Moving greater seismic capability to the Caspian Sea

Pursuing shear wave seismic

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The seismic survey vessel, Geco Gamma, shooting 3D.
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The Caspian Sea has become an exploration "hot spot," as political climate changes have opened it to international exploration companies. Relative to mature offshore petroleum regions such as the North Sea and Gulf of Mexico, the Caspian, although highly prospective, has relatively sparse seismic coverage. This is not surprising, as it is land-locked, preventing access to the worldwide fleet of seismic vessels, especially the latest generation of highly productive 3D vessels, which are, by necessity, rather large.

The State Oil Company of Azerbaijani Republic (SOCAR) recognized the value of high quality 3D seismic data for finding and producing hydrocarbons. In July 1999, Schlumberger acquired a majority interest in Caspian Geophysical, the leading provider of marine seismic acquisition services in the Caspian Sea. Located in Baku, the company, a joint venture with SOCAR, continues to operate under the trade name of Caspian Geophysical.

Caspian Geophysical already operated the M/V Baki, the most efficient 3D vessel in the Caspian, towing up to three streamers. The new joint-venture company transferred the Geco Gamma, which has eight-streamer capability and is equipped with the latest acquisition technologies, from the North Sea to Caspian Geophysical. The planning of the vessel's transit to the Caspian commenced six months earlier.

The preferred route was via the Don-Volga canal system from the Black Sea, but this presented a challenge. This waterway has a maximum depth considerably less than the draft of the Gamma. In addition, the 18 locks in the canal system were too narrow for the vessel's beam. Major temporary alterations were required to prepare the vessel for her journey to the Caspian.

Vessel transport

The Gamma's first conversion stage was performed in Den Helder, the Netherlands during April 1999. All of the heavy equipment not required during the voyage, such as seismic streamers, airguns and associated umbilicals, were removed. These items filled seventeen 40-ft containers, which were transported to the Caspian by road and sea.

Now much lighter, Gamma made her way to drydock in Istanbul, where prefabricated units were already being prepared to assist her subsequent transit through the canals. Twelve watertight sponsons were welded to each side of the hull. These not only reduced the draft by raising the hull from the water, but also reduced the width at the level required to fit between the narrow lock sides.

At the same time, temporary dismantling of the vessel was performed. The reduction of Gamma's water draft by "lifting" her up had removed the problem under the vessel, but exacerbated another. "Air draft" had to be greatly reduced due to the many fixed low bridges and electric cables that cross the canal.

The top of the vessel, including funnels, masts and the entire wheelhouse superstructure had to be completely removed, along with the booms and protruding portions of the helideck. Every item on the bridge, including the radar, positioning and communications systems, electronics and pneumatics, was taken off. A thorough record was kept of the dismantling process.

All items were photographed, coded and cataloged for the subsequent rebuilding. Lugs, guides, and steel reinforcements were fitted to the helideck and upper deck before the drilling and cutting operations began, to ensure their safe passage and speedy reinstallation at the other end of the journey. Everything was loaded onto a freighter, including the wheelhouse, which was welded to its back deck for the journey to Baku.

Two tugboats from Istanbul started the voyage of the lighter, thinner, and lower Gamma through the Volga-Don canal system. The job was subsequently taken over by two Russian tugboats, which maneuvered the hull through a difficult series of canals and locks. In many instances, there were just centimeters to spare between the vessel and lock walls and bridges.

In mid-1999, the Gamma's hull arrived in Baku, where it was taken to a floating drydock for sponson removal and wheelhouse replacement. The vessel was then taken to a nearby quay where the power and "brains" were refitted, followed by reinstallation of the seismic equipment. The job was likened to a giant 3D jigsaw puzzle, aided by complete and detailed plans.

By September 1999, the vessel was relaunched and renamed Gilavar, having been repainted in the distinctive red coloring of Caspian Geophysical. In October, Gilavar commenced shooting 3D seismic for BP Amoco in the Azerbaijan sector of the Caspian Sea. The vessel is equipped with proprietary in-sea equipment, including monowing technology, that enables very wide streamer separation for efficient 3D acquisition.

Caspian services

The vessel has enabled Caspian Geophysical to offer a full range of seismic services within the Caspian market, including multicomponent (4C), marine, land, and transition zone acquisition. The data processing center in Baku has been upgraded with a Sun 6000E computer and the Seismos processing and data analysis system.

The company will introduce new seismic technologies to the Caspian Sea as exploration moves towards development. In particular, shear wave services are expected to become an important tool during field development to improve the resolution of seismic where mud volcanoes, gas chimneys, and shallow gas cause distorted imaging in conventional seismic data.

Since 1994, Caspian Geophysical has been authorized by SOCAR with exclusive rights to perform non-exclusive 2D seismic data acquisition, processing and licensing. Consequently, Caspian Geophysical has 45,000 kilometers of non-exclusive 2D seismic data available for license, plus packages that include interpretation.

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