CGGVeritas is making Wide Azimuth the central focus of its EAGE booth, as the core technology for allowing explorers to meet the new challenges they face worldwide.
In the 1980’s, seismic exploration for oil and gas underwent a revolution with the move from 2D to 3D. We are now seeing the start of a further revolution with the development of wide-azimuth (WAZ) seismic surveying and true 3D processing.
WAZ is by no means a new concept. Land and seabed surveys have, for many years, often been shot with a wide-azimuth geometry, but usually with a sparse design which does not provide adequate sampling. However, the adoption of wide- and multi-azimuth acquisition for marine surveys is a relatively new phenomenon. It started in the Gulf of Mexico when CGGVeritas shot a wide-azimuth survey for BP in order to improve illumination beneath tabular salt. At the same time, multi-azimuth surveys were undertaken offshore Egypt and in the UK’s Southern North Sea.
One of the major findings of those early marine surveys was that several factors were contributing to the improved images from the WAZ data. In addition to the improved illumination, it was found that multiple and noise suppression could be significantly improved by wide- and multi-azimuth shooting geometries. It was clear from these early observations that WAZ had the potential to extend the capabilities of seismic surveying and supersede conventional “3D seismic”, in particular narrow-azimuth marine 3D.
It is now becoming widely recognized that WAZ is not just a specialised tool for deep water, sub-salt exploration but has a much broader appeal. The potential benefits can be seen for a variety of geological settings worldwide. These include providing a clearer image of sub-basalt targets, reservoirs beneath rugose seabeds and deep targets with weak signal strength. With this realisation we are entering a new phase in the development of acquisition and processing techniques to bring WAZ into widespread and routine use. For CGGVeritas this has driven a concerted effort across all of the company’s activities to make WAZ more efficient, effective and refined so that it achieves its full potential.
With WAZ land acquisition where it is relatively easy to achieve a wide-azimuth geometry, the challenge has been to increase source and receiver density to ensure adequate sampling of the 3D wavefield and scattered noise. CGGVeritas has developed V1 high-performance single-vibrator acquisition as part of the solution. Utilising single vibrators provides densely-sampled point-source data free of source array effects and significantly boosts source productivity. This allows shot points to be acquired at 2-4 times the density of conventional acquisition without increasing the survey duration. V1 results have consistently shown a marked improvement in image resolution and quality, making onshore high-density WAZ an attractive option.
Offshore, CGGVeritas has capitalised on its pioneering experience to develop and refine the complex marine operations critical to both the data quality and the economics of wide-azimuth towed streamer surveys. Efficiently coordinating and accurately positioning the streamer and source vessels is crucial in this respect, and to meet these challenges and provide an optimal solution, CGGVeritas has implemented a new generation of sophisticated integrated navigation systems and hydrodynamic modelling.
The company’s seismic fleet, which includes 6 WAZ-dedicated source vessels, is the largest and most flexible in the industry. This provides the resources to undertake extensive wide-azimuth projects, such as the ongoing multi-client data library programme in the Gulf of Mexico.
An important aspect of wide-azimuth surveying is selecting the optimum acquisition parameters, both for cost-effective operations and to ensure data quality meets processing requirements. CGGVeritas has gained extensive expertise in survey design through simulation and modelling studies, collaboration with industry partners and the company’s own field and processing experience. This enables CGGVeritas to provide the optimum combination of illumination, sampling, data quality and speed/cost of acquisition for all situations and all environments.
Finally, the processing and imaging of wide-azimuth data is a crucial part of the story. Wide-azimuth datasets represent a significant challenge for current processing techniques, many of which involve 2D assumptions for the processing of conventional 3D narrow-azimuth data. The notable exceptions in this case are 3D SRME and 3D imaging algorithms.
The transition to dense wide-azimuth surveys with well-sampled 3D gathers allows the adoption of true 3D algorithms and workflows throughout the processing sequence. CGGVeritas has prioritised the development of these WAZ-optimised techniques which include 3D radon de-multiple, wide-azimuth regularization and wide-azimuth tomography for imaging. It is no surprise that these new solutions perform better than their 2D narrow-azimuth equivalents and provide more effective discrimination and attenuation of noise and multiples.
As a result of this true 3D approach to processing and the improved illumination provided by WAZ data, we are seeing spectacular imaging results in a wide range of geological settings. And these benefits extend to reservoir characterization. Inherent within this new approach are the use of 3D WAZ gathers and the preservation of the azimuthal information they contain. This can already be exploited in fracture characterization and presents interesting opportunities for improving seismic inversion workflows.
CGGVeritas has been closely associated with wide-azimuth surveying from the beginning and continues to pioneer its development. The company offers an industry-leading combination of expertise and resources for WAZ survey design, acquisition and processing.
For more information, visit CGGVeritas on booth 7330 or go to www.cggveritas.com/WAZ.
CGGVeritas brings Gabon into Play
As Gabon prepares to issue an international call for participation in a new licencing round CGGVeritas has been selected to support the DGH in promoting this opportunity.
After a prolonged period without a formal offering, the Government of Gabon has responded to the upsurge in exploration interest in Central West Africa by announcing a new Licence Round for 2009. This new Round, due to be launched shortly by the Ministere des Mines, De L'Energie, Du Petrole, Des Hydrocarbures, Des Ressources et de la Promotion Des Energies Nouvelles, is expected to be for the offshore deep water areas, with particular emphasis on the pre-salt targets in the southern area of Gabon. Pre-salt targets are currently creating a considerable amount of interest following the recently announced successes in deep water offshore Brazil. In support of this Licence Round, CGGVeritas has announced a contract with the Direction Generale des Hydrocarbures (DGH) to acquire a new extensive non-exclusive 2D survey in Gabon's highly prospective waters, to be completed in 2008. This move is a further example of the company’s commitment to offering the most recent and technologically advanced data library in the world’s key locations.
Gabon is a country with proven hydrocarbon resources and recent years have seen an increase in licensing and exploration activity, encouraged by sustained high oil prices and growing worldwide demand. Gabon has a well established oil and gas industry and was producing significant amounts of oil in the 1970s with production peaking in 1997 at 371,000 barrels per day. By 2003 this had fallen to less than 290,000 barrels. However, reserves have doubled since 1996 and are now estimated at 2.6 billion barrels, giving significant statistical support to those promoting the region's potential.
Steve Toothill, Chief Geologist for CGGVeritas in Europe, Africa and Middle East (EAME), believes, "There is considerable untapped potential in the salt province of Gabon, especially in the pre-salt section which is currently poorly resolved on seismic. Petroleum systems have been identified in all the coastal basins and rich source rocks are present, the Melinia shale, for example, averaging 5-6% TOC. Sand-rich sediment supply along with both pre- and post-salt deposition provides excellent reservoir potential while an active tectonic history, together with salt movement, are ideal for generating large structural traps with potentially very significant reserves".
Oil and gas exploration in Gabon dates back to the 1920s with the first commercial discovery, the Ozouri field, being made by Elf and brought onstream in 1956. Between then and the late 1990s a large number of discoveries were made both on- and offshore by major and medium-sized oil companies with production having long been established from the pre-salt section onshore (e.g. the Gamba field). Extending its E&P activities into deep waters has the potential to bring a step-change to Gabon's regional hydrocarbon impact. Enormous improvements in exploration, imaging and drilling technology have now made unlocking this frontier an exciting reality. Key to this, CGGVeritas' plan to acquire a comprehensive new 2D survey using a large source array and long steamer cable will address previous imaging problems and, furthermore, pre-stack time and depth migration included in the processing sequence will give significantly improved clarity to explorers.
In support of the international call for participation in the new Licence Round by Gabon's Deputy Energy Minister, Sylvain Momoadjambo, it is expected that a number of open deep-water blocks will be made available, amounting to approximately 110,000 square kilometres of total acreage.
The statistical and geological opportunities offshore Gabon are complemented by its impressive record as a mature and stable environment in which to do business. The fiscal and production terms outlined by the DGH are tailored to the needs of the modern explorer and recognise the importance of both flexibility and stability in defining a productive business environment. Pressure continues to grow for reserve replacement throughout the hydrocarbon sector, whilst new opportunities to effectively meet these demands become fewer - in Gabon, CGGVeritas believes there is the potential for extensive new plays that will provide an important contribution to answering these challenges.
