On board the broadband bandwagon

Andrew McBarnet
Tuesday, May 1, 2012

Seismic surveys with increased bandwidth are the way forward. There will be some winners and losers, reports Andrew McBarnet.

Talk about the boss ignoring the spoiler alert. In the last few weeks new Schlumberger CEO Paal Kibsgaard has been letting the cat out of the bag regarding WesternGeco’s next generation seismic streamer. Launch of the technology, claimed to be a major advance, had been trailed as the showpiece of the company’s presentations in early June at the upcoming annual meeting of the European Association of Geoscientists & Engineers being held in Copenhagen.

Now about the only suspense left is what the streamer will be called. Currently the industry is referring to it as Nessie-6 after previous streamers developed by WesternGeco, but you can be sure that the commercial product name will have a Q in it as part of the Q-Marine acquisition portfolio.

None of which is to say that there is nothing to be excited about. Kibsgaard explained the implications pretty well in one or two recent presentations he has given. Up to now WesternGeco’s main differentiator has been based on Q-Marine. Uniquely among seismic contractors its streamer measures singlecomponent, single-sensor data whereas competitors record groups of receivers. The new-generation streamer is designed to acquire four-component single-sensor data. In principle this enables the measurement of the reflected wave in much more detail, including its direction.

Streamer sensors measure the waves that bounce back from the subsurface. To get a complete 3D picture of the subsurface would require streamers to be towed unrealistically close to each other. As a result streamers are towed anywhere between 50m and 140m apart, with each one giving a 2D slice of the subsurface. The 3D cube is then created by interpolating between these 2D slices, but in reality only providing a 2.5D representation of the subsurface.

Kibsgaard told delegates at the 40th Annual Howard Weil Energy Conference in March that using a novel multi-component sensor would allow the entire wavefield to be calculated at every point between the streamers, resulting in a full 3D picture of the subsurface. He said WesternGeco’s 12-streamer vessels will be able to produce the equivalent of 30, 50, or 60 streamers’ worth of data, but without the capex or the operational complexity. He called the advance ‘a massive step forward for marine seismic, similar to the medical industry moving from a 2D X-ray to a full 3D CAT scan’. It would, he said, further strengthen the company’s technology lead in marine seismic. It remains to be seen whether this is actually a game-changer. Any geophysicist you talk to agrees that a streamer capable of capturing multi-component data will be a remarkable achievement in terms of the resolution of images that company clients can expect from seismic surveys. It also has implications for reservoir characterisation strategies, especially the use of ocean bottom cable and nodes. Up to now this has been the only available method for acquiring true multi-component data, recording both P and S waves by deploying hydrophones and geophones (attached to the seabed).

The first question is obviously the simple one: does this thing work? It is unlikely that a company of Schlumberger’s repute would go public unless they were fairly confident that the new streamer can be commercialised. However, nearly a decade ago WesternGeco launched Q-Marine. On that occasion the first flush of announcements was followed by radio silence for two years or so, ie it took that time before it was genuinely up and running and the company could come up with case studies portraying the benefits of the new technology. Ironically, it was the steerable streamer aspect of Q-Marine that really caught the attention and was rapidly imitated by the competitors, and not the more remarkable technology achievement of single sensor recording.

Huge investment

It is reasonable to assume that WesternGeco won’t be bursting onto the scene with the new streamers any time soon. There is a huge investment involved when such a key change is made to a fleet’s capability. For example, its competitor Petroleum Geo-Service (PGS) took several years to bring its GeoStreamer technology from first public mention to being more or less standard equipment on its vessels. An interesting question is what kind of streamer WesternGeco will order for its batch of new vessels to replace ageing inventory rumoured to be in the pipeline.

What development of the multi-component streamer does tell us is that the race for what may loosely be called broadband or better marine acquisition capability is hotting up. Being able to record the full range of frequencies (low as well as high) is generally accepted as the key to high resolution imaging. High fidelity, low frequency data provides deeper penetration for the clear imaging of deep targets, as well as providing greater stability in inversion. Recording multi-component data with towed streamers would just be the icing on the cake.

The Big Three (WesternGeco, PGS, and CGGVeritas) sense that they can put some distance between themselves and the rest of the field. They believe that they are the only ones with the substantial R&D resources able to develop serious broadband services, and these will not be for sharing with the other competitors. The prize is significant because a growing segment of oil company clients around the world appreciate the dramatic improvement in imaging of the subsurface possible, especially in complex geological settings. Such companies are persuaded that broadband is the way ahead and are increasingly making broadband a requirement in their tenders.

In this context WesternGeco looks to have been caught on the hop. Whatever the merits of the technology, PGS with GeoStreamerGS and CGGVeritas with BroadSeis are out in the market with brand-name broadband solutions. PGS got there first and is already planning a second generation GeoStreamer although it is unclear whether this will be ready for its two enormous Ramform Titan class vessels currently under construction and, when built, destined to dwarf the competition.

Regarding broadband, PGS was persuaded that the accuracy and resolution in reservoir characterization, and success of drilling the optimal targets, would be improved by having extended low frequency seismic data and less well information (a priori information) included in the process. PGS provides this extended low frequency content with the ‘ghost-free’ streamer data that the dual-sensor, dual source GeoStreamerGS offers. The combination of the two sensors enables an effective removal of the seasurface ghost by wavefield separation, allowing the capture of the full bandwidth of the upcoming wavefield. The simultaneous extension of both low and high frequencies has a major positive impact on seismic reservoir characterization. Low frequencies provide better depth penetration of the seismic signal, which is extremely valuable for imaging in complex geological settings, such as sub-salt, basalt or even dense carbonate. Also seismic inversion, ie relating seismic to rock properties, should be greatly improved.

CGGVeritas works on the same principle that broader bandwidths produce sharper wavelets, therefore both low and high frequencies are required for high resolution imaging of important shallow features such as thin beds and small sedimentary traps. The company says it takes a two-sided approach to improving bandwidth: ‘We can actively generate a wider range of frequencies with our seismic sources and we can do our utmost to preserve them during recording and processing.’ With BroadSeis more of the broadband effect is achieved in the processing. It has not developed a dual sensor like PGS. Its source of supply for such technology would obviously be its subsidiary Sercel, which to date has shown no obvious enthusiasm to go down this route, but this could change if the parent and out-of-house customers put pressure on.

Up until last month WesternGeco’s specific broadband offering was DISCover, at one time referred to as Over/Under. Designing tow-depths for conventional towed-streamer surveys requires a compromise to optimise bandwidth and signal/noise for a specific target depth or two-way traveltime, often at the expense of other shallower or deeper objectives. Data recorded by streamers towed at different depths as in DISCover can avoid this compromise, delivering the high-frequency characteristics of conventional shallow-towed configurations and at the same time the low-frequency characteristics of deep-towed data. Further enhancements to data quality can be derived from deploying a multi-layered source array, according to the company.

In-house rival

For whatever reason, possibly market acceptance, operational issues with the towing of two streamers at different depths, or simply unsatisfactory results, DISCover now has an in-house rival.

It is not the evolving multi-component streamer!

Last month WesternGeco launched the ObliQ sliding-notch broadband acquisition and imaging technique. It is said to optimise the recorded bandwidth of the seismic signal by combining slant-streamer acquisition with a proprietary deghosting methodology and a newly developed broadband seismic source.

So instead of two streamers at different depths, one streamer is towed at a slant. WesternGeco states that the optimum depth of the streamer is generally defined in the marine seismic survey design and every attempt is made to maintain a constant depth. However, the compromises in selecting a tow depth are well known: in the shallower depths, the streamer is prone to ambient noise, while at deeper tow, a ghost notch is inserted into the useful bandwidth of the seismic signal.

The company’s ObliQ solution is to make the cable depth variable increasing from the near offset to the farthest offset. The minimum and maximum cable depths can be determined in the survey design and selected to optimise the recorded bandwidth to meet the geophysical objectives of the survey. In surveys that use the ObliQ technique, streamer depths can range from 5m to 50m, which is a wider selection of depths than is available in conventional acquisition.

According to WesternGeco, the ObliQ technique de-ghosts data acquired with a variable streamer depth. This is achieved with a de-ghosting workflow that improves the low-frequency information while maintaining the high-frequency content. The process minimizes the effect of the receiver ghosts on the prestack data making it possible to re-datum the cable to a constant depth and process the now deghosted data in a conventional fashion.

Enabled by the Q-Marine point-receiver marine seismic system, the ObliQ technique is intended for all types of surveys, from linear sail-line acquisition geometries including narrow-azimuth (NAZ) and wide-azimuth (WAZ), to curved sail-line acquisition geometries including the company’s proprietary Coil Shooting single-vessel and Dual Coil multi-vessel full-azimuth acquisitions. The combination of broad bandwidth with the Dual Coil full-azimuth, long-offset acquisition is particularly advantageous for imaging below complex structures such as subsalt and sub basalt, the company says.

In the broadband stakes, WesternGeco now has a new brand to sell, which will of course have to prove itself. That would seem to give PGS and CGGVeritas an edge on technology and possibly commercially, but all sorts of other considerations come into play when it gets down to the tendering process, like price, vessel availability, survey requirements, etc.

There is certainly every reason to believe that the Big Three will continue to at least hold market share and very possibly do better because of the broadband dimension.

Wriggle room

It could be argued that the other main seismic players like Polarcus, Fugro- Geoteam and Dolphin look a little exposed although the definition of broadband does leave some wriggle room. Polarcus, for example, talks about ‘right size, right plan, right design’. This rather ingeniously implies broadband in the sense the company can tailor the parameters of the survey to cover the targets requested by the client, but basically not all depths at the same time. The company’s main selling point is its fleet of eight new vessels planned and put into operation in just four years. Its only serious vulnerability is the level of debt should we see an unexpected dip in the market.

Fugro’s presentations are somewhat vague on the subject of broadband, which may suggest a deeper strategy malaise. The company recently renewed for six years its contract for the Hugin Explorer, the vessel that came with the ocean bottom cable (OBC) seismic business it bought from SeaBird Exploration, but OBC projects seem thin on the ground. In its fleet, which is now smaller than Polarcus, the company has its four C-Class vessels built a few years ago but they have no exceptional equipment for broadband. It may be that Fugro is thinking of developing a new cable with its recent acquisition JDR Cable, but that it is probably fanciful thinking.

Dolphin Geophysical may not yet be broadband capable but the company has shown intent of becoming a full service marine seismic contractor. Last month it bought Houston-based Open Geophysical (OGI), which develops and sells seismic processing software and has an existing client base including both major oil companies and seismic contractors. Recently developed software is already being used on the Dolphin’s Polar Duchess and in Dolphin’s new processing centre established in London. It is not hard to envisage a processing-based broadband solution emerging from the new set-up.

Even if broadband is a real differentiator as its proponents suggest, market conditions may confuse the issue in the short term. Vessel demand is currently more than steady, and prices have ticked up by as much as 10%. That means that there will soon be plenty of companies out there that just want some seismic shot as soon as possible while the exploration budget is available.

For those customers the broadband option will not be a factor. OE

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