Offshore drilling demands products and technologies that can be used cost-efficiently in harsh environments, particularly as development remains elusive due to high breakeven prices and increased risk. National Oilwell Varco (NOV) has developed several technologies in its XL Systems business unit to address this demand. The XLC-S connector, for example, was designed for greater structural strength and fatigue performance in applications such as jackup exploratory well or subsea well conductors, while the Viper conductor has been used in some of the most challenging regions and wells on the planet.

Increased structural strength

The XLC-S is a second-generation integral connector with the pin and box threads machined directly into the pipe wall. This design produces an ideal connector geometry: a true flush inside diameter (ID) and flush outside diameter (OD).

The thread form for XLC-S connectors has enhanced strength and fatigue performance, making the connectors suitable for conductors and other structural applications where connector strength and fatigue performance are primary design drivers.

Corrosion and corrosion fatigue in the threads are prevented by the connectors’ external metal-to-metal seawater exclusion seal. XLC-S connectors are made up in approximately three turns, the majority of which are low-torque spin-up until thread surfaces engage. Makeup torques are comparatively low, ranging from 30,000 ft-lb to 60,000 ft-lb depending on size, and the connectors are suitable for makeup with either power tongs or manual tongs.

Comprehensive physical testing of XLC-S connectors, including full-scale fatigue testing and pile-driving testing as well as field performance results have validated the connectors’ performance in harsh environments. XLC-S connectors are manufactured in diameters of 20 in. and larger and take up no more annular space than the pipe. This design eliminates large diameter forgings and welding costs.

GoM case study

NOV partnered with Walter Oil & Gas, an independent E&P company, to develop a custom version of the XLC-S connector for use on the Coelacanth platform. The Coelacanth platform is the Gulf of Mexico’s (GoM) third tallest fixed platform, with a 380-m (1,246-ft) jacket—almost the height of the Empire State Building— supporting the topsides.

Walter Oil & Gas placed the platform in Block 834 of the Ewing Bank (EW) area, located roughly south of New Orleans at the edge of the continental shelf. EW Block 834 was viewed as a particularly challenging prospect given water depths ranging from 152 m to 610 m (500 ft to 2,000 ft)—well beyond the range of existing jackup rigs—and the area’s lithology comprised unconsolidated deepwater shales with rock that never fully compacted. The fi xed platform option was chosen as the most economical choice and to eliminate various potential production issues in the area.

Walter Oil & Gas installed eight offshore conductor strings with the H&P 203 Rig in 361 m (1,186 ft) of water in EW Block 834. The application required the large diameter conductor pipe to meet four criteria. First, the conductor pipe had to be fully drivable. Also, as the connectors were to be installed through slightly offset platform guides, the OD of the connectors needed to be flush to minimize interference with the rig during deployment. The ID of the connectors also had to be flush due to buckling stabilizers welded to the OD of the smaller 22-in. casing string. Finally, the connectors needed full pipe body strength and excellent fatigue performance along the length of the conductor, especially close to the mud line.

Standing at 380 m, Walter Oil & Gas’ Coelacanth platform is the GoM’s third tallest fixed platform. (Source: NOV)

 

To address these requirements, NOV developed the XLC-S-HS connector for use on each 30-in. conductor string. The design was based on the original XLC-S connector, using a proprietary wedge thread form on high-strength forging material that is welded directly to the pipe body. This created a connector solution that was stronger than the pipe in tension, compression and bending.

To maximize the performance of the XLC-S-HS and minimize the risk of using the connector, NOV also supplied Walter Oil & Gas with line pipe manufactured to technical requirements more stringent than those mandated by American Petroleum Institute specifi cation 5L PSL2 standards.

The only alternative to using the XLC-S-HS connector was to weld the conductor pipe ends together as the string was run into the water. Although technically feasible, this was an extremely time-consuming option, as nondestructive examination (NDE) meant that each joint of pipe could take up to 4 hours to weld. In comparison, using the XLC-S-HS connector took an average of only 5.72 minutes per connection to make up. On pipe sizes of 30 in. by 1.5 in. and 30 in. by 1 in., with 40 joints per string, the connections were made up in the following times to achieve the average:

  • Slot A-2: 9.10 minutes per connection;
  • Slot A-3: 7.68 minutes per connection;
  • Slot A-4: 5.67 minutes per connection;
  • Slot A-7: 4.84 minutes per connection;
  • Slot A-6: 4.32 minutes per connection;
  • Slot A-8: 5.92 minutes per connection;
  • Slot A-9: 4.49 minutes per connection; and
  • Slot A-5: 3.70 minutes per connection.

NOV’s supply of a pipe and connector packaged solution met the specifi c technical needs of Walter Oil & Gas in this application. All eight conductors were installed safely and effi ciently, providing the customer with signifi cant cost savings on the project.

With an approximate spread rate of $180,000/day, average connection times with the XLC-S-HS being 5.72 minutes per connection, and average times to weld pipe (with NDE) being 225 minutes per connection, Walter Oil & Gas saved more than $27,000 per connection and more than $1 million per string.

International applications

An operator drilled a record-setting exploratory well in Uruguay that at 3,400 m (11,155 ft) is now the deepest well ever drilled by water depth. The operator used 36-in. and 22-in. Viper conductors for this application, installing the conductor from a drillship with no delays or nonproductive time related to the installation. A total of 84 m (276 ft) of 36 in.-by-2 in./1.5-in. Viper conductor was jetted and made up with belt tongs, and 613 m (2,011 ft) of 22-in.-by-1.5 in./1-in. Viper conductor was run in hole and made up with power tongs.

Another operator drilling offshore West Africa used the XLW connection—a hybrid connector with an integral pin thread and weld-on box—to deploy 36-in. and 20-in. conductor in 2,895 m (9,499 ft) of water. This established a new record well drilled by water depth for the African region.

In what may very well be a lower-for-longer offshore pricing environment, using products and technologies that decrease costs and increase effi ciencies is critical. NOV continues to partner with companies like Walter Oil & Gas and other operators to introduce offshore innovations and solutions that continuously drive improvements in reliability, safety and technical performance in deepwater and ultradeepwater wells.


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