The world's first guidelineless remotely operated vehicle (ROV) based flexible flowline pull-in connection was executed in December 1995 with a DmaC flowline and umbilical connection system. The operation was conducted by Subsea Offshore Ltd for the Foinaven Subsea Alliance. Almost four years later, on 11 August of this year, SubSea completed the 200th DMaC (diverless maintained cluster) tie-in on the nearby Schiehallion Field. The flowlines and umbilicals were connected for BP Amoco as part of a 5-year diverless connection campaign.
The Hercules work class ROV is shown fitted with the prototype Phoenix Tie-In System.
Foinaven and Schiehallion are only 10 km apart and share similar challenges. They are located 190 km west of the Shetland Islands in the Faroes/Shetland Trough Area of the Atlantic Ocean and are part of BP Amoco's Atlantic Margin Development. Water depths on these sites range between 350 meters and 550 meters.
Weather and current conditions there have consistently proved to be the worst ever encountered by SubSea in any offshore location in the world. Atlantic gales, high seas and severe and complex currents extending almost to the seabed are frequently encountered.
The fields have undergone equally aggressive fast-track development. First oil was achieved at Schiehallion in July 1998, approximately four years after discovery, via one of the world's largest new build floating production, storage and offloading (FPSO) vessels.
As on Foinaven, the production concept is based around the DMaC field design model, with clusters of subsea wells producing via central gathering manifolds on the seabed. These, in turn, are connected via flexible jumpers to rigid pipelines, and subsequently, via flexible risers to the FPSO.
The production system was developed by Fuel Subsea Engineering under contract to Esso Exploration and Production UK Limited. The initial development and testing program was completed in 1991.
Following further in-house development, Fuel Subsea Engineering undertook a joint industry program sponsored by BHP (Americas), BP, Exxon and Statoil to detail enhanced capability designs of the DMaC flowline and umbilical jumper connection systems and associated tooling - key components of the overall system.
The two major components of the system are the flexible flowline pull-in and connection system, and the umbilical jumper installation system. The system is designed to pull-in and connect flexible flowlines, control umbilicals, and umbilical jumpers to a structure fitted with a porch.
The flexible flowline assembly consists of either a single flowline or a bundle of flowlines fitted at each end with a pullhead containing the outboard hub and seal. The umbilical jumper is fitted at both ends with a multi-function termination plate.
The pull-in and connection system comprises a remotely operated vehicle (ROV) fitted with an interface skid, pull-in tool (PIT), and PIT deployment basket. Fitted to the interface skid is a suite of ancillary tools which are used to perform various functions during the pull-in and connection operation.
Examiner Work Class ROV is shown filled with the DMaC Interface Skid.
The umbilical jumper installation system comprises an ROV fitted with an umbilical tool interface skid, and an umbilical deployment basket. The umbilical installation system utilizes the same equipment as the pull-in and connection system, with the exception of the PIT, which is not required for this operation and the ancillary tooling module is replaced by the umbilical tool module.
The tooling is operated using computer based control software which displays mimic diagrams of each tool.
SubSea has made a total of 200 diverless connections on the Foinaven and Schiehallion fields. Working from a wide variety of vessels in the field, ranging from monohulls to semisubmersibles, flowline jumpers have been deployed to the seabed for immediate pull-in and connection, or for wet storage. Jumper diameters have ranged from 12 in. to 6 in., including multibore flowlines and have varied in type from flexible risers, to production flowlines and control umbilicals.
The disconnection system has also been field proven, with flowline jumpers requiring to be disconnected from central gathering manifolds at Foinaven during various phases of the installation campaign.
The work class ROV systems and DMaC systems are shown onboard the construction vessel Rockwater Semi 2.
Five DMaC Flowline pull-in and connection systems have now been built, three for the Foinaven and two for Schiehallion. The two Schiehallion systems have been upgraded and enhanced as a result of the knowledge gained from Foinaven operations. However, all systems can be used on both fields.
As a result of the lessons learned and experience gained, reliability has increased, while pull-in times for the system have significantly decreased.
The achievement has proven the ability of ROV based tooling systems to undertake difficult and complex work tasks in all water depths cost effectively. Despite this, SubSea does not necessarily regard DMaC, or any of the other systems currently in the market place, as a solution to all diverless field developments. Each new development has to be evaluated on its merit. Many factors will determine the type of system to be used. In addition to cost, these include:
- Environmental factors such as seabed conditions and currents
- Requirement for rigid or flexible flowline
- Horizontal or vertical connections
- Preferences for hardware, such as connectors.
Standardization, while highly desirable, will not be as easy to achieve as some may think and will probably not be the result of one particular system being dominant in the market place.
However, SubSea does believe that the future of diverless connection systems is in standardization, which relies on cooperation between both operators and contractors. A similar approach has already been successfully introduced in the North Sea by BP Amoco in the field of component replacement (insert chokes, control pods, etc).
To this end, SubSea in conjunction with various UK operators, has initiated a joint industry program to develop a standard interface that can be fitted by all manufacturers to their proprietary underwater hardware.
When complete, the interface will enable operators not only to choose what they believe to be the best pull-in and connection system for their particular project, but also their favored connector. In addition, it will provide the operator added flexibility when undertaking any remedial work following field commissioning.
Using the experience with DMaC and other diverless tie-in systems, SubSea has built and tested a new prototype tie-in system based on a standard interface. The Phoenix diverless tie-in system is designed to connect both flexible flowline jumpers and rigid pipe spools up to 16 in. in diameter and is suitable for clamp, collet, and flange connectors.
The Phoenix system was successfully demonstrated at SubSea's Greenwell Road Base in Aberdeen in April of this year. Connections were made both on land and in the SubSea test tank using a Vector International Optima connector fitted to a 12 in. diameter rigid pipe test rig. Further development of the system will continue throughout the remainder of 1999.