Sour Service Finds Feasibility with New Riser System

A new riser system makes it possible to access HP/HT wells from a jackup instead of having to use costly semisubmersible rigs.

Rated for 15,000 psi, 259 F (126 C) and sour service, Oil States Industries’ new Merlin 15K HP/HT Riser was developed with TotalEnergies. Developing a riser system that could meet those three criteria was challenging. In addition to reducing costs by making it possible to access wells from a jackup instead of a semi, the riser system relies on the Merlin Connector, which saves time on make-up.

Traditionally, for shallow-water HP/HT wells, operators needed to use a semisubmersible to handle the high pressures. But day rates for semis are much higher than for jackups. Having a riser capable of serving HP/HT wells, in addition to handling sour service, makes it possible to use jackups, which can save hundreds of thousands of dollars, Brian Mizell, vice president of business development and marketing at Oil States Industries said.

“This significantly reduces the cost” of reaching those pressures and temperatures in sour service conditions, he said.

The upshot, he said, is that marginal and difficult wells get a chance to be productive.

“If they can drill with a lower cost jackup instead of a semi, it makes projects feasible that may not have been feasible before,” Mizell said.

In addition to making it possible to drill previously inaccessible wells, Mizell said, the Merlin 15K HP/HT Riser System reduces fatigue, eliminates failure points, increases safety and promotes faster make-up times.

There was no riser that could handle 15,000 psi, 259 F (126 C) and sour service.

Previously, OSI offered a riser that could handle 10,000 psi and below 121 C, and some smaller risers that could handle sour service.

Bringing the Merlin 15K HP/HT Riser System to the market “took a bit of development,” Kirsten McNeill, projects manager at Oil States Industries, said.

“We didn’t give ourselves one challenge. We gave ourselves three challenges,” McNeill said.

One of the challenges of developing the riser was selecting a material suitable for high pressures, high temperatures and sour service, or the ability to handle H₂S or sulfuric acid (H₂SO4).

The development team had to balance the needs of the three requirements while ensuring the material was weldable, she said.

The main connection

Some risers rely on flange connections, which may take an hour for multiple nuts and bolts to be tightened for each joint, but the OSI system uses the Merlin connector. First used in the North Sea more than four decades ago, the Merlin connector reduces make-up time to around 10 minutes for each joint.

The Merlin Connector has a male part and a female part, and the two parts are essentially pressed together.

“It’s quick to assemble, compared to another solution like a flange,” McNeill said.

While the Merlin is field-proven, the connector in use on the new riser system has been tweaked to handle 15K, 259 F (126 C) and sour service conditions, she said.

“It’s a jump in existing technology from where it was two years ago,” she said.

As of late May, OSI was carrying out final qualification testing on the riser system at its mechanical test lab in Europe. The Merlin 15K HP/HT Riser System is available for rent or purchase in diameters.

The expectation is that the first Merlin will be in the water next year, she said.