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A Resolution Revolution – Multi-streamer High Resolution Seismic Accurately Positioned for Take-off

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Technology is pervasive in every business, and the exploration and production segment of the oil and gas industry is certainly no exception. Indeed, it is technology that drives our industry, from seemingly mundane things such as data storage or logistics to brutally necessary activities such as drilling and production. It is not incorrect to state that improvements and changes in technologies are key cogs in the starkly vivid business cycles that we experience. Safer, better, clearer and more efficient methods and equipment continually contribute to our ability to take a new look at old concepts, ideas, hardware, software, equipment – and the reservoirs and geology that we exploit with those myriad tools. We are on the cusp of one of these technology changes, and it is nothing short oftruly revolutionary.

For Those About To Rock
It all starts – or more accurately ‘started’ – with the rock. The precious hydrocarbon that we pursue is well guarded by stout protectors who have more than a few tricks in their bag to disguise or hide their treasures. Geology matters and history has shown us that the more knowledge we gained about geology, the more we understood just how much it mattered. Solving the geophysical jigsaw that the ‘rockers’ put before us has allowed us to understand not only where the hydrocarbons are but what their make-up and nature might be, and what tools and technologies would be best for extracting them. The better understanding of the hazards that surround oil and gas extraction is a component of this knowledge, and its importance cannot be overstated. Remaining true to the exponential nature of technological advance, as we march forward in our industry’s pursuit, we continue to learn more in shorter periods of time. The past 15 years have been truly startling in terms of how far our understanding of subsurface geology has advanced, owing so much to quantum leaps in the equipment and methods used to image this geology.

Sonic Boom
Imaging subsurface geology has been, and remains, the dominion of reflection seismic surveying. Our tireless march forward has taken us from being able to maybe define potential hydrocarbon hidey-holes, to being able to not only identify them, but also (and perhaps more importantly) to pinpoint where they are not. For the most part, it is low-frequency ‘deep’ seismic that has filled this role, and rightly so. The methods and equipment for doing this allow the accurate imaging of geological structures that exist thousands of feet below the earth’s surface. We can literally put on some virtual reality headsets and walk through the geology and reservoirs that have been imaged. The accuracy and precision with which the measurement and rendering of these structures is done can only be described as truly amazing. Yet the model is incomplete, and therefore, to a degree, untrue. In other words, ‘Houston, we have a problem’.

High Fidelity
The problem is a shallow one, literally. In the industry’s rush to better understand and image the full depth of the reservoir geology, we simply and intentionally disregarded, to a fairly high degree, the near surface geology. Certainly, we know that the initial objective matters as far as knowing where potential hazards may be. We do not want to plant the leg of a jackup or the tip of a drill bit in the wrong place – understanding that punching into a shallow gas pocket has less than desirable consequences.

Heretofore, we have used technology comprised of a small, high-frequency energy source and a single seismic streamer of about 48 channels, towed on a grid and typically used in conjunction with analogue acquisition via a subbottom profiler or sidescan sonar. While the sites being investigated with this methodology are small in terms of geography, it is still an inefficient endeavour in terms of use and subsurface imaging.

Enters the revolution. A core business of our company NCS SubSea is navigation and positioning for the marine seismic industry, and we have long recognised that there is room for improvement in the methods and technologies used in high-resolution seismic imaging, specifically with respect to improving the size and resolution of the footprint. Seeing that a new technology had been created that allowed true 3D acquisition of high-resolution seismic data, we investigated it and learned that it was indeed a game changer, with one slight problem – there was no true realtime navigation and positioning solution.

Well Adjusted
The technology revolution was brought on by P-Cable™, a concept developed by P-Cable 3D Seismic AS of Norway using industry and academic support. The concept was simple, yet effective: a powered tow cable running between two towed diverters, with take-outs at predefined intervals that allowed streamers to be plugged into the powered tow cable. The result was a very compact system that couldbe easily shipped, required a smaller vessel to tow and handle, and could be configured in 20+ streamers between 25 and 100 m in length. It featured cross-cable separation of 12.5 or 6.125 m and in-line receiver spacing of the same lengths. There now existed, finally, a true 3D footprint for high-resolution seismic imaging. Geometrics partnered with P-Cable to build and sell/lease the system under license. There were several academic surveys of the technology, with good results, until the navigation and positioningwas considered. The model was to use first breaks and assume symmetry across the heads of, and between, the streamers.

Observing the equipment during towing clearly showed that this was not the case. Using the post-line first breaks method did produce positions for the receivers, but there was far too much inaccuracy and inefficiency to attract the commercial sector. NCS SubSea, realising the full potential of this technology, partnered with Geometrics to supply a complete navigation and positioning solution, providing input to their engineering staff concerning necessary hardware changes and setting about the job of developing a fully integrated navigation system. The aim was to provide a realtime least squares adjusted network that could accurately position the shape of the towed power cable and the streamers. The result is NavPoint Trawler™, the NCS SubSea patented INS for the P-Cable technology, which provides the very high level of positioning accuracy and immediacy that the commercial sector demands.

A key component of the P-Cable system is its highly efficient operational footprint. The entire in-water spread can be deployed in approximately one hour and recovered just as quickly. Smaller vessels can be used, which adds to the lower cost of acquisition. This streamlined configuration required a fresh canvas in terms of considering how to position the cross-cable and streamers. Typically available hardware would not be feasible, as having externally fixated devices would be terminally disruptive to the deployment and recovery process. Geometrics and NCS SubSea sought new vision and thinking, and brought in Sparton to provide a new type of three-axis compass for use in the marine seismic industry. Sparton possesses a distinguished history in providing sophisticated technology solutions to governmental and technical sectors, and the company brought a fresh enthusiasm to this challenge. Using micro electro-mechanical systems (MEMS) technology, Sparton provided a digital three-axis compass that is ultra-compact and robust, resulting in excellent outcomes during testing and commercial deployment.

Realtime Reality
The P-Cable technology coupled with NavPoint Trawler has recently been used on a successful project in North America, succeeding in acquiring a significant programme ahead of schedule and without incident. The market now has a completely new way in which to image shallow geology, allowing for a significantly increased footprint, with much better resolution and accuracy than ever before. This opens the door to a higher level of understanding and confidence with respect to gas hydrates; chimney formations; reservoir monitoring (fluid migration); shallow water flows; and fault investigations. The ability to have extremely high quality, large and efficient datasets for near surface geology is now a reality. Position yourself for the revolution in high resolution!