a systematic seismo-stratigraphic model for the Lower Cretaceous over some 34,000 km2 of the Central North Sea.
June 2008
This TechLink discusses a case-history of the practical aspects of applying data-driven (SRME/IME) multiple removal techniques to complex onshore data from Libya.
May 2008
PGS has a comprehensive toolkit of regularization and interpolation technology that will help improve the imaging of all types of data and, in the case of 4-D data, the repeatability between data vintages.
April 2008
The history of the Ramform seismic vessel design begins with the Norwegian Navy surveillance ship Marjata in the early 1990s. The PGS engineers drew the conclusion that Marjata’s wide stern made her perfect for seismic acquisition where it is desired to have as little noise as possible from the vessel itself during data acquisition.
March 2008
PGS has developed two significant towed source and streamer technologies. Both are now in the early stages of full-scale production deployment, and are expected to gradually be rolled out across the PGS fleet.
February 2008
By addressing localized velocity anomalies in the shallow area of a 3D seismic volume, the imaging below the anomalies can be significantly improved. These improvements will then have a direct impact upon the interpretation of the data set.
January 2008
Multi-Transient EM (MTEM) is a proven remote sensing method for direct hydrocarbon detection and delineation. Profiles are rapidly derived to describe the resistivity of the earth, spatially correlated with the structural information provided by seismic data.
December 2007
Wide Azimuth Towed Streamer (WATS) seismic has found increasing commercial application on a large scale in recent years. WATS exploits acquisition geometries of increased effort and complexity in comparison to “conventional” 3D surveys, but the benefits delivered typically far outweigh the increased costs, particularly in areas where seismic imaging complexities have previously proven insurmountable.
November 2007
PGS has been developing an entirely new towed marine streamer concept for about five years. The project objective was to engineer a streamer that is capable of recording both the scalar pressure field and the vertical component of the vector particle velocity field.
October 2007
Reverse Time Migration (RTM) is a sophisticated wave equation depth migration method that has recently become achievable for large 3D surveys because of advances in computational power and clever programming.
September 2007
In July 2006 PGS conducted a new series of farfield signature measurements of single air guns and two-gun clusters in cooperation with the main vendors of marine seismic air guns; Bolt Technology Corporation and Sercel. The main objective of this project was to perform measurements of new guns for NUCLEUS source modelling calibrations.
December 2006
The traditional method of migration scanning for velocity analysis has been updated and modernized for use in sub-salt wave equation processing. A new set of tools along with an efficient methodology have been developed at PGS to accurately determine the velocity in these difficult areas.
November 2006
A method for efficiently modelling the effects of coverage holes in migrated data is presented. It is shown that the modelling predictions are in good agreement with the effects observed in real data.
October 2006
It is well established that modern airguns are inherently stable in a laboratory situation. However, when deployed at sea, the wavefield of arrays of airguns varies from shot-to-shot
because of gun drop-outs, and variations of geometry, depth, pressure, timing, water velocity, sea temperature, and sea surface conditions affecting the source ghost.
September 2006
Continuing the trend towards providing MegaSurvey data volumes over the worlds most promising and active petroleum provinces, PGS Reservoir has recently announced the availability of its interpretation package on the entire 3D seismic dataset in the Faroe-Shetland Basin (FSB) on the United Kingdom Continental Shelf (UKCS).
August 2006
Fiber optic seismic sensor systems have been under development for many years at PGS, who have produced several generations of prototype seismic equipment to demonstrate the technology. Ongoing projects include applications to 4C seafloor systems, streamers and near-field airgun recording.
July 2006
4D (time-lapse) seismic has become a powerful technology for oil companies to manage their reservoirs and optimize production.
May 2006
The gAS (generic Acquisition System) and Viper systems were developed in PGS for onboard data recording, quality control (QC) and data reformat, and are the standard on all PGS seismic vessels.
April 2006
Continuous Long Offset (CLO) acquisition is a patented, multi-vessel technique that can deliver the longer offsets and longer record lengths required to successfully image survey objectives without compromising on fold and shot sampling.
April 2006
The Valhall field is located in the Central Graben on the Norwegian continental shelf. The field consists of a weak and highly porous chalk reservoir which is thin and complex due to small-scale faulting.
March 2006
The Niger Delta is a proven prolific hydrocarbon system with a number of world-class oil discoveries and represents a cornerstone of PGS’ Multi-Client investment in the region.
February 2006
This is the case history of an ultra-deepwater 4C seafloor seismic program, recently acquired in the Campos and Santos Basins, offshore Brazil.
January 2006
As 3D survey sizes increase, and the acquisition and processing technologies improve, the demands upon seismic data processing centres increase even faster. Onboard processing resources are critical for total project turnaround, QC and quality.
November 2005
Overview of the ISO 9000 initiative in PGS Marine Geophysical. The ISO 9001:2000 standard
represents the most current management standard, and places Quality on equal footing with Health, Safety and Environment.
November 2005
PGS has developed and tested an electro-mechanical marine vibrator that produces comparable energy penetration and frequency bandwidth to a small airgun array or dynamite charge.
November 2005
Streamer overlap is a robust method to maximize the repeatability of azimuths at sail line boundaries for time-lapse 3D (“4D”) applications.
October 2005
PGS has invested significant resources in the development of wave equation pre-stack depth migration (WEPSDM) routines. These include Common Azimuth migration and shot migrations at increasing levels of sophistication.
October 2005
High resolution of seismic data results when high frequency geological features in close proximity can be precisely focused without any contamination from artefacts or noise (i.e. high signal-to-noise ratio).
September 2005
Solid streamers have become preferred to fluid filled streamers in marginal sea state conditions, as a consequence of the lower noise levels during acquisition.
September 2005
3D streamer configurations should always be customized to the specific geophysical requirements of each survey location.
August 2005
PGS’ holoSeisTM 3D visualization system has proven its effectiveness for the QC of seismic data processing and for demonstrating the quality of PGS seismic data volumes.
August 2005
Prestack depth migration is being used routinely to image areas with complex geologic structures. The ability to properly image these structures often depends on the ability to accurately discern the complex velocity field that accompanies them.
July 2005
PGS is now creating some of the worlds largest ever 3D seismic data sets. Hundreds of 3D surveys from the Central North Sea (CNS), the Southern North Sea and West of Shetlands are now being merged into three separate mega surveys.
July 2005
The North West Shelf Digital Atlas (hereafter referred to as NWSDA) provides the industry with a modern, adaptable digital map library of Australia's North West Shelf hydrocarbon province.
July 2005
In the last few years PGS have undertaken many large scale and challenging regional projects worldwide. The merging of PGS multi-client 3D library with other released 3D surveys has produced some of the largest single merged and interpreted datasets in the world.
June 2005
The ultimate goal in a seismic acquisition experiment is to perform dense and even sampling in both time and space, so that any aliasing is avoided.
May 2003
PGS has demonstrated the effectiveness of its 4D acquisition strategy many times since its original publication more than two years ago. The recent Draugen 4D survey in the North Sea is a compelling example of the 4D acquisition strategy yielding outstanding sourcereceiver azimuth repeatability.
April 2005
A key objective in 4D projects is to acquire and process seismic data in such a way that the differences between base and repeat surveys only reflects changes in the state of the reservoir.
February 2003
The Gulf of Guinea is proving to be one of the most prolific oil and gas provinces in the world. A series of new, worldclass discoveries have been made during the last few years, stepping out into deep water from proven nearshore oil provinces in Nigeria, Equatorial Guinea and Angola.
November 2002
The objective of migration of seismic data is to place reflected energy at the sub-surface positions where it originated. Ideally after migration, seismic data have correct reflection strength (amplitude) and phase.
September 2002
PGS is now creating some of the worlds largest ever 3D seismic data sets. Hundreds of 3D surveys from the Central North Sea (CNS), the Southern North Sea and West of Shetlands are now being merged into three separate mega surveys.
August 2002
PGS has introduced HD3D technology for onshore, seafloor and streamer surveys. This technology is well suited for 4D seismic.
March 2002