2.6 The Ultimate Marine Seismic Acquisition Technique? … vether it’s worthwhile goin’ through so much to learn so little, as the
charity-boy said ven he got to the end of the alphabet, is a matter o’ taste. Charles Dickens’ comic novel, The Pickwick Papers
Over the last decade we have experienced several step-changes in marine seismic acquisition technologies. Because acquisition and seismic imaging are inextricably linked, these changes have impacted positively on the seismic image of subsurface geology. But have we found the ultimate acquisition technique? In this section, we speculate on what the future may bring.
In reservoirs within geologically complex settings, the seismic images are still not perfect. Advanced 3D imaging requires huge amounts of data, densely recorded over a large area, to properly reconstruct the structures and stratigraphy at a high resolution. Te optimum seismic data collection technique is yet to be found. Te ultimate survey method may be unattainable, but it should try to satisfy three criteria: full illumination, full noise suppression, and low to moderate cost. Two routes of future development are envisaged. One is to
significantly expand the number of streamers towed behind the vessel, so that the receiver coverage gets much larger, preferably with the smallest receiver intervals possible, both crossline and inline. Another idea which has the potential to revolutionise
seismic acquisition is the development and deployment of autonomous underwater vehicles (AUVs). Tousands of these would float down to the seabed, in order to record seismic data over several periods of weeks, while a shooting vessel traverses the surface.
2.6.1 Autonomous Underwater Vehicles
Over the last 20 years the petroleum industry has witnessed enormous changes, especially within seismic and drilling, many of which were not anticipated. Tere is every reason to believe that technological advances during the next 20 years may well see even greater changes than those that occurred over the previous two decades. We therefore await future developments in seismic acquisition and imaging technology with excitement. If we look back in history, we find that many excellent
ideas have not always surfaced. Many years ago it was proposed that AUVs could be dropped from the back of a vessel one-by-one with an interval of only minutes. Driven by gravity and buoyancy, the AUVs would rapidly glide into a pre-planned grid on the sea bottom. When the survey is complete, they receive a return command, blow their water ballast, and ascend to the surface where they are picked up by the vessel. Unfortunately, this proposal did not get sufficient
support from the industry at the time. Tere are several major hurdles though which AUV technology must pass. Te single most important one will be to increase the life of the battery, while still keeping it small enough to fit into the AUV. But the idea was great, and it has slowly but steadily
83 b
received attention. In 2012 Saudi Aramco teamed up with CGG on a mission to develop autonomous seismic nodes that could largely eliminate the need to use remotely operated vehicles (ROVs) in seafloor seismic acquisition projects. At the EAGE Conference in Vienna in 2016, geophysicists discussed novel strategies for seismic acquisition to accomplish the goal of efficient and high-quality acquired data as well as the possibilities of employing customised robotic solutions for seismic equipment deployment, retrieval, data harvesting, and more. Robotic technology has the potential to seriously disrupt the offshore seismic market.
Figure 2.43: AUVs gilding down to the sea bottom (a) to record seismic data. When the survey is finished, the AUVs return to the mother ship (b).
a
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