New rig designs integrate the latest marine and well construction technologies to cut costs and improve suitability.
Fifth-generation semisubmersibles on the horizon target emerging deepwater markets and offer an array of new features. Virtually every desirable attribute of floating drilling units has been investigated and, where possible, improved.

Transocean Sedco Forex has three of its eagerly awaited Express Class semisubmersibles, two from DCN Shipyards in Brest, France, and one from Promet Shipyard in Singapore, nearing completion. As always, it is good to see the units "in person" rather than just as designs on a board as they have been viewed and written about up until now, and at first glance one can see these rigs are radically different from previous designs.
Sporting distinctive Tri-Act derricks, the rigs are geared for maximum pipe-handling efficiency. Company research established that more than 40% of nonproductive time on conventional drilling units was consumed handling tubular goods. That statistic alone provided incentive for improving efficiency. Added benefits were realized in safety - for individual personnel and vessel stability.
The Sedco Express rig design is estimated to be capable of reducing total well construction time by at least 25% and total well construction cost up to 30%. Drilling performance should be significantly improved through faster penetration rates, streamlined logistics, extensive mechanization and parallel operations of tubular handling, supported by a transparent, integrated well construction center.
A high-powered, integrated mud and cement pumping system along with innovative built-in systems for electric wireline logging, measurement while drilling (MWD), logging while drilling (LWD) and coiled tubing operations will also contribute to the expected time and cost savings.
Most conventional drilling operations require direct physical intervention, which consequently increases rig crews' exposure to injury risk.
Therefore, one of the most effective ways to improve safety is to reduce human interface in these operations. To do that, Sedco Express implemented comprehensive mechanization on labor-intensive operations - namely, the tubular handling process. This directly reduces the risks for rig personnel.
Ergonomics are being emphasized in Sedco Express rigs design. Advanced ergonomic design not only improves workplace quality and increases efficiency, but also enhances safety.

Carefully planned
Modularized deck components and mechanized pipe-handling systems reduce hazards and improve efficiency. Carefully planned equipment layout, simplified piping and cabling, as well as optimized drilling processes have created 30,000sq ft of unobstructed main deck area, which simplifies tubular and equipment arrangement. This consequently reduces tripping hazards.
Most of the main equipment in the integrated well construction center is ergonomically designed, including the control-console chairs, man machine interface and tubular handling joystick. They are comfortable, easy and intuitive to use.
To ensure a comfortable sleeping environment, the Sedco Express accommodation module is fully suspended on isolating shock absorbers.
This shock abatement system significantly reduces noise from the mud pump. In addition, noise and vibration are greatly reduced as the main engines are far below the water level, inside the pontoons. To ensure minimum disturbance to the crew and visitors, recreational rooms and the mess halls are relatively far from the bedrooms. Adding to the living comfort, all rooms on the rig have a maximum occupancy of two, with individual bathroom facilities.
Environmental protection has also been given great consideration in the rig's design.
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 generation of fuel-efficient diesel engines and a power management system are used to reduce energy consumption, engine emissions and air pollution.
Once riser, drill pipes and casing tubulars are onboard the rig, a combination of riser gantry crane, tubular pickup machines, tubular transfer system and Tri-Act derrick will carry out the entire process without direct human involvement.
A 190ft Tri-Act derrick with integral and externally adjacent setback areas, combined with two independent vertical pipe-handling and -racking machines and makeup stations, will reduce tubular handling time about 50% or more by enabling drillpipe, casing, tubing, riser and other tubulars to be picked up off the critical path prior to running. Since 40% of rig time is spent on handling tubulars, well costs will decrease dramatically.
A 30,000sq ft unobstructed deck area permits storage of all tubulars needed for the operation, and the derrick height allows crews to work with quadruple sections of 32ft drillpipe, triple sections of 41ft casing and double sections of 65ft riser. As a result, the Sedco Express rig will be able to run riser four times the rate of the existing rigs, casing three times as fast and drillpipe 25% faster. The Tri-Act derrick has a setback capacity of 2,550 metric tons, the equivalent of the total variance deckload of an average semisubmersible.
The rig floor on the Sedco Express does not have a standard V-door at the center front of the derrick. Instead, two landing areas for the horizontal tubular transfer systems are at each side of the derrick. At each of these outboard stations are casing and iron roughnecks for making up tubulars. Three or four 2,200-hp, 7,500-psi integrated mud pumps lower overall mud costs and increase penetration rates 120% to 325%, depending on hole size (compared to 5,000-psi pumps on conventional semisubmersibles).
The 7,500-psi pressure improves hole cleaning, allows increased section lengths, reduces wiper trips and enhances directional operations. With a high-pressure mud system, the cuttings tend to be larger. This increases solids-control equipment efficiency and minimizes the need for dilution and treatment. This will also minimize openhole time and formation damage.

Customer requirements
The rig has a flexible, modular solids-control area that can easily be outfitted to suit customer requirements. In its basic configuration, it has six scalping and six linear motion shale shakers. This allows very fine mesh screens to be used in most hole sections, reducing the amount of drilling solids entering the mud system and thus reducing treating cost. This flexibility and equipment arrangement should result in the reduction of overall mud cost. The primary objective for the fluid management and processing system was to provide the flexibility to manage two or three mud systems simultaneously, and still have the reserve volume necessary to displace the riser in the event of lower marine riser package disconnection.
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-bbl 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 bbl of weighted mud can be held in reserve in the pontoons. An additional 6,175 bbl of storage for brine and base oil is available in the pontoons.
This improved mud and cement mixing systems, along with high-pressure pumping, help ensure consistent fluid properties and maximize equipment usage to support an enhanced new construction process.

Weight distribution
With main machinery like heavy winches and main engines inside the pontoons, the Sedco Express 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. Another advantage of placing the engine room and machinery in the pontoons is completely redundant power supply and distribution, one of the primary criteria required for certification to DPS3 (the highest standard for dynamic positioning and propulsion systems).
Designed for the ultra-deepwater environment, Sedco Express rigs are fitted with the advanced Mermaid 7-mw variable-speed azimuthing pod propulsion system. One of the Mermaid system's prime features is its capability for underwater installation and removal. (Shaft seals and propellers can be changed in situ).
The dynamic positioning system will keep the rig in place in the Gulf of Mexico's loop current and changing wind directions. The unit has been designed to maintain station and continue to operate under severe environmental conditions. The rig's marine vessel characteristics have been optimized to achieve an estimated 10 knots self-propelled speed.
The Sedco Express rig design also can be equipped with an eight-point-spread wire mooring system for ultra-deepwater depth.
The mooring system is designed to work with prelaid mooring arrangements. Each anchor winch can accommodate up to 6,000ft of 600-metric-ton breaking strength wire. These anchor winches are at the bottom of the four columns, which results in lower rig CG and frees up a large area of deck space.
The concurrent pipe handling process is controlled by an integrated control system (ICS). This advanced system takes care of a wider array of operations than just pipe handling. ICS includes:
l a real-time control network, which involves events sequencing, data storage and collision avoidance calculation;
l a rig video network, which consists of a closed-circuit television network;
l vessel management system network, which provides vessel control and marine functions;
l a local area network, which provides user access to various data servers, printers and E-mails; and
l a rig area network, which integrates and improves rig communications through efficient data and information transmission.
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 and systems for wireline logging, MWD, LWD and coiled tubing operations reduce operating time and cost. Furthermore, the well construction process is integrated to enhance communication and understanding of the process experienced by the rig crews, service company and operator.
Rig Office software computerizes rig management functions. These, together with cross training of personnel, provide a multiskilled workforce better equipped to make informed decisions in real time.

Early cash flow
Dedicated areas for well testing (DST) and an early production system, totaling 10,600sq ft, are at the corner extremities of the rig's aft end. Early production systems give the operator the ability to collect extended production data for field evaluation and generate early cash flow.
One of the prominent examples of innovative equipment layout is the placing of the derrick and substructure at the rig's aft.
This is to efficiently handle the subsea equipment that would have exceeded the capacity of the deck cranes. This strategic placement permits the large subsea manifolds and templates to be lifted by a drawworks directly from a supply vessel during deployment.
Two Christmas tree carriers are in the moonpool. This arrangement saves time when there is a need to change trees or run multiple trees. When changing out trees, the old tree is pulled and set on the first carrier, which then will be moved off the well center toward the blowout preventer (BOP). The second carrier with the new, fully tested tree can be moved to the well center and run without any delay.
During short field transit, the BOP and riser string can be hung off the moonpool beams. This will significantly reduce the required time to run the entire string of riser and BOP at the new location.
Apart from being equipped with the mechanized and computerized systems, Sedco Express is manned with a highly competent and knowledgeable workforce.
But to ensure competency, an integrated drilling simulator, which mimics real-life tubular handling operations, is installed in the company's training center. Specific course modules and training materials are developed to supplement this training. Training of the rig crews has begun as early as 9 months prior to delivery of the rigs.
The Sedco Express design, says its owner, is an example of the fit-to-operator philosophy, where equipment and services meet specific operating and economic objectives. Customized contracts may include risk/reward or value-priced well construction incentives.