For decades, the offshore market evolved toward ultra-deepwater wells, with subsurface total depths that can exceed 3,000 m (9,840 ft). These extreme conditions increased the necessity for a product capable of performing in extreme conditions, without compromising the safety of either people or the environment.
A completion landing string is generally an assembly of a tubular with a gas tight connector used in deep offshore wells for diverse operations, such as landing Christmas trees; landing the tubing hanger and upper completion; sending instrumentation downhole; performing well testing; and for other completion and intervention operations at different times during the lifetime of the well.
The most important function of the workstring is to provide a gas-tight conduit between the seabed and the platform, where tools can be lowered and fluids circulated. The other main features include: guaranteeing the integrity of the string (people and equipment safety, mechanical performance under combined load, and corrosion resistance); ensuring a large drift for plug removal, as well as efficient hydraulics; and guaranteeing gas tightness, especially in the connector between each tubular.
Using a completion landing string also allows operators to perform pre-analysis of hydrocarbons, to evaluate the value of completing the well. These operations are, by definition, complex and expensive, so operators are seeking solutions continuously to improve their economic and operational performances.
Several technologies are already available on the market. The first option is an OCTG solution, which, thanks to its long-running history and availability in large diameters with gas-tight connectors, can make it a viable option. The main disadvantages of this solution include the limited numbers of make-and-breaks (since the connector is sensitive to galling, which could lead to leaks), long assembly time, and cost (expensive to run, due to special handling and the need for a different crew to run the casing string).
The second option is a drill pipe-based solution, where a threaded connector is welded on an upsetted pipe. There are shortcomings to using drill pipe-based solutions. First of all, the drill-pipe riser connector does not reach the required gas tightness for today’s high-pressure environments. Secondly, there is restricted drift, due to the limitation of welding, and the heat treatment of the weld cross-section. Lastly, there is limited tensile, resilience capacity, and corrosion resistance in the weld zone.
Despite these disadvantages, the use of drill pipe-based products as completion landing strings is becoming increasingly popular, because they can be used for both open-water and in-riser applications. Drill pipe-based products provide the same performance as conventional OCTG risers.
Drill pipe-based products are more cost-effective to run, as compared to conventional OCTG risers, because they are compatible with conventional drill pipe-handling equipment. Additionally, they are faster to make-up and run tougher, and, therefore, less sensitive to damage—resisting up to 100 make-and breaks—and they are more flexible and can be used for drilling, if needed.
TECHNOLOGY RESPONSE
To better address the drill pipe-based workstring segment, Vallourec developed a completion landing string with improved performance and benefits, as compared to existing systems. Vallourec’s solution is a completion landing string with a large drift diameter (6 in.), as well as a high working pressure (maxi mum of 20,000 psi, internal pressure). As required by ISO 13628-7, guaranteeing 20,000-psi working pressure, the connector and the pipe have to be tested successfully at 1.5 times the working pressure—meaning that the internal test pressure was up to 30,000 psi.
To reach such a challenging target, three innovations were combined: 1) a tubular, designed with a new outside diameter of 75/8 in., that permits an optimized balance between tensile capacity and drift diameter; 2) an innovative process to manufacture PFP pipes, a heat treated, forged product that preserves the high tensile capacity of the tubular; 3) a new high-performance, gas-tight connection, VAM Express-M2M, assuring gas-tightness.
FORGING OF SHAPED PIPE
The principal challenge during this stage was finding the most appropriate process to manufacture the required geometry and steel grades. From the initial design phase, it was decided to avoid the friction welding process, due to the limitations that it presents. With the forging process, it is now possible to reach larger outside-diameter pipe (75/8 in. versus 65/8 in.) and flush inside diameters (up to 61/4 in.) without having to reduce the inside diameter to compensate for the weld.
Weld-free design. The radial forge was used primarily to manufacture forged pipe, with a straight outside and internal diameter, named PFP pipe. This process combines a piercer (using the Mannesmann Effect) and a radial forge, equipped with four hammers and a patented cylindrical mandrel. To manufacture a weld-free R3 forged shape pipe, equipment, process, tooling and program were developed, Fig. 1. The result of this development is a PFP-shaped pipe with a larger diameter on the extremities to accommodate the tool joint. The product can also be customized with additional internal and/or external shapes to match the customer’s needs.
Extending our dimensional range. The external diameter’s range for drill pipe-based landing strings is usually limited to a 65/8-in. pipe, with a tool joint internal diameter up to 5.2 in. The latest technical requirements for completion landing strings require the drift diameter to reach a minimum of 6 in., to retrieve the BOP plug. This large internal diameter is also designed to optimize hydraulic performance during fluids circulation. With the forging process, the completion landing string is designed and manufactured with an internal diameter of 61/4 in. to guarantee a 6-in. drift, allowing our standard outside diameter limits to now reach 75/8 in.
In summary, the radial forge enables manufacturing of an integral shaped pipe with a variable outside diameter, preserving the metallurgical integrity of the pipe by getting rid of the weld, increasing the product range to accommodate the 75/8-in. size, and improving delivery time and price competitiveness, as compared to welded or machined assemblies.
GAS-TIGHT CONNECTOR
Deepwater drilling and completions operations, particularly in the Gulf of Mexico, have an increasing need for gastight connections. The need has been driven by wells requiring drillstem testing, high-pressure completions/well stimulation jobs, or managed pressure/ underbalanced drilling operations. Safety and well integrity concerns further accentuate the need for a “no compromise” approach when developing connections with gas-tight capabilities.
For smaller ID (5.102 in.) requirements, the industry has been using drillpipe products for years. Before drill pipe riser systems (DPRIS), most operators used conventional drill pipe available on rigs to install and retrieve the production adapter base and tree cap. These were simple, open-water operations that did not require annulus control, pressure containment or fluids circulation. Occasionally, companies used drill pipe as a work string in tubing hanger retrieval operations. Pipe could be deployed with a hydraulic jar to unstick tubing hangers. While success varied, the difficulties and risks of using a hydraulic umbilical inside the riser were identified. Technology improvement was needed to minimize interference between the pipe and the hydraulic lines. The existing designs for dual vertical-bore risers were adequate for shallow-water completions, but as subsea completions moved to increasingly deeper waters, risers became a more costly, and less desirable, solution.
Depending on the field requirements, two different types of drill pipe riser systems, using a proprietary double-shoulder connection, were used by operators. The first solution was developed in 1999 and featured a seal ring close to the external shoulder. Subsequently, a new solution, featuring a gas-tight, metal-to-metal seal (VAM DPR HP) on the pin nose, was developed to address increasingly demanding and challenging operations.
Though drill-pipe risers meet some of today’s requirements, operators have challenged the service industry to develop a new gas-tight tubular connection designed specifically for a number of applications: 1) high-pressure completions/fracture stimulations; 2) drillstem testing; 3) managed pressure/underbalanced applications.
In response to these needs, Vallourec developed a drill pipe-based gas-tight connection with a metal-to-metal rotary seal technology. The patented VAM Express-M2M double-shoulder gas-tight connection is based on Vallourec’s VAM Express connection, Fig. 2. The VAM Express premium connection VX-57 and 5½-in. S135 DP was chosen specifically for extended reach wells. This double-shoulder connection distinguishes from other double-shoulder connections because of its higher torque capacity, which averages 150% to 200% more than an API connection.
Another advantage of using the connection is to obtain a quick rig make-up of 6–7 turns from stab-in to full makeup, which is similar to API connections but provides a 16% faster trip-time, as compared to other high-performance double-shoulder connections. It also features better hydraulics, because the reduced OD and enlarged ID reduce the pressure and hydraulic horsepower requirements for circulating drilling fluids, viscous pills and cement.
In addition to all the characteristics from the VAM Express connection, the VAM Express-M2M connection is a cost-effective, gas-tight connection that combines the capabilities of a high-pressure drill-pipe riser with the robustness of a premium double-shoulder rotary connection. This combination of features gives operators and drilling contractors the flexibility to use the same tubular string for both drilling and completion operations, without compromising performance or safety.
The VAM Express-M2M provides one of the highest operating safety margins of any gas-tight connection and is qualified to 30,000 psi, internal pressure, and 25,000 psi, external pressure. The patented metal-to-metal seal enables the highest gas-tight operating envelope in the industry, reduced risk of galling on the seal, and prevention of gas entrapment (an important feature that prevents rig-floor personnel exposure to H2S, but also yielding of the connector, due to high-pressure differentials). It also has the ability to complete multiple fracing jobs without repair, and it is easy to fish from a wellbore, due to its slim-connection design.
CONVERGENCE OF INNOVATIONS
As a result of the combination of the forged shaped pipe and the new VAM Express-M2M connection, the company created an innovative solution to real industry challenges. The advantages of the new forged completion landing string include:
• Higher tensile capacity, due to the patented PFP pipe, which dimensionally increases the existing product range and eliminates the weld;
• Higher fatigue resistance, due to the patented thread profile;
• Higher gas tightness performance, due to the patented metal-to metal seal.
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