Shell to Start Seismic Operations in Libya

Shell EP Libya GmbH, together with its partner the National Oil Corporation of the Great Socialist People's Libyan Arab Jamahiriya (NOC) started seismic operations in the onshore Sirte Basin this week. The work follows a tender process and will result in one of the largest seismic programmes for the Shell Group in 2006.

Contracts have been awarded for the deployment of four seismic crews with a phased start up between November 2005 and March 2006. Seismic acquisition will be supplemented with a large aeromagnetic campaign, also planned to start in this month.

By the time the work is complete in mid 2007, Shell will have acquired nearly 8000 km of 2D and 3300 square km of 3D seismic, as well as 68,000 km of aeromagnetic data. Drilling is planned to start in the second half of 2007.

Shell's Executive Vice President Exploration, Matthias Bichsel, said: "The large work scope and aggressive pace of acquisition demonstrate Shell's commitment and enthusiasm for its exploration programme in Libya's northern Sirte Basin. This marks the start of activities on the ground for this major integrated gas exploration and production project and the beginning of a long-term strategic partnership with Libya in the development of a state-of-the-art LNG industry."

The first seismic crew, operated by BGP International Libya Inc, has established its base camp and started operations in the field. The second crew from PGS Exploration Ltd is due to start in late November, followed by crews from WesternGeco Overseas Inc in December and Veritas DGC Ltd in February 2006. The large aeromagnetic surveying campaign, awarded to Worley Parsons Geo-Physical Exploration and local partner, the National Bureau for Research and Development, is due to start operations from the Marsa El Brega airport in late November.

In May 2005, Shell signed an agreement to work together with NOC to develop a modern LNG industry, and explore for and develop gas. The project incorporates exploration in five blocks comprising a total area of some 20,000 sq. km and rejuvenation and upgrade of the existing Marsa El Brega LNG plant, which is operated by the Sirte Oil Company.

Surveying Techniques for Oil and Gas Deposits:

Aeromagnetic surveying - This surveying technique uses special instruments - called magnometers - mounted in an aircraft, which measure variations in the earth's magnetic field, and enables a wide area to be quickly surveyed from the air. Different rock compositions and structures cause slight variations in the magnetic field, which allows the density of rocks beneath the surface to be calculated. This enables the type of porous rocks required for potential oil and gas reservoirs to be identified for further investigation using seismic surveying techniques.

Seismic surveying - This is the method used to more accurately analyse the composition of the subsurface rock layers to locate potential gas (and oil) bearing structures. Sound is projected down through the subsurface rock layers by using an appropriate noise source - such as an airgun (used mainly offshore), or striking the ground with a large pad, or by using small explosive charges set a few metres below the surface. The sound is reflected back from the various layers of rock to sensors or receivers, and the differences in noise travel time, frequency and sound level can be used to map the composition of the subsurface rocks, and the various depths at which the rock layers and other structures are located. However, final proof of whether a potential structure actually contains gas or oil can only be obtained by drilling an exploration well.

2D seismic - This is two-dimensional seismic surveying, and produces a single vertical "snapshot" of the subsurface rock layers along a horizontal line. The seismic lines are shot at significant distances apart - i.e. 5 kilometres - and are used to quickly gather subsurface structural data across a wide area to locate possible gas (or oil) bearing structures.

3D seismic - This is three-dimensional seismic surveying, which utilises similar sound sources, and is used in the second stage of seismic surveying. It produces a much more detailed vertical, horizontal and lateral "picture" of the subsurface rock layers and composition. It is used to obtain a complete three-dimensional view of potential gas (or oil) bearing structures, and enables a map to be built up of the thickness, length and width of potential gas and oil reservoir rocks. 3D seismic uses a much smaller grid - as little as 25 metres between shot lines - and is used to more accurately map potential structures identified by 2D seismic.

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Posted 23/11/05

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