BRAZIL ADVANCES SUBSEA TECHNOLOGY IN MARLIM PILOT

March 29, 1993
Petroleo Brasileiro SA has extended several water depth records for subsea technology, during a pilot project in giant Marlim oil field in the Campos basin off Brazil. Petrobras finished the 10 well Marlim pilot last December. The field's pilot phase was intended to begin early production and enable Petrobras to gather more reservoir data.

Petroleo Brasileiro SA has extended several water depth records for subsea technology, during a pilot project in giant Marlim oil field in the Campos basin off Brazil.

Petrobras finished the 10 well Marlim pilot last December. The field's pilot phase was intended to begin early production and enable Petrobras to gather more reservoir data.

Ten satellite wells, including two prepilot wells, were completed during the Marlim pilot phase with guidelineless (GLL) wet Christmas trees designed and fabricated by FMC Corp., Houston, and CBV Industria Mecanica SA, Rio de Janeiro. The subsea wells are producing 52,000 b/d of oil and 21.19 MMcfd of gas in water depths of 1,847-2,562 ft.

Marlim pilot well flow is routed to a permanent semisubmersible floating production system (FPS). Oil moves from the FPS to a monobuoy that offloads to a shuttle tanker.

In addition to marking the first successful uses of purpose-built GLL wet trees, FMC said the Marlim pilot project allowed GLL subsea technology to evolve from conceptual status into a proven deepwater completion method.

Another 52 GLL wet trees will be needed for Marlim field phase one development to be finished by 1997. Petrobras last year began drilling the first of phase one's 32 production and 20 injection wells in water depths of 2,789-3,445 ft.

Marlim's phase one GLL completions are to begin by yearend 1993 with production expected to start during first quarter 1994. Phase one plans include installing two more FPSs in water depths of 3,000-3,215 ft.

Petrobras estimates Marlim oil in place at more than 8 billion bbl, including 1.53 billion bbl recoverable.

MARLIM PILOT RECORDS

Subsea operations for Marlim pilot wells extended many of the water depth records already claimed by Petrobras.

Petrobras set water depth records for subsea completions and production with three of Marlim pilot's 10 GLL completions. GLL wet trees were installed in Marlim field using flexible pipe layaway flow line connections.

The current deepwater completion record was set in April 1992 with the GLL installation of a wellhead system in 2,562 ft of water on Petrobras's MRL-9 well. Short lived deepwater completion records were claimed in March 1991 on MRL-3 well in 2,365 ft of water and in July 1991 on MRL-6 in 2,467 ft of water.

Since going on stream, MRL-9 has claimed the record for deepwater production as well.

Other water depth records established by Petrobras during the Marlim pilot project include installing and operating a permanent FPS in 2,062 ft of water and a monobuoy in 1,336 ft of water and laying a flexible flow line in 2,562 ft of water.

In addition, FMC and CBV on MRL-20, the last well completed during the pilot phase, for the first time used a flow line hub remote installation system (Fhris). FMC developed Fhris technology for use with CBV's second generation of GLI trees. The system allows pipelay vessels and completion rigs to work at different times.

GLL TREE COMPONENTS

The 10 GLL wet tree designed for and installed in Marlim are identical.

Fully assembled and installed on the wellhead, each GLL tree and utility guide base (UGB) stands 40 ft tall and weighs about 55 tons, including 45,000 lb each for the UGB and tree and 20,000 lb for the tree cap.

Each tree consists of two hydraulic connectors, a dual bore block with 4 in. and 2 in. flow control valves rated to 5,000 psi, a reentry manifold, a structural frame, and two remotely operated vehicle (ROV) intervention panels. GLL tree valves are attached to one ROV panel to allow diverless ROV mechanical override and to a second ROV panel that can be used to reroute hydraulic functions in case of a failure of hydraulic system controls.

The structural frame is tubular with orienting lugs around the tree connector. Atop the frame is a large diameter landing race with divots to align the tree cap and tree installation tool.

The GLL tree cap provides a secondary protective pressure barrier to the tree's dual tubing bores. The cap contains hydraulic control line loops that interface with the reentry manifold to complete the hydraulic circuit between the production umbilical and production control functions.

FMC designed the GLL tree to include funnel up and funnel down reentry ports to reduce unit height and weight. Another innovation by FMC was a hybrid high strength flange to handle bending moment stresses during tree installation.

The UGB, the keystone for the passive rotational orientation system used to align well completion components, is composed of the tubing head, hydraulic wellhead connectors, an upward facing funnel to guide the Christmas tree landing, and a cradle to house the flow line connector components.

The layaway flow line connection system is the other main part of Petrobras's GLL tree. It consists of a vertical 11 in., 5,000 psi connector and a structurally mounted hub that is connected during installation to the flow lines and flow line umbilical.

The connector and flow line bundle hub provide a single structural and sealing interface for a 4 in. flow line, a 2 in. annulus monitor flow line, and as many as 10 individual direct hydraulic control lines.

The tree attaches to the UGB with a 16 3/4 in. mandril style wellhead and connector. FMC designed the trees for use with 16 3/4 in. wellhead systems because many GLL drilling vessels are set up to handle GLL drilling systems of that size.

RUNNING A GLL TREE

A drilling-production (DP) semisubmersible and a pipelay barge were the two main vessels needed for Petrobras's GLL installations.

Crews in the Marlim pilot began the GLL installation sequence by removing the abandonment cap and installing the UGB on the wellhead. Here is a general description of the GLL installation sequence:

  • Crewmen on the lay vessel attach a flexible pipe bundle to the flow line hub, keelhaul the assembly between the DP and pipelay vessels, and allow it to be pulled into the moon pool of the DP vessel, where it is landed in a capture frame cradle.

  • DP vessel crewmen lower the GLL tree into the moon pool where it is landed on the capture frame. The flow line connector must be aligned with the flow line hub as the tree collector goes over the dummy tubing head on the capture frame to assure that flow line passages and hydraulic seal stabs will engage properly.

  • After the tree is landed on the capture frame, DP vessel crewmen move the tree cap into the moon pool and land it atop the tree where its hydraulic functions are tested through the production umbilical from the pipelay vessel. The tree cap has soft landing pistons that engage a ring atop the tree frame so the tree cap can be landed, rotated into position, and piston pressure relieved. On the seabed the soft landing pistons engage receptacles on the landing ring on the tree frame.

  • With the tree and tree cap in position, crewmen lower the tree running tool into the moon pool where it is landed and locked onto the tree manifold in a process identical to that used to land the tree cap.

  • The tree and tree running tool are moved over the center of the moon pool, and the completion riser is lowered through the rotary table and connected to the top of the tree running tool. With the riser attached and the hydraulic skid and capture frame removed, the tree is ready to be run.

  • The riser is lowered to allow the tree to enter the water where-just before running the tree to the wellhead-the control umbilical is secured near the bottom of the lower riser joint.

  • As the tree nears the wellhead, the lay vessel stops playing out the flow line while the DP vessel continues lowering the tree. This rotates the swivel lines upward into their final locking positions.

  • When the tree reaches the subsea wellhead area, surface vessels move into position to properly align the flow lines with the cradle in the UGB, and the landing procedure is carried out. Aligning pins on the outside of the tree connector engage Y-slots inside the UGB to properly position the tree.

Copyright 1993 Oil & Gas Journal. All Rights Reserved.