The MS-800 subsea wellhead system provides a cost-effective system that can be used in all applications including shallow water and deep wells. (All figures courtesy of VetcoGray)

According to the US Energy Information Administration, the world’s consumption of marketed energy is projected to increase by more than 50% between now and the year 2030. As a significant part of its efforts to find new resources for meeting this demand, the oil and gas industry continues to push the boundaries of deepwater exploration and development.

While deepwater operations can be highly productive, drilling in ultra-deepwater environments present significant challenges, in terms of higher pressure and weight requirements. For the deepwater sector to continue growing, new and innovative technologies will be required.

In response to the challenges of deepwater drilling, VetcoGray, a GE - Oil & Gas business, has developed the MS-800 Fullbore Subsea Wellhead System. Designed to help drillers reach deepwater targets in such promising regions as the Gulf of Mexico and offshore Brazil, the MS-800 has the capacity to withstand eight million lb of load at the wellhead — compared to 7.1 million lb for its predecessor in the product line, the MS-700.

Two million lb casing load capacity

The new system increases the casing load capacity to two million lb for the first position casing hanger and the 16-in. casing hanger. This increased capacity allows drillers to run longer strings, enabling larger diameter holes to go deeper, reaching pay zones with bigger production strings. Pressure capacity for the 16-in. hanger also increases from 6,500 to 10,000 psi. The shift in pressure capacity strengthens the MS-800 to withstand the higher geological formation pressures that come with deeper production. The system also incorporates an improved load-ring configuration on all three casing hangers to improve actuation. These improvements are expected to set new standards for subsea oil and gas fields of depths of 30,000 ft (9,150 m) or more.

The new wellhead system addresses emerging needs of the subsea market, including 15K Fullbore and 20K high-pressure/high-temperature requirements. A key challenge on the Fullbore system was finding a way to successfully run a half-dozen pipe strings in the well bore, and to seal each pipe with metal-to-metal seals. The solution required several technological and mechanical advances.

FullBore allows the operator to run one extra casing string under blowout preventer (BOP) control with a 21-in. drilling riser. The system also allows more flexibility by using larger drill bits, testing metal annulus seals to higher pressures, and having the option to run 18-in. and 16-in. casing strings below the mudline. Increasing the size of the production tubing used to pump out hydrocarbons enables the operator to maximize well productivity.

Snag prevention

A new feature of the MS-800 provides 100,000 lb snag prevention. As casing is lowered into the well bore, this snag prevention eliminates premature expansion of the hanger landing shoulder. In addition, the snag prevention design provides a 100,000-lb verification check, confirming that the part is in the right place.

This system allows potentially larger completion options, by reaching total depth with a larger production string. Load-bearing jewelry is located on the casing hanger and is actuated by a tag shoulder. Once the casing hanger is set, the running tool will actuate the metal-to-metal seal and test in a single trip.

The system provides operating values with 50% operating safety factor, designed at a 1.5 factor, an industry leading level. The advanced load sharing and load distribution features of the MS800 provide the operator with unsurpassed value in capacity.

In addition to its new technological capacities, the MS-800 system builds on the field-proven design of the MS-700, both with sealing technology and with the running and testing tools. The industry’s first all-metal sealing wellhead system, the MS-700 has been proven in nearly 20 years of operation and has been able to meet some of the industry’s most demanding requirements for high-pressure, critical service, deepwater drilling and production.

Some of the features of the MS-700 system that have now evolved to the new MS-800 product include:

  • True metal-to-metal sealing, with no electrometric seals inside high-pressure housing or in the 16 inches below mudline;
  • Ability to test the BOP stack at any time, before or after running hangers, wear bushings or nominal seat protectors;
  • New generation of running tools;
  • VX/VT dual metal-to-metal gasket prep;
  • High-capacity, fatigue-resistant conductor housing to high pressure housing interface;
  • Seals fully energized by the running tool; test pressure verifies the seal but is not required to energize it;
  • Redundant metal-to-metal seal areas; and
  • Compliance with industry standards API 17D, NACE MR-01-75, design certified by Lloyds.

The new MS-800 was developed and tested in 2007 at VetcoGray facilities in Houston, Texas. A 15-ksi version will be available for commercial applications in the second quarter of 2008, with a 20 ksi version (20,000 psi, 350o) to follow later this year.