Optimising bandwidth key to detailed subsurface imaging

Paul Boughton

Optimising bandwidth is a key consideration for the numerous new seismic programmes that have just got underway. Sean Ottewell reports.

In what is the largest marine seismic programme ever acquired in the country, CGG has been awarded a contract by a subsidiary of Anadarko Petroleum Corporation and partner Ecopetrol to acquire and process a 5500 km2 3D BroadSeis seismic survey on the Caribbean coast offshore Colombia. This will also be the first proprietary BroadSeis survey to be conducted in the country.

The survey, covering portions of the Col 5, Ura 4, Fuerte Norte, Fuerte Sur and Purple Angel blocks, will be acquired by the CGG Viking (Fig. 1) towing a 10 x 100 x 7050 m spread in a BroadSeis configuration using steerable Sercel Sentinel solid streamers and CGG’s proprietary Dovetail efficient acquisition solution designed to achieve more regular sampling and reduce infill. The survey will start in the third quarter of 2013 and is expected to take four months. The survey data set will be processed in CGG’s Houston data centre.

BroadSeis, CGG’s broadband marine solution, offers market-leading bandwidth, which will enhance imaging in this geologically challenging area known for its heavy faulting and strong multiple mask. BroadSeis will provide improved resolution of shallow targets and better penetration for the imaging of deeper objectives.

Jean-Georges Malcor, ceo CGG, said: “We look forward to working closely with Anadarko to maximise the benefits of BroadSeis for unlocking the potential of Colombia, a country where we have acquired ten surveys since 2006.”

For its part, WesternGeco has begun acquisition of a major multi-client seismic survey offshore Mozambique using the ObliQ sliding-notch broadband acquisition and imaging technique. The technique optimises the recorded bandwidth of the seismic signal enabling more detailed imaging of the subsurface and more reliable extraction of rock properties.

“This seismic survey is optimally located to help oil and gas companies evaluate play potential offshore Mozambique,” said Carel Hooykaas, president, WesternGeco. “The ObliQ technique is expected to provide valuable high-resolution broadband imaging in this geologically complex area where recent discoveries and regional appraisals indicate significant frontier exploration potential.”

The survey is being acquired in collaboration with the National Petroleum Institute of Mozambique (INP) and is fully supported by industry prefunding. It consists of more than 31,000 km of long-offset 2D data and covers the majority of the offshore territory of Mozambique where future licensing rounds are expected.

WesternGeco has also begun acquisition of its Ice Bear 2 multi-client 3D survey in the western Barents Sea using its new IsoMetrix marine isometric seismic technology. The isometric inline and crossline sampling delivered by the IsoMetrix technology will provide high-resolution broadband imaging in this geologically complex area.

“The Ice Bear 2 survey, which is supported by industry prefunding, will improve the understanding of play potential and economic viability for hydrocarbon production in the region,” said Celine Blachere, vice president, Europe, Africa, Russia and Caspian.

Ice Bear 2 lies to the north of the WesternGeco Bjørnøya Ice Bear and West Loppa 3D seismic survey areas where the Havis and Skrugard discoveries were made. Exploration and production activities in the region have increased as a result of these and other discoveries in the area.

Back in Africa, TGS has commenced acquisition of a 2D multi-client survey offshore Sierra Leone. The survey, SL13, will add 9191 km of new 2D data to infill the existing 5784 km of 2D data acquired in 2001. Upon completion of the SL13 survey, TGS will have approximately 15,000 km of contiguous 2D multi-client data and 6268 km2 of 3D data offshore Sierra Leone.

The seismic data is being acquired by the M/V Geo Arctic. Data processing will be performed by TGS and be available to clients in Q4 2013.

In a busy time for the company, TGS is also carrying out two 3D multi-client surveys in the Norwegian Barents Sea; Finnmark Platform 2013 (FP13) covering 3500 km2 and the Hoop to Fingerdjupet 2013 (HF13) covering 8600 km2.

Both 3D seismic surveys cover areas of complex geology and are designed to address specific customer imaging requirements. Data from both surveys will be processed utilising TGS’ proven Clari-FiTM broadband processing technology. The HF13 survey will also tie-in TGS’ successful Hoop 3D in the east.

The FP 13 survey is currently being acquired by the M/V Geo Barents towing eight streamers. The HF13 survey is scheduled to commence soon and will be acquired by the M/V Oceanic Challenger with 12 streamers. Initial data from both surveys will be available to clients during Q3 2013.

In another development, TGS has commenced acquisition of a 3D multi-client survey, Sunfish, which covers up to 7800 km2 of highly prospective acreage in the Harper Basin, offshore Liberia.

The South Atlantic and Russia

FOGL, the oil and gas exploration company focused on its extensive licence areas to the South and East of the Falkland Islands, has released an update on its ongoing 3D seismic operations in the region.

The PGS M/V Ramform Sterling has completed a 3D seismic survey over the mid Cretaceous Diomedia fan complex within the southern area licences. A total of 5235 km2 of full fold seismic data have been acquired. The survey was operated by Noble Energy on behalf of a joint venture which includes Edison International and FOGL.

The data will now be processed by PGS and a fast track product will be available for interpretation in approximately four months. It is anticipated that the final processed data will be available in the fourth quarter of 2013. The fast track data will be used to commence prospect mapping and well planning. Initial test lines from the survey indicate excellent data quality and imaging of the Cretaceous target interval.

A second 3D seismic survey, also using the Ramform Sterling, has just commenced. This survey will cover a minimum area of 1000 km2 and will target a number of prospects and leads in FOGL's southern licence area, immediately to the west and north-west of Borders and Southern's Darwin gas-condensate discovery. A further announcement regarding this survey will be made once acquisition is completed.

In a third development, the joint venture is also currently reviewing tender offers with respect to a third 3D seismic survey to be acquired in the northern licence area in the fourth quarter of 2013.

In Russia, Gazprom Neft and GEOTECH Holding have signed a three-year agreement jointly to carry out seismic exploration. The total area covered by the contract could be as large as 5000 km2 by the 2015. The work will be performed using 3D technology, as well as the innovative UniQ high density seismic data acquisition technology which will be used in Russia for the first time.

The high definition seismic exploration will cover some potentially productive deposits belonging to Gazprom Neft, including: the Ignyalinsk, Vakunaysk and Tympuchikansk sections of the Chonsky project in Eastern Siberia; the Gazpromneft-Noyabrskneftegaz sections in the Yamalo-Nenets autonomous district; and both the West-Chatylkinsk and Valyntoysk sections. Follow-up exploration of the West-Luginets section, where Gazpromneft-East  initiated development of the Nizhne-Luginets deposit three years ago, is also planned.

In technology news, SIGMA3 Integrated Reservoir Solutions has released Seismic StudioT v1.7, offering performance and data handling enhancements for large seismic surveys from complex geologic environments.

New, user-requested functionality enhancements also are incorporated in this release, including more efficient velocity and tomography processes and a more intuitive user interface, the company said.

“Robust seismic processing of land and OBC (ocean-bottom cable) data requires accurate geometry and statics solutions. With today’s seismic data sets measuring in the terabytes of digital data, the data handling task for front end processing is becoming more and more challenging,” said Alan R Huffman, chief technology officer of SIGMA3. “This new release of Seismic Studio will facilitate efficient handling and analysis of today’s very large data sets that will improve turnaround time and enhance the overall processing workflows for complex geologic environments.”

Two new generation Ramform series vessels ordered

Mitsubishi Heavy Industries (MHI) has received an order for two vessels capable of 3D seismic data acquisition for sea bottom resource exploration from Petroleum Geo-Services (PGS), a leading company in marine seismic and reservoir data acquisition, processing and analysis/interpretation services in Norway.

The order for the two vessels was placed when PGS exercised an option it had in place following an earlier order for two other similar vessels. The two newly ordered vessels are scheduled for delivery in the first and second half, respectively, of 2015. With this latest order, MHI will build a total of four vessels to support PGS's deep water natural prospecting services.

The vessels ordered are the Ramform Titan class, the newest generation in the Ramform series featuring today's most advanced 3D seismic data acquisition/analysis capability. The 104 metre long vessel has a very wide breadth of 70 metres. For quiet operation, the vessel adopts diesel electric for the main propulsion system. It is capable of receiving supplies at sea to enable a long-term exploration over an expansive area.

The Ramform vessel tows multiple streamer cables from the stern. The cables contain sensors which detect echoes of sound waves emitted from sound sources and bounced back from the sea bottom and stratum boundaries. The detected echoes are used for 3D seismic analysis. The Ramform Titan-class vessels ordered by PGS have a wider stern compared with existing vessels; this feature permits deployment of a greater number of streamer cables - up to 24 lines - enabling exploration of a wider area at one time.

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