Three-field tieback system first of its kind for US Gulf

July 1, 2000
First installation of subsea allocation metering
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The Canyon Express project appears ready to make subsea tieback history and possibly set the stage for the future of this technology. The three operators - Elf, BP Amoco, and Marathon - are nearing the approval for expenditure (AFE) phase of planning, which would mean the project will then be greenlighted for funding. This would make the project a reality.

Canyon Express is an ambitious plan to tie back three subsea fields, developed by three different operators, to Elf's Virgo platform in Vioska Knoll 823 in 1,100 ft water depths in the Gulf of Mexico. The three fields are located in deepwater near the border of Mississippi Canyon and Desoto Canyon, about 120 miles southeast of New Orleans.

Tieback follows wells

The tieback system will follow the field layout with the well locations already in place. This is a departure from the usual scenario of installing a template and drilling all of the wells from one centralized location, or tying infield flowlines back to a central manifold. Two main flowlines, one east and one west, will carry production from a total of nine wells, with plans to add three more.

The outlying field in the development is Marathon's Camden Hills, in Mississippi Canyon Block 348. This subsea development will feature two subsea wells with an option for a third. Production from one Camden Hill well will move down the eastern flowline, and the other down the western line.

Both will carry production to Elf's Aconcagua field in Mississippi Canyon Block 305. This will be a three-well development with an option for a fourth. The combined flow from two of the wells will tie into the western flowline. The third well, and future fourth well, will move down the eastern flowline, both lines will then head into the King's Peak field, operated by BP Amoco.

There the western flowline will pick up production from three wells, one in Mississippi Canyon Block 217, one in Mississippi Canyon Block 173, and one in Mission Canyon Block 133. The eastern flowline will pick up production from a well in Desoto Canyon Block 177. There is an option for a future, second, well in Mission Canyon Block 133 that would also tie into the eastern flowline.

The dual 12-in. flowlines will then travel from about 6,700 ft water depth, up the shelf to Virgo, 46 miles away. From a pipeline design and a pipelay standpoint, this is a difficult journey through difficult terrain. The water depths are greater than 7,000 ft in some areas. Reports indicate that seafloor features include a number of steep slopes that will be difficult to span or support a pipeline.

Flow assurance

There also are a number of flow assurance issues that will be critical to the success of this project. In addition to the normal flow assurance problems presented by deepwater tiebacks, Canyon Express will face the variety of flow rates from these wells, as well as the different chemical compositions of the production from each field. These wells are multi-zone completions, adding another factor to the composition question. It will be important to assure that the stronger wells don't choke off flow volumes from the weaker wells or zones, as well as keeping the entire production stream moving.

Beyond flow assurance, there is the question of what production originated from which field. To solve this, Canyon Express reportedly will pursue the first application of subsea allocation metering in the Gulf of Mexico. Discussions are underway with the MMS about the use of this technology.

Assuming the project clears AFE, reports are Canyon Express could begin production in late 2001 or early 2002.