Advancing Marine Seismic Imaging: From Sensor to Image
Can Our Industry Still Innovate Marine Seismic Acquisition ?
The story of marine seismic is one of constant innovation, facilitated by, and equally frustrated by, dramatic cyclical fluctuations in the oil price. As we emerge from the momentous industrial fire of the recent contraction, we find that certain treasures have been retained and others lost. The structure of the industry has changed dramatically, with companies divesting fleets, committing to multiclient models, removing high capacity vessels, and developing the ocean bottom acquisition sector.
Much attention has been given to the move away from integrated multiclient and vessel-owning companies, with emphasis on who is ‘asset heavy’ or ‘asset light’. There is, however, a challenging and pressing question for the transformed industry that is often neglected: have we preserved our industry’s capability to innovate and can we do it in a new and sustainable way?
Shearwater GeoServices was founded in 2016 through a visionary partnership of GC Rieber Shipping and RASMUSSENGRUPPEN AS to build a new marine seismic company, taking advantage of the opportunities made available during the industry downturn. That transaction brought with it a processing and imaging services and software business but was limited to four vessels until the acquisition of the Schlumberger marine seismic acquisition business last year. As well as the fleet and equipment, with that deal came intellectual property, the industry’s leading marine acquisition research and engineering centre (based in Oslo), and a modern manufacturing facility located in Malaysia. An important part of the industry’s capability to innovate and manufacture leading edge technology was preserved and is now part of a dedicated marine seismic company. The interest is in how that capability can be used to collaborate on the next generation of technology innovation.
The Source of Recent Success in Marine Acquisition Technology
For a long time it was clear that marine source technology had become relatively static, dependent upon the classic dual airgun source – a good reliable, economic and technologically simple approach. Through the downturn the industry has had to reinvent itself to a lower cost position. As larger spreads became possible, the challenge has been how to combine fine sub-surface sampling with large subsurface coverage. One cost-efficient method has been found to be simultaneous source technology, for example Shearwater’s FlexiSource. This has allowed wide streamer spacing, while retaining dense subsurface coverage, based on of multi-source capability and industry acceptance of shot deblending techniques.
The success of simultaneous sources in answering the demand for high quality dense subsurface coverage, at dramatically lower costs per square kilometre, has been striking. Early implementations of this method were developed through industry collaboration and focused on clear technical and economic objectives. The technology was developed rapidly, and at low cost, and is now one of the most common modes of marine acquisition. This collaborative and focused approach, both on technical and cost objectives, led to a transformation of towed streamer acquisition efficiency.
Advances in signal processing have led to further inventions in deblending methods. One of these is the apparition method, which involves the use of modulated codes instead of random time dithers, facilitating improved separation when processing the data. Such technology further pushes the envelope of what is achievable with airgun sources in marine seismic data acquisition, improving both productivity and the quality of the data acquired using existing equipment on the vessels.
A Peaceful Future: The E&P Sound and Marine Life Programme
Airgun impulsive sources have remained as the preferred choice of marine seismic source, although at the same time the potential impact of impulsive sources on marine life remains a discussion point for the industry. In the early part of the decade, with the oil price well over $100 per barrel and the marine seismic industry going strong, several initiatives were launched to ensure sustainability and continuity from a regulatory point of view. These included the formation of the E&P Sound and Marine Life Programme to improve the understanding of the effect of oil and gas exploration and production activity sound on marine life; the joint industry project on developing a non-impulsive marine vibratory source; and the joint initiative to develop a bandwidth-controlled airgun source, now known as eSource.
eSource is a drop-in replacement airgun which reduces the amount of unwanted high frequency energy as this may potentially be harmful to marine life. It does this by reducing the rate at which the air is released from the airgun, resulting in a lower peak that limits the high frequency energy while still preserving the low frequency energy crucial for seismic imaging.
Despite the downturn, the industry has managed to introduce the eSource and successfully deployed it on commercial surveys, while the joint industry marine vibrator project, although not deployed, continues to make progress. Furthermore, recent inventions around the use of marine vibratory sources to improve productivity and reduce acquisition time and costs have generated renewed interest in this technology.
Marine vibratory sources offer significant environmental benefits over airguns, even if the vibrator array emits exactly the same energy spectrum as the corresponding airgun array. In addition to the environmental benefit, marine vibrators allow control of the phase of the emitted waveform. Imaginative use of this freedom to specify the phase, combined with new developments in wavefield reconstruction, could make marine seismic surveying with vibrators dramatically more efficient than it is with airguns. (See GEO ExPro Vol. 15 No. 3 and No. 5 for more on this topic.)
Are You Receiving?
Nearly two decades ago Q technologies became available to the market, firstly with the Qmarine tower streamer system. The innovation that fed into Qmarine stretched for a decade before that and much of that legacy remains embedded in Shearwater’s Oslo technology and innovation centre.
Obtaining good seismic images requires a chain of factors:
- a good acquisition system,
- a good survey geometry
- and good processing algorithms and workflows.
The Qmarine system arose from a programme that aimed to move from conventional seismic acquisition to discrete sensor technology.
The technology included improvements in receiver sensitivity, signal to noise ratio, positioning accuracy, steerable streamers, greater source control and point-receiver acquisition which records traces from individual receivers to provide repeatable, high-quality data.
Later additions included source steering, dynamic spread control to facilitate techniques such as coil shooting, and continuous line acquisition. The system has become the leader in towed streamer 4D with a long, unparalleled reputation for quality acquisition and producing data ready for time-lapse studies.
The next generation technology, Isometrix, evolved from Qmarine and took the measurements to the next level, using very dense hydrophones, and accelerometer sensors to fully measure the seismic wavefield. These new measurements – the crossline and vertical gradients, or variations with distance, of a pressure wavefield – enable true 3D deghosting and the ability to reconstruct the wavefield between the streamers with unprecedented accuracy. This not only enabled geophysicists to achieve broad spatial and temporal bandwidth but also allows data from a seismic shot to be processed as a full 3D wavefield rather than a collection of 2D profiles (as for standard 3D surveys). This presents us with the opportunity to reprocess data with finer spatial sampling as we move from the exploration to appraisal and development stages without the need to revisit the survey area and reshoot. It is often undesirable to return to an area for dense appraisal surveys for cost, environmental or societal reasons; isometric multicomponent surveys make this unnecessary.
Shearwater's Reveal seismic data processing software was created with seismic processors in mind. Many seismic data processing software packages, still in use, have the old punch card computers of the 1970s in their DNA. A software wholly written in the 21st century, built around ease of use, extensibility and flexibility, has enabled a new generation of geophysicists to get to work. Increasingly, turnaround time of the entire seismic project cycle is a key focus for E&Ps. This, coupled with the interdependency of acquisition and processing innovations, makes a modern processing software essential.
A New Collaborative Basis
What is common amongst these innovations in seismic acquisition and processing is that success comes from collaboration between services company and client – the relationship between the two is symbiotic. When companies innovate in isolation there is a risk that the innovation will not meet the market’s need. When clients fail to invest and support innovation in their supply chain it is less likely they will see technology that achieves their goals – either in terms of quality or efficiency. The costs of innovation and risks of failure are significant enough to prevent companies investing in technology projects in isolation. The new generation of innovation will need to be based on shared investment and collaboration.
In answer to the question at the beginning of this article: yes, we have managed to preserve the industry’s capability to innovate. However, if the story of innovation in marine seismic is to continue it will have to be on a new collaborative basis – from sensor to image.