NEW JACK UP DESIGNED FOR SAFE, EFFICIENT DRILLING

A recently built jack up has incorporated the latest automated drilling technology for safe operation in the harsh North Sea environment. Santa Fe Drilling Co.'s Magellan jack up rig, delivered in August 1992, was designed to improve drilling operations and operate with zero discharge while keeping the rig workers removed from much of the ordinary dangerous rig operations.

May 10, 1993

9 min read

A recently built jack up has incorporated the latest automated drilling technology for safe operation in the harsh North Sea environment.

Santa Fe Drilling Co.'s Magellan jack up rig, delivered in August 1992, was designed to improve drilling operations and operate with zero discharge while keeping the rig workers removed from much of the ordinary dangerous rig operations.

The new jack up began combination exploration and development drilling in October 1992 for Amoco (U.K.) Exploration Co. in the North Everest field in North Sea Block 42/28. Initial plans were for Magellan to drill one exploration well and then move to the North Everest platform for a 6-month skid-off, tieback, and development drilling campaign.

Magellan, a hybrid rig of the Monarch class, is a sister to the Monarch and Monitor jack ups delivered in 1987 and 1989, respectively. Magellan was built with specifications similar to those of the larger Galaxy I jack up delivered in late 1991.

The rigs were designed by Friede & Goldman and built at the Far East Levingston Shipyard in Singapore.

The rig underwent sea trials in early 1992 and demonstrated a 310-ft (95 m) water depth rating for the central North Sea, according to independent assessments by Noble Denton & Associates.

The three-legged jack up has a hull length of 228 ft, a width of 222 ft, and a depth of 31 ft at the center line. The triangular legs are 496 ft tall, with 440 ft usable length below the hull.

The rig has complete onboard control of all fluids for a minimum impact on the marine environment. It is designed to maximize collection, retention, treatment, and monitoring of all effluent streams.

No environmentally unacceptable solids or fluids are discharged, even during adverse drilling and weather conditions. Additionally, the rig engines are designed to minimize air pollution through use of a lean fuel injection system.

EXPLORATION DRILLING

Exploration drilling in the central Graben region of the North Sea typically encounters both high temperature and high-pressure formations. The jack up's two-stack blowout preventer (BOP) system was built by Hydril Co. with several technical advances specifically for these difficult drilling conditions:

The rams are fitted with multiple-position locking systems and Inconel-lined ring grooves.
The annular and ram hydraulic functions use stainless steel piping. Hoses from a central manifold plate at the lower work platform supply hydraulic fluid to the stack.
The accumulator, annular blowout preventer, and valve designs allow close/open/close operations. The stripping surge bottles and double hydraulic open/close ports allow fast closing.
The test stumps have an hydraulic manifold to allow BOP testing without use of the main hydraulic unit control functions.

One stack has a Hydril GL 21-1/4 in. x 5,000 psi annular preventer, a Hydril 21-1/4 in. x 5,000 psi double ram preventer, and a Hydril 21-1/4 in. x 5,000 psi single ram preventer.

The other stack consists of a Hydril GX 13-5/8 in. x 10,000 psi annular preventer and two Hydril 13-5/8 in. x 15,000 psi double ram preventers.

The fixed Drilquip diverter is rated at 500 psi with a standard 2,000 psi housing to improve wear characteristics. The 16-in. overboard lines to both port and starboard extend horizontally without bends. A panel on the drill floor controls hydraulically operated isolation valves for the diverter and flow lines.

The choke and kill manifold is rated at 15,000 psi and is located on the drill floor. A key safety feature for the manifold is a loop-line buffer chamber with an automatic sequence system to shut down the degasser supply line and vent it overboard.

All active choke valves are hydraulic, with two automatic and two manual. The automatic chokes can be operated from either of two positions on the drill floor.

The solids-control system is designed for exploration drilling and high-efficiency development drilling; it includes high-speed, linear-motion, cascaded shale shakers with desilters, degassers, and centrifuges.

The two primary shakers are low profile with a slope design for scalping large cuttings and gumbo. The five secondary shakers are high-capacity linear motion models which can be hooked up in a variety of configurations for high, medium, and low flow operations. The system allows an operator to keep a large volume of mud conditioned for maximum penetration rates in large-diameter holes.

For improved drilling performance, Magellan carries three National Oilwell 14-P-200 mud pumps rated at 2,000 hp and 7,500 psi maximum operating pressure. A similar mud pump system on Galaxy I was used to drill 2,500 ft of 18-in. hole in 60 hr.

The 160 ft derrick is rated for 2 million lb gross nominal capacity and 1.6 million lb static hook load capacity with 16 lines strung to the traveling block. The derrick can rack 30,000 ft of drill pipe (10,000 ft of 6/8-in. drill pipe and 20,000 ft of 5-in. drill pipe simultaneously). The drill floor and pipe racking system are enclosed with 32-ft tall wind walls.

The top drive is the first of Varco BJ's TDS-6S design. This top drive can support 750 tons and therefore does not have to be set aside to run long strings of heavy casing. This top drive has an integral swivel and block which reduces overall height by 10 ft, allowing a correspondingly shorter derrick.

The unit has two General Electric 752 high-torque drive motors which produce high speed and torque; the double motor setup is advantageous in case one motor breaks down.

This innovative design eliminates the conventional rotary table. Drill floor rotation is supplied hydraulically when necessary.

PRODUCTION DRILLING

Magellan can drill production wells in the cantilever mode (both over a fixed platform and over a subsea template) and in the tender-assist mode with the drill floor and substructure skidded onto an adjacent platform. The jack up's outreach in cantilever mode is 65 ft beyond the transom and 15 ft on either side of the center line. The rig can maintain a drilling load of 2.6 million lb, allowing it to drill deep, highly deviated holes from any position within the expanded drilling envelope.

For drilling operations over a subsea template, the conductor is supported at 600,000 lb maximum vertical tension for any position of the drill floor in the envelope. Additional safety and efficiency features in the drilling equipment include lateral restraints above and below the BOPs to reduce riser bending moments caused by the large North Sea wave forces.

The 3,400-bbl mud capacity, active and reserve, allows an operator to maintain two separate mud systems simultaneously. The split mud system provides flexibility for drilling programs in which different muds or fluids are needed at various stages of the well. Additionally, brine and base oil are stored separately.

In the skid-off mode, Magellan can skid the drill floor and substructure forward on the cantilever beams. This setup provides an open area for installation of the skidbase and a transition between the substructure and the platform capping beams.

The skidbase is 65 ft wide, 30 ft high, and 45 ft deep. Its separate structural elements have a maximum weight of 20 tons. The skidbase design allows for several installation alternatives:

The skidbase elements can be delivered to the rig on supply boats for assembly at the stern with rig cranes.
A fully assembled skidbase can be delivered to the platform and installed with a derrick barge.
The rig can be taken to port for skidbase installation.
If installed directly on the platform, the skidbase can be aligned with a jack up for drill floor skidoff. If the skidbase is brought out with the rig, the rig can install it on the platform.

The skidbase contains a complete BOP handling and storage system and first-tier shale shakers. This system is designed to minimize nipple up times to improve efficiency and increase safety.

A conventional catenary suspension system supports electric cables running between the cantilever and the drill floor. An additional 150 ft of cable is permanently installed on the rig and can be extended when the rig floor operates in the skid-off mode; no extra cable connections are needed.

The extensions in the piping runs are provided in the skidbase.

AUTOMATION AND SAFETY

The rig was designed with as many automated processes as practical to keep at a minimum the rig workers' exposure to hazardous operations.

For example, there is no need for a derrickman--the most hazardous position on a drilling rig. The Varco PHM-31 automatic pipe-handling machine and a Dreco Energy Services Ltd. Javelin transport the drill pipe and casing from the pipe rack into the derrick.

Except for incidental duties, the drill floor is normally unmanned. All drilling operations are controlled by the driller and his assistant operating side-by-side in the driller's cabin designed by Hitech-Dreco. The cabin is a temperature-controlled electronic control center and is virtually noise-free to allow the driller and the pipe-handler operator to communicate easily.

BOP HANDLING

The cellar storage deck was enlarged for BOP storage forward of the rotary table. The storage space, usually cramped in older rigs, is 18-ft long and runs the full 60-ft between the cantilever beams.

A 30-ton overhead bridge crane services the storage area for maintenance work on the BOPS. The rig cranes have access to the storage area through hatches large enough to accommodate a fully assembled subsea tree.

A specially designed handler unit can transport either BOP stack intact between the storage area and the wellhead without having to use conventional chain hoists (Fig. 1). The unit has a lift and transport rating of 100 tons and was developed and built jointly by Santa Fe and Victoria Machine Works.

The BOP handler unit can pick up and transport a fully assembled stack under control of a single remotely located operator. The BOP handler can lift the stack from the wellhead with the overshot in place.

The handler has twin pickup forks suspended from an overhead bridge crane with a vertical travel of 18 ft. lt can reach any lateral or longitudinal location in the cellar deck. Table I lists the handling times for each BOP stack under actual operating conditions.

Magellan's BOPs include integral work platforms and handrails so they can be safely serviced and maintained either during storage or while in use.

Because the storage area is large, fully assembled stacks are stored side-by-side without having the wing valves removed. The valves are mounted with choke-and-kill lines stabbed vertically and are supported overhead from a small utility hoist suspended from the handling-unit beams.

Other features include eight hydraulic jacks mounted around and under a lifting ring and a tensioning assembly on a suspended platform. All areas are covered with plates to protect workers from the weather and to ensure that no one works over open water.