Building a tour de force

Andrew McBarnet
Wednesday, August 1, 2012

CGGVeritas marine seismic operations have undergone a major modernisation programme and the introduction of new technology. Andrew McBarnet reviews progress.

Something of a Gallic flourish can be detected about the CGGVeritas multi-client survey in the Keathley Canyon area of the US Gulf of Mexico, announced last month. By Gulf of Mexico standards the full-fold 3D seismic data survey, christened IBALT, is ambitious. Described as the first phase of a multiclient programme to be carried out over the next few years, the survey will cover 221 blocks (5150km2), involve five or six vessels, and feature a new seismic acquisition method.

IBALT is likely to be followed closely by the industry. It has to be an extremely expensive investment which will have to be justified to potential buyers by the quality of the new data from an area which has seen plenty, if less illuminating, seismic coverage in the past. The survey will effectively be showcasing the company's latest top of the line technology. This will allow everyone to assess just how effectively CGGVeritas is meeting the challenge of differentiating its high end marine seismic acquisition and processing from the competition, especially its immediate rivals WesternGeco and Petroleum Geo-Services.

The survey will see the debut of StagSeis. This is intended to be a serious contender in the continuing efforts by the major contractors to come up with wide-azimuth marine seismic acquisition techniques that can deliver improved seismic images of complex geology such as the subsalt structures of the Gulf of Mexico. In this context WesternGeco and PGS are the only other companies offering industry accepted wide-azimuth methods; this is a reflection of having the resources and expertise to mobilise these giant surveys. WesternGeco and the multi-client specialist TGS (using WesternGeco vessels) are currently the only companies shooting multi-client wide-azimuth in the Gulf with PGS expected to return to this arena in 2013.

CGGVeritas CEO Jean-George Malcor has no doubts about the significance of StagSeis. CGGVeritas has always been at the forefront of developing and applying the most advanced seismic technologies in the Gulf of Mexico where we have a very strong multi-client data library. After being the first to use wide-azimuth technology in the Gulf of Mexico five years ago, we are proud to go one step further with the introduction of StagSeis. Its power to illuminate under the salt heralds a new era for subsalt exploration in the most challenging areas and is especially suited to large-scale multi-client surveys such as IBALT.

StagSeis turns out to be a variation on the multi-azimuth techniques which have already been established in the Gulf of Mexico and a few other areas. The most notable difference is that this dual-vessel, longoffset, full-azimuth multi-client survey will use a staggered vessel configuration with the longest offsets to date of up to 20km providing full-azimuth coverage up to 10km. Its most direct challenger is probably the Coil Shooting technique developed by WesternGeco leveraging it Q-Marine acquisition system which offers 14km offset. Coil Shooting is designed to extend conventional multi- and wideazimuth survey capabilities by acquiring marine seismic data using a single vessel sailing in a series of overlapping, continuously linked circles. There is also a multi-vessel Dual-Coil Shooting variation. Going round in circles, so to speak, is said to deliver a greater range of azimuths and offsets than parallel wide-azimuth geometries, and there are no non-productive intervals for line changes. CGGVeritas believes it can provide the desired full-azimuth imaging with the linear approach of StagSeis and the data will be easier to process than Coil Shooting. The company is hoping to prove the point with some fast track data to show at the Society of Exploration Geophysicists meeting in Las Vegas this November.

StagSeis is enabled by the portfolio of emerging technology being developed by the CGGVeritas and its manufacturing equipment subsidiary Sercel. It incorporates BroadSeis, introduced two years ago as the company's challenger in the stakes to produce broadband (a wider range of frequencies) seismic. The importance of recording the full range of frequencies (low as well as high) is now widely regarded as the way forward for high resolution imaging. High fidelity, low frequency data provides deeper penetration for the clear imaging of deep targets, as well as delivering greater stability in inversion. An unexpected and possibly unintended benefit of broadband techniques for oil company clients is that contractors can extend the weather window for operations because the streamers are towed at lower depths than conventional arrays and are therefore less vulnerable to deteriorating sea conditions.

PGS was the first on the scene in 2007 and is now offering its GeoStreamer GS broadband system with a dual streamer and special dual-source. This is said to produce high resolution images free of both source and receiver ghosts, the barrier to recording a wider range of frequencies. The way PGS describes it, the surface of the ocean acts as an almost perfect acoustic mirror, causing unwanted ghost effects inescapable in conventionally recorded seismic data. At the source location for each shot, a timedelayed reflection from the sea surface trails the seismic wavefield travelling directly into the earth from the shot. This penalises both low and high frequency information. Similarly at each receiver location along a streamer, a time-delayed reflection from the sea surface interferes.

Deghosting works: Conventional image (left) and clear image from BroadSeis (right).

The nature of the interference between the primary wavefield and the ghost wavefield varies with the depth of the source (for the source ghost) or the depth of the streamer (for the receiver ghost). Regarding the receiver ghost, for any given streamer depth the amplitude of certain frequencies will be completely cancelled at the recording sensor (notches), and the amplitude of other frequencies will in fact be doubled (peaks). Overall, the peak frequencies move towards lower values as streamer depth increases, and vice-versa. This receiver ghost phenomenum has always been a problem for hydrophone-only streamer surveys, both geophysically and operationally.

In essence, 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 PGS approach to improving bandwidth has put the main emphasis on acquisition strategy, notably the dual streamers towed at different depths and the dual sources, and then to preserve these gains in processing.

With our strengthening operational performance and reinforced technical differentiation, CGGVeritas should continue its journey of growth in 2012. Jean-Georges Malcor

Significant alternative

BroadSeis has proved to be the most significant alternative to the PGS technology achieving plenty of traction in the market with some 42,000km2 of 3D seismic shot or in progress around the world. Of this only one-third has been multi-client, an indication that many oil companies see a competitive advantage in using BroadSeis on an exclusive basis.

The company is sensitive to the charge that its solution relies on the black box arts of data processing, at which the company excels although there is always the potential risk of being too complicated for the client to understand. This is of course a real dilemma for all forwardlooking service companies which, with the exception of some oil companies with the deep pockets to afford the staff and research resources, are now the drivers of new technology.

CGGVeritas wants it to be understood that the BroadSeis solution is in fact the full package for 3D and 4D seismic achieved by a variable depth towing configuration. WesternGeco has very recently followed this approach with the introduction of its ObliQ slant streamer. CGGVeritas says that a key element of its system is the use of the Sentinel solid streamers produced by Sercel and widely used in the industry by most players other than PGS and WesternGeco which have their own proprietary equipment. The solid streamers offer the desirable low frequency and low noise performance as well as the ability to be towed at greater depths than industry norms. New generation electronics also allow the recording of data down to 2Hz, adding an extra one or two octaves to the low frequency end of the spectrum where the challenge is to record signal rather than noise at these frequencies. This combination of low frequency hydrophone recording and reduced noise provided by solid streamers is the basis of the new broadband solution.

One early CGGVeritas paper describes how with this configuration the receiver ghost notch varies along the cable and this notch diversity is exploited by new proprietary deghosting and imaging techniques. The resulting wavelet yields both a high signal-to-noise ratio and maximum bandwidth, thereby providing the clearest images of the subsurface for any target depth. The variability of the streamer depth and shape of the cable, and hence the diversity of the streamer ghost notch, can be tuned for different targets so that the notch diversity and output spectra are optimized for each survey. This cable shape is designed according to the water depth, target depth, and velocity profile of the survey area

CGGVeritas is now adding BroadSource, a synchronized multi-level source combined with specially developed processing algorithms for source deghosting. This is said to provide the same low frequencies as its deep-towed conventional source, but fills the source ghost notch, extending the spectrum in the high frequencies to provide better resolution and clearer images of the subsurface.

According to the company, the most significant improvement observed over BroadSeis data with BroadSource is the removal of the visible source ghost and the increase in high frequencies. Since BroadSeis already provides low frequencies when using a conventional source, there is minimal uplift at low frequencies from a multi-level source, as increased pressure at depth is acting against source power. Sources are already emitting requencies below 3Hz that are being recorded using BroadSeis, the company says. At the same time, with a deep-deployed broadband source there is a boost in the 7-20Hz range, which is useful for subsalt and sub-basalt imaging.

Ocean Sirius: on the way to work.

An integral part of CGGVeritas marine seismic acquisition is the continuing roll out of the Sercel Nautilus device which manages the acoustic positioning, depth control, and automatic steering in one integrated survey unit. Nautilus regularizes the spread automatically to give better 3D coverage, and reportedly provides improved 4D repeatability by combining this with feather-matching, depth control, and more accurate steering to pre-plot positions.

Dovetail has also been introduced to the portfolio of equipment. This is a streamer acquisition solution to counter significant and unpredictable feathering, for example caused by strong currents. It is a combination of fanning the streamers at the end of the array using Nautilus, offset-dependent bin size expansion for steering, and intelligent interpolation during processing.

The major benefit claimed is that it significantly reduces the need for infill (going back over some survey areas where data is inadequate) while remaining within bin fold specifications, thereby reducing survey time and HSE exposure and faster data receipt, with no degradation of data quality. With Dovetail CGGVeritas says that a recent 3D survey off the Bahamas required zero infill.

Surveys like IBALT and the take-up of BroadSeis suggest that CGGVeritas is doing its utmost to emerge from the shadow of WesternGeco and PGS in its marine seismic acquisition operations worldwide.

It has not been an easy road. In the 1990s the company, then plain CGG, was a relatively minor player in the marine seismic acquisition market dominated in those days by Western Atlas, Geco Prakla and a surging PGS. A hint of CGGVeritas ambitions under new chairman Robert Brunck came in 1996 when the company's Sercel subsidiary was beefed up with the purchase of Syntron, a leading marine seismic supplier. In 2001 two modern vessels were acquired from a struggling Norwegian startup company Aker Maritime. Then in 2003 Sercel bought the air gun company Sodera.

Modest fleet expansion continued with the buying of another Norwegian marine seismic investment vehicle Multiwave Geophysical in 1995, but the big move was still to come. It was in 2006, the 75th anniversary of the company's founding by Conrad Schlumberger in 1931, that CGG merged with major competitor Veritas DGC to become CGGVeritas. In the process it finally acquired a fleet large enough to genuinely compete on a global basis. Just for good measure, in 2009 the company outbid Fugro to purchase Wavefield Inseis, another home-grown Norwegian marine geophysical company built largely on investor enthusiasm.

Location map of CGGVeritas IBALT survey.

Largest in the world

CGGVeritas at this point was able to stake its claim to be the largest marine seismic company in the world, but the company's aggressive acquisition policy over a decade saddled its operations with an uncomfortable debt-equity ratio recently ranging between 37% and 39%, which is proving hard to reduce. Specifically on the marine side the company has been obliged to embark on a $1 billion fleet upgrade programme to benefit from the efficiencies of a standardised technology on board all its vessels which on acquisition had varied pedigrees. Last year as part of its fleet renewal strategy, the company added the Oceanic Sirius, its second newbuild using the Ulstein X-Bow design favoured by Polarcus and by WesternGeco through its purchase of Eastern Echo a few years ago.

Today CGGVeritas talks about a modern versatile fleet, maintaining a mix of high-capacity 3D vessels and lower-capacity 3D/2D vessels allowing it to implement specific multi-vessel configurations for wide-azimuth acquisition, undershooting, and other specialized acquisition techniques. There are 15 high capacity 3D and four 3D/2D vessels.

The company is also trying to gear its services to specific regional markets, epitomised by the new agreement with Russian seismic operator Sevmorneftegeofizika (SMNG) to form a strategic alliance intended to address the growing Russian and CIS high-end seismic vessel market and coordinate their complementary capacities worldwide. Previous strategic alliances have been created in Vietnam and Indonesia.

The company has also added a small purpose-built vessel to work the shallow water seismic market in Asia-Pacific.

In the first quarter the challenge facing CGGVeritas was clear. Marine contract revenue was actually down 5% year-onyear and sequentially down 23%, said to be mainly related to the higher rate of 23% of the fleet dedicated to multi-client programmes. However, the company's marine performance plan reached completion at the end of March and the entire fleet is expected to be BroadSeis ready by the end of the year.

Commenting on the first quarter results CEO Jean-Georges Malcor reported significantly increasing backlog confirming the recovery in demand for the high end seismic equipment and services market, with marine prices strengthening year on year. With our strengthening operational performance and reinforced technical differentiation, CGGVeritas should continue its journey of growth in 2012 while benefiting from both the excellent financial performance of Sercel and an expected significant improvement of services, especially in the second half of the year.

The company's second quarter results, due out as this edition of OE went to press, may provide a better indication as to whether the marine modernisation plan is paying off. OE

Categories: North America Geophysics

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