HD3D. Better than any other data.
Marine seismic acquisition technology has now advanced to a stage where it is possible to entertain ambitious and innovative survey solutions that to a large extent may overcome many of the deficiencies historically inherent in 3D seismic.
High density 3D (HD3D) data will meet the first-order challenges to data quality and resolution presented by poor target illumination or wavefield sampling.
HD3D is a robust and efficient solution that can be customized to most exploration and reservoir monitoring challenges. The HD3D acquisition and processing strategies are geophysically transparent, and have been proven worldwide. The methods are particularly applicable for high resolution imaging and 4D monitoring, but also have applications to high-end noise and multiple removal in difficult data areas.
Our Mission
PGS will deliver HD3D data with the best processing quality, the best survey efficiency, the best 4D repeatability, supported by the most dedicated research and development, and provided with the best service. Our goal is to build and defend our position as the leading provider of HD3D data. We add value for our customers and provide a clearer image of the reservoir every time.
The PGS HD3D product is the most geophysically transparent and robust seismic solution available, able to consistently deliver the best results for almost any seismic challenge.
Introduction to HD3D: The 'perfect' seismic survey
A 3D seismic survey must satisfy three important criteria in order to deliver the best final products: - Complete illumination of the target geology. In other words, a high density of seismic energy is uniformly reflected from each subsurface point on the target.
- The reflected seismic wavefield is densely sampled in all directions without aliasing as it encounters the surface. Conventional multi-streamer acquisition delivers coarse sampling of shots and receivers in the ('cross-line') direction orthogonal to shooting.
- Processing accurately reconstructs an image of the subsurface, yielding high-resolution, high-quality products. If criteria one or two are not fully satisfied, then criteria three is doomed to at best only partial success.
Poor target illumination and/or wavefield sampling will result in processing artefacts, poor signal-to-noise ratio, and an inability to extract useful information about the reservoir. In the worst case, data quality and resolution will be so poor that confidence cannot exist in interpretation, exploratory drilling will be cancelled, field development will be incomplete or stalled, and field production is mismanaged. The risk of poorly-acquired seismic data is the wasted cost of seismic acquisition, and the cascading effects upon delayed/ cancelled/ incorrect exploration and production drilling programmes.
The HD3D product is an outstanding example of project synergies between pre-survey planning, acquisition, and processing. For brevity, the following discussion applies to marine multi-streamer HD3D, but HD3D is equally applicable to seafloor and land seismic.
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To view HD3D as simply towing streamers closer together is incorrect. HD3D begins with the acquisition of more traces per square kilometre (higher trace density). Higher trace densities can be achieved in 3D streamer surveys by many methods, including closer streamers, more frequent shot intervals, longer streamers, closer vessel sail lines, streamer overlap shooting, or multi-azimuth shooting. Higher trace densities can be achieved in 3D land surveys by using a larger receiver patch per shot, using more shot and/or receiver lines, closer line spacings, or smaller source and receiver interval. The choice of method used to increase trace density is tailored to the specific survey objectives and challenges, always constrained by the pursuit of uniform target illumination and dense wavefield sampling. HD3D data will then present the optimal platform for high-end processing and imaging success.
Several HD3D case study examples are provided lower on this page.
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UNIFORM TARGET ILLUMINATION
In many 3D survey locations the geology between the surface and the target will result in non-uniform target illumination. Contributing factors can be rugose seafloor, structurally complex overburden (including high velocity layers such as chalks, carbonates, basalts and salt), or rugost target surfaces. In the worst scenario, large 'holes' in target illumination will result in seismic images that completely fail to resolve the target geology. Irregular illumination will always create artefacts in processing and imaging that degrade the clarity, quality and resolution of the final results.
PGS has pioneered the Multi-Azimuth seismic method as a robust solution to poor target illumination during 'conventional' 3D seismic surveys.
Several PGS case experiences demonstrate a significant return on investment (ROI), with accelerated drilling successes, prolonged field lives, and significantly improved data clarity, interpretability, and resolution.
Multi-Azimuth Seismic Multi-Azimuth 3D seismic acquisition is a robust solution to target illumination problems that involves the following:
A 3D streamer survey is acquired in two or more directions over the same survey location. Different shooting directions illuminate different parts of the target. Collectively, the overall target illumination will be more uniform and complete. The datasets are collectively processed to output a single 3D seismic cube. The Multi-Azimuth processing can be 'targeted' to combine azimuths or isolate specific azimuths as appropriate to optimize data quality and resolution at specific locations in the subsurface.
Multi-Azimuth is only cost effective because of the great efficiencies provided by the PGS Ramform vessel technology. |  |
In the most severe cases of poor target illumination, such as sub-salt targets in the Gulf of Mexico, Wide-Azimuth acquisition may be required. Wide-Azimuth Seismic uses additional source vessels to acquire very large cross-line aperture and offsets, complemented by a much larger range of source-receiver azimuths than can be acquired using single-cessel 3D acquisition. The complexities inherent in Wide-Azimuth data will typically necessitate Wave Equation Pre-Stack Depth Migration (WEPSDM) to create optimal seismic images. PGS has a very comprehensive portfolio of WEPSDM technology.
Overall, uniform target illumination is achieved by customizing the shooting template to the specific survey location challenges.
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High resolution, high quality seismic images can only be achieved by acquiring 3D surveys with dense and even sampling in both time and space, complemented of course by uniform target illumination.
Unfortunately, 3D marine streamer acquisition has been historically forced to compromise spatial sampling in the name of efficiency and cost. This compromise translates to noise and degraded resolution when processing the data. A significant component of the seismic 'noise' contaminating 3D images actually arises during processing, as an unfortunate and inescapable artifact from poor 3D spatial sampling. Aliased data create noise during the application of any multi-channel processing operation, notably pre-stack migration. If the cross-line acquisition dimension could be sampled at an equally small interval as the inline dimension, then a much larger frequency bandwidth than typical of standard 3D marine streamer acquisition could be preserved throughout all stages of processing, free of aliasing, free of artifacts, and not necessitating heavy low-pass filtering.
The PGS HD3D acquisition method explicitly addresses the issue of tight 3D spatial sampling. HD3D acquisition offers a data product that is properly sampled, of high quality, and cost efficient.
Every processing algorithm used for 'true 3D' (i.e. a simplifying 2D model assumption is not used) noise or multiple removal makes certain assumptions about the data being recorded without aliasing and with sufficient aperture. Likewise, all pre-stack migration methods, notably the 'wave equation' depth imaging methods, assume that the data is unaliased and meeting the criteria of uniform target illumination and dense wavefield sampling. Dense 3D wavefield sampling will avoid aliased noise and multiple events, and will optimize 3D data regularization schemes. A properly regularized dataset will in turn will present the optimum platform for the successful application of 3D SRME multiple removal and Wave Equation PSDM. HD3D-4D will deliver the best 4D repeatability for reservoir monitoring (see below).
Overall, dense wavefield sampling is achieved by customizing the streamer spread parameters and shot density to the specific survey location challenges.
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Applications to time-lapse 3D (4D): HD3D-4D
HD3D can be customized to be the most robust and transparent platform for time-lapse (4D) reservoir monitoring applications, delivering outstanding survey repeatability and resolution. Several oil companies have consistently demonstrated that dense streamer towing complemented by accurate data regularization can reduce the 4D repeatability error to the minimum theoretical 4D threshold in ideal conditions.
Consequently, the HD3D-4D methodology is the most robust and accurate strategy for acquiring time-lapse 4D seismic data, namely:
Acquire the monitor surveys so that each shot position in the baseline survey is repeated. This approach provides a first-order improvement in the match in source-receiver azimuths between baseline and monitor surveys, and therefore the amplitudes of the monitor surveys will have high repeatability compared to the baseline survey
Deploy additional streamers for a given sail line separation, so that an 'overlap' of streamers is available at each sail line boundary. This surplus of data provides significant benefits for processing, and greatly improves survey efficiency by reducing the requirement for 'infill' lines
Use a HD3D strategy to provide optimal 3D spatial sampling of the seismic wavefield, and each source-receiver azimuth can be closely matched between baseline and monitor surveys
Apply sophisticated data processing to exploit the HD3D + overlap benefits
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PGS believes that the foundation to any seismic experiment is a complete knowledge of all physical phenomena involved:
- The capability must exist to model all aspects of the seismic experiment. PGS achieves this with it's NucleusTM modelling package
- Quality control (QC) of all acquisition and processing steps must be a rigorous discipline, ideally performed in real-time, as events happen. PGS achieves this with the onboard gAS-VIPER QC and recording system on all streamer and seafloor seismic vessels, linked in real-time by satellite telemetry to onshore installations
- QC must be multi-disciplinary, assimilating several seismic attributes and data types, thereby providing the most information possible during any decision-making process. PGS achieves this by using the holoSeisTM visualization system, integrated with the NucleusTM modelling package and the CubeManagerTM processing package, to seamlessly share modelling, operation, and processing data
New developments of the NucleusTM modelling and processing package, the gAS-VIPER onboard recording and QC systems, the holoSeisTM visualization technology, and the suite of technologies contributing to the HD3D data products, are all done in concert. NucleusTM and holoSeisTM are installed on all PGS vessels. Most notably, all PGS technologies are being developed to provide new complements to the PGS HD3D value chain of products.
Six PGS Ramform seismic vessels hold virtually every streamer towing record on Earth, each capable of routinely towing 12 – 16 streamers at 25 – 50 m separation. In comparison, a small minority of competitor vessels can tow 6 – 10 streamers at 50 m streamer separation. The PGS Ramform seismic vessels have demonstrated unmatched towing capabilities, efficiencies, flexibility, along with industry leading HSE performance, in a wide variety of conditions encountered around the world.
Using sophisticated 3D processing technologies, backed by dedicated research and development programs, PGS rapidly delivers a diverse array of HD3D data products and services.
The HD3D data products are designed from the outset to exploit the best technologies that can be offered in pre-survey planning, acquisition, processing, and visualization. Therefore, the fundamental objectives of the seismic method will have been satisfied with the highest quality, and with the greatest efficiency and minimized risks.
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HD3D is a robust and efficient solution that can be customized to most exploration and reservoir monitoring challenges. The HD3D acquisition and processing strategies are geophysically transparent, and have been proven worldwide. The methods are particularly applicable for high resolution imaging and 4D monitoring, but also have applications to high-end noise and multiple removal in difficult data areas. PGS intends to grow and consolidate their HD3D strengths by developing new technologies that further improve efficiencies and that fully exploit the potential value of properly sampled seismic data.
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Some HD3D case-study examples
HD3D applied to yield 150 Hz resolution in an area of complex faulting and stratigraphy:
High resolution displays from HD3D data in the Gulf of Thailand. High trace densities were acquired by towing streamers at 50 meter separation and using short shot interval. Source array design emphasized very high frequency recovery from shallow targets.
The HD3D data were acquired with 6.25 x 12.50 m bin size and 12.5 m dual-source shot interval (614,400 traces/km2). A section across a deviated well demonstrates a good match between the seismic and a synthetic (right). The gamma ray and sonic logs illustrate the ability of the HD3D seismic to resolve the top and base of individual sand bodies. Time slices at 494 ms TWT (upper left) and 958 ms TWT (lower left) of a Similarity cube generated from the HD3D data demonstrate the outstanding resolution of complex channel patterns and en echelon faults.
The new HD3D data significantly revised the structural reservoir models, and all well trajectories were revised. Several wells consequently intersected large commercial oil and gas columns. Data courtesy of Pearl Energy Ltd.
HD3D applied to yield 150 Hz resolution in an area of complex faulting and stratigraphy:
Comparison of Standard 3D data vs. HD3D data in the Gulf of Thailand.
Note the significant improvement in both vertical and spatial resolution with the HD3D data, which delivers frequency content in excess of 150 Hz. Spatial coherency is also excellent for the HD3D data. Data courtesy of Pearl Energy Ltd.
HD3D applied to address poor resolution beneath complex overburden in a deepwater setting:
Comparison of standard 3D vs. HD3D data in the Philippines. High trace densities were acquired by towing 12 streamers at 50 meter separation. Alternating sail lines were used to improve target illumination.
The standard 3D data were acquired with 13.33 x 26.66 m bin size (left: 95,000 traces/km2) vs. HD3D data acquired with 6.25 x 12.5 m bin size (right: 691,000 traces/km2). The new HD3D data has much better frequency content and spatial resolution at all depths.
HD3D applied to address poor resolution of steeply-dipping shallow data in an area characterized by extreme noise problems:
Very shallow time slice at 0.15 seconds two-way time (TWT) of HD3D data in Indonesia. High trace densities were acquired by towing 12 streamers at 62.5 meter separation, and by using 12.5 meter dual-source shot interval.
The resolution of the complex meandering channel systems is outstanding, and signal-to-noise quality is a step improvement over historical seismic data.
HD3D applied to deliver outstanding 4D (Time Lapse) repeatability of source-receiver azimuths between Base and Monitor surveys:
4D source-receiver azimuth difference plots between the 2001 and the 1998 survey (left) and between the 2001 and the 2004 surveys (right). The 1998 survey was shot as a 3D survey, the 2001 as a new ideal base survey using overlap, and the 2004 survey as a HD3D-4D repeating the shot lines of the 2001 acquisition, using 37.5 meter streamer separation, and using overlap. The colour maps display azimuth differences from 0 (blue) to 20 degree (red).
The repeatability of the new HD3D-4D survey is outstanding. Most azimuths are repeated to within two degrees.
HD3D applied to address poor resolution and high drilling risks beneath a fast chalk layer:
Comparison of base Cretaceous (target) amplitude maps for 3D seismic data acquired in one direction (left: 270/90° acquisition) vs. HD3D seismic data composed of three directions (right: 270/90°, 150/330°, and 30/210°). High trace densities were acquired by the use of Multi-Azimuth shooting to combine three different shooting directions.
Both the acquisition footprint and other processing artifacts are greatly decreased on the right (multi-azimuth HD3D acquisition), demonstrating how pre-stack imaging benefits from improved azimuthal sampling and illumination. Resolution is excellent. Two new wells were successfully drilled, more than doubling the recoverable reserves.
HD3D applied to address poor reflectivity and imaging quality:
Comparison of standard 3D vs. new HD3D data in the North Sea. High trace densities were acquired by towing 16 streamers at 50 meter separation and using single-source shooting.
The new HD3D data have significantly better amplitudes and spatial continuity.
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REFERENCES AND PUBLISHED ARTICLES RELATED TO HD3D
HD3D Survey Planning:
Gulf of Thailand HD3D (SEG Conference, 2006)
East Java HD3D (Petromin, 2004)
HD3D Calibration (The Leading Edge, 2004)
HD3D Case Studies:
Gulf of Thailand HD3D (The Leading Edge, 2005)
East Java HD3D case study (PESA News, 2004)
Asia-Pacific HD3D case studies (CSEG Recorder, 2004)
Varg Multi-Azimuth HD3D case study
HD3D Theory and Technical Discussions:
Spatial sampling theory for HD3D (EAGE Research Workshop, 2004)
High frequency content of 3D surveys (First Break, 2004)
Multi-Azimuth Seismic (TechLink Newsletter, 2005)
High Resolution Seismic (TechLink Newsletter, 2005)
HD3D-4D Theory (TechLink Newsletter, 2005)
HD3D-4D Case Studies (First Break, 2005)
Wave Equation PSDM Portfolio (TechLink Newsletter, 2005)
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