A new generation of solid streamers enables the marine seismic industry to operate in conditions that would overwhelm traditional cables.

The deployment of solid streamers was long a goal of the seismic industry. The advantages of a successful development were many - the streamers, made of a solid, flexible material rather than filled with oil - were expected to improve the efficiency and productivity of marine data acquisition while reducing maintenance and lifecycle costs. An added benefit would be better stability in high sea states where traditional streamer operations must be shut down due to sea noise affecting the data quality. Their buoyancy would make them fully recoverable at sea, avoiding expensive replacement costs.
In 1992, an effort was begun to develop a marine seismic solid streamer. Experience with military solid arrays was combined with seismic contractor requirements, and the first commercial marine seismic streamer, Sentry, was designed, tested and released for manufacture in 1996. The technology set new acoustic performance standards, and end users immediately realized productivity benefits. Figure 1 demonstrates the acoustic performance benefits of solid streamers over traditional liquid-filled streamers.
After the Sentry solid streamer was in the field for a year, an in-depth Parado analysis was completed to identify areas for continuous improvement. This analysis revealed the primary failure mode to be associated with the inner core cable. Several iterations of the core later solved this issue, and the continuous improvement process identified new areas to address.
But seismic contractors still pushed for a faster, better and cheaper solution. It was time to address the next generation of solid streamers. Sentry's successor, Guardian, was conceived with this background. How could a solid streamer be built faster, better and cheaper? Through the reuse of technology.
First, it was determined that the Guardian solid streamer, at a minimum, must equal Sentry in acoustic performance. Second, the reliability of the product needed to be improved. Third, the diameter of the streamer needed to be reduced so that more product could be added to a vessel without a significant upgrade of the back deck. And fourth, the cost had to be reduced. To add to the challenge, several of the objectives were in direct contradiction to each other.
Maintaining the same acoustic performance is a simple thing to do until you throw diameter and cost reduction into the equation. When reducing the diameter of the streamer, the turbulent boundary layer noise increases. And one way to reduce cost is to decrease the number of hydrophones per group. A reduction in hydrophones translates into a reduction in signal-to-noise ratio. Increasing boundary layer noise and decreasing signal-to-noise ratio are undesirable.
The solution was the reuse of core technology. The key to acoustic performance is in the design of the hydrophone carrier. By modifying several design parameters of the hydrophone carrier, a reduction in self-noise was achieved while the diameter of the streamer was reduced. This also allowed for a cost performance trade-off on self-noise vs. the number of hydrophones per group.
Table 1 shows the impact on acoustic performance as a function of diameter reduction and hydrophone count reduction.
If you ask, "What are the most important parameters for marine streamers?" you most likely will hear reliability, reliability, reliability. A major goal of the Guardian development project was to build this streamer with reliability equal to or better than the last revision of the Sentry solid streamer. Five years of field experience taught the developers many things about solid streamer manufacturing and end-user applications. Guardian offered a clean slate to implement reliability improvements. These improvements addressed failure modes, operational handling of the streamer and the constant and consistent buoyancy of the solid streamer.
Reducing the diameter sounds simple enough, but there are two major hurdles to cross. Setting aside the acoustic performance goal, the use of exotic materials to drive down the diameter can easily drive up the cost. Second, solid streamers are delivered in a neutrally buoyant state (with a positive reserve); therefore, any decrease in the volume of buoyancy material must be offset by a reduction in weight, a decrease in the specific density of the buoyancy material or, in Guardian's case, both. This objective was addressed through the use of new materials to achieve a diameter reduction from 64 mm to 58 mm, resulting in an 18% decrease in volume.
Last but not least, a goal was established to reduce cost 15%. The easy approach was to reduce the number of hydrophones. A reduction in the number of hydrophones from 14 to eight phones per 12.5-m group resulted in about a 5% decrease in cost. The next 10% offered a bigger challenge. Manufacturing engineers played a significant role in the development stage, ensuring that the design was compatible with manufacturing processes. New hydrophone assembly processes and buoyancy material installation methods were just two of many modifications implemented by the manufacturing engineers. This investment resulted in a 26% reduction in the labor content of the product.
The Guardian design effort was completed in May 2001, and production started in July. The first Guardian streamer was staged, tested and shipped to the Veritas Searcher in September. In typical seismic fashion, the installation was delayed until December due to the award of another survey prior to heading to the shipyard. The solid streamer was installed on the vessel with no issues, and the system was deployed without a hitch. Sea trials confirmed that the operational performance of the Guardian solid streamer met the design goals of the project.
So from an end user's perspective, how does the Guardian solid streamer development program translate into "faster, better and cheaper?" Immunity to sea noise breakout increases vessel productivity (faster), the improved acoustic performance produces higher quality data (better), and the cost-reduction program has moved solid streamer into the same price range as liquid streamer (cheaper). These goals were achieved through continuous improvement processes and the reuse of technology.
Seismic contractors will continue to recite their "faster, better, cheaper" mantra as long as their clients push for the same improvements. This will result in the Guardian solid streamer's "reuse" as the platform for the next-generation marine seismic data acquisition system.

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