Advanced multilateral junction technologies are beginning to establish successful track records.

Each year, 50,000 oil and gas wells are drilled worldwide, and 10% are candidates for multilateral completions. Service companies have endeavored to provide operators better, more reliable options for installing multiple drainage points to tap their reservoirs, and success stories are on an upswing.
In the future, half of new subsea production wells are expected to be multilateral wells. Successful development of offshore reservoirs with multilateral well technology requires superior reliability and versatility. One of the most vulnerable parts of a multilateral well is the junction between the lateral and main wellbores, which can break down under high production pressures.
Schlumberger's new junctions
Schlumberger's RapidConnect system is a multicomponent Technology Advancement for Multilaterals (TAML) Level 3 junction designed to last for the life of the reservoir. Compared with conventional multilateral technology, it has exhibited a hundredfold increase in junction strength to resist the forces that cause collapse. It can be installed faster than conventional hardware in new and existing wells. The retrievable RapidConnect junction consists of a lateral liner mechanically connected to the cased main bore with integral through-tubing selective access to both wellbores for remedial work or evaluation. It is a good choice for unconsolidated formations as it prevents formation solids from plugging either lateral.
Schlumberger's RapidSeal technology, a new TAML Level 6 pressure-sealed junction, provides drilling, completion and production systems in one integrated package. Intelligent components allow remote monitoring and control of flow, even from hundreds of miles away. The two ductile legs of the junction are plastically compressed to an effective diameter of 12 in. for easy installation through 133/8-in. casing. When the junction is in place in the well, the two legs are re-formed to their original round 7-in. geometry (Figure 1) using an expansion tool that is run on wireline (Figure 2). Power is provided through the wireline cable to operate the pump that provides the hydraulic pressure to develop 240 tons of opening force. This process takes about 40 to 45 minutes. Real-time surface control and monitoring during this cold reforming process ensures that forces are applied slowly and uniformly to minimize induced stresses. As the junction legs are re-formed, a map of internal diameters and a chart of force vs. time are generated for comparison with laboratory standards to confirm that the final geometry has been achieved. About 3,000 hours of finite element analysis verified the structural design and metallurgy of the RapidSeal junction and optimized geometry vs. pressure performance.
Pressure integrity with the casing is achieved at the multilateral junction with conventional drilling procedures. A RapidSeal junction can be installed at any well inclination, including horizontal. Well completion options range from simple commingled production in the junction to dual tubing strings with isolated lateral production. The commingled well design is used for injection or production wells in which the junction is in the same reservoir as the two laterals. The dual-string design is used when the junction is not placed in the same pressure regime as the two laterals or when the two laterals must be isolated.
System flexibility allows the well to be completed with either dual tubing strings or, using the Intervention Discriminator, with a single tubing string. In addition, the Intervention Discriminator allows selective intervention operations to be performed in each lateral while permitting commingled production through a single tubing string.
Weatherford buys a star
The recent acquisition of Starfield multilateral well completion technology from Starfield Holdings gave Weatherford International the patented "keyway" technology for ensuring precise and reliable placement for drilling, completing and re-entering laterals. A spring-loaded key lands in a keyway profile formed in the upper apex of a premilled or milled window, providing positive indication of correct positioning and orientation. This technology is particularly suited for deepwater and high-angle applications. Weatherford has several tools that use
this technology:
• The StarGate system for Level 2-5 multilaterals is the only system that offers self-orienting premilled windows. The system can be used to install an unlimited number of laterals in the well, with selective re-entry for each.
• The MillKeyWay system is used to form a keyway in existing wells after milling a window in the casing. The MillKey tool is run in with the whipstock retrieval system, transforming the upper apex of the rough-milled window into a well-defined profile.
• The StarDeflector and StarLocator completions are one-trip systems for Level 2-5 laterals that can be made up and tested at the surface prior to running in. Laterals can be re-entered for workover or stimulation purposes.
• The StarTracker re-entry system doesn't require a packer to remain in the well to orient and position a whipstock or deflector with respect to the window, obstructing production or limiting access to laterals below it. Neither does it use the hit-or-miss method of using a bent sub to locate the window opening. The keyway provides positive indication at the surface when the tool is correctly oriented and positioned. This one-trip system can be used for new and existing wells.
Besides the keyway technology, Weatherford's Passive Inertia Guidance tool, StarPig, is another easy and cost-effective way to orient premilled windows. The device incorporates an eccentric design and an offset center of gravity such that the weighted side causes the window to have a specific orientation in relation to the high side of the hole. In the Mossoro region of Brazil, Weatherford's multilateral team completed a junction that involved setting a premilled window at an angle greater than 90°. This record-setting achievement was possible because the tools work in tension. The StarPig performed flawlessly on both runs during the installation, keeping the premilled window within 5° of the desired orientation. The whipstock assembly remained in the well for several weeks and was recovered without any washover or milling operations, said Greg Nazzal, vice president of downhole services.
Mara-Split technology
Marathon Oil Co. and Baker Oil Tools jointly developed four Level 6 multilateral products with full mechanical and hydraulic integrity at the junction.
The Downhole Splitter allows two wells to be drilled, cased and completed in one wellbore while sharing surface casing. Each well has its individual tree, allowing it to be produced, serviced and worked over independently. The Downhole Splitter is screwed onto the bottom of the surface casing and hung off conventionally. An orienting cam and riser assembly is run in and landed in the first side of the Splitter containing the cement float equipment. The Splitter and casing are cemented through the riser, the first leg is directionally drilled, and a production liner and hanger are hung. The liner is cemented, and the riser is oriented to the second leg for a repeat of the process. Casing is tied back to the two liner tops and hung off in a dual wellhead at the surface.
With the DeepSet Splitter, like the Downhole Splitter, two wells can be drilled, cased and completed using this premanufactured junction. Besides the orienting cam and riser assembly, DeepSet Splitter has the option of a stand-alone orienting cam that is run in place with the Splitter or separately on drill pipe.
The Formation Junction, winner of a Hart's E&P 2001 Meritorious Engineering Award, has one leg that is compressed for running in then expanded in place after underreaming the junction area. This cold-formed junction can be run in smaller hole sizes than the DeepSet Splitter. "The Formation Junction has had 100% installation success so far," said Dave Westgard, business development manager for multilateral systems at Baker Oil Tools.
The Stackable Splitter allows as many wells as needed to be drilled, cased and completed from a common wellbore, with individual access using a diverter. Splitters and casing are lined up at the correct depths and cemented in place using a newly developed wiper assembly. After cementing, a diverter is used for drilling or re-entry into any junction at any time. Completions can be annular dual or single with commingled production. Flow control in the laterals can be accomplished with wireline plugs or cement. Unlike the other three systems, the junction inlet and outlet legs are the same size.
Marathon exclusively licenses these Mara-Split technologies to Baker Oil Tools.
In November 1999, a new Level 6 multilateral was installed on 133/8-in. casing at the Imo River field in Nigeria. A 171/2-in. hole was drilled to 4,900 ft (1,495 m) with a 6° deviation at the final section to allow the measurement-while-drilling tool to determine orientation. After cementing the DeepSet Splitter, two 41/2-in. laterals were drilled more than 8,000 ft (2,440 m) into the sandstone formation. The Riser Diverter System was deployed to isolate the first leg, which was drilled using reaming-while-drilling (RWD) bits. A 51/2-in. lateral liner then was run and cemented back to the casing, and a standard liner hanger and packer were used to link the liner to the 75/8-in. casing. Then a 5-in. hole was drilled with RWD bits, and a 31/2-in. production liner was run and cemented back to the 51/2-in. casing. A completion tubing string was run and landed into the top of the 31/2-in. liner packer and anchored with a production packer set about the liner hanger in the 75/8-in. casing. The Riser Diverter System then was switched to isolate the other lateral leg, drilled and completed identical to the first. A dual-completion tubing string was run using a Scoophead Diverter System to maintain correct tubing orientation and positioning. Even though this was the first deployment of this size DeepSet Splitter, Riser Diverter and Scoophead Diverter systems, all project objectives were met with no rig time lost. The operator plans to use Level 6 technology as a standard field development option for multilaterals.
Set to grow
The multilateral service industry is advancing rapidly in terms of systems capabilities and operational efficiencies. These sophisticated systems are viable, commercial multilateral tools that can have a large impact on field and reservoir development strategies.
By 2004, more than 5,000 multilateral wells are projected to be completed. That may be a conservative number, because PDVSA alone expects to drill somewhere between 5,000 and 10,000 multilaterals in the next 5 years. Savvy operators will be able to apply the latest Level 5 and Level 6 multilateral technologies for optimal reservoir development.