The Sedco Express-class deepwater semisubmersible rigs are setting a new industry benchmark to meet the challenges of well construction in the 21st century. Transocean has delivered three of these "fifth-generation" units, the Sedco Express, Cajun Express and Sedco Energy.

The Sedco Express rigs are estimated to be capable of reducing total well construction time by at least 25% and total well construction cost up to 30%. Faster penetration rates, streamlined logistics, extensive mechanization and parallel tubular handling operations are supported by a transparent integrated well construction center.

Savings contributions also come from a high-powered, integrated mud and cement pumping system, innovative built-in Electric Wireline Logging, Measurement While Drilling (MWD), Logging While Drilling (LWD) and coiled tubing operations.

Health, Safety and Environment
To improve safety, a Sedco Express-class rig reduces human interface in drilling operations with a mechanized "tubular handling process." Modular deck components and 30,000 square feet of unobstructed main deck area also reduce hazards and improve efficiency. Most main equipment in the Integrated Well Construction Center (WCC) is ergonomically designed, including the control-console chairs, Man Machine Interface (MMI) and tubular handling joystick.

To reduce noise in the living quarters, the Sedco Express-class accommodation modules are fully suspended on isolating shock absorbers and the main engines are located inside the pontoons below water level. All rooms on the rig have a maximum occupancy of two, with individual bathroom facilities.

To safeguard the environment, discharge is controlled. Sack cutting is dust-free and dust collectors are used at manual hoppers. To prevent an accidental spill, the mud tanks have no discharge valves, and all exposed areas of columns and pontoons are double-skinned. The latest, fuel-efficient diesel engines and a power management system reduce energy consumption and engine emissions.

Mechanization & Parallel Operations
Once riser, drill pipes and casing tubular are on board a Sedco Express-class rig, the riser gantry crane, tubular pick-up machines, tubular transfer system and the Tri-Act Derrick carry out the tubular process without direct human involvement.

A 190-foot Tri-Act derrick with integral and externally adjacent setback areas, combined with two independent vertical pipe handling/racking machines and makeup stations, can reduce tubular handling time about 50%. Drill pipe, casing, tubing, riser and other tubulars are picked up off the critical path before running. Since 40% of rig time is spent handling tubulars, well costs can be decreased with this technology.

A 30,000-square-foot unobstructed deck area permits storage of all tubulars needed for the operation, and the derrick height allows crews to work with quadruple sections of 32-foot drill pipe, triple sections of 41-foot casing and double sections of 65-foot riser. As a result, the Sedco Express-class rig is able to run riser at four times the rate of existing rigs, casing three times as fast and drill pipe 25% faster. The Tri-Act derrick has a total set back capacity of 2,550 metric tons, which is the equivalent of the total variance deckload of an average semisubmersible.

Instead of a standard V-door at the center front of the derrick, there are two landing areas for the horizontal tubular transfer systems located at each side of the derrick, where casing and iron roughnecks make up tubulars.

High-Pressure Pumps for Increased Drilling Efficiency
Three or four 2,200-horsepower, 7,500-psi integrated mud pumps lower overall mud costs and increase penetration rates by 120-325%, depending on hole size (compared to 5,000-psi pumps on conventional semisubmersible).

With high-pressure mud system, cuttings tend to be larger. This increases solids control equipment efficiency and minimizes the need for dilution and treatment, which minimizes open hole time and formation damage. The flexible modular solids control area is easily outfitted to customer requirements.

Advanced Mud Systems
An improved mud mixing system (which has the ability to accurately control the density of the drilling fluid while mixing) coupled with large capacity mud storage volume significantly reduce the time spent in switching mud. The 4,500-barrel mud pit system at the surface can be split to allow crews to swiftly change over mud systems when hole conditions change. Another 7,000 barrel of weighted mud can be held in reserve in the pontoons. An additional 6,175 barrel of storage for brine and base oil is available in the pontoons.

Low Center of Gravity
By locating such main machinery as heavy winches and main engines inside the pontoons, the Sedco Expres-class rig has better weight distribution than conventional semisubmersibles. With much of its mass below the water line, the center of gravity (CG) is lowered and stability is improved. Having the engine room and machinery spaces located in the pontoons facilitates completely redundant power supply and distribution, which is one of the primary criteria required for certification to DPS3 (the highest standard for dynamic positioning and propulsion systems).

Dynamic Positioning and Mooring
Designed for ultra-deepwater environments, the Sedco Express-class rigs are fitted with the advanced Mermaid seven-megawatt variable speed azimuthing (fully rotating) pod propulsion system. One of the prime features of the Mermaid system is its capability for under water installation and removal. Shaft seals and propellers can be changed in place. Marine vessel characteristics of the rig have been optimized to achieve an estimated 10 knots self-propelled speed.

Designed to maintain station and continue to operate even during severe weather, the dynamic positioning system will keep the rig in place in the Gulf of Mexico's loop current and changing wind directions.

The Sedco Express-class rig design can also be equipped with an eight-point-spread, wire mooring system for ultra-deepwater depth. The mooring system is designed to work with pre-laid mooring arrangements. Each anchor winch can accommodate up to 6,000 feet of 600-metric-ton breaking strength wire. These anchor winches are located at the bottom of the four columns, which results in lower rig center of gravity and at the same time freeing up a large area of deck space.

Process Control System
The concurrent pipe handling process is being controlled by an integrated control system (ICS). In fact, this advanced control system takes care of a much wider array of operations. ICS comprises networks like Real Time Control Network (RCN) [involves events sequencing, data storage, collision avoidance calculation, etc], Rig Video Network (RVN) [consists of CCTV video network], Vessel Management System Network (VMS) [provides vessel control and marine functions], Local Area Network (LAN) [provides user access to various data servers, printers, emails, etc.] and Rig Area Network (RAN) [integrates and improves rig communications through efficient data and information transmission].

Information Sharing and Integrated Services
Modularity allows facilities upgrades and better integration of well services. A built-in active compensated Electric Wireline Logging Winch and permanent, built-in alarm sensors & systems for Wireline Logging, Measurement While Logging (MWD)/Logging While Drilling (LWD) and coiled tubing operations reduce operating time and cost. The integrated well construction process enhances communication and understanding among rig crews, the service company and operator.

Rig Office software computerizes rig management functions that help multi-skilled workers to make better informed decisions.

Extended Well Test and Floating Production Capabilities
Dedicated areas for well testing (DST) and Early Production System, totaling 10,600 square feet of space, are situated at the corners of the rig's aft end. Early Production Systems allow the operator to collect extended production data for field evaluation and generate early cash flow.

Template, BOP and Christmas Trees Handling System
A prominent equipment layout innovation is the placement of the derrick and the substructure at the aft of the rig to efficiently handle subsea equipment that would have exceeded the capacity of the deck cranes. The large subsea manifolds and templates can now be lifted by a drawworks directly from a supply vessel.

Two, dedicated Christmas tree carriers in the moonpool can significantly save time when changing or running multiple trees.

During short field transit, the BOP and the riser string can be hung off on the moonpool beams to significantly reduce the required time to run the entire string of riser and BOP at the new location.