Oryx Energy Company has successfully completed the fast track development of three subsea Mississippi Canyon 400 Unit wells in water depths ranging from 1355 feet to 2088 feet. The first well came on line in July 1993, just ten months after project approval, and all three wells were producing within thirteen months of project initiation. Flexible flowlines from each well were tied back to a shallow water platform, resulting in the longest and deepest flexible pipe installation in the Gulf of Mexico to date.
This paper reviews the selection and design of a flexible flowline system for surface connect/layaway from each well and tieback to a host platform covering distances of four to seven miles. The rationale for flowline system selection and actual field experiences of installing flexible pipe with welded connections are discussed. The challenges of coordination and scheduling with the drilling rig, lay barge, and host platform are reviewed. In addition, the inspection and repair of an anchors nagged flexible pipe section is addressed.
The Mississippi Canyon (MC) 400 Unit is located in the Gulf of Mexico approximately one hundred miles southeast of New Orleans, Louisiana (Figure 1). The Unit consists of Blocks 356, 357, 400, 401, 444, and 445. The Operator became 100% owner of these blocks by acquiring leases, drilling to earn rights, and assuming relinquished ownership interests1.
In 1988, two exploratory wells were drilled in Block 401 (MC 401#1 and 401#2) in water depths of 1355 feet and 1697 feet. The wells were temporarily abandoned pending evaluation and eventual formation of the Unit.
In July 1992, preliminary engineering studies were undertaken to evaluate development options for the Unit. Various scenarios were considered, including well counts ranging from two to five. Concurrent with these studies, an evaluation was performed on the construction of a new platform in MC 357 for the tieback and processing of Unit wells. This evaluation was then compared with tieback opportunities at existing platforms in the area; this was an attractive option because early production could be achieved with lower capital requirements. Negotiations with the platform operator at West Delta (WD) 152 eventually led to a lease space agreement for tieback and production of MC 400 Unit wells.
In October 1992, a project plan was approved to develop three subsea wells in the Unit. The two MC 401 wells were to be completed, while a proposed location in MC 445 would be drilled and completed; all three wells would be tied back to the WD 152 platform (Figure 2).
During the preliminary engineering phase, one of the first tasks was to perform an initial screening of various flowline scenarios. The objective of the screening evaluation was to focus engineering effort on cases most likely to be recommended, and avoid parallel effort on unlikely scenarios.
