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Mensa Subsea Development
Mensa is located in approximately 5,300 feet of water, 140 miles southeast of New Orleans and encompasses Mississippi Canyon Blocks 686, 687 and 730. Shell acquired Mississippi Canyon Blocks 730 and 731 in OCS Lease Sale 98 in May 1985. In June 1993, Shell traded with Pennzoil, Amoco and Arco for Mississippi Canyon Blocks 686 and 687. Mensa is 100% Shell owned.
The discovery well was drilled in 1987 by Transocean’s drillship, Discoverer Seven Seas. One delineation well was drilled. The target reserves are in the Upper Miocene "I" sand, at a depth of approximately 15,500 feet. The average net thickness is approximately 100 feet.
Development
Mensa initially consisted of three wells connected via individual 6-inch infield flowlines to a subsea manifold five miles away, which is then tied back to a shallow water platform at West Delta 143 via a 63-mile 12-inch flowline. This 68-mile tieback formerly held the record for the longest in the world. The previous tieback record was 30 miles for the Troll Oseberg Gas Injection project in the Norwegian sector of the North Sea.
Shell then developed and began production from Mensa's fourth well in 2003. Transocean's Marianas drilled Mensa 4. The Mensa 4 well produces through a 4 mile long 8-inch infield flowline to the subsea manifold.
The Mensa A-5 was drilled in 2007 (drilled by the Noble Jim Thompson) and the A-6 in 2010 (drilled by the Transocean Nautilus). The A-5 well shares an infield flowline with the A-3 well, and A-6 shares an infield flowline with the A-1 well. These wells draw from the same sands as the first three wells.
| Timeline for Installation of the major components | |
|---|---|
| January 1997 | Electrical distribution structure |
| March 1997 | Subsea manifold/template |
| February/March 1997 | All hydraulic and electrical umbilicals and the three infield 6-inch flowlines |
| May 1997 | 12-inch flowline from the manifold to West Delta 143 |
| July 1997 | First tree |
| Fall 1998 | Tree installation continued as the final well was drilled and completed. Jumpers were installed following each tree installation. |
| 1Q 2003 | Mensa 4 tree and 4 mi flowline to central manifold installed, and well began production |
| July 2007 | Mensa 5 begins production through new expansion sled to the A-3 infield flowline. |
| December 2010 | Mensa 6 begins production through new expansion sled to the A-1 infield flowline. |
Production of Mensa's initial three-well system began in July 1997. Production began from the Mensa 4 in March 2003, Mensa 5 in July 2007 and Mensa 6 in December 2010. The additional development wells were needed to replace wells that either mechanically failed or watered out. Currently, the A-1, A-3 and A-4 wells are either partially or fully abandoned. The field has produced 844 BCF to through May 2011.
