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Out of the loop

The race is on for technologies that help operators cut development spending or operating expenses. Engineers working on an automated subsea pig launching system say the equipment can do both.

Subsea field design involves a lot of time spent weighing options and considering the costs and benefits of various technologies.

If a production line is likely to require frequent pigging, for example, a twin pipeline, or loop system, may be justified. But the cost to build and install a second pipeline is significant, especially in very long subsea tie-back developments.

Subsea pig launchers enable pigging with a single pipeline. The downside is that they must be deployed and retrieved with a vessel and remotely operated vehicle (ROV), which is costly — and time-consuming if the pigging operation is not part of a scheduled maintenance programme.

SAPL.Polarled REFERENCE PROJECT: In 2015, NOV’s SAPL team delivered the 36-inch Polarled PLEM, including pig launch receiver, to Statoil. Photo: NOV

NOV engineers in Norway are developing the Subsea Automatic Pig Launcher (SAPL), a pigging system that can be permanently installed on the seabed.

The SAPL draws on established topsides pigging technology but promises several cost-saving features, the company says. It eliminates the capital cost of a second flowline.

On the operational side, it minimises the use of a vessel with an ROV and encourages the frequent pigging that can help avoid blockages and production shutdowns.

“With this automated pig launcher, the main idea is that you can sit onshore, or on a vessel, and push a button to launch a pig,” says Marius Bjorn, department manager, process and controls with NOV’s Completion & Production Solutions business.

The SAPL will be equipped with an internal cassette that can hold two to 10 pigs, depending on the operation — pre-commissioning and commissioning, wax removal or slug pigging — or one “smart” pig for inspection missions.

The multiple-pig cassette means pigs can be stored on the seabed and deployed as needed. The cassette is equipped with an ROV-operated ball valve barrier that allows it to be replaced without interrupting production.

Complex pigging operations require a tracking system to locate stuck or slow-moving pigs. To avoid using a radioactive tracking system, NOV developed a magnetic sensor that relays position and movement information.

NOVcrop.jpg NOWHERE TO HIDE: NOV designed a magnetic pig tracking system for a major North Sea project, technology that will be applicable in a development equipped with the SAPL. Photo: NOV

The sensors measure the presence and shape of a magnetic field using a three-axis magnetometer.

Sensors are mounted on the pipe with subsea clamps. Magnetic arrays are mounted on the pigs, and electrical jumpers or batteries provide power.

The system may be installed in three configurations - battery-powered with an ROV display for temporary use, with an acoustic communication link to a vessel or platform, or in a connector interface configuration for hardwired communication to the data processing unit.

The tracking system, developed in collaboration with Statoil, has been in use since 2016 at one of the operator’s major North Sea developments.

Bjorn calls the magnetic pig tracking technology “one of the main components in this system”. Conventional systems rely on radioactive isotopes and therefore carry inherent safety risks and handling costs.

“We have developed a magnetic system that can also locate stuck pigs with no batteries located on the pig. We think this is better,” he says.

Full-scale tests

The SAPL’s roots can be traced to the Norwegian engineering services company Apply Nemo, which was acquired by Kongsberg in 2012.

Apply Nemo had participated in several studies for pipeline operator Gassco regarding the feasibility of subsea-to-subsea pigging.

Following the acquisition, Kongsberg launched a development project with Shell to design and build a “simplified prototype”, Bjorn says.

By the time that NOV acquired Kongsberg’s subsea products division, in 2016, Total and the Research Council of Norway had joined the effort to build a full-scale prototype of the SAPL.

“Now we are building this prototype on the west coast of Norway and the tests will be finished in the first quarter of next year,” Bjorn says.

NOV2add.jpg INGREDIENTS: A sketch shows the SAPL’s individual modules, from bottom: pipeline end manifold (PLEM), control and instrumentation, and cassette with replacement frame. Photo: NOV

Bjorn describes the prototype as a “full-flow system” running through a 12-inch line. The prototype is pressure-rated to 5000 psi and includes multiple pumps, an installation frame and a “quite simple” cassette that holds four pigs.

While preparations for the SAPL tests are under way, NOV is laying the groundwork for further research and development.

“Now we are planning a new Phase D in Brazil,” Bjorn says. “In Phase C, we are testing with water. In Phase D, we want to use a multiphase test rig and perform a shallow-water test.”

Successful tests in Norway next year will qualify the SAPL concept. “But after Phase D, we will have a more robust system that is qualified for more pipelines and easier to adapt to other conditions,” he says.

The multiphase tests will be conducted with varying mixtures of water and gas, he adds.

“We will also adapt the system to the Brazilian market, with deep water and high pressures.”

Current subsea pig launching systems are restricted by the amount of mono-ethylene glycol (MEG) that can be pumped from a support vessel to the launcher.

SAPL.Marius.jpg Photo: NOV

"The main idea is that you can sit onshore, or on a vessel, and push a button to launch a pig."
Marius Bjorn, NOV

The pressure to “kick” the pig cannot exceed the maximum pressure capacity of the down line. The SAPL, however, uses the flow from the well for propulsion. “So, there’s no need to reduce the pressure,” Bjorn says.

Phase D will expand the cassette capacity to 10 pigs and could include development of a subsea automatic pig receiver — a challenge in pipelines prone to wax build-up, he says. NOV is also considering an all-electric version of the SAPL.

A robust system could help operators achieve cost-saving goals for subsea projects.

Total has cited the SAPL in cases, such as the Laggan-Tormore field, where current and in-development technologies could have reduced both capital and operational costs (citation/link needed).

Oil and gas companies “want to minimise the umbilicals and use only electrical lines”, Bjorn says.

“To minimise the MEG line is also important. With this system, we only need a small, ½-inch MEG line,” compared with much larger lines in use now, such as Laggan-Tormore’s eight-inch line for continuous MEG injection.

NOV is seeking additional partners for the development project and says several operators are keenly interested in the SAPL technology.

“I think it’s in line with the long tie-back, reduced cost philosophy,” he says.

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