New tree technology rethinks traditional system design
In early 2016, when the oil price dropped below $30/bbl, the oil and gas industry took a close look at offshore development costs and realized things needed to change. Operators worked with suppliers to achieve cost reductions and cooperated in some cases to share services like crew transfers. Today, with oil prices at a 21-year low, making changes is even more critical, and the solutions that were feasible four years ago are not equal to the task. New technologies and new thinking are needed if offshore developments are going to be economically viable.
According to Dril-Quip CEO Blake DeBerry, delivering better solutions does not mean tweaking components in traditional designs. “It is about rethinking how we do things to deliver permanent cost savings,” he said, “and that means new ideas.”
DeBerry jumpstarted plans for differentiation when he became CEO in 2011. He ramped up the company’s R&D program and invested in full-scale testing of the entire subsea wellhead system.
“This was our first foray into how to develop products that structurally change how customers drill wells offshore,” DeBerry said.
The decision to pursue a different direction for the subsea vertical tree was initiated by a comment from a frustrated operator. The operator’s question was simple: “Why can’t we run the tubing hanger in the wellhead without regard to orientation, lock it down, get a good test and land the tree at any orientation required?
“That was an ‘aha moment,’ DeBerry said. “It seemed to me that, compared to traditional systems, there had to be a simpler and less complicated solution.” DeBerry and his team of 30 engineers and designers began brainstorming about how to land the tubing hanger, and five days later, Dril-Quip filed a provisional patent. “Then, the real work started,” he said.
There are several challenges with traditional subsea vertical tree designs. Wellhead interfaces must be capable of handling the stack-up tolerances of casing hangers, and the tubing hanger must be oriented relative to the flowline connection system. Most conventional systems use a tubing head spool, which creates the need for temporary well barriers and additional BOP trips. Alternatively, other complicated means of orienting the tubing hanger within the BOP can be performed, enabling the tubing hanger to be installed directly into the wellhead. Dril-Quip’s new concept needed to simplify the landing and connection processes without introducing additional risks or hazards.
The VXTe system addresses those challenges with the industry’s first non-oriented 15 ksi, in-the-wellhead completion, vertical tree design. This unique tree allows operators to move from drilling to completion without pulling the BOP stack.
One of the most critical design elements of the tree is that it eliminates the tubing head, DeBerry explained. For conventional systems, installing a tubing hanger in the wellhead requires the use of BOP pins, rotational orientation tools or other equipment to align and run the tubing hanger. The Dril-Quip tree system eliminates the need for orientation because the stab sub assembly on the tree allows the tubing hanger to be installed like a casing hanger without regard for orientation and allows drilling and completion to be carried out without temporary well suspension or pulling the BOP stack. It also removes the need for well barriers, which eliminates risk and saves time.
The stab sub-assembly – with 7-in./10 ksi, 5-in./15 ksi, and 5-in./20 ksi ratings – uses the same sealing interface for the stab to the tubing hanger. “A single tubing hanger running tool works for all these systems,” he said.
The coupler body housing element of the stab assembling contains the hydraulic and electric couplers. It can rotate +/- 180 degrees to allow the 13 hydraulic and two electrical coupler lines to connect to the corresponding couplers in the tubing hanger. This exceeds IOGP specification requirements for nine downhole hydraulic functions and one electrical function, providing optionality for future innovations in smart completions that could require more downhole lines.
Automatic space-out adjustment is another design advantage, DeBerry said. The tubing hanger of the VXTe contains a mechanism to automatically adjust to variances in the hanger’s position.
When the tubing hanger is landed, a pressure test verifies the hanger is in the correct position. Then, a hanger lock mandrel is placed with a tubing hanger running tool, creating a flat lock mandrel-to-lock ring interface. “The tubing hanger can be picked up and loaded against the shoulders of the wellhead to establish a known elevation, and the VXTe tubing hanger adjustment mechanism automatically activates and removes any gaps,” he said.
A 15-ksi rated annulus isolation valve inside the tubing hanger provides a reliable barrier in place of a wireline plug for installation and interventions. The annulus flow path isolates the hydraulic and electrical couplers, which protects the wellhead gasket from contact with the annulus fluid and adds another barrier between the annulus fluid and the environment.
The ingenuity of the VXTe system earned it a Spotlight on New Technology Award from the 2020 Offshore Technology Conference (OTC).