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.

Hart Energy June 2022 - Oil States Industries Merlin 15K HPHT Riser System image 1
Oil States Industries says its Merlin 15K HP/HT Riser System is the first riser system ISO13628-7 rated for 15K psi, 259 F (126 C) and sour service. (Source: Oil States Industries Inc.)

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.

Hart Energy June 2022 - Oil States Industries Merlin 15K HPHT Riser System laboratory
Oil States Industries’ structural-test laboratory meets the ISO Standard BS/EN/ISO/IEC 17025 and is designed to simulate normal and extreme operational load cases for product evaluation, prototype development and design validation of FEA analytical models. This is where OSI tested the Merlin 15K HP/HT Riser System. (Source: Oil States Industries Inc.)

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.

Hart Energy June 2022 - Oil States Industries Merlin 15K HPHT Riser System Merlin Connector image
The Merlin 15K HP/HT Riser System saves make-up time by using the field-proven Merlin Connector, which enables a 10-minute make-up time. (Source: Oil States Industries Inc.)
Hart Energy June 2022 - Oil States Industries Merlin 15K HPHT Riser System Merlin Connector image 2
Oil States Industries' Merlin Connectors are designed and manufactured to meet a range of dynamic fatigue and pressure loads up to 15K psi, and incorporate a non-helical interlocking profile featuring a specially-designed geometry to ensure a correct connection every time. There are more than 400,000 Merlin connections in the field to date. (Source: Oil States Industries Inc.)

“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.